Carbon Sequestration - DOE - National Energy Technology Laboratory

CarbonCarbonSequestrationSequestration

State of the Science

roadmappingfuture carbon sequestration R&D

February 1999

A working paper for

U.S. Department of Energy

Office of Science

Office of Fossil Energy

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Carbon Sequestration DRAFT (February 1999)

Dave Reichle, ORNLJohn Houghton, DOE

Sally Benson, LBNLJohn Clarke, PNNLRoger Dahlman, DOEGeorge Hendrey, BNLHoward Herzog, MITJennie Hunter-Cevera, LBNLGary Jacobs, ORNLRod Judkins, ORNL

WORKING PAPER ONCARBON SEQUESTRATION SCIENCE

AND TECHNOLOGY

Office of ScienceOffice of Fossil Energy

U.S. Department of Energy

Bob Kane, DOEJim Ekmann, FETC

Joan Ogden, PrincetonAnna Palmisano, DOERobert Socolow, PrincetonJohn Stringer, EPRITerry Surles, LLNLAlan Wolsky, ANLNicholas Woodward, DOEMichael York, DOE

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DRAFT (February 1999) Carbon Sequestration

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CONTENTS

FIGURES ......................................................................................................... vii

TABLES .......................................................................................................... xi

ABBREVIATIONS, ACRONYMS, AND INITIALISMS ........................................... xiii

EXECUTIVE SUMMARY ................................................................................... xv

1. CARBON SEQUESTRATION: A THIRD APPROACH TO CARBONMANAGEMENT .......................................................................................... 1-11.1 CARBON MANAGEMENT .................................................................... 1-1

1.1.1 The Challenge ........................................................................ 1-11.1.2 The Vision .............................................................................. 1-21.1.3 Three Approaches to Carbon Management .............................. 1-21.1.4 What is Carbon Sequestration? ............................................... 1-31.1.5 Necessary Characteristics for Carbon

Sequestration Systems ........................................................... 1-41.2 THE GLOBAL AND THE FOSSIL FUEL CARBON CYCLES ..................... 1-4

1.2.1 The Global Carbon Cycle ........................................................ 1-41.2.2 The Fossil Fuel Cycle ............................................................. 1-5

1.3 APPROACH AND SCOPE OF THIS REPORT ........................................ 1-61.4 TOWARD DEVELOPMENT OF A CARBON SEQUESTRATION

ROAD MAP ........................................................................................ 1-81.4.1 Foundations for an Expanded National Program

in Carbon Sequestration ......................................................... 1-81.4.2 The Need for a National R&D Plan for

Carbon Sequestration ............................................................. 1-101.5 END NOTES ....................................................................................... 1-111.6 REFERENCES .................................................................................... 1-121.7 ACKNOWLEDGMENTS ....................................................................... 1-13

2. SEPARATION AND CAPTURE OF CARBON DIOXIDE .................................. 2-12.1 CHARACTERIZATION OF CARBON FLOWS (SOURCE TERMS) ............ 2-12.2 CURRENT AND POTENTIAL SCIENCE AND TECHNOLOGY

REQUIREMENTS ................................................................................ 2-42.3 CURRENT AND POTENTIAL SCIENCE AND TECHNOLOGY

CAPABILITIES ................................................................................... 2-42.3.1 Chemical and Physical Absorption ......................................... 2-42.3.2 Physical and Chemical Adsorption ......................................... 2-62.3.3 Low-temperature Distillation.................................................. 2-72.3.4 Gas-Separation Membranes .................................................... 2-8

2.4 SCIENCE AND TECHNOLOGY GAPS ................................................... 2-92.4.1 Chemical and Physical Absorption ......................................... 2-92.4.2 Physical and Chemical Adsorption ......................................... 2-102.4.3 Low-Temperature Distillation ................................................. 2-112.4.4 Gas-Separation Membranes .................................................... 2-112.4.5 Product Treatment and Conversion ........................................ 2-12

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2.4.6 Transportation ........................................................................ 2-122.4.7 Advanced Concepts ................................................................ 2-12

2.5 ALIGNMENT OF REQUIREMENTS TO CAPABILITIES(R&D ROAD MAP) .............................................................................. 2-13

2.6 REFERENCES .................................................................................... 2-14

3. OCEAN SEQUESTRATION .......................................................................... 3-13.1 DIRECT INJECTION OF CO2 ............................................................... 3-3

3.1.1 Science and Technology Requirements ................................. 3-33.1.2 Current Scientific and Technological Capabilities ................. 3-43.1.3 Science and Technology Gaps ................................................ 3-73.1.4 Research and Development Plan ............................................ 3-9

3.2 ENHANCEMENT OF NATURAL CARBON SEQUESTRATIONIN THE OCEAN ................................................................................... 3-93.2.1 Science and Technology Requirements ................................. 3-113.2.2 Current Science and Technology Capabilities ........................ 3-113.2.3 Science and Technology Gaps ................................................ 3-123.2.4 Research and Development Plan ............................................ 3-13

3.3 LONGER-TERM, INNOVATIVE CONCEPTS FOR OCEAN CO2

SEQUESTRATION .............................................................................. 3-143.4 CONCLUSION .................................................................................... 3-153.5 ACKNOWLEDGMENTS ....................................................................... 3-163.6 REFERENCES .................................................................................... 3-16

4. CARBON SEQUESTRATION IN TERRESTRIAL ECOSYSTEMS ...................... 4-14.1 TERRESTRIAL ECOSYSTEMS: NATURAL BIOLOGICAL

SCRUBBERS ...................................................................................... 4-34.2 POTENTIAL FOR CARBON SEQUESTRATION ..................................... 4-54.3 CURRENT CAPABILITIES ................................................................... 4-84.4 TERRESTRIAL ECOSYSTEM SCIENCE AND TECHNOLOGY

ROAD MAP ........................................................................................ 4-104.4.1 Objectives ............................................................................... 4-114.4.2 Strategies ............................................................................... 4-144.4.3 Research and Development Needs .......................................... 4-19

4.5 SUMMARY ......................................................................................... 4-254.6 ACKNOWLEDGMENTS ....................................................................... 4-274.7 END NOTES ....................................................................................... 4-274.8 REFERENCES .................................................................................... 4-27

5. SEQUESTRATION OF CARBON DIOXIDE IN GEOLOGICFORMATIONS ............................................................................................ 5-15.1 SEQUESTRATION IN GEOLOGIC FORMATIONS BUILDS

ON A STRONG EXPERIENCE BASE ..................................................... 5-15.1.1 Sequestration Mechanisms .................................................... 5-15.1.2 Sources and Forms of CO2 ...................................................... 5-35.1.3 Capacity of Geologic Formations Suitable

for Sequestration .................................................................... 5-35.1.4 Drivers for R&D....................................................................... 5-3

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5.2 ASSESSMENT OF CURRENT CAPABILITIES AND R&D NEEDS............ 5-55.2.1 Opportunities for CO

2 Sequestration in Oil

and Gas Formations ............................................................... 5-65.2.2 CO2 Sequestration in Aqueous Formations ............................. 5-85.2.3 Opportunities for CO

2 Sequestration in

Coal Formations ..................................................................... 5-115.3 CROSS-CUTTING R&D NEEDS FOR GEOLOGIC FORMATIONS........... 5-13

5.3.1 CO2 Trapping Mechanisms...................................................... 5-13

5.3.2 CO2 Waste Stream Characteristics .......................................... 5-135.3.3 Formation Characterization .................................................... 5-145.3.4 Injection, Drilling, and Well Completion Technology ............. 5-165.3.5 Performance Assessment ........................................................ 5-165.3.6 Monitoring ............................................................................. 5-165.3.7 Cross-Cutting Fundamental Research Needs ......................... 5-17

5.4 ADVANCED CONCEPTS FOR SEQUESTRATION IN GEOLOGICFORMATIONS .................................................................................... 5-18

5.5 OVERALL R&D PRIORITIES ............................................................... 5-195.6 WORKS CONSULTED ......................................................................... 5-20

6. ADVANCED BIOLOGICAL PROCESSES ...................................................... 6-16.1 BACKGROUND AND RATIONALE FOR ADVANCED BIOLOGICAL

PROCESSES TO SEQUESTER CARBON .............................................. 6-16.2 CARBON CAPTURE TECHNOLOGY SUPPORT ..................................... 6-2

6.2.1 Current Science and Technology Capabilities ........................ 6-26.2.2 Science and Technology Requirements ................................. 6-36.2.3 Research Implementation ....................................................... 6-4

6.3 SEQUESTRATION IN REDUCED CARBON COMPOUNDS ..................... 6-56.3.1 Current Science and Technology Capabilities ........................ 6-56.3.2 Science and Technology Requirements ................................. 6-56.3.3 Research Implementation ....................................................... 6-6

6.4 INCREASING PLANT PRODUCTIVITY ................................................. 6-86.4.1 Current Science and Technology Capabilities ........................ 6-96.4.2 Science and Technology Requirements ................................. 6-136.4.3 Research Implementation ....................................................... 6-13

6.5 ALTERNATIVE DURABLE MATERIALS................................................ 6-146.5.1 Current Science and Technology Capabilities ........................ 6-146.5.2 Science and Technology Requirements ................................. 6-156.5.3 Research Implementation ....................................................... 6-16

6.6 SUMMARY AND CONCLUSIONS ......................................................... 6-166.7 REFERENCES .................................................................................... 6-19

7. ADVANCED CHEMICAL APPROACHES TO SEQUESTRATION ..................... 7-17.1 INTRODUCTION ................................................................................. 7-1

7.1.1 Introduction to the Problem and Solutions............................. 7-27.1.2 Potential Chemical Approaches to Sequestration ................... 7-2

7.2 CHEMICAL PROCESSES FOR SEQUESTRATION ................................. 7-47.2.1 Inert Benign Long-Term Storage Forms .................................. 7-57.2.2 Products from Carbon Dioxide Utilization............................... 7-8

7.3 ENABLING CHEMICAL TECHNOLOGIES ............................................. 7-10

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7.4 SUMMARY ......................................................................................... 7-127.5 END NOTES ....................................................................................... 7-147.6 REFERENCES .................................................................................... 7-14

8. DEVELOPING AN EMERGING TECHNOLOGY ROAD MAP FOR CARBONCAPTURE AND SEQUESTRATION ............................................................... 8-18.1 INTRODUCTION ................................................................................. 8-18.2 A CARBON CAPTURE AND SEQUESTRATION SYSTEM ....................... 8-18.3 BUILDING AN EMERGING TECHNOLOGY ROAD MAP ........................ 8-38.4 BUILDING THE CARBON CAPTURE AND SEQUESTRATION

ROAD MAP ........................................................................................ 8-48.5 BUILDING THE R&D CAPACITY ......................................................... 8-6

8.5.1 Advanced Sensors and Monitoring Systems ........................... 8-78.5.2 Carbon Processing Platforms .................................................. 8-98.5.3 Biological Absorption Platforms .............................................. 8-108.5.4 Engineered Injection Platforms .............................................. 8-10

8.6 NEXT STEPS ...................................................................................... 8-11

9. FINDINGS AND RECOMMENDATIONS ....................................................... 9-19.1 FINDINGS .......................................................................................... 9-29.2 RECOMMENDATIONS ........................................................................ 9-4

9.2.1 Beginning the R&D Program .................................................. 9-49.2.2 Developing the Road Map ....................................................... 9-6

9.3 PRINCIPAL FOCUS AREA RECOMMENDATIONS ................................ 9-79.3.1 Separation and Capture of CO2 ............................................... 9-79.3.2 Ocean Sequestration .............................................................. 9-79.3.3 Carbon Sequestration in Terrestrial Ecosystems .................... 9-89.3.4 Sequestration in Geological Formations................................. 9-99.3.5 Advanced Biological Processes .............................................. 9-99.3.6 Advanced Chemical Approaches ............................................. 9-10

9.4 REFERENCES .................................................................................... 9-11

Appendix A: CARBON SEQUESTRATION WORKING PAPERCONTRIBUTORS AND WORKSHOP ATTENDEES ................................ A-1

Appendix B: DETAILED DESCRIPTIONS OF ECOSYSTEMS ANDRESEARCH AND DEVELOPMENT NEEDS ........................................... B-1

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FIGURES

1.1 One representation of the reductions in CO2 that would benecessary to reach atmospheric stabilization compares theIS92A (business as usual) scenario with a scenario (WRE550)that leads to stabilized atmospheric CO2 concentrations of550 ppm ............................................................................................... 1-2

1.2 Human-induced changes in the global carbon cycle resultingfrom increases in the combustion of fossil fuels and changingland-use patterns ................................................................................ 1-5

1.3 Carbon flows in the energy system and sources of emissionsin the United States in 1995 ................................................................ 1-6

1.4 Deploying an effective carbon sequestration system willrequire an integrated program of science, enablingtechnology, and advanced power systems—all dependenton better understanding of environmental carbon dynamics .............. 1-7

2.1 Separation and capture R&D road map. ............................................... 2-13

3.1 Every year the ocean actively takes up one-third of ouranthropogenic CO2 emissions .............................................................. 3-2

3.2 A schematic diagram of the biological pump ........................................ 3-3

3.3 For injection of CO2 at depths of 1000 to 2000 m, it has beensuggested that liquid CO

2 be transported from shore through

a pipeline for discharge from a manifold lying on the oceanbottom .................................................................................................. 3-5

3.4 Simulated distribution of carbon injected into the ocean at adepth of 1720 m off the coast of Cape Hatteras, North Carolina,after 20 years of continuous injection, as computed by thethree-dimensional ocean model of Lawrence LivermoreNational Laboratory .............................................................................. 3-6

3.5 The multiple unit large-volume in situ filtration system(MULVFS) allows the precise determination of propertiesof particulate matter that is needed for a systematicsurvey of ocean carbon inventory and for the evaluationof ecosystem function .......................................................................... 3-11

3.6 R&D road map for ocean sequestration of CO2 ...................................... 3-15

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4.1 Overall system view of the science and technology road mapfor the terrestrial ecosystems ............................................................... 4-11

4.2 Detailed view of the system level showing the ecosystem categoriesthat are part of the overall system ......................................................... 4-12

4.3 Detailed view of the objectives level showing the various componentsthat feed into the three primary objectives that are describedin equation (1) ..................................................................................... 4-13

4.4 Detailed view of the strategies level illustrating the options forwhich R&D will be required for effective implementation .................... 4-15

4.5 Detailed view of the R&D needs level illustrating the fundamentalR&D needed to support the development of carbon sequestrationoptions for terrestrial ecosystems ......................................................... 4-22

5.1 Location of gas-producing areas in the United States .......................... 5-4

5.2 Location of deep saline aquifers in the United States ........................... 5-4

5.3 Location of coal-producing areas in the United States andpower plants......................................................................................... 5-5

5.4 Gravity segregation, viscous fingering, heterogeneity, andpreferential flow through faulted cap rocks could influenceCO2 migration in the subsurface .......................................................... 5-10

5.5 Comparative evaluation of the technological and scientific maturityof operational requirements for sequestering CO2 in geologicformations ............................................................................................ 5-15

5.6 Key elements of the R&D road map for sequestration of CO2 ingeologic formations .............................................................................. 5-19

6.1 Typical leaf anatomy in a C3 plant ....................................................... 6-10

6.2 Typical leaf anatomy in a C4 plant ....................................................... 6-10

6.3 Carbon fixation as it occurs via the Hatch-Slack pathwayin C4 plants ......................................................................................... 6-11

6.4 Key elements of the R&D road map for advanced biologicalprocesses ............................................................................................. 6-17

7.1 Mixtures of gas clathrates have been found near coasts aroundthe world .............................................................................................. 7-7

7.2 Paths to utilize CO2 in synthetic chemistry .......................................... 7-8

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7.3 A road map of needed research into advanced chemicalapproaches ........................................................................................... 7-11

8.1 The top-level diagram of a carbon capture and sequestrationtechnology system showing the relationship to the fossilenergy system ...................................................................................... 8-3

8.2 The structure of an emerging technology road map for carboncapture and sequestration ................................................................... 8-5

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TABLES

4.1 Global estimates of land area, net primary productivity (NPP),and carbon stocks in plant matter and soil for ecosystemsof the world .......................................................................................... 4-4

4.2 The categorization of biomes used in this road-mapping exercise ....... 4-6

5.1 Range of estimates for CO2 sequestration in U.S. geologicformations ............................................................................................ 5-5

5.2 R&D priorities for CO2 sequestration in oil and gas fields .................... 5-9

5.3 R&D priorities for CO2 sequestration in aqueous formations ................ 5-12

5.4 R&D priorities for CO2 sequestration in coal formations ....................... 5-14

6.1 Prioritization of advanced biological options ....................................... 6-18

7.1 Thermodynamics of chemical/physical transformationsinvolving CO2 ....................................................................................... 7-4

7.2 Approaches to sequestration using chemical processes andexamples of their use ........................................................................... 7-13

8.1 System technology platforms ................................................................ 8-6

8.2 System component technologies .......................................................... 8-7

8.3 Science and technology capabilities .................................................... 8-8

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ABBREVIATIONS, ACRONYMS, AND INITIALISMS

BER Office of Biological and Environmental Research (DOE)BES Office of Basic Energy Sciences (DOE)CO carbon monoxideCO

2carbon dioxide

DEA diethanolamineDOE U.S. Department of EnergyEOR enhanced oil recoveryESA electrical swing adsorptionFACE Free Air CO2 EnrichmentGtC billion tonnes of atmospheric carbonH2 hydrogen gasHNLC high-nutrient, low-chlorophyll (ocean waters)IEA International Energy AgencyIGCC integrated gasification combined cycleIPCC Intergovernmental Panel on Climate Changem meterMBARI Monterey Bay Aquarium Research InstituteMDEA methyldiethanolamineMEA monoethanolamineMIT Massachusetts Institute of TechnologyMPa million Pascal (a measure of pressure)nm nanometerNOx oxides of nitrogenOCMIP Ocean Carbon-Cycle Model Intercomparison ProjectOGCM ocean general circulation modelPCAST President’s Council of Advisors on Science and TechnologyPOC particulate organic carbonppm parts per millionPSA pressure swing adsorptionR&D research and developmentROV remotely operated vehicleSOx oxides of sulfurTSA thermal swing adsorption

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EXECUTIVE SUMMARY

Predictions of global energy use in the next century suggest a continued increasein carbon emissions and rising concentrations of carbon dioxide (CO

2) in the

atmosphere unless major changes are made in the way we produce and useenergy—in particular, how we manage carbon. For example, theIntergovernmental Panel on Climate Change (IPCC) predicts in its 1995 “businessas usual” energy scenario that future global emissions of CO2 to the atmospherewill increase from 7.4 billion tonnes of carbon (GtC) per year in 1997 toapproximately 26 GtC/year by 2100. IPCC also projects a doubling of atmosphericCO2 concentration by the middle of next century and growing rates of increasebeyond. Although the effects of increased CO2 levels on global climate areuncertain, many scientists agree that a doubling of atmospheric CO

2

concentrations could have a variety of serious environmental consequences.

One way to manage carbon is to use energy more efficiently to reduce our need fora major energy and carbon source—fossil fuel combustion. Another way is toincrease our use of low-carbon and carbon-free fuels and technologies (nuclearpower and renewable sources such as solar energy, wind power, and biomassfuels). Both approaches are supported by the U.S. Department of Energy (DOE) andare not the focus of this report.

The third and newest way to manage carbon, capturing and securely storingcarbon emitted from the global energy system (carbon sequestration), is trulyradical in a technology context. The development of today’s fossil energy-basedsystem is rooted in the Industrial Revolution. For over 200 years, the developmentof energy technology has been focused on lowering costs through increasedefficiency to support economic growth. Because of their abundance, availability,and high energy content, coal, oil, and natural gas have proved to be attractiveenergy sources to produce electricity, run industrial processes, propeltransportation vehicles, and provide energy for residential and commercialapplications. As fossil energy use increased and adverse environmental effectsbecame apparent, energy technology also evolved to minimize them. However, allof this enormous technology development has assumed that the free venting of CO

2

to the atmosphere was environmentally harmless. Only recently has theincreasing concentration of CO2 in the atmosphere been considered to represent aserious environmental problem. The consequence is that we have developed anintricate, tightly coupled energy system that has been optimized over 200 years foreconomy, efficiency, and environmental performance, but not for the capture andsequestration of its largest material effluent, CO

2.

The goal of this report is to identify key areas for research and development (R&D)that could lead to an understanding of the potential for future use of carbonsequestration as a major tool for managing carbon emissions. Under the leadershipof DOE, researchers from universities, industry, other government agencies, andDOE national laboratories were brought together to develop the technical basis forconceiving a science and technology road map. That effort has resulted in thisreport, which develops much of the information needed for the road map.

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This report identifies the R&D topics necessary to understand and develop criticaloptions for the capture, transport, conversion, and sequestration of carbon. Itaddresses known sources of carbon (industrial sources, power plant flue gases,preprocessed fossil fuels before combustion); carbon forms for sequestration (CO2,elemental carbon, and minerals that contain carbon); and options forsequestration sinks—oceans, geologic formations, soils and vegetation (seeChaps. 3 through 7).

THE ROAD MAP VISION AND GOALS

The vision for the road map is to

Possess the scientific understanding of carbon sequestration and developto the point of deployment those options that ensure environmentallyacceptable sequestration to reduce anthropogenic CO2 emissions and/oratmospheric concentrations. The goal is to have the potential to sequestera significant fraction of 1 GtC/year in 2025 and 4 GtC/year in 2050.

The purpose of carbon sequestration is to keep anthropogenic carbon emissionsfrom reaching the atmosphere by capturing them, isolating them, and divertingthem to secure storage and/or to remove CO

2 from the atmosphere by various

means and store it. Any viable system for sequestering carbon must be safe,environmentally benign, effective, and economical. In addition, it must beacceptable to the public.

Why is carbon sequestration important? Given the magnitude of carbonreductions needed to stabilize the atmosphere, capture and sequestration couldbe a major tool for reducing carbon emissions to the atmosphere from fossil fuels;in fact, sequestration may be essential for the continued large-scale use of fossilfuels. It will allow greater flexibility in the future primary energy supply. Inaddition, it could offer other benefits such as the manufacture of commercialproducts (e.g., construction materials and plastics); improved agriculturalpractices that could reduce soil erosion, conserve water, and increase thesustainability of food production; the restoration of wetlands, which would helppreserve wildlife and protect estuaries; increased biodiversity; enhanced recoveryof oil and methane (from coal beds); and the development of exportabletechnologies to help the U.S. economy.

THE GLOBAL CARBON CYCLE AND FOSSIL FUELS

Most anthropogenic (human-activity-related) emissions of carbon to theatmosphere result from combustion of fossil fuels for the economical production ofenergy. If the demand for energy continues to increase, it is possible that the onlyway that fossil fuels can be used for large-scale energy production is through thedevelopment and implementation of carbon capture and sequestration options.

Given the magnitude of carbon emission reductions needed to stabilize theatmospheric CO2 concentration, multiple approaches to carbon management

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STRATEGIC ISSUES

Following are the general recommendations of the report addressing strategicissues regarding a comprehensive carbon sequestration program.

• Sequestration R&D could expand the world’s future options for dealing withgreenhouse gases.

• Many carbon sequestration options are particularly amenable to improvingexisting activities—such as CO2 injection during secondary oil recovery—andoften provide important secondary benefits, such as improving ecosystemsduring reforestation.

• Some carbon sequestration options, such as improved agricultural practices, areavailable practically immediately. Examining ongoing, field-scale sequestrationinvestigations in terrestrial, geological, and ocean systems can provide criticalexperience for designing the necessary environmental research programs.

• Some carbon sequestration options that have limited capacity or relatively shortcarbon residence times could nonetheless make important near-termcontributions during a transition to other longer-term carbon managementoptions. Other carbon sequestration options can provide significant long-termcontributions.

• For carbon sequestration to be a viable option, it needs to be safe, predictable,reliable, measurable, and verifiable; and it needs to be competitive with othercarbon management options, such as energy-efficient systems and decarbonizedenergy technologies.

• Carbon sequestration is an immature field, so multiple fundamental R&Dapproaches are warranted and significant breakthroughs can be expected. Thefederal government is an appropriate sponsor of carbon sequestration R&D.

• Integrated analyses of the carbon sequestration system should be periodicallyupdated to evaluate the potential contributions, costs, and benefits of variouscarbon sequestration options.

• The information from the R&D program should be provided to policy makers toaid them in developing policy and selecting the most efficient and effectivesolutions to the issues of climate change.

(i.e., improved energy efficiency and clean energy systems) will be needed. Allpotentially important technical options should be explored.

SCIENTIFIC AND TECHNICAL NEEDS FOR CARBON SEQUESTRATION

Separation and Capture of CO 2 from the Energy System

Several currently available technologies can be used to separate and capture CO2

from fossil-fueled power plant flue gases; from the effluents of industrial processessuch as iron, steel, and cement production; and from hydrogen production byreforming of natural gas. However, these technologies have not been applied at thescale required to use them as part of a CO2 emissions mitigation strategy. CO2 canbe absorbed from gas streams by contact with amine-based solvents or coldmethanol. It can be removed by adsorption on activated carbon or other materialsor by passing the gas stream through special membranes.

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Advanced methodsmight includeadsorbing CO2 onzeolites or carbon-bonded activatedcarbon fibers andseparating it from fluegases or process gasesfrom industrialoperations using

inorganic membranes. The use of commercial CO2-removing processes that scrub

gases with amine-based solvents is projected to raise the cost of producingelectrical power from coal-fired power plants using existing technology. Captureand sequestration could increase the cost of electrical power generation fromcoal by as much as 20 to 30 mills/kWh. Thus, although CO2 separation is doneroutinely, dramatic improvements are necessary to make the process economical(Chap. 2). Techniques will be needed to transform the captured CO

2 into

materials (1) that can be economically and safely transported and sequestered fora long time or (2) that can be used to make commercial products (e.g.,construction materials) that could offset the costs of separation and capture.

There are numerous options for the separation and capture of CO2, and many ofthese are commercially available. However, none has been applied at the scalerequired as part of a CO2 emissions mitigation strategy, nor has any method beendemonstrated for all the anthropogenic sources considered in this R&D map.Many issues remain regarding the ability to separate and capture CO

2 from

anthropogenic sources on the scale required, and to meet the cost, safety, andenvironmental requirements for separation and capture. In our assessment of thescientific and technological gaps between the requirements for CO

2 separation

and capture and the capabilities to meet these requirements, many explicit andspecific R&D needs were identified.

• A science-based and applications-oriented R&D program is needed toestablish the efficacy of current and novel CO2 separation processes asimportant contributors to carbon emissions mitigation. Important elements ofsuch a program include the evaluation, improvement, and development ofchemical and physical absorption solvents, chemical and physicaladsorbents, membrane separation devices with selectivity and specificity forCO2-containing streams, molecular and kinetic modeling of the materials andprocesses, and laboratory-scale testing of the selected processes.

• Field tests are needed of promising new CO2 separation and capture optionsin small bypass streams at large point sources of CO2, such as natural gaswells and hydrogen production plants.

Sequestration in the Oceans

The ocean represents a large potential sink for sequestration of anthropogenicCO2 (Chap. 3). Two methods are proposed for the sequestration of carbon in theocean: (1) A relatively pure CO

2 stream that has been generated by a power plant,

decarbonized fuel production system, or industrial facility could be injected

Geologic or ocean storage sequestration options thatuse a concentrated source of CO2 require low-costcarbon separation and capture techniques to be viableoptions. The scale of the industrial system required toprocess gigatonnes of carbon warrants investigationinto new solvents, adsorbents, and membraneseparation devices for either pre- or post-combustionseparation.

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directly into the ocean.The injected CO

2 may

become trapped in oceansediments or ice-likesolids, called hydrates.(2) The net oceanicuptake from theatmosphere could beenhanced through a

method such as iron fertilization. These approaches will require betterunderstanding of marine ecosystems to enhance the effectiveness of applicationsand avoid undesirable consequences.

• Field experiments of CO2 injection into the ocean are needed to study the

physical/chemical behavior of the released CO2 and its potential for ecologicalimpact.

• Ocean general circulation models need to be improved and used to determinethe best locations and depths for CO2 injection and to determine the long-termfate of CO

2 injected into the ocean.

• The effect of fertilization of surface waters on the increase of carbonsequestered in the deep ocean needs to be determined, and the potentialecological consequences on the structure and function of marine ecosystemsand on natural biogeochemical cycling in the ocean need to be studied.

• New innovative concepts for sequestering CO2 in the ocean need to beidentified and developed.

Sequestration in Terrestrial Ecosystems

Terrestrial ecosystems,which are made up ofvegetation and soilscontaining microbialand invertebratecommunities, sequesterCO

2 directly from the

atmosphere (Chap. 4).The terrestrial ecosystemis essentially a hugenatural biological scrubber for CO2 from all fossil fuel emissions sources, such asautomobiles, power plants, and industrial facilities. Computer models indicatethat terrestrial ecosystems—forests, vegetation, soils, farm crops, pastures,tundras, and wetlands—have a net carbon accumulation of about one-fourth (1.5to 2 GtC) of the 7.4 GtC emitted annually into the atmosphere by fossil fuelcombustion and land use changes. If there were an increased focus on practicesto enhance the natural carbon cycle, the potential for terrestrial ecosystems toremove and sequester more carbon from the atmosphere could be increased by, forexample, improving agricultural cultivation practices to reduce oxidation of soilcarbon and enhancing soil texture to trap more carbon, and protecting wetlands.

The ocean provides a large potential reservoir. Activeexperiments are already under way in ironfertilization and other tests of enhanced marinebiological sequestration, as well as deep CO2

injection. Improvements in understanding marinesystems will be needed before implementation ofmajor marine sequestration campaigns.

The terrestrial biosphere is a large and accessiblereservoir for sequestering CO2 that is already presentin the atmosphere. Natural carbon fluxes are huge, sothat even small forced changes resulting from R&Dadvances would be very significant. It will beimportant to address the consequences of altering thenatural flux.

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• The terrestrial ecosystem is a major biological scrubber for atmospheric CO2

(present net carbon sequestration is ~2 GtC/year) that can be significantlyincreased by careful manipulation over the next 25 years to provide a critical“bridging technology” while other carbon management options are developed.Carbon sequestration could conceivably be increased by several gigatonnesper year beyond the natural rate of 2 GtC per year, but that may implyintensive management and/or manipulation of a significant fraction of theglobe’s biomass. However, those potentials do not yet include a totalaccounting of economic and energy costs to achieve these levels. Ecosystemprotection is important and may reduce or prevent loss of carbon currentlystored in the terrestrial biosphere. The focus for research, however, should beon increasing the rate of long-term storage in soils in managed systems.

• Research on three key interrelated R&D topics is needed to meet goals forcarbon sequestration in terrestrial ecosystems:

— Increase understanding of ecosystem structure and function directedtoward nutrient cycling, plant and microbial biotechnology, moleculargenetics, and functional genomics.

— Improve measurement of gross carbon fluxes and dynamic carboninventories through improvements to existing methods and throughdevelopment of new instrumentation for in situ, nondestructive below-ground observation and remote sensing for aboveground biomassmeasurement, verification, and monitoring of carbon stocks.

— Implement scientific principles into tools such as irrigation methods,efficient nutrient delivery systems, increased energy efficiency inagriculture and forestry, and increased byproduct use.

• Field-scale experiments in large-scale ecosystems will be necessary tounderstanding both physiological and geochemical processes regulatingcarbon sequestration based upon integrative ecosystem models. Such carbonsequestration experiments are needed to provide proof-of-principle testing ofnew sequestration concepts and integration of sequestration science andengineering principles.

Sequestration in Geologic Formations

Three principal types ofgeologic formations arewidespread and have thepotential for sequesteringlarge amounts of CO

2. They

are active anduneconomical oil and gasreservoirs; aqueousformations; and deep andunmineable coal formations. About 70 oil fields worldwide use injected CO2 forenhanced oil recovery. CO

2 sequestration is already being practiced in a sub-

seabed reservoir in the North Sea of Norway. The United States has sufficient

Limited geological sequestration is being practicedtoday, but it is not yet possible to predict withconfidence storage volumes and integrity over longtime periods. Many important issues must beaddressed to reduce costs, ensure safety, and gainpublic acceptance.

xxi


capacity, diversity, and broad geographic distribution of potential reservoirs to usegeologic sequestration in the near term (Chap. 5). The primary uncertainty is theeffectiveness of storing CO2 in geological formations—how easily CO2 can beinjected and how long it will remain. Only through experience will enoughknowledge be gained to assess the ultimate sequestration potential of geologicformations.

• Fundamental and applied research is needed to improve the ability tounderstand, predict, and monitor the performance of sequestration in oil, gas,aqueous, and coal formations. Elements of such a program include multiphaseflow in heterogeneous and deformable media; phase behavior; CO

2 dissolution

and reaction kinetics, micromechanics and deformation modeling; coupledhydrologic-chemical-mechanical-thermal modeling; and high-resolutiongeophysical imaging. Advanced concepts should be included, such asenhancement of mineral trapping with catalysts or other chemical additives,sequestration in composite geologic formations, microbial conversion of CO2 tomethane, rejuvenation of depleted oil reservoirs, and CO

2-enhanced methane

hydrate production.

• A nationwide assessment is needed to determine the location and capacity ofthe geologic formations available for sequestration of CO2 from each of themajor power-generating regions of the United States. Screening criteria forchoosing suitable options and assessing capacity must be developed inpartnership with industry, the scientific community, and public andregulatory oversight agencies.

• Pilot-scale field tests of CO2 sequestration should be initiated to develop costand performance data and to help prioritize future R&D needs. The tests mustbe designed and conducted with sufficient monitoring, modeling, andperformance assessment to enable quantitative evaluation of the processesresponsible for geologic sequestration. Pilot testing will lay the groundwork forcollaboration with industrial partners on full-scale demonstration projects.

Advanced Biological Processes

Advanced biologicalprocesses (Chap. 6) couldbe developed andimplemented to limitemissions and captureand sequester carbonfrom both relativelyconcentrated utility andindustrial combustiongases, as well as from dispersed point sources. Bacteria and other organismscould be used to remove carbon from fuels and to recycle carbon from man-madewaste streams. In addition, crop wastes and dedicated crops could be used asfeedstocks for biological and chemical conversion processes to manufacture fuelsand chemicals. Advanced crop species and cultivation practices could bedesigned to increase the uptake of atmospheric CO

2 by terrestrial and aquatic

Advanced biological techniques may produce optionstoo radical to predict. Some biologic processes cansequester carbon products at low cost. New carbonsequestration options could become feasible andothers could be improved using advanced biologicaltechniques.

xxii


biomass and decrease CO2 emissions to the atmosphere from soils and terrestrialand aquatic biomass.

The 21st Century has been referred to as the “Century for Biology.” Indeed, manynew molecular tools have been developed that will aid in new discoveries andassist in providing solutions to key problems facing humankind and the planet.The difference that advanced biological techniques can make will be evidentwhen they are integrated with land, subsurface, and ocean managementpractices. The following recommendations will promote cost-effective and stablebiological solutions to carbon sequestration.

• Research should be initiated on the genetic and protein engineering of plants,animals, and microorganisms to address improved metabolic functions thatcan enhance, improve, or optimize carbon management via carbon capturetechnology, sequestration in reduced carbon compounds, use in alternativedurable materials, and improved productivity.

• The objectives and goals of the advanced biological research should be linkedto those specific problems and issues outlined for carbon sequestration ingeological formations, oceans, and soils and vegetation so that an integratedresearch approach can elucidate carbon sequestration at the molecular,organism, and ecosystem levels.

• Short-, mid-, and long-term goals in advanced biological research should beinstituted so that scale-up issues, genetic stability in natural settings, andefficacy in the field can be assessed.

Advanced Chemical Approaches

Many of thesequestrationtechnologies describedin this documentdepend on chemistry.Improved methods ofseparation, transport,and storage of CO2 willbenefit from research onand development of advanced chemical techniques to address sequestration viachemical transformations (Chap. 7). Any viable sequestration technique muststore vast amounts of carbon-rich materials, so environmental chemistry will bevaluable to determine whether these materials will be stable when sequestered.Many issues pertaining to aqueous carbonate/bicarbonate chemistry are relevantto sequestration of carbon in oceans, geological formations, and groundwater.Carbonate chemistry in very basic solutions may lead to a method for extractingCO2 from air. Clathrates, compounds that can enclose molecules such as CO2

within their crystal structure, may be used to separate CO2 from high-pressure

systems. Learning clathrate properties may be important to understandingchemical approaches to ocean storage of carbon, and subsurface arctic and

Most carbon sequestration options rely on chemicalreactions to achieve benign, stable, and inertproducts. Studies to enhance the relevant chemistryalmost certainly will reduce the costs or increase theeffectiveness of these options. Results from R&D onadvanced chemical topics also may make it possibleto generate useful and marketable byproducts.

xxiii


marine hydrate formations may also be evaluated as geologic sequestrationoptions.

• The proper focus of R&D into advanced chemical sciences and technologies ison transforming gaseous CO

2 or its constituent carbon into materials that

either are benign, inert, long-lived and contained in the earth or water of ourplanet, or have commercial value.

— Benign by-products for sequestration should be developed. This avenuemay offer the potential to sequester large (gigatonne) amounts ofanthropogenic carbon.

— Commercial products need to be developed. This approach probablyrepresents a lesser potential (millions of tonnes) but may result incollateral benefits.

• The chemical sciences can fill crucial gaps identified in the other focus areas.In particular, environmental chemistry is an essential link in determining theimpact and consequences of these various approaches. Studies to address thespecific gaps identified in Chap. 7 should be conducted to ensure that otherfocus areas meet their potential.

DEVELOPING A CARBON SEQUESTRATION ROAD MAP

An emerging science and technology road map seeks to identify the scientific andtechnological developments needed to achieve a specific policy goal. The processof identifying the needed science and technology must be focused by developinga concept of the technological system (Chap. 8). This task is particularly difficultin the case of carbon capture and sequestration because the understandingnecessary to design such a system is still immature.

Today, carbon is emitted to the atmosphere from many sources that were notdesigned to capture, let alone sequester, these emissions. There are many ideasfor, and even demonstrations of, technology to capture and sequester carbon fromfossil fuel combustion. Many of the requisite new energy production technologiesare already under development at DOE. However, the current energy systemprobably must be modified significantly to make an economical capture andsequestration system possible. Thus, the emerging technology road map forcarbon capture and sequestration cannot be constructed apart from considerationof current and emerging energy technologies. It will involve an iterative processto connect this road map with others being developed by DOE for various parts ofthe energy technology system.

This report is a significant first step toward the development of an emergingtechnology road map for carbon capture and sequestration. We start from a boldvision of having the scientific and technical knowledge to make carbonsequestration a major carbon management option by 2025. Guided by this vision,each of the technical focus chapters (2–7) identifies key areas for scientific and

xxiv


technical development, including new areas outside traditional energytechnology development.

We have begun the process of exploring the mutual relationships andinterdependencies of the scientific and technological developments in all thesefields by building a series of road map linkages. This process has illuminated howprogress in one area affects the total system. However, R&D priorities andperformance requirements have not yet been defined. Nor has the phasing ofpotential R&D schedules been considered. Developing linkages has allowed us toeliminate overlaps to some extent, but gaps in the technology needs have not yetbeen examined. Before proceeding much further, much more work must be doneon specifying the economic constraints and technology needs of the integratedcarbon capture and sequestration system. The road map outline presented in thisdocument, especially the research needs delineated in chapters 2–7, provides thesound basis for taking these next steps toward a fully realized program in carbonsequestration. This report should be used as a framework in organizing a widerexamination by diverse stakeholders of the science and technology required forcarbon capture and sequestration.

Carbon Sequestration: A Third Approach to Carbon Management 1-1


V isionisionisionisionision

11111 CARBON SEQUESTRATION: ATHIRD APPROACH TO CARBONMANAGEMENT

1.1 CARBON MANAGEMENT

1.1.1 The Challenge

In the past 60 years, the amount of anthropogeniccarbon dioxide (CO2) emitted to the atmosphere,primarily because of expanding use of fossil fuelsfor energy, has risen from preindustrial levels of280 parts per million (ppm) to present levels of over365 ppm (Keeling and Whorf 1998).

Predictions of global energy use in the nextcentury suggest a continued increase in carbonemissions and rising concentrations of CO2 in theatmosphere unless major changes are made in theway we produce and use energy—in particular,how we manage carbon. For example, the widelycited IS92a (“business as usual”) energy scenariodeveloped by the Intergovernmental Panel onClimate Change (IPCC 1995) predicts that futureglobal emissions of CO2 to the atmosphere willincrease from 7.4 billion tonnes of atmosphericcarbon (GtC) per year in 1997 to approximately26 GtC/year by 2100. Although the effects ofincreased CO2 levels on global climate areuncertain, there is scientific consensus that adoubling of atmospheric CO2 concentrations couldhave a variety of serious environmentalconsequences in the next century.

What would it take to stabilize the atmosphericconcentrations of CO2? Two widely usedscenarios, a “business as usual” and anatmospheric stabilization scenario, are comparedin Fig. 1.1. The difference between the twoscenarios, about 1 GtC per year in 2025 and about4 GtC per year in 2050, represents one estimate ofthe CO2 reductions required to reach atmosphericstabilization. This road map identifies a frameworkfor research and development (R&D) that would

The vision for theroad map is topossess thescientificunderstanding ofcarbonsequestration anddevelop to the pointof deploymentthose options thatensure environ-mentally acceptablesequestration toreduce anthro-pogenic CO

2

emissions and/oratmospheric con-centrations. Thegoal is to have thepotential tosequester asignificant fractionof 1 GtC/yearin 2025 and4 GtC/yearin 2050.

1-2 Carbon Sequestration: A Third Approach to Carbon Management


allow carbon sequestration to provide asignificant fraction of that reduction.

1.1.2 The Vision

The vision for the road map is topossess the scientific understanding ofcarbon sequestration and develop tothe point of deployment those optionsthat ensure environmentallyacceptable sequestration to reduceanthropogenic CO

2 emissions and/or

atmospheric concentrations. The goalis to have the potential to sequester asignificant fraction of 1 GtC/year in2025 and 4 GtC/year in 2050.

1.1.3 Three Approaches to CarbonManagement

Carbon sequestration is distinguishedfrom, but complements, two otherapproaches to carbon management thatare supported by the U.S. Department ofEnergy (DOE) (National LaboratoryDirectors 1997).

The first approachis to increase theefficiency ofprimary energyconversion andend use so thatfewer units ofprimary fossilenergy arerequired to providethe same energyservice. DOE issponsoring avariety of R&Dprograms todevelop moreefficient supply-and demand-sidetechnologies (e.g.,more efficientfossil-fuel-firedpower plants,buildings,appliances, and

transportation vehicles) and to findways to produce and deliver electricityand fuels more efficiently. Moreefficient energy conversion and enduse will result in lower CO

2 emissions

per unit of energy service.

A second approach is to substitutelower-carbon or carbon-free energysources for our current sources. Forexample, this strategy might involvesubstituting lower-carbon fossil fuelssuch as natural gas for coal or oil;using renewable energy supplies suchas solar, wind, or biomass; orincreasing the use of nuclear power.DOE has major R&D programs todevelop more efficient fossil energy aswell as renewable energy and nuclearenergy technologies.

Carbon sequestration could representa third approach in addition toefficiency improvements and evolutiontoward low-carbon fuels. However, it

Fig. 1.1. One representation of the reductions in CO2 that wouldbe necessary to reach atmospheric stabilization compares the IS92A(business as usual) scenario with a scenario (WRE550) that leads tostabilized atmospheric CO2 concentrations of 550 ppm (about twicepreindustrial levels). The WRE550 scenario is commonly used byanalysts of climate change. Source: Wigley, Richels, and Edmonds 1996.



has received much less attention todate than these other two approaches.

1.1.4 What is Carbon Sequestration?

Carbon sequestration can be definedas the capture and secure storage ofcarbon that would otherwise be emittedto or remain in the atmosphere. Theidea is (1) to keep carbon emissionsproduced by human activities fromreaching the atmosphere by capturingand diverting them to secure storage,or (2) to remove carbon from the atmos-phere by various means and store it.

One set of options involves capturingcarbon from fossil fuel use before itreaches the atmosphere. For example,

CO2 could be separated from powerplant flue gases, from effluents ofindustrial processes (e.g., in oilrefineries and iron, steel, and cementproduction plants), or duringproduction of decarbonized fuels (suchas hydrogen produced fromhydrocarbons such as natural gas orcoal). The captured CO2 could beconcentrated into a liquid or gasstream that could be transported andinjected into the ocean or deepunderground geological formationssuch as oil and gas reservoirs, deepsaline reservoirs, and deep coal seamsand beds. Biological and chemicalprocesses may convert captured CO

2

directly into stable products.Atmospheric carbon can also be

Why is Carbon Sequestration Important?

It is important to carry out research on carbon sequestration for severalreasons:

• Carbon sequestration could be a major tool for reducing carbon emissions fromfossil fuels. However, much work remains to be done to understand the scienceand engineering aspects and potential of carbon sequestration options.

• Given the magnitude of carbon emission reductions needed to stabilize theatmospheric CO2 concentration, multiple approaches to carbon managementwill be needed. Carbon sequestration should be researched in parallel withincreased energy efficiency and decarbonization of fuel. (These efforts shouldbe closely coordinated to exploit potential synergies.)

• Carbon sequestration is compatible with the continued large-scale use of fossilfuels, as well as greatly reduced emissions of CO2 to the atmosphere. Currentestimates of fossil fuel resources—including conventional oil and gas, coal, andunconventional fossil fuels such as heavy oil and tar sands—imply sufficientresources to supply a very large fraction of the world’s energy sources throughthe next century.

• The natural carbon cycle is balanced over the long term but dynamic over theshort term; historically, acceleration of natural processes that emit CO2 iseventually balanced by an acceleration of processes that sequester carbon, andvice versa. The current increase in atmospheric carbon is the result ofanthropogenic mining and burning of fossil carbon, resulting in carbonemissions into the atmosphere that are unopposed by anthropogenicsequestration. Developing new sequestration techniques and acceleratingexisting techniques would help diminish the net positive atmospheric carbonflux.



captured and sequestered byenhancing the ability of terrestrial orocean ecosystems to absorb it naturallyand store it in a stable form.

1.1.5 Necessary Characteristics forCarbon Sequestration Systems

Any viable system for sequesteringcarbon must have the followingcharacteristics.

Capacity and price. The technologiesand practices to sequester carbonshould be effective and cost-competitive. This road map will focuson options that allow sequestration of asignificant fraction of the goal.

Environmentally benign fate. Thesheer scale and novelty ofsequestration suggests a careful lookat environmental side effects. Forexample, the long-term effects ofsequestration on the soil or vegetationneed to be understood. Until recently,dilution into the atmosphere wasconsidered acceptable. Vast quantitiesof materials would be generated. Thesafety of the product and the storagescheme have to be addressed.

Stability. The carbon should reside instorage for a relatively long duration.

1.2 THE GLOBAL AND THEFOSSIL FUEL CARBONCYCLES

Carbon sequestration is intimately tiedto two carbon cycles— the natural andthe fossil fuel cycles. Understandingaspects of both cycles provides acontext for developing carbonsequestration options.

1.2.1 The Global Carbon Cycle

Improving our understanding of theglobal carbon cycle, its fluxes, and itsreservoirs, is intimately tied tosuccessful implementation of carbonsequestration technologies.Decreasing atmospheric CO

2

concentrations by reducing CO2

emissions or by changing themagnitude of the fluxes betweenreservoirs is controlled by the carbonbudget of a reservoir. From a carbonsequestration perspective,understanding the potential to altercarbon budgets through theintervention of carbon sequestrationtechnologies to reduce futureatmospheric CO2 concentrations is oneof the principal challenges.

Human activities during the first half ofthe 1990s have contributed to anaverage annual emission ofapproximately 7.4 GtC into theatmosphere (Fig. 1.2). Most of theseemissions were from fossil fuelcombustion. The net result of theseCO

2 emissions during the first part of

the 1990s was an annual netemissions increment to the atmosphereof 3.5 GtC. Storage of carbon interrestrial systems due tophotosynthesis and plant growth was1.7 GtC. Another 2.2 GtC per year wastaken up by oceans.

Carbon fluxes between the atmosphereand ocean/terrestrial reservoirs arequite large (hundreds of GtC per year),while net carbon exchange is over anorder of magnitude smaller. Forexample, the average net ecosystemaccumulation of the terrestrialbiosphere was 0.3 GtC per year (1.7 GtCper year net ecosystem productiondiminished by 1.4 GtC per year due toland clearing), while terrestrial



ecosystems photosynthetically fixed61.7 GtC per year—the photosynthesisuptake being offset by 60 GtC per yeardue to plant/soil respiration. Similarly,the net ocean uptake of 2.2 GtC peryear is the difference of ocean/atmosphere fluxes each exceeding 90GtC per year. The significance ofunderstanding these complicatedcarbon exchanges is that developingthe ability to alter these gross annualcarbon exchanges of the global carboncycle by a small percentage through

carbon sequestration technologieswould increase net storage of carbonin the major reservoirs and lessenatmospheric carbon concentrations.

1.2.2 The Fossil Fuel Cycle

About 75% of the world’s commercialenergy comes from fossil fuels, andabout 84% of the energy used in theUnited States is derived from fossilfuels (EIA 1998a; PCAST 1997). Giventhe advantages inherent in fossil fuels,

Fig. 1.2. Human-induced changes in the global carbon cycle resulting from increases in thecombustion of fossil fuels and changing land-use patterns. Solid arrows indicate the averagemagnitude of perturbation in carbon fluxes and the fate of carbon resulting from these activitiesaveraged for the first half of the 1990s. Net fluxes (black arrows) and gross fluxes (gray arrows) arein billions of tonnes of carbon per year. Annual net additions of carbon (shown as + numbers) to theatmosphere, ocean subsystems, and terrestrial systems from anthropogenic sources are in billions oftonnes of carbon per year. Pool sizes (circles) are shown in billions of tonnes of carbon. For moreinformation, see Houghton 1995 and Marland et al. 1998. Source: Technology Opportunities to ReduceU.S. Greenhouse Gas Emissions, modified from IPCC 1995.



such as their cost-competitiveness,their availability, their ease of transportand storage, and the large fossilresources, fossil fuels are likely toremain a major player in global energysupply for at least the next century.

Figure 1.3 shows the energy flowsthrough the U.S. economy from fossiland other fuels. This diagram helps toidentify places where CO2 could beseparated and captured, but there areenergy and cost implications that mustbe considered (Hoffert et al. 1998). Inthe near term, most CO

2 is likely to

come from electricity generated fromfossil fuels, because large quantities ofit could be processed at fixed locations.However, other possibilities becomemore likely in the longer term. Fossilfuels, solid waste, or biomass can be“decarbonized” so that a higher-energy-content and environmentallybenign fuel is separated from CO

2. For

example, either a fossil energy source

or another carbon source such as solidwaste or biomass could be pretreated toproduce hydrogen and CO

2. These

central pretreatment facilities couldbecome other new sources of carbonfor capture.

1.3 APPROACH AND SCOPE OFTHIS REPORT

The goal of this report is to identify keyareas for R&D that could lead to abetter understanding of the potentialuse of carbon sequestration as a majortool for managing carbon emissions.Under the leadership of DOE,researchers from universities,industry, other government agencies,and DOE national laboratories werebrought together to develop thetechnical basis for developing an R&Droad map. This report develops much ofthe information needed for the roadmap.

Fig. 1.3. Carbon flows in the energy system and sources ofemissions in the United States in 1995 (in millions of metric tonsequivalent). Electricity produced by the combustion of fossil fuels is likelyto remain a significant contributor to greenhouse gas emissions. Sources:EIA 1998a,b.



Six scientific/technical “focus areas”relevant to carbon sequestration wereidentified, and groups of experts ineach area reported on the R&D issues.These focus areas are

1. Separation and Capture of CO2

2. Ocean Sequestration3. Carbon Sequestration in Terrestrial

Ecosystems (Soils and Vegetation)4. Sequestration of CO

2 in Geological

Formations5. Advanced Biological Processes for

Sequestration6. Advanced Chemical Approaches to

Sequestration

These six focus areas represent oneway to organize the scientific andengineering issues underlying carbonsequestration.

Our vision for a carbon sequestrationroad map is to conduct the appropriateR&D so that options will be availablefor significantly reducinganthropogenic carbon emissions in thetime frame of 2025 and beyond.

This report describes the R&Dnecessary to understand and developto the point of deployment all criticaloptions bearing on the capture,transport, conversion, andsequestration of carbon (Fig. 1.4). Itaddresses known sources of carbon(industrial sources, power plant fluegases, carbon split away from fossilfuels before combustion); carbon formsfor sequestration (CO2, elementalcarbon, and minerals that containcarbon); and options for sequestrationsinks (oceans, geologic formations,enhancing the natural carbon cycle).

Fig. 1.4. Deploying an effective carbon sequestration systemwill require an integrated program of science, enablingtechnology, and advanced power systems—all dependent onbetter understanding of environmental carbon dynamics.



1.4 TOWARD DEVELOPMENT OF ACARBON SEQUESTRATIONROAD MAP

An emerging technology road mapprovides—and encourages the use of—a structured R&D planning process.Emerging technology road mapsfurnish a framework for managing andreviewing the complex, dynamic R&Dprocess needed to achieve importantstrategic goals by identifying howspecific R&D activities can relate tointegrated technical capabilitiesneeded to achieve strategic objectives.The process of identifying the neededscience and technology must befocused by developing a concept of thetechnological system that wouldenable achievement of that goal. Thistask is particularly difficult in the caseof carbon capture and sequestrationbecause there has been, heretofore, noparadigm for such a system (Victor1998).

Our road map gives a top-level pictureof a carbon capture and sequestrationsystem and its linkages to the energysystem. We have concentratedprincipally on the development ofscientific understanding that isneeded for specific capture andsequestration functions, includingspecific changes in components of theexisting energy system that wouldsimplify and/or lower the cost ofcapture and disposal. Many captureand sequestration technologies arediscussed in detail in Chaps. 2–7. Eachcan be developed and improvedindividually. However, the economiccost and effectiveness of the overallcarbon capture and sequestrationsystem depend on the effectivecombination of many scientificadvances. Their relative importancemust finally be judged in the context ofthe integrated technology system.

After identifying the technology goalsand the integrated technology systemneeded to satisfy those goals, our nextstep was to assess the alternativetechnological pathways that might leadto an integrated carbon sequestrationtechnology system. The approach wasto construct these pathways within atechnological hierarchy. The highestlevel of the hierarchy is the integratedtechnology system—in this case, thecarbon capture and sequestrationsystem. The hierarchy base issupported by the science andtechnology capabilities that are neededto develop the technologies that makethe system economical and effective.

1.4.1 Foundations for an ExpandedNational Program in CarbonSequestration

Sequestration studies began in 1977(see End Note 1), but an upsurge ofinterest in them has occurred onlyrecently. In the past two years, severalkey government studies of carbonmanagement and energy havehighlighted carbon sequestration as anapproach with high potential wheremuch R&D is needed.

For example, the potential importanceof carbon sequestration has beenunderscored by the President’sCommittee of Advisors on Science andTechnology report titled FederalEnergy Research and DevelopmentAgenda for the Challenges of the 21st

Century (PCAST 1997). Specifically, thereport recommends that a much largerscience-based CO2 sequestrationprogram be developed with the budgetincreasing from the current $1 millionper year to the vicinity of tens ofmillions. The report further states thatthe R&D should be performed in acollaborative way between DOE’soffices of Fossil Energy and Energy



Research (now Office of Science) andthe U.S. Geological Survey.International collaboration is alsostrongly encouraged.

Although the current DOE carbonsequestration program is modest inscale, many of the foundations havealready been built for significantlyexpanding this effort. The DOE Office ofScience program on CO

2 sequestration

includes both the Office of BasicEnergy Sciences (BES) and the Office ofBiological and EnvironmentalResearch (BER). The primary relevantgoal for BES is to develop major newfundamental knowledge that crosscutsDOE’s applied programs related tocarbon management, including suchdisciplines as materials sciences,chemical sciences, geosciences, plantand microbial biosciences, andengineering sciences. BES haslongstanding programs in fundamentalresearch, such as improved materialssynthesis and combustion engineeringfor more efficient energy technologies,improved catalysts for low-carbonindustrial processes, improvedunderstanding of biologicalmechanisms of carbon fixation, andimproved understanding of fluid flowin the subsurface for geologicalsequestration (www.er.doe.gov/production/bes/bes.html).

In 1999, a new program in BES andBER will be initiated to conductresearch in carbon management,including carbon sequestration, as aresult of the climate changetechnology initiative. The subjects willinclude sequencing genomes ofmethane- and hydrogen-producingmicroorganisms; enhancing thenatural terrestrial and oceanic fluxesof CO

2; and improving the

understanding of biological carbonfixation, materials, catalysts,

combustion chemistry, and physicsand chemistry of geological reservoirs.

BER has a longstanding fundamentalresearch program on the global carboncycle. Current research focuses onatmospheric measurements of carbonfluxes and related processes, terrestrialcarbon fluxes, and advanced biologicalinvestigations of carbon in terrestrialand ocean margin systems. A keyelement of terrestrial carbon researchinvolves Ameriflux, which is a networkof CO

2 flux measurements across North,

Central, and South America to quantifynet CO2 exchange between theatmosphere and representativeterrestrial ecosystems. Free Air CO2

Enrichment (FACE) experimentsprovide information about changes inthe carbon content of ecosystemsunder increased concentrations ofatmospheric CO

2, altered temperatures,

and altered precipitation regimes.Relevant information can be found atwww.er. doe.gov/production/ober/gc/accc-fr.html and www.cdiac.esd.ornl.gov/programs/ameriflux. Oceanresearch focuses on molecularbiological approaches tounderstanding the coupling betweencarbon and nitrogen cycles(www.er.doe.gov/production/ober/GC/acc-ft.html). BER also sponsors aprogram, Integrated Assessment ofGlobal Climate Change, that supportsresearch in understanding carbonmanagement frameworks for integratedassessment modeling activities.

DOE’s Office of Fossil Energy has aprogram on CO2 capture andsequestration to develop anddemonstrate technically,economically, and ecologically soundmethods to capture, reuse, and disposeof CO

2. In 1998, DOE made awards for

12 “cutting-edge” research projects,ranging from the use of CO2-absorbing



algae growing on artificial reefs todeep-ocean or deep-saline-reservoirgreenhouse gas disposal. Some of theseprojects may be selected for furtherdevelopment. (Details on thissolicitation can be found atwww.fe.doe.gov).

The Office of Fossil Energy has recentlyundertaken an initiative to provideformal management direction tosequestration program activities and toestablish program content and fundingpriorities. A team has been assembledto define a research strategy clearlyand to ensure coordination withinternal and external stakeholders. Inmaking its recommendations, the teamwill draw heavily from this report. InFY 1999, the second phase of the FossilEnergy novel concept investigationswill obtain the required engineeringand economic data to proceed to proof-of-concept. In the areas of geologicaland ocean sequestration, internationalgovernment/industry projects willcontinue.

In 1991 the International EnergyAgency (IEA) established a GreenhouseGas R&D Programme focused onanalyzing technologies for capturing,using, and storing CO2. It hasexpanded to include methane, as wellas forestation options. The program iscurrently in its third 3-year phase andhas support from 16 countries(including the United States) and agrowing number of industrialorganizations. (Details on this programcan be found at www.ieagreen.org.uk.)

In addition to government studies,industry is moving ahead withdevelopment of CO2 sequestrationtechnologies:

• The World Resources Institute hasformed a consortium with GeneralMotors, Monsanto, and British

Petroleum to address thefundamental issues of globalenergy supply, climate change, andeconomic growth—paths tostabilizing CO

2 concentrations at

levels reducing risks of climatechange (WRI 1998).

• Since October 1996, STATOIL, aNorwegian energy company, hasbeen separating CO2 from naturalgas and injecting it, at a rate of1 million tonnes per year, into adeep saline reservoir 800–1000meters below the ocean floor in theNorth Sea (see Chap. 5).

• About 70 oil fields use CO2

injection to recover additionalcrude oil.

• Various oil companies haveproposed to sequester CO

2 at the

rate of 30 million tonnes of carbonper year in the deep aquifersadjacent to the Natuna gas field, inthe South China Sea, when thatfield comes into production.

• Many domestic and internationalforest preservation andmanagement projects sequestercarbon by reducing deforestationand harvest impacts. Forestmanagement can also enhanceexisting carbon sinks.

These industrial efforts are veryimportant, but the amounts of CO

2

sequestered are very small comparedwith overall emissions. ConsiderableR&D investment by government andindustry is needed to enablesequestration of sufficient quantities ofCO

2 to mitigate any adverse effects

resulting from CO2 emissions.

1.4.2 The Need for a National R&DPlan for Carbon Sequestration

Carbon sequestration is promising as acarbon management strategy, but itspotential cannot be evaluated andrealized without a broad program of



research, development, anddemonstration. The specificcomponents of such a plan are thesubjects of Chaps. 2–7. The frameworkfor an integrated carbon sequestrationsystem is presented in Chap. 8.

There are many ways to move ahead onsequestration. Some technologies arealready sufficiently developed to betested in field research experiments(e.g., injecting CO2 into a geologicalformation and monitoring its form,location, and stability). As technologiesprogress, their implications for globalclimate change policy should beevaluated (Parson and Keith 1998).

Many sequestration technologies andpractices will require furtherfundamental scientific andengineering studies before fieldtesting. For example, there are knownagricultural practices for increasingstorage of carbon in plant roots andsoil, but much research needs to bedone to design effective methods forenhancing carbon storage inecosystems and determine theirimpacts.

1.5 END NOTES

1. Avoidance of CO2 emissionsthrough physical capture of CO2

from power plants and disposal ofCO2 in the deep ocean was firstproposed by Marchetti (1977). In theUnited States, preliminary studieswere conducted at BrookhavenNational Laboratory (Steinberg1984).

However, it was not until 1990 thatplanning research efforts wereundertaken in this field. Sincethen, many conferences andstudies have been conducted onoptions for the capture and disposal

or reuse of CO2 from largestationary sources. Much of thiswork has been done under theauspices of IEA’s Greenhouse GasR&D Programme and the successfulconference series on CO2 removaland disposal. It should also benoted that the Offices of FossilEnergy and Science jointlysponsored a research needsassessment (Herzog 1993) and awhite paper (Herzog 1997) on thissubject. Both of these reports werecompleted at the MassachusettsInstitute of Technology.

In the past two years, four importantgovernment documents haveappeared that highlight thepotential for carbon sequestrationand the need for further work.There are recent reports by thePresident’s Council of Advisors onScience and Technology; theFederal Energy R&D Report; thestudy by 11 DOE laboratories calledTechnology Opportunities to ReduceU.S. Greenhouse Gas Emissions(National Laboratory Directors1997); and Carbon Management:Assessment of FundamentalResearch Needs, a product of aseries of DOE workshops (DOE1997). Important conferences andworkshops that have addressedcarbon sequestration have beenfour international conferences onCO

2 removal, the International

Conference on Greenhouse GasControl Technologies in Interlaken,Switzerland in August 1998; theFuels, Decarbonization, andCarbon Sequestration Workshop(Socolow 1997); the Stakeholders’Workshop on Carbon Sequestration(Herzog 1998); and “CarbonSequestration in Soils: Science,Monitoring, and Beyond” heldDecember 1998 in St. Michaels,Maryland, and organized by Pacific



Northwest and Oak Ridge NationalLaboratories. These reports andothers indicate that the potential forsequestration is quite high butlargely unexamined.

2. Several road-mapping activitiesunder way at DOE are related to thedevelopment of this carbonsequestration road map. Forexample, the Office of IndustrialTechnologies is carrying out theIndustries of the Future programthat involves the development andimplementation of technology roadmaps for the most energy-intensiveindustries, including aluminum,steel, chemicals, glass, and forestproducts. Among these activities isa joint effort under way with thechemicals, forest products, andagricultural industries to plan forthe future of plant/crop-basedresources, which includes thedevelopment of new bioenergytechnologies for the coproduction offuels, power, and industrialfeedstocks.

There is also a road map underdevelopment for power generationtechnologies by the offices of FossilEnergy, Nuclear Energy, andEnergy Efficiency and RenewableEnergy in collaboration with theheat and power generationindustries. The Electric PowerResearch Institute is developingtechnology road maps for electricpower generation, transmission,distribution, storage, and end use.These efforts all involve the jointdevelopment and deployment bygovernment and industry ofadvanced technologies, many ofwhich will result in lower carbonemissions, thus affecting the sourceand amount of man-made carbonemissions to be sequestered in thefuture.

1.6 REFERENCES

DOE (Department of Energy) 1997.Carbon Management: Assessment ofFundamental Research Needs, USDOE/ER-0724, Washington, D.C.

EIA (Energy InformationAdministration) 1998a. Annual EnergyReview 1997, DOE/EIA-0384(97), U.S.Department of Energy, Washington,D.C.

EIA (Energy InformationAdministration) 1998b. Emissions ofGreenhouse Gases in the United States1997, DOE/EIA-0573(97), U.S.Department of Energy, Washington,D.C.

Herzog, H. J., E. M. Drake, J. Tester,and R. Rosenthal 1993. A ResearchNeeds Assessment for the Capture,Utilization, and Disposal of CarbonDioxide from Fossil Fuel-Fired PowerPlants, DOE/ER-30194, U.S.Department of Energy, Washington,D.C.

Herzog, H., E. Drake, and E. Adams1997. CO

2 Capture, Reuse, and Storage

Technologies for Mitigating GlobalClimate Change: A White Paper,Massachusetts Institute of TechnologyEnergy Laboratory.

Herzog, H. J., ed. 1998. Proceedings ofthe Stakeholder’s Workshop on CarbonSequestration, MIT EL 98-002,Massachusetts Institute of TechnologyEnergy Laboratory, June.

Hoffert, M. I., K. Caldeira, A. K. Jain,E. F. Haites, L. D. D. Harvey, S. D.Potter, M. E. Schlesinger, S. H.Schneider, R. G. Watts, T. M. L. Wigley,and D. J. Wuebbles 1998. “EnergyImplications of Future Stabilization ofAtmospheric CO

2 Content,” Nature

(395): 881–4.



Houghton, R. A. 1995. “Land-UseChange and the Carbon Cycle,” GlobalChange Biology 1: 275–87.

IPCC (Intergovernmental Panel onClimate Change) 1996. Climate Change1995: The Science of Climate Change,J. T. Houghton, L. G. Meira Filho, B. A.Collander, N. Harris, A. Kattenberg,and K. Maskell, eds., CambridgeUniversity Press, Cambridge, UK.

Keeling, C. D., and T. P. Whorf 1998.“Atmospheric CO

2 Records from Sites

in the SIO Air Sampling Network,” inTrends: A Compendium of Data onGlobal Change, Carbon DioxideInformation Analysis Center, OakRidge National Laboratory.

Marchetti, E. 1977. “OnGeoengineering and the CO2 Problem,”Climate Change 1(1): 59–68.

Marland, G. H., R. J. Andres, T. A.Boden, C. Johnston, and A. Brenkert1998. Global, Regional, and NationalCO

2 Emission Estimates from Fossil Fuel

Burning, Cement Production, and GasFlaring: 1751–1995 (rev. January1998), available at http://cdiac.esd.ornl.gov/ndps/ndp030.html (accessed1/6/99).

National Laboratory Directors 1997.Technology Opportunities to Reduce U.S.Greenhouse Gas Emissions, Oak RidgeNational Laboratory.

Parson, E. A., and D. W. Keith 1998.“Fossil Fuels Without CO

2 Emissions,”

Science 282 (Nov. 6).

PCAST (President’s Committee ofAdvisors on Science and Technology)

1997. Federal Energy Research andDevelopment Agenda for the Challengesof the Twenty-First Century, U.S.Department of Energy, Washington,D.C., November.

Socolow, R., ed. 1997. FuelsDecarbonization and CarbonSequestration: Report of a Workshop,Report 302, Princeton University/Center for Energy and EnvironmentalStudies, September.

Steinberg, M. 1984. An Analysis ofConcepts for Controlling AtmosphericCarbon Dioxide, DOE/CH/00016-1,Brookhaven National Laboratory.

Victor, D. C. 1998. “Strategies forCutting Carbon,” Nature (395): 837–38.

Wigley, T. M. L., R. Richels, and J. A.Edmonds 1996. “Economic andEnvironmental Choices in theStabilization of Atmospheric CO2

Concentrations,” Nature 379(January 18): 240–3.

WRI (World Resources Institute) BritishPetroleum, General Motors, andMonsanto 1998. Climate ProtectionInitiative: Building a Safe Climate, SoundBusiness Future. Washington, D.C.

1.7 ACKNOWLEDGMENTS

Special appreciation is due to MichaelP. Farrell for providing the discussionof the global carbon cycle in Sect. 1.2.1and to Marilyn A. Brown for translationof the Energy InformationAdministration (EIA) U.S. energy flowdata into carbon equivalents inFig. 1.3.

Separation and Capture of Carbon Dioxide 2-1


By 2020, possessthe scientificunderstanding ofCO

2 separation and

capture techniquesand have developedto the point ofdeploymentreadiness thosetechniques thatensure the deliveryof a stream of CO

2,

or other carbonform, at acceptablecosts and ofacceptable purity atthe requisiteconditions ofpressure andtemperature for therespectivesequestrationoptions discussed insubsequentchapters.

SEPARATION AND CAPTURE OFCARBON DIOXIDE

2.1 CHARACTERIZATION OF CARBONFLOWS (SOURCE TERMS)

This chapter and road map address the separationand capture of anthropogenic CO2 only. Separationand capture have been identified as a high-prioritytopic in other reports (Socolow 1997; Herzog 1998;FETC 1998). The costs of separation and capture,including compression to the required pressure forthe sequestration option used, are generallyestimated to make up about three-fourths of thetotal costs of ocean or geologic sequestration(Herzog 1998). A study conducted for the IEAGreenhouse Gas R&D Programme suggests thatsignificantly increased power generation costs willresult from CO2 separation and capture (IEA 1998).Using a base case pulverized coal plant with fluegas desulfurization for comparison, the cost ofeliminating CO2 emissions from advanced powergeneration plants ranged from $35 to $264 pertonne of CO2, and power cost increases rangedfrom 25 to 215 mills/kWh.

The wide range of costs is indicative of thepeculiarities of the advanced power generationplants and the wide range of separation andcapture possibilities. Although some of the moreexpensive methods may be used in certainproduction enterprises with high–value-addedproducts, the less expensive approaches will likelybe used in conventional and advanced powerplants. These less expensive approaches areappropriate for power generation, and anindependent analysis (Herzog 1998) suggeststhese separation and capture approaches wouldincrease power generation costs by about 20 to30 mills/kWh.

The scope of this element of the road map includesall anthropogenic emissions of CO2, with a focuson those sources most amenable to various


22222

2-2 Separation and Capture of Carbon Dioxide


separation and capture methods.Sources that appear to lend themselvesbest to separation and capturetechnologies include large-pointsources of CO

2 such as conventional

pulverized-coal steam power plants;natural-gas-fired combined cycleplants; and advanced power generationsystems, including coal or natural gascombustion plants employing enriched

Primary Energy Sources

This chart depicts energy use inthe United States by primary energysources. For the last 4 years, coalproduction in the United States hasbeen at record levels of over a billionshort tons per year. Most of the coal isconsumed in power generation, as issome natural gas. Most of the naturalgas is used for space heating andother domestic, commercial, andindustrial applications. The greatmajority of oil produced is used fortransportation, and essentially noneis used for electricity generation.This road map focuses on the CO2

sources most adaptable to separationand capture; these include, primarily,power generation, hydrogenproduction, natural gas production,refineries, and industrial processes.

air or oxygen to support combustionwith CO2 recycling, integrated coalgasification (especially oxygen-based)combined cycles, hydrogen turbines,and fuel cells. Many of the advancedsystems will use enriched air oroxygen to support the combustionprocess. The reduction or eliminationof the large volume of diluent nitrogenin process and flue gases dramaticallyimproves the opportunity for theseparation and capture of CO2 fromthese systems. The equipment used forcombustion and processing will rangefrom existing technology (e.g., coal-fired steam plants and gas turbines) toadvanced technology (e.g., productionof hydrogen from fossil fuels).

In addition to power plants, numerousother high-CO2-emitting industrialsources are being considered forapplication of capture andsequestration technologies. In naturalgas production, CO

2 is often generated

as a by-product. Natural gas maycontain significant amounts of CO2

(20% or more by volume), most ofwhich must be removed to producepipeline-quality gas. Therefore,sequestration of CO

2 from natural gas

operations is a logical first step inapplying CO2 capture technology, asdemonstrated by the Sleipner Westproject in Norway, the proposed Natunaproject in Indonesia, and the proposedGorgon project in Australia. Othersignificant industrial sources of CO2

include oil refineries, iron and steelplants, and cement and limeproducers. Although these sourcescontribute only a small fraction of totalCO

2 emissions, separation and capture

of these emissions are feasible andwould contribute significantly tooverall CO

2 emission reduction goals.

Dispersed sources of CO2 emissions,particularly residential buildings andmobile spark ignition and diesel



engines, are especially challengingsources for applying cost-effectiveseparation and capture methods.Although these sources are collectivelylarge, they are not a primary focus ofour road map. However, theintroduction of fuel cells for vehicularpropulsion and power generation mayoccur within the time frame of this roadmap, and depending on the extent oftheir deployment, the need to use fossilfuels to produce hydrogen (H2) for fuelcells could have a significant impacton CO2 separation and capture. Forexample, if buses and vehicle fleetsmove toward on-board H2 storage,central H2 production facilities may bebuilt that would allow CO2 separationand capture. Such central H2

production facilities are considered inthis road map. Other advanced powersystems, such as hydrogen turbinesthat would use H2 as fuel, also have

important implications with respect tothe need for central H

2 production

facilities and the opportunity for CO2

separation and capture. Electricvehicles may also come intowidespread use during the time frameof this road map. Should that occur,separation and capture of CO

2 at the

central power stations that produce theelectricity for recharging electricvehicle batteries would indirectlyreduce CO2 emissions from thetransportation sector. However, one ofthe consequences of the deregulationof the electric power industry may bethe introduction of a significantdistributed power supply. Dependingon the size and nature of these powergeneration plants, such a changemight have a negative impact on theability to separate and capture CO2.

Carbon dioxide concentrations ineffluent streams will range from ~5%for current power generation plants toalmost 100% for some advancedtechnologies. All separation andcapture feed streams are likely tocontain small amounts of impuritiessuch as oxygen, sulfur oxides, andnitrogen oxides from combustion ofnatural gas or advanced processing offossil fuels to yield hydrogen. For somecurrent and emerging technologiesinvolving combustion of coal, the feedstreams will contain large amounts ofnitrogen, oxygen, water vapor,particulates, and volatile andsemivolatile chemical species as well.The feed stream may also becontaminated with chemicals used toremove other constituents (e.g., sulfuror nitrogen oxides). Feed-streampressures will range from essentiallyambient for current technologies totens of atmospheres for some advancedprocesses. Feed-stream temperatureswill range from very warm (~50°C) tohot (hundreds of degrees).

Advanced Power Plants

Advanced coal-fired power plants,such as this 800-ton-per-day coalgasification pilot/demonstrationplant, will have energy conversionefficiencies 20 to 35% higher thanthose of conventional pulverized coalsteam plants. These advanced plantsare also much more amenable tocarbon management than areconventional plants. (Photo courtesy ofTom Lynch of Dynegy)



2.2 CURRENT AND POTENTIALSCIENCE AND TECHNOLOGYREQUIREMENTS

The goal of CO2 separation and capture

is to isolate carbon from its manysources in a form suitable for transportand sequestration. The technologyrequired to perform this functiondepends on the nature of the carbonsource and carbon form(s) that aresuitable for subsequent steps leadingto sequestration. Many forms arepossible, including gaseous andsupercritical CO2 and even clathrates.High levels of purity (99+%) arepossible, but at significant cost.

The impurities in the product must beof sufficiently low concentrations thattransportation and sequestrationoperations are not compromised. Thepurity requirements imposed bysequestration operations are notknown because sequestrationtechnology is being developedconcurrently. Some initialinvestigation to develop provisionalpurity requirements will be necessaryand will be reviewed and modified asthe requirements of varioussequestration options become clear.End-state specifications may be for thefinal product of separation and captureor for an intermediate product that isconverted to another form (e.g., acarbonate) before transport. Separationand capture processes that operate oneffluent streams, as well as those thatare integral elements of optimizedadvanced processing flow sheets, willbe considered.

2.3 CURRENT AND POTENTIALSCIENCE AND TECHNOLOGYCAPABILITIES

Categorized in this section are whatare believed to be conventional

separation and capture options that areapplicable for anthropogenic CO

2

emissions. It is not presumed that thecategories or methods within thecategories are exhaustive; certainly,little-known or as-yet-unknowntechniques could ultimately becomepreferred options. For those CO

2

separation and capture methodsidentified, performance characteristics,including CO

2 product purity and

operating conditions, differ because ofoperational or technicalconsiderations. These characteristicsof CO2 separation and capturetechnologies are the basis for matchingthem with the technologies that are theanthropogenic sources of CO2.

The most likely options currentlyidentifiable for CO2 separation andcapture include

• chemical and physical absorption• physical and chemical adsorption• low-temperature distillation• gas-separation membranes• mineralization and

biomineralization• vegetation

These were identified and included asprobable options because of processsimplicity, environmental impact, andeconomics. Currently, several CO

2

separation and capture plants use oneor more of these methods to produceCO

2 for commercial markets. The

vegetation separation and somemineralization methods are alsosequestration methods and arediscussed in the appropriate focus areachapters.

2.3.1 Chemical and PhysicalAbsorption

Carbon dioxide can be removed fromgas streams by physical or chemicalabsorption. Physical absorption



processes are governed by Henry’s law(i.e., they are temperature and pressuredependent with absorption occurringat high pressures and lowtemperatures). Typically, theseprocesses are used when theconcentration (i.e., partial pressure ofCO

2) is high (>525 kPa). The removal of

0.1 to 6% CO2 from natural gasproduction wells by chemicalabsorption using amines can bedeployed conveniently in remotefields. Currently, this approachrepresents the most widely deployedcommercial technology for capture.However, in other commercialapplications, the typical solvents forphysically absorbing CO2 includeglycol-based compounds (e.g., thedimethylether of polyethylene glycol)and cold methanol.

Chemical absorption is preferred forlow to moderate CO2 partial pressures.Because CO2 is an acid gas, chemicalabsorption of CO

2 from gaseous streams

such as flue gases depends on acid-base neutralization reactions usingbasic solvents. Most common amongthe solvents in commercial use forneutralizing CO2 are alkanolaminessuch as monoethanolamine (MEA),diethanolamine (DEA), andmethyldiethanolamine (MDEA). Otherchemical solvents in use are ammoniaand hot potassium carbonate. Fluegases are typically at atmosphericpressure. Depending on the CO

2

content of the flue gas, the partialpressure of CO2 can vary from 3.5 to21.0 kPa. At such low partial pressures,alkanolamines are the best chemicalsolvents to enable good CO2 recoverylevels; however, use of these solventsmust be balanced against the highenergy penalty of regenerating themusing steam-stripping.

Flue gases typically contain con-taminants such as SO

x, NO

x, O

2,

Sleipner T Platform

The Sleipner T (T = treatment)platform in the North Sea is usedby Statoil, the Norwegian state oilcompany, to remove CO2 from sub-quality natural gas. An amineabsorption process is used toremove the CO2, which is thencompressed and piped to theadjacent Sleipner A platform forinjection into the Utsira formation1000 m below the seabed (seeChap. 5). Sleipner T is represen-tative of the absorption technologythat could be used for separationand capture of CO2, and it is usedspecifically as a CO2 mitigationstrategy. This is the largest CO2

separation, capture, and seques-tration operation in the world,sequestering about a million tonesof CO2 per year. (Photo courtesy ofOlav Kaarstad of Statoil.)



hydrocarbons, and particulates. Thepresence of these impurities canreduce the absorption capacity ofamines as well as create operationaldifficulties such as corrosion. To avoidsuch problems, these contaminants areoften reduced to acceptable levelsthrough the use of suitablepretreatment techniques. Somecommercial processes handle thesedifficulties through pretreatment and/or the use of chemical inhibitors in theabsorption process. However, theseprocesses tend to be more expensivethan conventional alkanolamine-based absorption processes.

Some of the typical operating problemsencountered in using conventionaltrayed or packed columns for gas-liquid contact are foaming, vaporentrainment of the solvent, and theneed to replenish the solvent in lowquantities. However, these problemshave a relatively small effect on thetotal system costs of the alkanolamine-based absorption process. Membranecontactors that typically use polymericmembranes can offer some advantagesover conventional contactors, whichare expected to be most advantageouswhere system size and weight need tobe minimized (e.g., on oceanplatforms). Potential benefits includethe elimination of foaming and vaporentrainment, as well as the ability tomaintain liquid and gas flow ratesindependently.

2.3.2 Physical and ChemicalAdsorption

Selective separation of CO2 may beachieved by the physical adsorption ofthe gas on high-surface-area solids inwhich the large surface area resultsfrom the creation of very fine surfaceporosity through surface activationmethods using, for example, steam,oxygen, or CO

2. Some naturally

CO2 Separation in HydrogenProduction

Separation of CO2 and othercontaminant gases usingadsorption systems is acommercial practice in theproduction and purification ofhydrogen. The reformer hydrogenplant shown produces 35 millionstandard cubic feet of hydrogenand about 9 million standardcubic feet of CO2 per day. Theseplants are not usually operated ina mode that results in completeconversion of methane tohydrogen and CO2. However,operational modifications couldbe made in which essentiallypure hydrogen and CO2 would beproduced. Numerous plants suchas this one are in use worldwide,but the CO2 is typically vented tothe atmosphere. (Photo courtesy ofJoe Abrardo of Air Products andChemicals)



occurring materials (e.g., zeolites) havehigh surface areas and efficientlyadsorb some gases. Adsorptioncapacities and kinetics are governedby numerous factors includingadsorbent pore size, pore volume,surface area, and affinity of theadsorbed gas for the adsorbent.

An IEA study (1998) evaluated physicaladsorption systems based on zeolitesoperated in pressure swing adsorption(PSA) and thermal, or temperature,swing adsorption (TSA) modes. In PSAoperation, gases are adsorbed at highpressures, isolated, and then desorbedby reducing the pressure. A variant ofPSA, called vacuum swing adsorption,uses a vacuum desorption cycle. InTSA operation, gases are adsorbed atlower temperatures, isolated, and thendesorbed by heating. These processesare somewhat energy-intensive andexpensive. The IEA report concludesthat PSA and TSA technologies are notattractive to the gas- and coal-fueledpower systems included in that study.Nevertheless, PSA and TSA arecommercially practiced methods of gasseparation and capture and are used tosome extent in hydrogen productionand in removal of CO

2 from subquality

natural gas. Therefore, these methodsclearly are applicable for separationand capture of CO

2 from some relatively

large-point sources.

2.3.3 Low-Temperature Distillation

Low-temperature distillation is widelyused commercially for the liquefactionand purification of CO2 from high-purity sources (typically a stream with>90% CO

2). In low-temperature

distillation, a low-boiling-temperatureliquid is purified by evaporating andsubsequently condensing it. However,such processes are not used forseparating CO2 from significantlyleaner CO

2 streams. The application of

distillation to the purification of leanCO

2 streams necessitates low-

temperature refrigeration (<0°C) andsolids processing below the triple pointof CO

2 (–57°C). A patented process to

separate CO2 from natural gas,providing liquid CO2, is an example ofsuch a low-temperature process(Valencia and Denton 1985; Victoryand Valencia 1987).

Distillation generally has goodeconomies of scale, as it is cost-effective for large-scale plants, and itcan generally produce a relatively pureproduct. Distillation is most cost-effective when feed gases containcomponents with widely separatedboiling points, and when the feed gasis available at high pressure and mostof the products are also required athigh pressure. Low-temperaturedistillation enables direct productionof liquid CO2 that can be stored orsequestered at high pressure via liquidpumping. The major disadvantage ofthis process is that, if othercomponents are present that havefreezing points above normal operatingtemperatures, they must be removedbefore the gas stream is cooled to avoidfreezing and eventual blockage ofprocess equipment. Anotherdisadvantage is the amount of energyrequired to provide the refrigerationnecessary for the process.

Most CO2 emissions being considered

for CO2 capture are produced incombustion processes. Such streamscontain water and other tracecombustion by-products such as NOx

and SOx, several of which must beremoved before the stream isintroduced into the low-temperatureprocess. These by-products are usuallygenerated near atmospheric pressure.These attributes, coupled with theenergy intensity of low-temperaturerefrigeration, tend to make distillation



less economical than other routes. Theapplication of low-temperaturedistillation, therefore, is expected to beconfined to feed sources at highpressure and with high CO

2

concentrations (e.g., gas wells).

2.3.4 Gas-Separation Membranes

Gas-separation membranes are ofmany different types, and although theefficacy of only a few of these types inseparating and capturing CO2 has beendemonstrated, their potential isgenerally viewed as very good.Diffusion mechanisms in membranesare numerous and differ greatlydepending on the type of membraneused. Generally, gas separation isaccomplished via some interactionbetween the membrane and the gasbeing separated. For example,polymeric membranes transport gasesby a solution-diffusion mechanism(i.e., the gas is dissolved in themembrane and transported through themembrane by a diffusion process).Polymeric membranes, althougheffective, typically achieve low gastransport flux and are subject todegradation. However, polymermembranes are inexpensive and canachieve large ratios of membrane areato module volume.

Palladium membranes are effective inseparating H2 from CO2, but gas fluxesare typically very low, and palladium issubject to degradation in sulfur-containing environments. Porousinorganic membranes, metallic orceramic, are particularly attractivebecause of the many transportmechanisms that can be used tomaximize the separation factor forvarious gas separations. Porousinorganic membranes can be 100 to10,000 times more permeable thanpolymeric membranes. (Permeance isthe volume of gas transported through

a membrane per unit of surface areaper unit of time per unit of differentialpressure.) However, the cost forinorganic membranes is high, and theratio of membrane area to modulevolume is 100 to 1000 times smallerthan that for polymer membranes.These factors tend to equalize the costper membrane module. The inorganicmembrane life cycle is generallyexpected to be much longer. Inorganicmembranes can be operated at highpressures and temperatures and incorrosive environments, yet still havevery long life cycles. They are also lessprone to fouling and can be used inapplications where polymermembranes cannot.

Considerable interest and R&D arebeing focused on zeolite-type materialsto achieve a membrane with molecularsieving characteristics. However, thepermeance of such membranes tendsto be substantially lower than desired.These are high-cost membranesbecause the methods for fabricatingthem are expensive.

Inorganic membranes can be madewith effective pore diameters as smallas 0.5 nm and as large as desired.Membranes can be made with a widerange of materials, and pore size andmaterial can be changed to improvepermeance and separation factor. Largeseparation factors are essential toachieve desired results in a singlestage. Inorganic membranes can bemade to separate small molecules fromlarger molecules (molecular sieves) orto separate certain large moleculesfrom smaller molecules (enhancedsurface flow). This latter effect isimportant because it allows separationthat will keep the desired gas either onthe high-pressure or the low-pressureside of the membrane. Note that theoperating conditions play an importantrole in determining the change in



mole fraction across a membrane andthe amount of the desired gas that canbe recovered (captured). There must bea partial pressure gradient of thedesired gas across the membrane toachieve a flow of that gas through themembrane.

With all the design parametersavailable, it is likely that an inorganicmembrane can be made that will beuseful for separating CO2 from almostany other gas if appropriate operatingconditions can be achieved. However,for multiple gas mixtures, severalmembranes with differentcharacteristics may be required toseparate and capture high-purity CO2.

2.4 SCIENCE AND TECHNOLOGYGAPS

We present here our views on the gapsin science and technology and theR&D required to fill or span these gapsin order that our vision may beachieved. As a result in large measureof the state of separation and capturetechnology, the R&D projects requiredto address these needs will be of thetype that has been described as“Pasteur’s Quadrant” research. Thistype of research seeks to extend thefrontiers of understanding but is alsoinspired by considerations of use. Weextend that description somewhat inthat our R&D recommendations refer toa science-based technologydevelopment approach.

2.4.1 Chemical and PhysicalAbsorption

The issue of the recovery of volatiletrace elements, such as mercury, infossil fuel is a factor in the regulatoryprocess and must be considered in thecontext of this road map. The optimalrecovery strategy for trace elements

may not be consistent with an optimalstrategy for CO

2 capture. Also, using

current technologies, minimizingenergy costs for CO2 capture willprobably not be compatible with a100% CO2 capture strategy. Betteroptions must be developed to reducetotal system costs for CO

2 recovery.

Specific needs are listed below.

• Significant development work onmembrane contactors is needed toimprove their chemicalcompatibility with alkanolaminesand high-temperature resistance,as well as to lower costs.

• Commercially availablealkanolamines such as MEA, DEA,and MDEA have different costs,rates of reaction with CO

2,

absorptive capacities, and corrosionrates. Researchers have anopportunity to optimize existingsolvents or develop new solvents toreduce total capital and operatingcosts. Some development ofchemical and physical solvents andsystems will be required to achievethe vision of this road map.

• It is likely that novel solvents andsystem components will reduce thecapital and energy costs for flue gastreatment to separate and captureCO2. Prudent courses of actioninclude investment in R&D onnovel solvents, particularly thoseamenable to use in advancedsystems, and investment in systemstudies to identify the best possibleconfigurations of processes andequipment, particularly as theyrelate to cost and processsimplicity.

• Considerable interest has beenshown in the concept of retrofittingconventional pulverized-coalboilers for CO

2 recycling to increase

the CO2 concentration to the pointwhere recovery becomeseconomically feasible.



• Molecular modeling of theabsorption process is indicated toaid in the selection of absorbents.

• Kinetic modeling is needed toestablish or confirm rate-limitingsteps in the absorption process.

• Synthesis of absorbents based inpart on molecular and kineticmodels is an appropriate R&Dinvestment.

• Systems that use air to supportcombustion present difficulties inseparation and capture of CO2

because of the large amount (~80%)of nitrogen diluent in the processstream. Integrated gasificationcombined cycle (IGCC) power plantscould provide an ideal opportunityfor CO2 capture when oxygen ratherthan air is used to support thegasification process. (In combinedcycles, which include gas turbinesand steam turbines, the hot exhaustgases from the gas turbines areused to generate steam to drive thesteam turbines.) Coal-derived gasfor gas turbines is produced in ahighly concentrated, pressurizedform that allows for the use of avariety of solvents that can captureCO2 from the gas stream beforecombustion, which may also be inoxygen rather than air. As abaseline case, the cost and energybenefits of chemical absorptionprocesses integrated into an IGCCor other advanced power systemmust be demonstrated in acommercial setting as a real-caseoption.

• Novel gas/liquid contactors mustbe developed to minimize mass-and heat-transfer effects in gasscrubbing. The contactors mighttake advantage of so-called“structured packing” or even“microchannel reactors.” Usingmicrochannel hardware, highlycompact and efficient absorption

systems could be developed thatconsist of an absorber/heatexchanger and desorber. Becausethe dimensions of the channels aremeasured in micrometers, heat-and mass-transfer effects arelimited. Isothermal operation couldproduce higher absorption capacity.The technical challenges formicrochannel reactors will be costcontainment, prevention ofplugging, and high throughput.Other potential problems includescale-up, corrosion, and solventcarryover.

2.4.2 Physical and ChemicalAdsorption

H2 production plants that use PSA

produce an impure CO2 streamcontaining unrecovered hydrogen,methane, CO, and nitrogen. Thisstream is recycled to the reformer asfuel, becoming the flue gas from thereformer. Physical adsorbents sufferfrom low selectivity and low capacity,and they are limited to operation at lowtemperatures.

• Adsorbents that can operate athigher temperatures in thepresence of steam must bedeveloped and are already underconsideration.

• Indicated programs include R&Daimed at the synthesis ofadsorbents with increasedadsorptive capacity and improvedkinetics and capable of producing apure CO

2 product, as well as R&D

directed to improving methods foreffecting the adsorption-desorptionprocess.

• Molecular modeling of adsorbentsis needed to aid in theidentification of adsorbentsselective to CO2.



• Kinetic modeling to identify rate-limiting steps and to provide afocus for adsorbent development isneeded.

• New steam-tolerant, high-temperature sorbent materials needto be developed and coupled withnovel process concepts. Unlikezeolites and other inorganicsorbents, these sorbent materialswould be capable of adsorbing CO

2

in the presence of steam. Thesorbent would be regenerated in alow-energy-intensive manner.Regenerability would eliminatematerial-handling problems whennonregenerable natural mineralsare used. Stability of the sorbentover thousands of cycles needs tobe demonstrated.

• Other novel adsorption concepts forCO2 separation and capture arelikely, and R&D on novel conceptsshould be pursued. If adsorbentscan be developed that are capable ofadsorption at high temperature anddesorption using novel processes,they could significantly improvethe ability to control CO

2 emissions

from fossil-fueled power systems.

2.4.3 Low-Temperature Distillation

To extend the viability of low-temperature distillation processes,several development activities wouldbe required.

• Process cycle development andprocess integration studies forspecific applications are needed.

• Integration with sequestrationprocesses and development ofefficient and novel refrigerationcycles may enable competitive low-temperature distillation processes.Comparison with other technologyoptions will ultimately depend onthe specific application andopportunity.

2.4.4 Gas-Separation Membranes

Considerable R&D is required torealize the potential of membranes forseparation and capture of CO

2,

particularly at higher temperaturesand pressures.

• R&D on polymeric membranes isessentially restricted to changingthe composition of the polymer toincrease the dissolution anddiffusion rates for the desired gascomponents.

• Experience has shown an apparentlimit to the effectiveness ofpolymeric membranes. The polymercomposition can be changed toincrease the membrane permeance,which invariably decreases theseparation factor. The converse isalso true: changing the compositionto increase the separation factorreduces the membrane permeance.Although there is not nearly soextensive an accumulation of datafor inorganic membranes, theavailable data do not indicate acorresponding relationship forinorganic membranes.

• R&D in molecular modeling isneeded to indicate the potential ofmembranes to separate CO2.

• Kinetic modeling should be used toestablish the potential flux of gasesin membrane systems.

• Novel membrane synthesis methodsshould be developed.

• Inorganic, palladium-basedmembrane devices could bedeveloped that reform hydrocarbonfuels to mixtures of hydrogen andCO2 and that, at the same time,separate the high-value hydrogen.The remaining gas, predominantlyCO2, would be recovered in acompressed form. The hydrogencould be used in future fuel cellsystems or advanced turbine powersystems. Pure hydrogen, when



burned to generate power, produceswater vapor as the only product ofcombustion. Daunting issuesinclude capital costs andstabilization of the membrane inhighly corrosive gases if coal isused.

2.4.5 Product Treatment andConversion

As noted previously, the product of theseparation and capture function willbe CO2. However, the attributes of theCO2, such as its concentration,impurities, pressure, and temperature,will differ for the respectivecombinations of sources andseparation and capture methodsemployed. Absorption processes, forexample, may be manipulated to yieldCO2 streams of very high purity, andthose CO2 streams will generally be atsource pressures. For those optionsthat will sequester carbon as CO2, it isassumed that the CO2 will be subjectedto the purification treatment andpressurization required fortransportation and for sequestration.The CO

2 product may be provided at

90 to 99+% purity, at temperaturesranging from cryogenic to a fewhundred degrees Celsius, and atpressures from atmospheric to morethan 3.5 MPa. Different carbon forms(other than CO

2) may also be required

for some of the sequestration options.R&D should address

• full-cycle analysis of producttreatment and conversion to meetthe requirements of transportationand sequestration

• conversion of CO2 to the requiredform for the particular seques-tration option

• the disposition of the variety of by-products that may be producedduring conversion of the CO2 toother products

2.4.6 Transportation

In some scenarios, the separation andcapture process will be remote from thesequestration process. Any R&Dprogram must include carbon transportto the sequestration site and shouldaddress primarily systems aspects suchas optimization and integration of thecarbon sources, separation andcapture, transportation, andsequestration.

2.4.7 Advanced Concepts

This section addresses advancedconcepts that have been identifiedand/or advocated as having significantpotential for CO2 separation andcapture. In one advanced concept,CO2-containing gases are dissolved inwater, followed by the formation of CO2

hydrates in which CO2 is trapped in a

crystalline ice-like solid. The processrequires gases at about 0°C and 1 to7 MPa, depending on the other gasespresent and on the partial pressure ofCO2 in the gas stream. The formation ofCO

2 hydrates may be especially

amenable to removal of CO2 frompressurized gas streams with minimalenergy losses.

An advanced approach, calledelectrical swing adsorption (ESA), thataddresses many of the issues of PSAand TSA systems uses a novel carbon-bonded activated carbon fiber as theadsorption medium (Burchell et al.1997). Activation conditions for theseadsorbents may be varied to increaseor decrease pore size, pore volume, andsurface area to improve the effective-ness of the carbon fiber as a CO

2

adsorbent. This material is also highlyconductive electrically, so adsorbedgases can be rapidly, effectively, andefficiently desorbed by passing a low-voltage electrical current through thematerial. This adsorption-desorption



process may be used with no variationof system pressure and with minimalvariation in system temperature. Theelectrical energy required fordesorption is approximately equal tothe heat of adsorption of the adsorbedgas; thus the ESA process is promisingas an energy-efficient, economical gasseparation and capture method.

Another novel technology is referred toas “chemical-looping combustion,” ormore recently as “sorbent energytransfer.” In this process, the fossil fuel(gasified coal or natural gas) transfersits energy to reduce a metal oxide,producing steam and high-pressureCO2 that can be sequestered with littleadditional compression energy. Thesteam is used in a steam turbine toproduce electricity. The metal is thenreoxidized in air, producing heat to

raise the temperature of a high-pressure stream of air or nitrogen todrive a gas turbine to generate moreelectricity. The oxidized metal is sentto the reducing vessel to repeat thecycle. The barriers to any newcombustion system are legion; this isalso true even of conventional coalcombustion using oxygen instead ofair with CO2 recycling.

2.5 ALIGNMENT OF REQUIREMENTSTO CAPABILITIES (R&D ROADMAP)

As indicated in the preceding section,numerous R&D needs and oppor-tunities exist for improvements andinnovations related to CO2 separationand capture. Figure 2.1 presents anR&D road map for pursuing the stated

Fig. 2.1. Separation and capture R&D road map.



goal. Based on the analysis presentedhere, as well as analyses presented inthe references to this chapter,separation and capture of CO2 fromanthropogenic sources for seques-tration via any of several optionsappear to be possible. Notwithstandingthis possibility, a disciplined R&Dprogram directed to improvements incurrently available technology,extension of current developments,and pursuit of innovative and novelapproaches is critical to ensuring theability to effectively and efficientlycapture CO2 at costs that are notprohibitive.

2.6 REFERENCES

Burchell, T. D., R. R. Judkins, M. R.Rogers, and A. M. Williams 1998. “ANovel Process and Material for theSeparation of Carbon Dioxide andHydrogen Sulfide Gas Mixtures,”Carbon, 35(9): 1279–94.

FETC (Federal Energy TechnologyCenter) 1998. Proceedings of theGovernment Workshop on CarbonSequestration, Morgantown, WestVirginia, July 23–24, 1998(forthcoming).

Herzog, H. J. 1998. “The Economics ofCO2 Capture,” presented at the Fourth

International Conference onGreenhouse Gas Control Technologies,Interlaken Switzerland, August 30–September 2.

Herzog, H. J., ed., 1998. Proceedings ofthe Stakeholders’ Workshop on CarbonSequestration, MIT EL 98-002,Massachusetts Institute of TechnologyEnergy Laboratory, June.

IEA (International Energy Agency)1998. Carbon Dioxide Capture fromPower Stations, available atwww.ieagreen.org.uk/sr2p.htm.

Socolow, R., ed. 1997. FuelsDecarbonization and CarbonSequestration: Report of a Workshop,Report 302, Princeton University/Center for Energy and EnvironmentalStudies, September.

Valencia, J. A., and R. D. Denton 1985.“Method and Apparatus for SeparatingCarbon Dioxide and Other Acid Gasesfrom Methane by the Use of Distillationand a Controlled Freezing Zone,” U.S.Patent 4,533,372, August 6.

Victory, D. J., and J. A. Valencia 1987.“The CFZ Process: Direct Methane–Carbon Dioxide Fractionation,”presented at the 66th annual GasProcessors Association Convention,Denver, Colo., March.

Ocean Sequestration 3-1


OCEAN SEQUESTRATION

The ocean represents a large potential sink forsequestration of anthropogenic CO

2 emissions.

Although the long-term effectiveness andpotential side effects of using the oceans in thisway are unknown, two methods of enhancingsequestration have been proposed:

• the direct injection of a relatively pure CO2

stream that has been generated, for example,at a power plant or from an industrialprocess (see Sect. 3.1)

• the enhancement of the net oceanic uptakefrom the atmosphere, for example, throughiron fertilization (see Sect. 3.2)

Other pathways are also possible but wouldprobably require longer time frames to bedeveloped (see Sect. 3.3). For a given pathway,our goal is to analyze the tradeoffs among cost,long-term effectiveness, and undesirablechanges to the ocean ecosystem.

On average, the ocean is about 4000 m deepand contains 40,000 GtC (IPCC 1996). It ismade up of a surface layer (nominally 100 mthick, but the depth varies), a thermocline(down to about 1000 m deep) that is stablystratified, and the deep ocean below 1000 m. Itswaters circulate between surface and deeplayers on varying time scales from 250 years inthe Atlantic Ocean to 1000 years for parts of thePacific Ocean. The amount of carbon thatwould cause a doubling of the atmosphericconcentration would change the deep oceanconcentration by less than 2%.

Currently, net oceanic uptake of 2 ± 0.8 GtC/year1 results from the growth of anthropogenic


33333

By 2025,develop (1) thetechnology toimplementoceansequestrationof CO

2, (2) the

knowledge tounderstand itseffects onmarineecosystemsand on theocean’sbiogeochemicalcycles, and(3) themodeling toolsto determinethe long-termfate ofsequesteredCO

2.

1This number for net ocean uptake is from IPCC and is

based on data for the mid-1980s. Changes in sea-airforcing since then should have increased this fluxslightly.

3-2 Ocean Sequestration


CO2 in the atmosphere. On a time scaleof 1000 years, about 90% of today’santhropogenic emissions of CO2 will betransferred to the ocean (see Fig. 3.1).Ocean sequestration strategies attemptto speed up this process to reduce bothpeak atmospheric CO2 concentrationsand their rate of increase.

Although the ocean’s biomassrepresents about 0.05% of theterrestrial ecosystem, it converts aboutas much inorganic carbon to organicmatter (about 50 GtC/year) as doprocesses on land. The photosyntheticfixation of CO2 by ocean organisms,followed by the sinking and reminer-alization (conversion to CO2) of organiccarbon, is a natural process forsequestering CO

2 in the deep sea. This

process is often referred to as the“biological pump” (see Fig. 3.2).

The question is whether we can usethe deep sea as a site for sequestrationof additional anthropogenic CO

2. Many

people are wary of ocean sequestration,including some authors of this chapter,because it is known that small changesin biogeochemical cycles may havelarge consequences, many of which aresecondary and difficult to predict.Nevertheless, ocean sequestration isoccurring on a large scale today, andentrepreneurs are already trying tocommercialize ocean sequestrationtechnologies. Therefore, it is imperativeto conduct research to betterunderstand the risks as well as theopportunities. The ocean plays animportant role in sustaining thebiosphere, so any change in ocean

ecosystem function must be viewedwith extreme caution.

How much carbon can the oceansequester? Because of high pressuresprevailing in deep ocean environ-ments, a large quantity of CO2

(exceeding the estimated availablefossil fuel resources of 5,000 to10,000 GtC) may be dissolved in deepocean waters. However, a more realisticcriterion needs to be based on anunderstanding of the biogeochemistryof the oceans. At present, we do nothave enough information to estimatehow much carbon can be sequesteredwithout perturbing marine ecosystemstructure and function; obtaining thisinformation is one of the goals of theproposed research (Takahashi et al.1981; Sarmiento and Bender 1994).2

Fig. 3.1. Every year the ocean activelytakes up one-third of our anthropogenic CO2emissions. Eventually (over 1000 years), about90% of today’s anthropogenic emissions of CO2

will be transferred to the ocean. Oceansequestration strategies attempt to speed upthis ongoing process to reduce both peakatmospheric CO2 concentrations and their rateof increase.

2As an example calculation with no implications as to what an environmentally acceptable amountis, adding about 1300 GtC to the ocean would result in a pH decrease of 0.3. This pH change issimilar to the change that will occur in the surface ocean as a result of doubling the preindustrialamount of atmospheric CO2. The change in surface seawater pH today, from that of preindustrialtimes, is already 0.1.



3.1 DIRECT INJECTION OF CO2

The direct injection of CO2 into theocean requires starting with a fairlyconcentrated stream of CO

2 and

delivering it to locations in the oceanwhere it will be effectively sequesteredfor hundreds of years, if not longer. Toaccomplish this, CO2 will most likely beinjected as a liquid below thethermocline at depths greater than1000 m (Herzog 1998). One limitationof this approach is that it is best suitedto large, stationary CO

2 sources with

access to deep-sea seques-tration sites—sources thatmay account for about 15 to20% of our anthropogenic CO2

emissions.

We have the technology toproceed with this option.However, we do not have theknowledge to adequatelyoptimize the costs, determinethe effectiveness of thesequestration (i.e., its impactin mitigating climate change),and understand the resultingchanges in the biogeochemi-cal cycles of the oceans. Thissection addresses how we maygain this knowledge.

3.1.1 Science and TechnologyRequirements

There are many technicaloptions for sequestration bydirect injection of CO

2. For

example, injections may occurat moderate depths (1000–2000 m), at deep depths(>3000 m), in depressions onthe ocean floor, or even intothe suboceanic crust of theearth. The CO2 may besequestered by dissolution in

the water column or by the formation ofCO2 hydrates, which are solid, ice-likecompounds. The delivery of the CO2

may be by pipeline or tanker. In allcases, on the scale of kilometersaround the injection point, near-fieldcomputer models are needed tounderstand the physical and chemicalinteractions between CO2 and seawaterand the interaction between CO

2-

enriched seawater and stratifiedsurrounding water. One challenge is todetermine how to use the bufferingeffect of bottom sediments (e.g., theability of calcium carbonate to reactwith the CO

2) to increase the capacity

Fig. 3.2. A schematic diagram of the biologicalpump. In this generalized pelagic food web, CO2 is beingfixed by phytoplankton through photosynthesis.Phytoplankton are consumed by zooplankton that may, inturn, be consumed by higher trophic organisms, such asfish. Organic carbon in the form of detritus (e.g., fecalpellets, decaying organisms) sinks to the ocean depths,where it is remineralized to CO2 by bacteria en route.



and effectiveness of oceansequestration (Archer 1996). Anotherchallenge is to understand thekinetics associated with the formationof CO

2 hydrates and to try to take

advantage of their properties (e.g.,increased density, lower mass transfercoefficient) for carbon sequestration.Finally, engineering analysis isrequired to estimate the costs of thevarious injection pathways.

Sequestration effectiveness willdepend on the exact depth andlocation of the injection. In general,the deeper the CO2 is injected, themore effectively it is sequestered; butinjecting deeper requires moreadvanced technologies and mayincrease costs. Regional and globalocean general circulation models(OGCMs) are required to quantifysequestration effectiveness bycalculating the reduction inatmospheric CO2 as a function of timeas a result of various ocean seques-tration strategies. However, OGCMsmust be improved to reduce theuncertainty associated with theirresults.

Environmental impacts near theinjection point must be detailed, andthe long-term, broad-scale impacts onthe function of the ocean ecosystemmust be understood. The mostsignificant environmental impact isexpected to be associated with loweredpH as a result of the reaction of CO2

with seawater. Non-swimming marineorganisms residing at depths of about1000 m or greater are most likely to beaffected adversely by more acidicseawater; the magnitude of the impactwill depend on both the level of pHchange and the duration of exposure.The microbial community would alsobe affected, causing unknown impactson biogeochemical processes that playa crucial role in the ocean carbon

cycle. Local environmental impactsmay be minimized by designing theinjection system to disperse the CO2.Specific needs for R&D includegathering baseline data andimplementing cost-effectivemonitoring. Robust, predictive modelscould help reduce the costs ofmonitoring by focusing sampling onareas of greatest potential impact.

3.1.2 Current Scientific andTechnological Capabilities

Led by offshore exploration andproduction activities of the oil and gasindustry, great strides have been madein the development of underseaoffshore technology. It is becomingroutine to work in depths approaching2000 m. Work at much deeper depths,even approaching 10,000 m, is possibleat reduced scales and/or timehorizons, as has been shown in deepdrilling and other scientific programs.However, many technical challengesstill exist in going deep at large scalesfor extended times. Therefore, as a firststep, it appears that the best strategy isto discharge the CO2 below thethermocline at moderate depths of1000 to 2000 m.

To implement that strategy, severalmethods of injection have beenproposed (Fig. 3.3). One method is totransport the liquid CO2 from shore in apipeline and to discharge it from amanifold lying on the ocean bottom,forming a rising droplet plume.Another method is to transport theliquid CO2 by tanker and thendischarge it from a pipe towed by themoving ship. Although the means ofdelivery are different, the plumesresulting from these two options wouldbe quite similar and, therefore,research on these two injectionmethods should be consideredcomplementary.



Once the CO2 leaves the pipe, our

current capabilities are much morelimited. Models do exist to characterizethe near-field plume, but they have notbeen validated with experimental data.We know that CO2 hydrates may beformed from the injected CO

2 (see the

sidebar on formation of CO2 hydrates).The thermodynamic behavior ofhydrates is well understood and theirkinetics have been extensivelyinvestigated. However, we do not fullyunderstand the kinetics that willcontrol the formation and dissolutionof hydrates in seawater, especiallyunder the dynamic conditions in theplume.

Regional and global OGCMs areavailable to describe the ultimate fateof the injected CO2 by modeling itsbehavior in the mid-field (tens tohundreds of kilometers from theinjection point) and in the far field(hundreds of kilometers and greaterfrom the injection point) (Fig. 3.4).

These models cansimulate broad charac-teristics of observedtransient tracer fields(e.g., chlorofluoro-carbons, carbon-14, andtritium), whose move-ments can be detected inthe open ocean.However, for modelingthe fate of a point sourcesuch as injected CO2, theuncertainties are largeand the results will notbe definitive.

Perhaps the area we areleast capable of under-standing is the environ-mental consequences ofCO2 injection. We dounderstand the ocean’scapacity to neutralize

the water that is acidified by injectedCO2. We have models to predict pHchanges to tens of kilometers aroundthe injection point. However, we havevery little knowledge of how the pHchange or other impacts due to CO

2

injection would affect the biogeo-chemistry and ecosystems in the deepocean.

These are selected research activitiesnow under way to evaluate the oceansequestration of CO2:

International Field Experiment. Isocean sequestration of CO2 technicallyfeasible? What are its environmentalimpacts? Can these impacts beminimized economically? Aninternational research project isaddressing these questions. Japan,Norway, and the United States signed aProject Agreement for InternationalCollaboration on CO

2 Ocean

Sequestration in December 1997;since that time, Canada and ABB(Switzerland) have joined the project,

Fig. 3.3. For injection of CO2 at depths of 1000 to 2000 m,it has been suggested that liquid CO2 be transported from shorethrough a pipeline for discharge from a manifold lying on theocean bottom. Another proposal is to transport the liquid CO2 bytanker and then discharge it from a pipe towed by the movingship.



which will continue through March 31,2002. A field experiment will beperformed in the summer of 2000 offthe Kona Coast of Hawaii. Theimplementing research organizationsare the Research Institute of InnovativeTechnology for the Earth (Japan), theNorwegian Institute for Water Research(Norway), the Institute of OceanSciences (Canada), and theMassachusetts Institute of Technology[(MIT) United States]. The generalcontractor for the project is the PacificInternational Center for High-Technology Research in Hawaii. Toinvestigate longer-term acute andchronic biological impacts, a phase 2project may be conducted in anenclosure or at a semi-enclosed site

such as a fjord (Adams et al.1998).

Experiments at the MontereyBay Aquarium ResearchInstitute (MBARI). In April1998, MBARI scientistssuccessfully carried out acontrolled experiment with a9-L liquid CO2 release at adepth of 3650 m (in situtemperature about 1.6°C) fromTiburon, an unmanned,remotely operated vehicle(ROV) tethered to a ship. Forseveral hours they observedthe transformation of liquidCO2 into solid hydrate (seesidebar).

Comparison of Ocean CarbonCycle Models. TheInternational Geosphere-Biosphere Programmeinitiated the Ocean Carbon-Cycle Model IntercomparisonProject (OCMIP) in 1995through the Global Analysis,Interpretation, and Modelingtask force. OCMIP is an

international project devoted toimproving marine carbon cycle modelsby comparing them with each otherand by evaluating them usingobservational data sets. Thanks in partto some additional funding provided bythe IEA Greenhouse Gas R&DProgramme, the European researchprogram on Global Ocean Storage andAnthropogenic Carbon will also look atglobal scientific aspects of the deep-ocean CO2 sequestration issue.Specifically, the researchers willcompare models of dispersion of CO

2

from seven hypothetical point sourcesto get a better understanding ofsequestration efficiency. The U.S.component of OCMIP (funded by theNational Science Foundation and theNational Aeronautics and Space

Fig. 3.4. Simulated distribution of carbon injectedinto the ocean at a depth of 1720 m off the coast ofCape Hatteras, North Carolina, after 20 years ofcontinuous injection, as computed by the three-dimensional ocean model of Lawrence LivermoreNational Laboratory. At this depth, the model predictsthat the carbon would be swept south with anundercurrent that flows beneath the Gulf Stream. Thiskind of simulation is necessary to determine the mosteffective depths and locations for deep-sea CO2 injection.



Administration and involving MIT,Pennsylvania State University, theNational Center for AtmosphericResearch, Lawrence LivermoreNational Laboratory, and PrincetonUniversity) is positioned to perform thesame set of analyses with U.S. models,but no funding is available yet for thisactivity.

The CO2 Ocean Sequestration Projectin Japan. In April 1997, a 5-yearnational program looking at oceansequestration of CO

2 began in Japan.

Annual funding is in excess of $10million per year. The lead researchinstitutes for this program are theResearch Institute of InnovativeTechnology for the Earth and theKansai Environmental EngineeringCenter. This project encompasses jointresearch activities involving nationalinstitutes, private companies, anduniversities. The R&D agenda includesstudying the behavior of liquid CO2

released into the ocean, developing anengineering system for CO2 injection,assessing the impacts of CO2 on marineorganisms, developing a near-fieldenvironmental impact assessmentmodel, predicting the long-term fate ofsequestered CO

2, and participating in

the international field experiment(Masuda 1998).

3.1.3 Science and Technology Gaps

By comparing our technicalcapabilities with the technicalrequirements for developing effective,economical, and environmentallyacceptable ocean sequestrationtechnologies, we identified thefollowing gaps:

• Insufficient information is availableto optimize an injection strategy.For example, we must obtainanswers to these questions:

– Should dilute CO2 streams beinjected to try to avoid anyenvironmental impacts? Will thisstrategy have an impact on cost?

– Should CO2 streams be injected

deep in the ocean to maximizeretention time? Will it be worththe extra cost? Will the technicalcapability to do so be available by2025?

• On the engineering side, thesespecific research gaps must beaddressed:– Develop injection technology.

Even though CO2 can be injectednow, we need a technology that islow in cost and maintenance andthat can be used at greater oceandepths, if necessary.

– Experimentally demonstrate thebehavior of CO2 near the injectionpoint. This understanding maylead to injection strategies thatcan minimize any environmentalimpacts.

– Better understand the dynamicresponse (i.e., kinetic behavior)corresponding to hydrateformation and dissolution. This isa first step in developingstrategies that could use hydrateformation to our advantage forsequestering CO2 (see Chap. 7).

– Assuming no environmentalconstraints, develop strategiesthat maximize the neutralizationof the acidified water by deep-ocean calcium carbonatesediments. This approach wouldhave two positive effects: reducingpH changes in the water columnand increasing the sequestrationcapacity of the ocean.

– Develop monitoring technology toobserve changes in the ocean’sbiogeochemical processes andecosystems.

• Concerning the effectiveness ofinjection technologies, some



specific research gaps can beclosed if researchers accomplishthe following:– Address weaknesses in OGCMs,

specifically western boundarycurrents, ocean bottom currents,and sub-grid scale processes (e.g.,eddies); and test the models usingnatural and, perhaps,experimentally released tracers.

– Couple near-field with far-fieldeffects of CO2 injection through ahierarchy of models (ornonuniform grids). Specifically,plume modeling should becoupled with basin- and global-scale ocean circulation models.

• Related to the environmentalimpacts of direct injection, somespecific research gaps can be filledif researchers accomplish thefollowing:– Understand the carbon cycle of

the ocean to determine thebaseline. CO2 goes into the oceannaturally, even with noenhancement or direct injection.These effects need to beunderstood.

– Determine parameters for directinjection of CO2 that willminimize environmental impacts.

– Understand the effect of thesustained release of elevated

Formation of CO2 Hydrates in the Deep Sea

The accompany photo from theMBARI experiment shows the overflowof liquid CO2 onto the sea floor.

One suggested strategy for oceansequestration of CO2 by direct injectionis to create a long-lived “CO2 lake” onthe ocean floor. To investigate thisconcept, a group of scientists at MBARIperformed a series of deep oceanexperiments for the disposal of fossilfuel CO2 in the form of solid hydrate(CO2 5.75 H2O). One recent experimentwas carried out with the MBARI ROVTiburon off the central California coast.The ROV carried about 9 L of liquid CO2

to a depth of 3650 m, where thepressure is ~36 MPa and the

temperature is 1.6°C. The CO2 was in a steel accumulator in which a pistoncontinually adjusted to ambient pressure. The CO2 was expelled by applyingpressure on the piston from a water pump powered by vehicle hydraulics. Partlybecause CO2 is denser than seawater at this depth, hydrate formation theredramatically differs from that observed at shallower depths.

MBARI scientists observed a rapid increase in the volume of the containedexperiments as the CO2-water interface rose, causing overflow of the liquid ontothe sea floor about 100 min after the experiment started. They attributed thiseffect to the formation of a hydrate, readily seen as an accumulating mass at thebottom of the containers. This incorporation of large amounts of water in the solidphase resulted in an expansion of system volume by about a factor of 7, causing theremaining liquid CO2 to spill over. High interfacial tension maintained a strongbarrier, preventing the released liquid CO2 from interacting with the sediments.



levels of CO2 on oceanbiogeochemistry and ecosystems.Are there any other impacts thatare important beyond thelowering of pH?

– Find answers to these questions:Should the injected CO2 stream bepure (i.e., >99%)? Can oceanecosystems tolerate other gasessuch as nitrogen, oxygen,hydrogen, CO, carbon oxysulfide,argon, hydrogen sulfide, NOx, SO2,and trace metals? To what levels?What effects do these gases haveon ocean ecosystems?

– Investigate the impact of CO2 onbioturbation of sediments.(Bioturbation is the disruption ofmarine sedimentary structures bythe activities of benthicorganisms.) Bioturbation makesskeletal calcium carbonateburied in the upper 10 or morecentimeters of sedimentsavailable for the neutralizationreaction of sequestered CO

2.

3.1.4 Research and DevelopmentPlan

To close the gaps, these specific lineitems are recommended for an R&Dplan:

• Increase understanding of thebehavior of CO2 released in theocean through laboratory studies,small-scale field experiments (e.g.,the international field experimentand MBARI experiments) as well asnear-field modeling efforts.

• Perform laboratory experiments tomeasure the effects of changes inpH and in CO

2 concentrations on

organisms from mid-water anddeep-sea habitats.

• Determine the environmentalimpacts of the business-as-usualscenario (i.e., natural CO2 uptakeby the ocean).

• Improve global/regional modelingto quantify benefits and identifysites.– Conduct an OGCM

intercomparison exercise onpoint sources of CO2 in the deepocean with the goal of answeringtwo questions: How good are themodels? How can the models beimproved?

– Support measurement programsthat can provide validation data,including the results of betteranalyses of natural tracers.

• Conduct a pilot experiment todetermine the feasibility of CO2

injection, monitor its ecologicalimpact, and characterize its far-field effects by collecting time-series data.

• Integrate the results of the previousefforts into specific injectionscenarios (including recommendedsites and modes of discharge) thatoptimize the tradeoffs among cost,environmental impacts, andeffectiveness.

3.2 ENHANCEMENT OF NATURALCARBON SEQUESTRATIONIN THE OCEAN

The natural process of carbon fixationby phytoplankton (primary production)results in sequestration of carbon inthe deep ocean via the biological pump(see Fig. 3.2). The biological pumpinvolves the gravitational settling,decomposition, and burial of biogenicdebris formed in the upper levels of theocean. Phytoplankton in surfacewaters are rapidly grazed byzooplankton, which in turn may beconsumed by larger animals such asfish. While it is estimated that 70–80%of the fixed carbon is recycled insurface waters (Sarmiento 1993), therest is exported as particulate organic



carbon (POC) to the deep ocean, whereit is slowly mineralized by bacteria.

Fertilization of the oceans withmicronutrients (such as iron) andmacronutrients (such as nitrogen andphosphorus) is a strategy that is beingconsidered to enhance drawdown ofCO2 from the atmosphere and thusaccelerate the biological pump.Because certain areas of the oceanhave low levels of phytoplankton yet ahigh concentration of nitrogen andphosphorus, it was realized that a lackof iron might limit phytoplanktongrowth (see the IRONEX sidebar)(Chisholm 1992). Initial studies of ironfertilization in high-nutrient, low-chlorophyll (HNLC) waters havedemonstrated that in situ fertilizationof surface waters with iron to promotegrowth of phytoplankton is feasible atscales of tens of square kilometers(Coale et al. 1996).

Some commercial ventures are tryingto capitalize on ocean fertilization forincreasing their fish harvest. Whilethese ventures have a primary goalother than carbon sequestration, thestrategies of fertilization and potentialfor environmental impact are the same,and all commercial ventures usingfertilization to enhance fish productionalso claim carbon sequestration as asecondary benefit. For example, OceanFarming, Inc., has planned a large-scale fertilization of the coastal watersof the Marshall Islands with iron,silicon, and phosphorus to increase theyield of tuna. This enterprise claimscarbon sequestration as a secondarygoal. Similarly, MARICULT, a Europeanconsortium of government andindustry, is currently exploring thecommercial feasibility of fertilizingcoastal waters to increase the fishharvest. These commercial venturesare proceeding even though the

IRONEX: Iron Fertilization Experiments

The equatorial Pacific and Southern Oceans have excess macronutrients,nitrogen and phosphorus, in their surface waters. The late John Martin of MossLanding Laboratories hypothesized that these nutrients are abundant in theseregions because the micronutrient iron is very scarce, thus limitingphytoplankton growth. To test this hypothesis, two unenclosed transient ironfertilization experiments (IRONEX I and II) were conducted in the equatorialPacific in 1993 and 1995, and a third experiment is being planned for theSouthern Ocean. The results from IRONEX II, in which 500 kg iron was added to a72 km2 patch of surface water, were particularly dramatic. Quantum yield ofphotosynthesis increased significantly within 2 hours, nitrogen and phosphoruswere drawn down, and chlorophyll concentrations increased 30-fold within a week,approaching levels typical of coastal waters. The species composition of thephytoplankton community shifted dramatically, with larger cells dominating by theend of the experiment. The bloom caused a decrease in the partial pressure of CO2

in the middle of the patch and a three-fold increase in dimethyl sulfide production,both of which have implications for climate regulation. The duration of theexperiment was 18 days—not long enough for significant changes at highertrophic levels—and the bloom dissipated shortly after the last injection of iron. It isnot at all clear how sustained fertilization would affect ecosystem structure, exportof carbon to the deep sea, and fluxes of greenhouse gases. These effects cannot bepredicted from a transient experiment, so longer-term fertilization experimentsare needed.



potential ecological consequences ofocean fertilization are not yet known.Such consequences could range fromchanges in species diversity toinduction of anoxia and significantadverse effects on communitystructure and function. Thefundamental question that should beanswered is whether any alterations inthe ocean ecosystem are justifiedrelative to the benefits to society.


An urgent need exists to determine thepotential ecological consequences oflarge-scale ocean fertilization on thebiosphere and on biogeochemicalcycling. We need to be able to predictaccurately how ecosystems will changein response to either short-term orsustained fertilization of the oceans.We also need to understand overallnatural carbon sequestrationefficiency in the oceans. Moreover, thefeasibility of ocean fertilization willdepend on optimization of fertilizerdesign, delivery, and ecologicalmonitoring. Long-term ecologicalmonitoring may prove extremelycostly, so robust, dynamic models thatpredict ecosystem response will be thekey to designing an economical andeffective monitoring strategy.

3.2.2 Current Science andTechnology Capabilities

Small-scale ocean fertilization isfeasible from both an engineering andan economic perspective. Thetechnology for fertilizing surfacewaters is fairly straightforward; itinvolves releasing microalgalnutrients such as iron, phosphorus, ornitrogen from platforms such as boatsor airplanes. Recent iron fertilizationexperiments (IRONEX I and II)demonstrated that a deficiency of iron

limits primary production (photo-synthesis) in HNLC areas of the oceanwhere nitrogen and phosphorus areabundant (see the IRONEX sidebar).The application of 500 kg of iron to72 km2 in the equatorial Pacificresulted in a 30-fold increase inphytoplankton biomass, a dramaticshift in species composition andelevated carbon fixation rates.

A number of technologies are availablefor monitoring ecosystem response tofertilization (or deliberate CO2

injection), including assays for primaryand secondary production usingradiotracer techniques. Determiningecosystem response below the euphoticzone (the zone where the net rate ofphotosynthesis is positive) could use insitu filtration techniques thatdetermine size distributions andchemistry of POC with minimaldisturbance to the samples (Bishop etal. 1987; Bishop 1999) (see Fig. 3.5).An ocean carbon inventory survey will

Fig. 3.5. The multiple unit large-volume insitu filtration system (MULVFS) allows theprecise determination of properties ofparticulate matter that is needed for asystematic survey of ocean carbon inventoryand for the evaluation of ecosystem function.MULVFS samples are large enough to meet thediverse needs of multiple research groups.



use improved technologies tocharacterize the dissolved andparticulate organic and inorganiccarbon pools and ecosystem function.More efficient shipboard samplingtechnologies for many key parametershave been developed or are underdevelopment. A growing suite ofautonomously operating carbon andnutrient sensors is under developmentfor deployment on moored, floating, orautonomous profiling platforms. Theuse of optical approaches for remotesensing of water column primaryproductivity and carbon biomass israpidly progressing.

To simulate the effectiveness of oceanfertilization as a CO2 sequestrationstrategy, two challenges must be met.First, we must be able to predict thechange in biological carbon exportfrom the surface ocean to the deepocean as a result of ocean fertilization.Second, we must be able to predict thefate of this carbon after it reaches thedeep ocean.

The problem of predicting changes incarbon export from the surface oceanresulting from fertilization is a difficultone, because it depends on hard-to-predict changes in ecosystemstructure. Surface ocean biologymodels have simulated biologicalcarbon export at specific locationsreasonably well, but these models havegenerally been “tuned” to match someobservations at these locations. Work isunder way to try to develop a singlemodel that can be applied across theglobal ocean to predict carbon exportfrom physical and nutrient conditionsalone. Although much progress hasbeen made in this area, this goal hasnot yet been attained. It will beimportant to monitor closely any oceanfertilization experiments to developsolid data sets for use in evaluatingocean biology and ecosystem models.

Predicting the fate of biogenic carbonafter it is transported to the deep oceanis also a thorny problem. An importantcomponent of this prediction is theestimation of the depth at which theorganic carbon will be oxidized, andthis depth will depend on whether theorganic carbon is particulate ordissolved, the size of the particles, andother factors. Once the organic carbonhas oxidized in the deep ocean, theproblem is largely equivalent to thedeep-ocean CO2 injection problem—predicting ocean transport, CO2

degassing (returning to the atmos-phere), and sediment interactions.Several simulations of this aspect of theproblem have already been made usingassumptions about the change inocean biological carbon export and thedepth of its oxidation. These studieshave concluded that the effectivenessof ocean fertilization as a CO2 seques-tration strategy is very sensitive to therate of ocean mixing between theocean’s surface layers and its deeplayers. If some carbon in the deeplayers is brought to the surface throughmixing, then it could return to theatmosphere through degassing ratherthan become buried in the sediments.

3.2.3 Science and Technology Gaps

A number of critical gaps exist in ourunderstanding of ocean fertilization asa strategy for enhanced carbonsequestration.

• The impact of long-term oceanfertilization on the structure andfunction of marine ecosystems isunknown. Changes inphytoplankton structure are aninevitable consequence offertilization, and this would lead tochanges in ocean food webstructure and dynamics. Suchchanges could have long-term (bothpositive and negative) impacts on



fisheries, many of which are alreadydeclining primarily because ofover-fishing. Fertilization with ironand phosphorus in lake ecosystemsselects for the growth ofcyanobacteria over other types ofphytoplankton; this proliferationcould be a problem because certainspecies of cyanobacteria producepowerful toxins. Whether a toxicform of cyanobacteria might occurin marine ecosystems is unknownat present.

• The impact of sustainedfertilization on the naturalbiogeochemical cycles in the oceanis completely unknown. Thebiogeochemical cycles of carbon,nitrogen, phosphorus, silicon, andsulfur in marine environments arehighly complex and intertwined,and recent evidence suggests thatthey are regulated by theavailability of iron on a global scale.A perturbation of one elementalcycle can have repercussions thatare unanticipated.

• The potential risk of fertilizationleading to eutrophication must bedetermined. Eutrophication causesoxygen depletion, which could killspecies that require oxygen; insome cases, it can lead to theproduction of methane (anothergreenhouse gas) bymicroorganisms. On the otherhand, lack of oxygen in thesediments of the ocean floor couldlead to an increase in thepreservation of buried carbon dueto slow rates of mineralization. Theimpact of fertilization on sediment-dwelling (benthic) organisms isunknown.

• At present, we do not have a goodunderstanding of the effectivenessof ocean fertilization at a largescale. Will enhanced carbonfixation in surface waters result inan increase in carbon sequestered

in the deep ocean? Somepreliminary modeling work hasbeen done, but these models arebased on simplified biologicalassumptions and have not beenvalidated against real-world data.

3.2.4 Research and DevelopmentPlan

Sustained longer-term fertilizationexperiments are vitally important toassess the ecological consequences ofin situ fertilization. More important,such experiments yield informationthat is vital to understanding themechanisms that have triggered pastclimate changes such as glacial-interglacial transitions. We need toknow how marine food webs change inresponse to nutrient enrichment. At aminimum, such research should seekto accomplish the following:

• Increase understanding of theexisting “biological pump” andidentify the nutrients that regulateit on a global scale. Naturallyoccurring fertilization byupwelling, wind-driven dustdeposition, or iron-rich coastalrunoff may provide insights into therole of nutrients in oceansequestration of carbon.

• Determine to what extent increasedprimary production in surfacewaters enhances the biologicalpumping of carbon to deeperwaters. This determination willrequire an inventory of oceancarbon, including export of POCand particulate inorganic carbon tothe deep sea and the mineralization(oxidation) or dissolution of allcarbon at depth. Development oftechnologies for autonomousdetermination of all forms of carbonis needed.

• Determine the impact of seques-tration on biogeochemical cycling.



For example, if carbon is seques-tered, the available nitrogen andphosphorus in surface waters willbe reduced. How long will it takefor natural nitrogen andphosphorus to be replenished tosupport ongoing primaryproduction?

• Determine the relationship betweeniron and nitrogen fixation. Wouldfertilization with iron and phos-phorus in the ocean causecyanobacterial blooms that wouldincrease the oceans’ nitrogeninventory? Would an increase innitrogen lead to an increase incarbon export?

• Monitor the effects of fertilizationon phytoplankton communitystructure and trophic dynamics.Can nutrient ratios be “designed”to increase productivity withoutchanging the community structure,thus minimizing environmentalimpacts?

• Validate models of sustainedfertilization with improvedbiological parameterization. Weneed to couple physical, chemical,and biological models to predict theeffectiveness of ocean seques-tration. We especially need to knowhow long anthropogenic carbon willremain sequestered in the ocean.

3.3 LONGER-TERM, INNOVATIVECONCEPTS FOR OCEAN CO2SEQUESTRATION

Whereas most of the research in oceanCO2 sequestration has been in theareas of deep-sea CO2 injection andocean fertilization, both of theseconcepts are less than 25 years old,and a plan written 25 years ago mighthave missed these strategies.Therefore, we should encourage thedevelopment of innovative concepts forsequestering CO2 in the oceans that

may be the basis for advancedtechnologies in the coming years anddecades. A few concepts are describedbelow for illustrative purposes only—atpresent we do not have enoughinformation to judge their feasibility.

• Converting concentrated CO2 at apower plant to relatively strongcarbonic acid, using the acid todissolve carbonate minerals, andthen releasing the dissolvedcarbonate and dissolved fossil-fuelCO2 into the ocean. This techniquewould greatly enhance oceanstorage capacity and wouldeliminate concerns about changesin pH because the dissolvedcarbonate mineral wouldneutralize much of the acidity ofthe carbonic acid. This approachwould greatly diminish eventualdegassing back to the atmosphere,circumventing the need forpumping CO2 to great distances anddepths. Limitations of the conceptinclude the need for large amountsof water and the need to transportas much carbonate mineral as coalto the power plant.

• Burial of organic carbon in theocean. Organic waste could bestored as a thick layer on the oceanbottom. Sources of this organiccarbon could include farm waste,carbon-black from decarbonizedfuel, or organic-rich dredgedsediments. Biomass from fast-growing sea grasses, kelp forests, orterrestrial plants could beharvested for burial in the ocean.Transportation of large volumes ofbiomass to the ocean depths,however, may prove too costly.Moreover, anoxia and theproduction of methane may presenta serious problem with thisapproach.



• Mining hydroxides and bicar-bonates (e.g., sodium hydroxide,potassium hydroxide, sodiumbicarbonate) and dissolving themin the ocean. These minerals, whendissolved, will neutralize theacidity produced by anthropogenicCO

2 and will effectively sequester

that CO2 in the oceans. The limitedavailability of these materials innature may preclude this approach.

3.4 CONCLUSION

Because the ocean already is a largerepository for carbon on the planet, it isnot unreasonable to consider directinjection of CO

2 or enhancement of CO

2

fixation through fertilization aspossible options for carbon seques-tration. Technologies exist for directinjection of CO2 at depth and forfertilization of the oceans with micro-algal nutrients. However, we lacksufficient knowledge of the conse-quences of ocean sequestration on thebiosphere and on natural biogeo-chemical cycling. Such knowledge iscritical to responsible use of oceans as

a carbon sequestration option. Long-term studies on the impact of oceansequestration on ecosystem dynamicsand global biogeochemical cycling areneeded (Fig. 3.6). The ocean plays animportant role in sustaining thebiosphere, so any change in oceanecosystem function must be viewedwith extreme caution.

Public perception of ocean seques-tration will undoubtedly be an issuefor its broader acceptability. Much ofthe public, as well as ocean advocacygroups, believe that the oceans mustremain as pristine as possible. Thefisheries industry will also beconcerned about possible economicimpacts resulting from ocean seques-tration activities. Legal issues willundoubtedly be complicated. With theexception of the coastal economiczones, the ocean is international indomain and is protected by inter-national treaties or agreements suchas MARPOL or the Law of the Sea.Ultimately, both scientific under-standing and public acceptability willdetermine whether ocean seques-tration of carbon is a viable option.

Fig. 3.6. R&D road map for ocean sequestration of CO2.



3.5 ACKNOWLEDGMENTS

The authors express their appreciationto the following reviewers:

Makoto AkaiEdith AllisonKen CoaleThomas GrahameRichard JahnkeShigeo MasudaRolf MehlhornDwain SpencerGilbert StegenRobert WarzinskiC. S. Wong

3.6 REFERENCES

Adams, E., M. Akai, L. Gomen,P. Haugan, H. Herzog, S. Masuda,S. Masutani, T. Ohsumi, and C. S.Wong 1998. “An InternationalExperiment on CO2 Ocean Seques-tration,” presented at the Fourth Inter-national Conference on GreenhouseGas Control Technologies, Interlaken,Switzerland, August 30–September 2,1998.

Archer, D. 1996. “An Atlas of theDistribution of Calcium Carbonate inSediments of the Deep Sea,” GlobalBiogeochemical Cycles 10:159–174

Bishop, J. K. B. 1999. “Transmiss-ometer Measurement of POC,” Deep-Sea Research I 46 (2):355–71.

Bishop, J. K. B., J. C. Stepien, and P. H.Wiebe 1987. “Particulate MatterDistributions, Chemistry and Flux inthe Panama Basin Response toEnvironmental Forcing,” Progress inOceanography 17:1–59.

Chisholm, S. W. 1992. “What LimitsPhytoplankton Growth?” Oceanus 35(3):36–46.

Coale, K. H., et al. 1996. “A MassivePhytoplankton Bloom Induced by anEcosystem-scale Iron FertilizationExperiment in the Equatorial PacificOcean,” Nature 383:495–501.

Herzog, H. 1998. “Ocean Sequestrationof CO2: An Overview,” presented at theFourth International Conference onGreenhouse Gas Control Technologies,Interlaken, Switzerland, August 30–September 2, 1998.

IPCC (Intergovernmental Panel onClimate Change) 1996. Climate Change1995: The Science of Climate Change,J. T. Houghton, L. G. Meira Filho, B. A.Callander, N. Harris, A. Kattenberg,and K. Maskell, eds., CambridgeUniversity Press, Cambridge, UK.

Masuda S. 1998. “The CO2 OceanSequestration Project in Japan,”presented at the Fourth InternationalConference on Greenhouse GasControl Technologies, Interlaken,Switzerland, August 30–September 2,1998.

Sarmiento, J. L. 1993. “Ocean CarbonCycle,” C&E News, (May 31):30–43.

Sarmiento, J. L., and M. Bender 1994.“Carbon Biogeochemistry and ClimateChange,” Photosynthesis Research39:209–34.

Takahashi, T., W. S. Broecker, and A. E.Bainbridge 1981. “The Alkalinity andTotal Carbon Dioxide Concentration inthe World Oceans,” in Carbon CycleModelling, SCOPE, Vol. 16, B. Bolind,ed., J. Wiley & Sons, New York,pp. 271–86.

Carbon Sequestration in Terrestrial Ecosystems 4-1


Research anddevelopmentaccomplishments bythe year 2025 thatwill lead to anability tounderstand,predict, assess,measure, andimplementsubstantiallyincreasedsequestration ofcarbon in soil andvegetation systems.


44444 CARBON SEQUESTRATION INTERRESTRIAL ECOSYSTEMS

This chapter addresses the scope of the potentialfor sequestering carbon in the terrestrialbiosphere. The aim of developing enhanced carbonsequestration in the biosphere is to enable a rapidgain in withdrawal of CO

2 from the atmosphere

over the next 50 years in order to allow time forimplementation of other technological advancesthat will help mitigate CO

2 emissions.

Carbon sequestration in terrestrial ecosystems iseither the net removal of CO

2 from the atmosphere

or the prevention of CO2 net emissions fromterrestrial ecosystems into the atmosphere. Carbonsequestration may be accomplished by increasingphotosynthetic carbon fixation, reducingdecomposition of organic matter, reversing landuse changes that contribute to global emissions,and creating energy offsets through the use ofbiomass for fuels or beneficial products. The lattertwo methods may be viewed more appropriately ascarbon management strategies. However, becauseof the need to integrate R&D issues related toecosystem dynamics, we include information onthese but focus primarily on sequestration.

The terrestrial biosphere is estimated to sequesterlarge amounts of carbon (~2 GtC/year). Our visionis that we will increase this rate dramaticallywhile properly considering all the ecological,social, and economic implications. There are twofundamental approaches to sequestering carbonin terrestrial ecosystems: (1) protection ofecosystems that store carbon so that sequestrationcan be maintained or increased and(2) manipulation of ecosystems to increase carbonsequestration beyond current conditions. Weemphasize manipulative strategies and the R&Dnecessary to understand, measure, implement,and assess these strategies.

4-2 Carbon Sequestration in Terrestrial Ecosystems


In this chapter, we review theinventories of carbon in terrestrialecosystems and the roles of thebiosphere in the global sequestrationprocess and then estimate the potentialfor carbon sequestration in each ofthem (Sects. 4.1 and 4.2). We next

summarize the current capabilities incarbon sequestration (Sect. 4.3). Thegap between the potential for carbonsequestration and the currentcapabilities establishes the drivers forR&D needs. Section 4.4 begins theactual road map. It starts at the system

Soil—The Earth’s Living Membrane

Soil, which has been described as a living membrane between bedrock and theatmosphere (CNIE 1998), is actually a diverse ecosystem containingmicroorganisms and many types of invertebrates and vertebrates as residents.Soils are critical to plant production, but they also are essential for carbonsequestration (soils currently contain ~75% of the terrestrial carbon). Soils inwhich high levels of carbon are present as soil organic matter (SOM) exhibitimproved nutrient absorption, water retention, texture, and resistance to erosion,making them particularly useful for both plant productivity and sequestration. R&Dis needed to better manage soils to increase carbon sequestration.

Storage of carbon in belowground systems is the best long-term option forcarbon storage in terrestrial systems because most SOM has a longer residencetime than most plant biomass. SOM is a complex mixture of compounds withdifferent residence times. The more stable compounds are the most important forcarbon sequestration because they have turnover times of hundreds to thousandsof years. R&D can determine ways to increase the presence of the most stablecompounds in SOM.

Prevention of erosion can be a major contributor to carbon sequestration. TheFood and Agricultural Organization (FAO 1992) estimates that 25 billion tons ofsoils are lost through erosion each year. The Committee for the National Institutefor the Environment (CNIE 1998) provides a dramatic description for this lost soil:“If dropped on Washington, D.C., this amount of soil would cover the city undermore than 100 meters, burying the Capitol dome.” If this soil contained an averageof 4% soil organic carbon, that would be equivalent to emissions of roughly 1 GtC/year (CNIE 1998). Even though erosion cannot be completely prevented, researchmay identify possible strategies to enhance the capture and longevity of SOMreleased by erosion and transported by rivers into wetlands and coastal areas.

Land-use management and agricultural practices have great potential tosequester carbon by protecting soils. About one-third of the current 1.5 billiontonnes of carbon emitted to the atmosphere because of changes in tropical landuse is from oxidation of soil carbon. It is estimated that 40 to 60 billion tonnes ofcarbon may have been lost from soils as the result of forest clearing and cultivationsince the great agricultural expansions of the 1800s. When land is converted fromnatural perennial vegetation and cultivated, SOM generally declines by 50% in thetop 20 cm of soil and 20 to 30% in the top meter of soil. Because less organicmatter is introduced to the soil and because soil aggregates are destroyed (causingthe loss of physical protection mechanisms that trap soil carbon), SOM declinessignificantly. In addition, cultivated soil is exposed to the air, so, duringdecomposition by soil organisms, the SOM is oxidized and the carbon carried off asCO2. With good management to protect soils and the development of methods toimprove texture of soils so they trap more carbon, it may be possible to exceed theoriginal native SOM content of many soils.



level with our vision for carbonsequestration in the terrestrialecosystem. From this, we establishthree objectives (Sect. 4.4.1) and thenpropose strategies that will help inmeeting those objectives (Sect. 4.4.2).The final leg of the road map is toidentify the R&D that is required torealize the strategies (Sect. 4.4.3).

The world’s terrestrial environmentcomprises a wide diversity ofecosystem types that can becategorized into several biomes toaddress unique aspects of their carbonsequestration potential. A single,realistic set of R&D needs covering allissues in these highly variable systemscannot be stated. Therefore, wedeveloped a primary set of R&D needsthat represent cross-cutting topics.These R&D needs, which are broadlyapplicable to several of the majorecosystems, are discussed in the mainbody of this chapter. Appendix Bcontains information specific to each ofthe ecosystems.

4.1 TERRESTRIAL ECOSYSTEMS:NATURAL BIOLOGICALSCRUBBERS

The total amount of carbon “stored” interrestrial ecosystems is large (~2000 ±500 GtC). Table 4.1 shows estimates ofthe distribution of this carbon amongthe major ecosystems of the world.Carbon sequestration in theseterrestrial ecosystems will beenhanced by increasing the amountsof carbon stored in living plant matter,roots, and soil carbon (inorganic andorganic) and in long-lived materialsthat contain woody matter, or byprocessing wood into long-lived carbonproducts. Net removal of CO

2 from the

atmosphere by terrestrial ecosystems(~2 GtC/year) occurs when plantphotosynthesis exceeds all processes of

consumption and respiration,resulting in aboveground plant growthand increases in root and microbialbiomass in the soil. Plant matter isconsumed when it is eaten, dead oralive, by an animal. In addition, plantsreturn stored carbon to the atmospherethrough respiration, as do animalsthrough their waste or death anddecay. When a plant sheds leaves and

Multiple Benefits of TerrestrialSequestration of Carbon

Increasing the storage of carbonin vegetation and soils could offersignificant accompanying benefits:improved soil and water quality,decreased nutrient loss, reduced soilerosion, better wildlife habitats,increased water conservation, andmore biomass products. Restoringwetlands to sequester largerquantities of carbon in sediment willalso preserve wildlife and protectestuaries. Understanding how toincrease soil carbon stocks inagricultural lands is critical toincreasing sustainability of foodproduction. Finally, creatingconditions for higher plantproductivity and accumulation of soilcarbon to increase carbonsequestration will have the sidebenefit of restoring degradedecosystems worldwide.

Increases in soil carbonsequestration alone can providesignificant benefits by delaying theneed for more technically complexsolutions. Edmonds et al. (1996, 1997)estimated that, for agricultural soilcarbon only, 35 years of time might be“bought” (potentially saving at least$100 million) before majoradjustments in the world’s energyproduction system would be requiredto meet a goal of 550 ppmvatmospheric CO2. As a result, over thenext quarter century, other carbonmanagement options could beevaluated and implemented.



Table 4.1. Global estimates of land area, net primary productivity (NPP), and carbon stocks inplant matter and soil for ecosystems of the world

Ecosystem Area NPP NPP Plant C Plant C Soil Ca

Soil Total(1012 m2) (gC/m2/year) (Pg C/year) (g/m2) (Pg) (g/m2) (Pg) (Pg)

Forest, 14.8 925 13.7 16500 244.2 8300 123 367tropical

Forest, 7.5 670 5.0 12270 92.0 12000 90 182temperateandplantation

Forest, 9.0 355 3.2 2445 22.0 15000 135 157boreal

Woodland, 2.0 700 1.4 8000 16.0 12000 24 40temperate

Chaparral 2.5 360 0.9 3200 8.0 12000 30 38

Savanna, 22.5 790 17.8 2930 65.9 11700 263 329tropical

Grassland, 12.5 350 4.4 720 9.0 23600 295 304temperate

Tundra, 9.5 105 1.0 630 6.0 12750 121 127arctic andalpine

Desert and 21.0 67 1.4 330 6.9 8000 168 175semi-desert,scrub

Desert, 9.0 11 0.1 35 0.3 2500 23 23extreme

Perpetual 15.5 0 0.0 0 0.0 0 0 0ice

Lake and 2.0 200 0.4 10 0.0 0 0 0stream

Wetland 2.8 1180 3.3 4300 12.0 72000 202 214

Peatland, 3.4 0 0.0 0 0.0 133800 455 455northern

Cultivated 14.8 425 6.3 200 3.0 7900 117 120andpermanentcrop

Human 2.0 100 0.2 500 1.0 5000 10 11area

Total 150.8 59.1 486.4 2056 2542

aSoil C values are for the top 1 m of soil only, except for peatlands, in which case they account for

the total depth of peat. Source: Amthor et al. 1998.



roots die, this organic material decays,adding carbon to the soil. Soil carbonis lost to the atmosphere throughdecomposition by soil organisms (e.g.,fungi and bacteria). This process alsomineralizes organic matter, makingavailable the nutrients needed forplant growth. The total amount ofcarbon stored in an ecosystem reflectsthe long-term balance between plantproduction (inputs) and all respirationand decomposition (losses).

Biological transformation of carbon hasbeen, and quite likely will continue tobe, a primary mechanism for removingCO

2 from the atmosphere. This is

reflected in the standing stock ofvegetation and the accumulation ofsoil organic matter. Methods that relyon biological transformation can play acentral role in the management ofcarbon sequestration in the future.This biospheric carbon sequestration isessentially a huge natural biologicalscrubber for all emission sources (e.g.,fossil fuel plants, cement plants,automobiles). The value of 2 GtC/yearremoved from the atmosphere eachyear by the earth’s mantle of vegetationis the net ecosystem production. Thisvalue is uncertain because it is anestimated difference betweenphotosynthesis and respiration—bothvery large fluxes and highly uncertain(Chap. 1). We can “observe” thecontemporary, world-wide netdifference between global carbonuptake by photosynthesis (P) andreleases by respiration (R) throughmeasuring annual changes inatmospheric CO2 and accounting foroceanic carbon dynamics. However,we cannot use this information toassess how the biosphere will regulateatmospheric CO2 in the future. This isbecause the P:R ratio is highlysensitive to environmental variablessuch as temperature, moisture, andnutrient availability and differs among

ecosystems. If atmospheric CO2

increases enough to cause climatechange, the global P:R ratio maychange in ways that we cannot nowpredict accurately. Small changes inthese large numbers could dwarf anycarbon management strategy imposedby humans.

4.2 POTENTIAL FOR CARBONSEQUESTRATION

The biomes that make up the terrestrialecosystem are categorized in Table 4.2.The estimates of potential carbonsequestration include the currentnatural rate of carbon sequestration,which totals about 2 GtC/year. Notethat achieving the potential indicatedin the table, particularly the highernumbers, may imply an intensivemanagement and/or manipulation of asignificant fraction of the globe’sbiomes. The table also does not reflectestimates of economic, energy, orenvironmental costs to achieve such arate, which could be unacceptablylarge for higher numbers. Theassumptions also include expectedadvances from an intensive R&Dprogram.

Estimating the potential for increasingcarbon sequestration in terrestrialecosystems is difficult because thebiogeochemical dynamics that controlthe flow of carbon among plants, soils,and the atmosphere are poorlyunderstood. Additionally, there will besocioeconomic issues, energy costs(such as possible hydrocarbonfeedstock for fertilizers), and potentialecological consequences that wouldneed to be compared with the benefitsof sequestration or other carbonmanagement options. However, theupper limit on terrestrial sequestrationis large should extraordinary measuresbe needed at some time in the future.



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Using the estimated distribution ofcarbon stored in the major ecosystemsof the world (Table 4.1), we projectedpossible rates of carbon sequestration,assuming advances from R&D and aglobal emphasis on carbonsequestration. These are presented foreach of the nine biomes in Table 4.2.Although land-use changes, such asgrowing new forests and decreasingdeforestation, have great potential tomitigate increasing carbon emissions,the carbon sequestration potential forsuch optimization across globalsystems requires a morecomprehensive and systematicanalysis than was possible during thiseffort. The major land-use changeincorporated into the present analysiswas an assumption that the results ofR&D would allow 10 to 15% ofagricultural crop land to be convertedto biomass energy crop production. Theestimate for deserts and degradedlands also contains severalassumptions with respect to land-usechange (Lal, Hassan, and Dumanski1998). With the caveat of theassumptions noted above, and inTable 4.2, it is possible that ~5 to10 GtC/year could be sequesteredglobally when all ecosystems areconsidered, compared with currentrates of ~2 GtC/year. One of the keyresearch questions is how long theserates of carbon sequestration in thesebiomes could be maintained. Also,there clearly will be some maximumcapacity for sequestration, but thatcapacity is far from certain. Refiningsuch estimates should be one of theR&D tasks undertaken.

Although perhaps surprisingly large,these relatively high ranges of potentialcarbon sequestration may not beunreasonable. For example, a 5%increase in the total carbon containedin global terrestrial ecosystems over a25-year period would sequester

>100 GtC. Sequestering 100 GtC over25 years requires increasing the rate ofcarbon sequestration in terrestrialecosystems (~2000 GtC) by an averageof only 0.2% per year—roughly halfwhat our provocative estimates projectas possible.

Strategies for sequestration a fewdecades from now will be implementedin a world different from today’s.Human responses to climatic changeand other environmental issues,population growth, economicdevelopment, and technologicalchange may well lead to changes inpatterns of land use, settlement, andresource management. It seemsunlikely that carbon sequestration willbe the highest-priority use for anyland; instead, sequestration will haveto be compatible with a host of otherdemands on ecosystem goods andservices.

There are some limitations anduncertainties related to carbonsequestration potential in terrestrialecosystems. First, it is critical at theoutset to take a whole ecosystemapproach. Having the capability toassess potential impacts on aparticular ecosystem from an emphasison sequestering carbon is a majorneed. For example, the dynamics ofcarbon storage and allocation are atpresent not well known undertemperature, moisture, and nutrientconditions of a changing climate.Second, carbon sequestrationstrategies may have consequencesbeyond simply increasing carbonstorage. Increasing organic matter inwetlands could result in higheremissions of methane, a greenhousegas with a 20 times higher contributionto global warming than CO2, althoughhydrologic controls or increases in thefraction of recalcitrant organic mattercould offset this process. Converting



croplands to grasslands may increaseemissions of nitrous oxide (N2O),another greenhouse gas, to theatmosphere (Marland et al. 1998).

Third, land use and sequestrationactions also could alter the flow ofmicronutrients. For example, as aresult of controls on erosion, might thefluxes of phosphorous and nitrate inaquatic systems increase or decreaseto levels that cause ecological impacts?Strategies to “improve” carbonsequestration in deserts throughincreases in drought-tolerantvegetation could lead to decreasedfluxes of wind-blown nutrients such asiron, with possible adverse impacts onthe ability of the ocean to sequestercarbon through iron-fertilizedphytoplankton (Chap. 3). Thus researchshould support the development ofeffective yet flexible strategies forcarbon sequestration and seekunderstanding of the interplay of thesestrategies with other human activitiesand goals.

4.3 CURRENT CAPABILITIES

Historically, little emphasis was givento developing strategies for carbonsequestration. Rather, other prioritiesand practices actually promotedcarbon release. For example, in theUnited States, 50% of the originalwetlands have been lost. Fortunately,the trend now is to protect or evenincrease wetland acreage to preserveecosystems and maintain biodiversity.Globally, losses of wetlands are notwell documented but probably are asgreat as they are in the United Stateson a percentage basis. Changes inforest stocks and land clearing arecontinuing throughout most of theworld.

Implementation of no-till practices,return of residues to soil, and theactivities of the Conservation ReserveProgram are increasing the amount ofcarbon in agricultural systems. (Themain reason: the soil is less exposed toair, so less soil carbon is oxidized andcarried off as CO

2.) Estimates suggest

that the potential for soil carbonsequestration may be 8 to10 teragramsper year (Tg/year, or 1012 g/year),offsetting a third of the 28 TgC/year offossil carbon emissions fromagricultural production (Lal et al.1995; Lal, Kimble, and Follett et al.1998). The concomitant increase inbelowground carbon can besubstantial; there is some evidencethat levels of soil organic carbon havedoubled over the past 20 years in theupper 18 cm of soil placed in theConservation Reserve Program(Gutknecht 1998).

The cutting of forests of eastern NorthAmerica in the previous century is nowbeing replaced by forest regrowth, andNorth America might even be a sink forcarbon at this time (Fan 1998). Forestsin the United States are beingmanaged to maintain cover, increasewater storage, and retain litter.Globally, however, there are still majorchallenges to slowing the rate ofdeforestation. The challenge is toreverse deforestation to gain 1.4 GtC/year and go beyond that to perhaps>2 GtC/year. Trexler (1998) andSohngen et al. (1998) summarizemodeling studies that suggest forestscould sequester from 200 to 500 GtCby 2090.

Although the use of biomass as analternative fuel supply is notimplemented yet on a large scale, theR&D program is succeeding inshowing the promise of this renewable



Soil Processes that Influence Carbon Fate and Transport

The dynamics of carbon transformations and transport in soil are complex andcan result in either carbon sequestration or even increased emissions of CO2.Bicarbonate (HCO3) ions dissolved in water could be sequestered if the dissolvedcarbonate enters a deep groundwater system that has a residence time ofhundreds to thousands of years. Natural organic matter is another type of soilcarbon that could be transported to deep groundwater systems. Natural organicmatter can be mobilized during intense precipitation following prolonged dryperiods, based on observations at Walker Branch Watershed in Oak Ridge. Thiscarbon-rich material may be sequestered if it is transported to deeper groundwatersystems or deposited deeper in soil. Thus there may be opportunities to encouragegeohydrologic systems to promote the deep transport of carbon into groundwatersystems.



energy technology. Perhapssequestration of 0.5 to 0.8 GtC/yearfrom crop-to-biofuel conversion couldbe achieved by converting 10 to 15% ofagricultural cropland to energy crops.It is important to point out that the useof biomass products can haveadditional benefits beyondsequestration in carbon management.For example, they may replace aproduct that is energy-intensive tomanufacture (e.g., cotton can replacefiberglass as insulation), or they maybe more energy-efficient inperformance (e.g., plastic car panelsmanufactured from biomass feedstockare lighter than steel).

For tundra and taiga, unfortunately,the trend is in the wrong direction.These areas are being impacted so as tobecome carbon sources rather thansinks. Desertification and landdegradation are still increasingglobally, and little emphasis is beingplaced on how to use these areas forcarbon sequestration. Lal, Hassan, andDumanski (1998) and Lal, Kimble, andFollett et al. (1998) show that soilcarbon sequestration can be a majorbenefit in these systems. Urbanizationeliminated 10 million hectares (ha) ofagricultural and forested land in theUnited States between 1960 and 1980.These highly impacted environmentsoffer interesting opportunities. Thedensity of carbon under these“intensively managed” systems (e.g.,lawns with trees) is high—attributableto the high rates of fertilization andirrigation, with nitrogen oxidepollutants perhaps playing a minorrole. Ancillary benefits from urbanforestation might include local coolingeffects and water retention that wouldreduce emissions from fossil fuel use.

In summary, despite historical andpresent practices such asdeforestation, many beneficial

practices that sequester carbon areeither in place or being developed forimplementation. However, these alonecannot meet the vision for carbonsequestration. More specific andfocused efforts will be required.

4.4 TERRESTRIAL ECOSYSTEMSCIENCE AND TECHNOLOGYROAD MAP

Figure 4.1 summarizes the entirescience and technology road map forterrestrial ecosystems. Our estimatedtarget for sequestering carbon interrestrial ecosystems is 4 to 10 GtC/year. One of the first R&D needs is torefine these targets and assess thefeasibility of reaching the goals (i.e.,the limits on the sequestration rateand capacity).

The technology system level of Fig. 4.1illustrates one of the major R&Dlinkages: the development of productsfrom biomass using advanced chemicalor biological methods (note the linkagecircle labeled “Biomass Products”).

Recall the importance of looking at themajor ecosystems of the world, as wasdiscussed earlier. The system level isexpanded in Fig. 4.2 to illustrate adetailed view of the road map thatincludes the major ecosystemscategorized by management intensity.In this figure and following road mapfigures, the level of the road map beingdiscussed in detail is highlighted atthe far left of the figure.

After establishing a vision, objectivesare defined to meet that goal.Sect. 4.4.1 and Fig. 4.3 present thethree technology objectives that, if met,would allow the vision to be achieved.After objectives have been established,a variety of strategies can be developedthat would focus on meeting the



objectives (see Sect. 4.4.2 and Fig. 4.4).The final step is to identify R&D tosupport implementation of thestrategies (see Sect. 4.4.3 and Fig. 4.5).

4.4.1 Objectives

Our carbon sequestration system hasthree objectives (Fig. 4.3): increase theamount of carbon in belowgroundsystems (soil or sediment), increase thecarbon in aboveground biomass, and/or manage land area with an emphasistoward carbon sequestration. Asimplified representation of how onemight quantify the potential carbonsequestration (PCS) is

PCS = å (aiAGC

i + b

iBGC

i) ́ c

iLA

i(1)

where

ai

= potential increase in above-ground carbon in the ith

ecosystem;b

i= potential increase in below-

ground carbon in the ith

ecosystem;c

i= potential change in land area

due to management for carbonsequestration in the ith

ecosystem;AGC

i= aboveground carbon; biomass

of the ith ecosystem in theindex year;

Fig. 4.1. Overall system view of the science and technology road map for the terrestrialecosystems.



BGCi

= belowground carbon; rootbiomass + soil carbon (organicand inorganic) in the ith

ecosystem in the index year;LA = land area of each ecosystem in

the index year.

To arrive at a global total for potentialcarbon sequestration, we must obtainthe above- and belowground carboninventory for each ecosystem in theindex year, multiply that number bythe potential change coefficient,assume an optimization of land use tomaximize carbon storage potential, andsum across all ecosystems.

Although represented as independentvariables, the three terms (aboveground

carbon, belowground carbon, and landarea) can be tightly coupled. There canbe great synergism among plantbiomass and soil organic carbon.Changes in the allocation of land areabetween different ecosystem types (e.g.,conversion of annual cropland tobiomass plantations) can increaseaboveground carbon, which can lead toincreases in belowground carbon. Therate of increase in aboveground carbonwill initially be much faster thanincreases in belowground carbon, butthe rates of change will depend on thetype of land use reallocation. Inaddition, major changes in both ratesare possible within ecosystem types(independent of land reallocation)through various types of management

Fig. 4.2. Detailed view of the system level showing the ecosystem categories that are partof the overall system.



interventions. We use the equationsimply as a means to highlightobjectives for carbon sequestration andto drive the development of R&D needs.

Using potential carbon sequestration(Eq. 1) to define sequestration options,we discuss each of the variablesseparately. The detailed view of theobjectives in Fig. 4.3 illustrates fourways to increase belowground carbon:

• increase the depth of soil carbon• increase the density of carbon

(organic and/or inorganic) in thesoil

• increase the mass and/or depth ofroots

• decrease the decomposition rate ofsoil carbon

One key link to another technologysystem is the possible use ofbyproducts created by advancedchemical or biological methods as soiladditions to increase organic content,water retention, and protection oforganic matter, and to improve thetexture of the soil so that it can holdmore carbon. An example might becreation of “smart fertilizers” or the useof mixtures of minerals (e.g.,carbonates, silicates, and oxides)formed at fossil fuel power plants(Chap. 7) blended with biosolids suchas sewage sludge. See the “Soil

Fig. 4.3. Detailed view of the objectives level showing the various components that feedinto the three primary objectives that are described in equation (1).



Amendments” link between advancedchemical and biological processes tobelowground carbon in Fig. 4.1.

For the aboveground system, there arealso four ways to increase carbonsequestration (Fig 4.3):

• increase the rate of accumulationof aboveground biomass

• increase the density of totalbiomass per area and/or thedensity of carbon in theaboveground biomass

• increase the longevity of biomasscarbon (decrease decompositionrate)

• increase beneficial use of biomasscarbon in long-lived products

An important component from theaboveground carbon term is the use ofbiomass products. Increasing thedensity of total biomass or theaccumulation rate offers high carbonsequestration potential. However,storage due to increased plantproductivity is most efficient if thecarbon is moved to a long-term pool,such as long-lived woody biomass orsoils. Another alternative is tosubstitute products manufactured frombiomass for products that are madeusing fossil fuels, addressing bothsequestration and management.Obvious examples that address bothcarbon management and sequestrationinclude biofuels and wood products.Less obvious but perhaps importantexamples that are focused on carbonsequestration might include the use ofbiomass products in structuralmaterials (e.g., cement) or combinedwith other materials to create newsoils. These are illustrated by the“Biomass Product” link to “AdvancedChemical and Biological” at the systemlevel (Fig. 4.2).

The land area term is the largemultiplier. As seen by the large areasin Table 4.1, in some ecosystems, asmall change in carbon content couldresult in large increases in totalcarbon sequestered. Although the totalland area of the world cannot beincreased, R&D might allow the landarea term to increase total carbonsequestration by any or all of thefollowing detailed objectives:

• social drivers• economic drivers• ecosystem management drivers

Optimization among ecosystems forcarbon sequestration will be a complexfunction. Research in this area shouldinclude issues such as transformingland from low carbon sequestrationuses to high carbon sequestrationuses, as well as reversing land usechanges that have made land areasinto sources of CO2 emissions.

4.4.2 Strategies

The next level of the road mapaddresses strategies (Fig. 4.4) thatsupport the objectives. Three generalstrategies directly support theobjectives of terrestrial ecosystems. Thefourth strategy is an integrative onethat is absolutely critical to consider ascarbon sequestration is attempted interrestrial ecosystems:

• Soil improvements primarily tosupport the objective of increasingbelowground carbon

• Crop and land management toinfluence the aboveground biomassobjective, the belowground carbonobjective, and the optimization ofland area

• Species selection, biotechnology,and molecular genetics that woulddirectly benefit both above- and



belowground systems and,indirectly, land use through, forexample, increased agriculturalproduction to free land for carbonsequestration

• Ecosystem dynamics focused onwhole ecosystem behavior tooptimize carbon sequestrationperformance, as well as onassessing potential negativefeedback to other ecosystemfeatures

4.4.2.1 Soil improvements

A variety of detailed strategies could beimplemented or developed to increasethe carbon content of soil, increasingbelowground carbon directly andaboveground carbon indirectly. One ofthe key questions is whether soil

texture, topographic position, andclimate ultimately determine thecarbon content of a soil or whether itcan be changed by manipulation. Weknow little about the processes ofhumification (formation of humus,which consists of decayed organicmatter that provides nutrients forplants and increases the soil’sretention of water) or stabilization ofdecomposable organic carbon in soils.However, our current level ofunderstanding is adequate to begin toaddress the questions: To what degreecan these processes of stabilization bemanaged? What would be theconsequences for plant productivityand ecosystem functions?

Figure 4.4 offers a detailed view ofcomponents of the soil improvement

Fig. 4.4. Detailed view of the strategies level illustrating the options for which R&Dwill be required for effective implementation.



strategy. Opportunities for innovationexist in the following areas if R&D canaddress these key questions:

• Irrigation and water retention.How can we minimize the amountof water required, or perhaps usewater of lower quality to increasecarbon accumulation? Forexample, groundwater of marginalquality could be used forrestoration of large tracts ofdegraded lands. Urban forests andgrasslands would benefit fromutilization of “gray” water fromhomes, businesses, or cities ratherthan irrigation using potable watersupplies. Surface treatments or soilamendments that improve retentionof water in soil between rain eventsand irrigation would also be ofgreat benefit. Could desalination belinked to irrigation and carbonsequestration via production ofcarbonates with brines and CO2?

• Fertilization and nutrientacquisition. Can we improve theefficiency at which nutrients aretaken up by plants through novelmicrobial manipulations or soilamendments? Can we determineand enhance the role of mycorrhiza(a mutual association between afungus and the root of a seed plantit invades) in carbon fixation andplant productivity? We mustaddress the availability of othercritical nutrients and traceelements, not just nitrogen andphosphorous.

• Enhance production and retentionof soil carbon. Can the formation ofstrongly-adsorbing and highly-recalcitrant organicmacromolecules be enhancedthrough soil amendments,microbial manipulation, or geneticselection of biomass? Can soilorganic carbon profiles bedeepened to provide a greater mass

of soil available for carbonsequestration? Can inorganiccarbon formation be enhanced inan arid system?

• Erosion control. Beyond no-tillagriculture, what methods can beused to minimize soil erosion? Arethere soil additions or surfacetreatments that will significantlyinhibit the susceptibility of soils towater erosion? Are thereengineering innovations to at leasttrap organic matter that might bereleased from erosion (e.g.,sediment trapping to enhancewetlands)? Can the current~0.5 GtC (Stallard 1998) trapped insediments each year behind damsbe permanently sequestered?

• Soil amendments or creation ofnew soil. Can waste byproducts(e.g., fly ash, concrete, sewagesludge) be used alone or mixedwith other materials to improve soilcharacteristics safely andeconomically to help the retentionof carbon? Can materials createdfrom byproducts be used to reclaimdegraded lands, or perhaps evenhelp mitigate land subsidencewhile at the same time sequesteringcarbon?

4.4.2.2 Crop and land management

Opportunities for increasing carbonsequestration by managementpractices vary in intensity and arespecific to each ecosystem. There arealso complexities to implementingsome strategies. For example, no-tillpractices reduce oxidation of soilorganic matter but do not necessarilypromote increased incorporation ofsurface organic matter into the soil topotentially enhance soil organiccarbon in the long term. There areopportunities to use naturalbiodiversity as well. For example, ashift from annual to perennial grains



would benefit soil carbonsequestration. Management ofagricultural ecosystems by plantingtrees and legumes mixed with cropplants can add organic carbon to soil.Proposed strategies include:

• afforestation of marginal crop andpasture land

• tillage management, crop rotation,residue management

• forest management (reducingdeforestation, improving stockingcontrol, implementing firemanagement)

• range land management• improved cropping systems and

precision farming focused on soilmanagement

• management for pest and diseasecontrol and control of invasivespecies

• decrease urbanization and landconversion of forests to agriculturaluse

4.4.2.3 Species selection, biotech-nology, and molecular genetics

Opportunities to select or geneticallyengineer species for carbonsequestration behavior can directlyimpact both aboveground andbelowground carbon. It will beimportant to understand carbonpartitioning into biomass as we attemptto engineer or select for carbonsequestration traits. R&D can alsoindirectly make more land areaavailable for carbon sequestration (e.g.,by improving food production perhectare so that more land is availablefor carbon sequestration). This strategyshould include (1) research on plantsand microbial communities with afocus on near-term (next 25 years)biotechnology options and speciesselection using extant knowledge and(2) relevant fundamental research on

functional genomics that will haveimpacts in later years (>50 years).

For research in plant genetics, genesmust be available for insertion into theplant of choice. Many genes inagriculture have come from a small setof annual plants (e.g., Arabidopis), forwhich information on gene function(e.g., disease resistance or flowerformation) is easily obtained. Most ofthe genes found in such plants wouldnot have direct value to a carbonsequestration strategy because genesfor long-term carbon storage may havelittle agronomic value. Thus, to enableuse of genetic engineering for carbonsequestration, there is a need todiscover genes in perennial plants thatallocate more carbon to belowgroundcomponents, that code for highercontent of extractives (componentsdesired from the plant), or that provideresistance to microbial degradation. Toenable the discovery of such genes, afunctional genomics effort mustprecede the genetic engineeringefforts.

It is not always necessary to start withfunctional genomics to modify theplant genome. For example, genes forproducing higher lignin content inmaize have been bred out of currentvarieties. (Lignin is a complex polymerthat hardens and strengthens the cellwalls of plants and that does notdecompose easily.) Genetic stockspossessing higher lignin content exist,and these could be reintroduced if theobjective were to produce thischaracteristic for carbon sequestration.R&D on altering the Rubisco enzyme toincrease biomass production through amore efficient uptake of carbon alsomight have huge potential benefits.Opportunities in this area and othersare discussed in more detail inChap. 6. Strategies central to thistheme include developing methods to



• increase standing biomass• maximize lignin content for

longevity of woody biomass• increase pest and disease

resistance• improve photosynthetic efficiency• extend growing seasons of plants• increase root:shoot ratios• increase carbon allocation in

belowground components of lessdecomposable carbon compounds(e.g., lignin, phenolics)

• engineer new plants that haveimproved water efficiency, nutrientutilization, salt tolerance, and pHtolerance

Metting et al. (1998) provide details onsome of the microbial biotechnologyoptions available for sequestering morecarbon in soil and vegetation,including species selection andgenetic engineering to

• improve microbial symbioses(mycorrhizal fungi, bacterialfixation of nitrogen, and othernutrient acquisition features ofsoil)

• grow mycorrhizal fungi in pureculture (especially those that mightimprove water and nutrient uptake)

• increase production ofpolysaccharides and humicsubstances to stabilize soil organicmatter

4.4.2.4 Ecosystem dynamics

A rational strategy to sequester carbonmust consider all the components ofthe terrestrial ecosystem. Single treespecies cannot be considered inisolation from other plant species orfrom soil because of the interactionsand interdependencies among speciesin an ecosystem. Likewise, soilmanagement cannot be separated fromplant productivity. This integrativestrategy element—ecosystem

dynamics—is driven by four basicneeds:

• Balance decomposition of biomassand soil organic matter as a sourceof carbon loss to the atmosphereagainst decomposition as a sourceof nutrients essential to plantgrowth. Sequestration strategiesthat attempt to decreasedecomposition rates mayinadvertently result in lowerecosystem carbon storage because,without decomposition, insufficientnutrients are available for plantgrowth. Plants, soil, and nutrientcycling must be consideredtogether.

• Balance instantaneous or optimumplant productivity with the desirefor long-term, predictable/stableproductivity. An ecosystem that ismanaged for a single species likelywill not maintain productivityunder a wide range of conditions,such as climatic anomalies ordisease outbreaks, withoutintensive management inputs.Target species, species diversity,and ecosystem resilience must beconsidered together.

• Design strategies that arecompatible with other humandemands on land and naturalresources. It is necessary tounderstand both the impacts ofcarbon management on otherecosystem services and ways todesign carbon managementstrategies that work in concert withother goals for terrestrialecosystems, such as production offood, fuel, and fiber; clean water;climate moderation; or aesthetic orcultural value.

• Determine the potential feedbackfrom carbon sequestration actions.What is the impact of carbonsequestration on the production orconsumption of trace gases that



affect radiative forcing (N2O andCH

4) or that otherwise have

significant roles in atmosphericchemistry (CO and NO)? Forexample, increased organic mattercontent in wetlands might increasenet methane emission. Willincreased reservoirs of organicmatter in soils significantly affectweathering and subsequenttransport in rivers of iron, silica,and other micronutrients? If so, inwhat direction might changesoccur, and what are the potentialimpacts? What consequenceswould an emphasis on desertcarbon sequestration have on aeolian transport of iron and othermetals or nutrients to the oceans orother terrestrial ecosystems?

R&D related to sequestering carbon insoils and vegetation will be diverse andmust include integrated assessment toaddress several features that willinfluence, or be influenced by, othercarbon sequestration strategies. Keyfeatures of these assessments will be(1) land use inventories,(2) assessments at scales fromwatersheds to global, and (3) life-cycleanalysis, which is the estimation of allcosts (real dollars and carbon costs) toperform R&D and implement carbonsequestration options. Many dynamicparameters and processes must bemeasured and assessed over time,including

• Carbon sequestration impacts to theatmosphere (e.g., increased CH

4,

CO, or N2O emissions) andresponses to climate changes(temperature, water, CO

2), in

addition to CO2 withdrawal bycarbon sequestration

• Loss of sequestered soil carbon tothe atmosphere as a result of globalwarming

• Carbon sequestration responses toatmospheric chemistry changes(nitrogen deposition and fixation,ozone, oxidants, other pollutants)

• Dynamics of fluxes and inventoriesof carbon at all scales as theychange with response to carbonsequestration

• Changes in species diversity andresiliency (e.g., if you design aplant species for early rapid growth,you may limit its long-term growthand/or life expectancy) as aresponse to carbon sequestration

• Soil processes important to theallocation of carbon among above-and belowground systems(transformations, transport, andfate)

• Whole ecosystem behavior as aresponse to carbon sequestration(e.g., alteration of nutrient fluxes asa result of a sequestrationemphasis, including soils, windtransport of iron and silica tooceans, and transport of organicmatter to aquatic systems)

4.4.3 Research and DevelopmentNeeds

We have now reached the bottom andfinal level of the road map—scienceand technology needs. The R&Drecommended to address these cutsacross several ecosystems and isintended to be general so as tostimulate thought rather than prescriberesearch for investigators. There arefour critical aspects to be consideredin planning an R&D program toaddress carbon sequestration interrestrial ecosystems

Understanding. What is the potentialfor a given strategy to actually work?What are the scientific principles thatgovern carbon sequestration?



Assessment R&D Opportunity—A Pleistocene Park

The arctic tundra and boreal taiga currently store much of the world’s soilorganic matter. Although few readily apparent opportunities exist for greatlyincreasing carbon stores in these regions, there is one novel opportunity forenhanced carbon storage in the tundra—restoring and managing the Siberianloess-derived grasslands.

Russian and American scientists seek to create a grassland ecosystemmaintained by large northern herbivores similar to that which existed in theregion 10,000 to 100,000 years ago during the late Pleistocene Epoch (Stone 1998).The test area of Pleistocene Park is 150 km2, but the Siberian region covered byloess that could potentially be managed for grassland restoration is approximately106 km2. Bison, horses, musk oxen, caribou, and moose would be introduced to“Pleistocene Park,” a scientific reserve in northeast Siberia. This regionsupported large herds of these animals, as well as mammoths, during thePleistocene. These animals were important in maintaining this grasslandecosystem just as large grazers currently maintain African grasslands.

The proposed transplant would reestablish a significant area of northerngrassland, an ecosystem type that has disappeared but was formerly one of theworld’s most widespread biomes. Significantly, this ecosystem is characterized bymuch higher soil carbon (and total ecosystem carbon) than the shallow-rootednorthern ecosystems found in this region today. The vegetation transition isexpected to result in warmer, drier soils that would promote deeper-rootinggrassland species. Excerpted with permission from a proposal by Zimov and Chapin(1998).



Measurement. How can we measurethe rates of current carbonsequestration by terrestrialecosystems? Are these rates likely tochange significantly as a result ofchanges in atmospheric chemistry andclimate? Can we detect changes incarbon sequestration rates afterimplementing various strategies? Canthese changes be verified at largescales?

Implementation. If a strategy appearsfeasible, how should it actually bepursued? What advances inengineering are required? What arethe costs associated withimplementation? These costs can be interms of actual dollars but also interms of costs of carbon as fuel ormaterials (e.g., fertilizer may berequired). How can we verify that aparticular carbon sequestrationimplementation is effective and not theconsequence of simultaneous changesin other factors?

Assessment. Where are the bestopportunities to implement variousstrategies? What are the possibleconsequences of implementation overboth the short and long term to thelandscape, local, regional, or globalecosystems?

Process-level research will directlyaddress the questions that must beanswered to increase ourunderstanding of carbon sequestrationsystems. This research is closelylinked to and dependent on researchinto measurement and sensingmethods to enable study of processes ata variety of scales. New measurementmethods can also lead to newbreakthroughs in our understanding ofkey processes. Advances inmeasurement and sensing directlysupport the critical need forverification and monitoring of carbonsequestration. Both of these areas will

provide direct benefits to research inecosystem response and modeling.This R&D area primarily links to theneeds in assessment and representsan integrative R&D topic. Clearly,advances in engineering technologywill be required to support theimplementation of carbonsequestration strategies. Asengineering advances are developed,though, information should be linkedto ecosystem response and modelingso as to support assessment. Wepresent specific R&D topics as itemizedbullets for clarity to align with thedetails of the road map found inFig. 4.5.

This discussion is intended tohighlight the integrative nature of R&Dfor carbon sequestration in terrestrialecosystems. In the road map, thisimportance is illustrated by the linksfrom all R&D needs (Understanding,Measurement, Implementation, andAssessment) into the strategy“Ecosystem Dynamics” (Fig. 4.5), aswell as the multiple links feeding theecosystem response and modelingR&D needs.

4.4.3.1 Process-level research

Process-level research in the followingareas will directly aid ourunderstanding of carbon sequestrationsystems. R&D is needed to focus on thefollowing:

• Biogeochemical dynamics ofcarbon, nitrogen, phosphorus,calcium, magnesium, potassium,and trace elements that controltransformations of carbon and itstransport and fate among plants,soil, water, and the atmosphere. Thedynamics must be investigatedwithin the context of a system thatincludes soil, water, plant, microbe,and climate interactions.



• Plant physiology, biotechnology,and molecular genetics. R&D topicswould include development ofmethods to select and engineerplant species for improved nutrientacquisition, growth, carbon density,and/or carbon sequestration. Howcan we alter the composition ofcellular components and designplants for effective byproduct use byincreasing energy content,durability, and lignin content toreduce decomposition rates, orrecyclability? How can pest anddisease resistance be improved?(See also Chap. 6.)

• Microbial community structure andfunctional genomics. R&D shouldbe directed toward (1) plantrhizosphere microbial communityfunctions, (2) the microbial

community role in stabilizing soilorganic matter or slowingdecomposition of organic matter,and (3) impact studies of effects ofaltered soil processes on nitrogenmineralization and fixation andplant acquisition of other nutrients.

4.4.3.2 Measurement and sensing

Developing measurement and sensingtechniques to verify the occurrence ofcarbon sequestration in terrestrialecosystems and to monitor its effectswill be challenging (Post et al. 1998).Methods are needed to ensure thatresearchers sample sites where thechanges are occurring in ways thatreduce sampling errors. Detection ofchanges in terrestrial carbon at largescales will also offer challenges. It is

Fig. 4.5. Detailed view of the R&D needs level illustrating the fundamental R&D neededto support the development of carbon sequestration options for terrestrial ecosystems.



Field-Scale R&D on DOE Reservations

Advancing the science and technology needed to enable the mitigation ofclimate change resulting from CO2 emissions through carbon sequestration willrequire long-term research, evaluation, assessment, and demonstration. DOElands and associated facilities offer research sites and test beds for evaluatingsequestration in terrestrial ecosystems. DOE lands offer great diversity—fromshrub-steppe at Hanford, Washington, to tall-grass prairie at Argonne, Illinois, todeciduous forest at Oak Ridge, Tennessee (Brown 1998). Our vision is to have anintegrated program of field-scale research, development, and assessment thatwould allow evaluation of CO2 separation science and terrestrial sequestrationoptions. Early research at field scale often results in meaningful feedback to guideprocess-level research. DOE lands represent well-studied sites, offer goodopportunities to involve the public in evaluating carbon sequestration, and couldassess transportation and other costs of sequestration at a small scale in earlystudies.

possible that rules of thumb could bedetermined for carbon sequestrationaccomplished by certain practices, butat this time the basis for developingquantitative rules is severely lacking.Because of these challenges, we

believe the following R&D topics areparticularly important.

• In situ, nondestructivebelowground sensors are needed toquantify rates and limits of carbon



accumulation both spatially andtemporally. Three areas ofimportance are (1) soil carbon,water, and nutrients as a functionof depth; (2) biomass (root andmicrobial community) imaging; and(3) porosity or soil structurechanges. An example of a sensorthat might be developed to measurechanges in carbon concentrationsin soil would be a miniaturizednuclear magnetic resonanceimaging device for scanning avolume of soil below ground.

• Remote sensing (e.g., by satelliteimaging) is needed for abovegroundbiomass systems. Improvements areneeded in the frequency, accuracy,and scale of measurements toevaluate land cover andmanagement differentiation andaddress the variability caused byheterogeneity at these scales.

• New methods of extrapolatingacross the scale of belowgroundprocesses are needed to enabletracking of changes measured inbiogeochemical dynamics.

• Verification and monitoring. Willnew sensors be required or willprocess knowledge (rules of thumb)be sufficient to estimate carbonsequestration based on theimplementation of observablepractices?

4.4.3.3 Engineering technology

Once new concepts based onunderstanding are put forth, some keyengineering issues must be addressedto allow for effective implementation ofstrategies. We offer the followingexamples:

• Effective irrigation. How can waterusage be minimized? Are thereopportunities to develop gray watermanagement for urban areas? Howmight wetland restoration be

combined with waste watertreatment? What are theimplications of using groundwaterof marginal quality?

• Nutrient delivery and utilization. Akey issue will be nitrogen fixation.Also, with a mandate to reduceorganic matter decomposition,nutrient availability will be anissue. Are there innovative soilamendments that can bedeveloped? How can more litter beincorporated effectively into thesoil? Are there ways to use largevolumes of animal wastes or sewagesludge to improve carbonsequestration while solving thisvexing environmental challenge?

• Energy efficiency. Many carbonsequestration methods will requirethe use of materials that must behandled with heavy equipment:how can the energy penalty beminimized? What alternatives toclassic fertilizers can be developedto avoid the fossil fuel emissionsfrom fertilizer production?

• Byproduct use. There are importantR&D links to existing programs. Forexample, the DOE biomass programis examining fossil fueldisplacement and the DOE Office ofIndustrial Technology isinvestigating feedstock programs.Are there innovative options tostore or bury harvested biomassproducts? How can biomassproducts like wood be included instructural materials (e.g., to replacecement, which is produced by aCO2–emitting process) to bothsequester carbon and reduce CO2

emissions?

4.4.3.4 Ecosystem response andmodeling

The fundamental R&D needed forEcosystem Response and Modelingfalls into two broad categories. First,



key measurements will be required forcomputer models that will evaluate thelong-term effects of carbonsequestration. These measurementsdiffer in emphasis from those inSect. 4.4.3.2 by requiring larger scales,probable manipulative experiments,and integrated measurementstrategies. Second, integrative modelswill be required at scales fromlandscapes to global ecosystems.

• Networks of process-based, globallyintegrated ecosystem-scalemonitoring and experimentalfacilities.

• Measurement of plant andecosystem-scale responses tochanges in atmospheric chemistryand climate variables such as CO2,temperature, water, nutrients,ozone, and pollutants. For example,increases in emissions of CO, N2O,and CH4 as a feedback fromincreased carbon sequestrationactivities.

• Measurement of ecosystemresponses to sequestration. Forexample, species diversity andresiliency may be affected byimplementation of some strategies.

• Integrative models that addressplant-, watershed-, landscape-, andecosystem-scale processes up toregional and global systems. Thesemodels must also make use of andfacilitate use of massive data setsthat will be collected through someof these activities. For example,work is needed to assess possibleimpacts from a focus on restorationof degraded lands, or carbonsequestration and erosion controlin deserts that could reducetransport of iron and silicamicronutrients by air currents tothe ocean.

• Life-cycle analysis models that canidentify opportunities for biomassgains, evaluate social and

economic issues, and estimate totalsystem costs (real costs and carboncosts).

4.5 SUMMARY

Carbon sequestration in terrestrialecosystems will provide significantnear-term benefits (over the next25 years), with the potential for evenmore major contributions in the long-term (> 50 years). There are manyancillary positive benefits from carbonsequestration in terrestrial ecosystems,which are already a major biologicalscrubber for CO2. The potential forcarbon sequestration appears to belarge for terrestrial ecosystems(5–10 GtC/year). However, this value isspeculative, and a primary R&D needis to evaluate this potential and itsimplications for ecosystems. Inaddition, economic and energy costswere not fully considered in theanalysis to estimate the carbonsequestration potential. As carbonsequestration strategies are developed,a whole ecosystem approach underchanging climate conditions must beconsidered. Potential feedbackmechanisms (both positive andnegative) must be addressed.

Our primary focus has been onmanipulative strategies to increasecarbon sequestration rather thanprotect ecosystems. We wish toemphasize that carbon stored belowground is more permanent than plantbiomass. However, even soil carbonmust be managed in the long term.One of the key questions is whethersoil texture, topographic position, andclimate ultimately determine thecarbon content of a soil, or whether itcan be permanently changed bymanipulation and to what extent. Forplant biomass, transformation ofcarbon into long-lived products or



belowground storage is essential. Withthis perspective, it appears that thefollowing ecosystems offer significantopportunity for carbon sequestration(not in any order of priority):

• Forest lands. The focus shouldinclude belowground carbon andlong-term management andutilization of standing stocks,understory, ground cover, andlitter.

• Agricultural lands. The focusshould include crop lands,grasslands, and range lands, withan emphasis on increasing long-lived soil carbon.

• Biomass croplands. As acomplement to ongoing effortsrelated to biofuels, the focus shouldbe on long-term increases in soilcarbon.

• Deserts and degraded lands.Restoration of degraded lands offerssignificant benefits and carbonsequestration potential in bothbelow- and aboveground systems.

• Boreal wetlands and peatlands.The focus should includemanagement of soil carbon poolsand perhaps limited conversion toforest or grassland vegetation whereecologically acceptable.

In developing the road map, weestablished three interrelatedobjectives that transcend ecosystems:increase belowground carbon (soilcarbon), increase aboveground carbon(plant biomass), and optimize land areafor sequestration of carbon.

These objectives can be accomplishedby the following strategies: improve soilcharacteristics, manage crops andlands for sequestration, select andengineer species for sequestration, andassess impacts to ecosystem dynamicsfrom sequestration.

Research on four key interrelated R&Dtopics is needed to meet goals forcarbon sequestration in terrestrialecosystems:

1. Increased understanding ofecosystem structure and functiondirected toward nutrient cycling,plant and microbial biotechnology,molecular genetics, and functionalgenomics.

2. Improved measurement of grosscarbon fluxes, dynamic carboninventories with the development ofnew or improved instrumentationfor in situ, nondestructivebelowground observation, remotesensing for aboveground biomassmeasurement, and verification andmonitoring of carbon stocks.

3. Implementation of improvedknowledge and tools such as betterirrigation methods, efficientnutrient delivery systems,increased energy efficiency inagriculture and forestry, andincreased byproduct use.

4. Assessment of ecosystemresponses to changes in bothatmospheric chemistry and climate,and other processes that might beimpacted by implementation ofcarbon sequestration strategies.Suites of models would be used,integrating across scales rangingfrom physiological processes toregional scales as inputs to global-scale modeling and including lifecycle analysis models.

Finally, field-scale research should beimplemented in the near term withmanipulations in large-scaleecosystems aimed at clarifying bothphysiological and geochemicalprocesses regulating carbon



sequestration. This research should beclosely linked to integrative ecosystemmodeling. The creation of such carbonsequestration test facilities on DOEreservations would provide proof-of-principle testing of new sequestrationconcepts and an integration of diversesequestration science and engineeringchallenges.

4.6 ACKNOWLEDGMENTS

All members of the team who helpeddevelop this chapter are identified inAppendix A. In addition, we expressour appreciation to the followingindividuals who provided thorough andmeaningful review comments: GaryKing, David Nowak, Richard Pouyat,Jerry Tuskan, Donn Viviani, and StanWullschleger. Melissa and TerryChapin provided a photograph for thePleistocene Park concept andpermission to include the concept inthis report.

4.7 END NOTES

As discussed in Chaps. 1 and 2,several activities include R&Dplanning for carbon sequestration. Onespecific event that paralleled this roadmap activity, with a topic of closerelevance, was the workshop entitled“Carbon Sequestration in Soils:Science, Monitoring and Beyond.” Thisworkshop, organized by Oak Ridge andPacific Northwest National Laboratoriesand the Council of AgriculturalScience and Technology, was heldDecember 3–5, 1998. It addressed therole of carbon sequestration in soils infar greater detail than does this road-mapping exercise. By engaging severalparticipants in that workshop in oureffort, we have tried to maintain aconsistent view of the most importantR&D topics. For excellent and detailed

discussions on specific topics, consultthe papers prepared for the workshop:Lal, Hassan, and Dumanski; Marland,McCarl, and Schneider; Metting et al.;and Post et al.

4.8 REFERENCES

Amthor, J. S., M. A. Huston, et al. 1998.Terrestrial Ecosystem Responses toGlobal Change: A Research Strategy,ORNL/TM-1998/27, Oak RidgeNational Laboratory.

Armentano, T. V., and E. S. Menges1986. “Patterns of Change in theCarbon Balance of Organic Soil-Wetlands of the Temperate Zone,”Journal of Ecology 74: 755–74.

Birkeland, P. W. 1974. Pedology,Weathering, and GeomorphologicalResearch, Oxford University Press, NewYork.

Brown, K. S. 1998. “The Great DOELand Rush?” Science 282: 616–17.

Buyanovsky, G. A. and G. H. Wagner1983. “Annual Cycles of CarbonDioxide Level in Soil Air,” Soil ScienceSociety of America Journal 47: 1139–45.

CNIE (Committee for the NationalInstitute for the Environment) 1998.Conserving Land: Population andSustainable Food Production, availableat www.cnie.org/pop/conserving/landuse2.htm (accessed 12/31/98),Washington, D.C.

Edmonds, J., M. Wise, R. Sands,R. Brown, and H. Kheshgi 1996.Agriculture, Land-Use, and CommercialBiomass Energy: A PreliminaryIntegrated Analysis of the Potential Roleof Biomass Energy for Reducing Future



Edmonds, J., M. Wise, H. Pitcher,R. Richels, T. Wigley, andC. Maccracken 1997. “An IntegratedAssessment of Climate Change and theAccelerated Introduction of AdvancedEnergy Technologies: An Application ofMiniCAM 1.0,” Mitigation andAdaptation Strategies for Global Change1(4): 311–39.

Fan, S. 1998. “A Large TerrestrialCarbon Sink in North America Impliedby Atmospheric and Oceanic CarbonDioxide Data and Models,” Science282: 442–46.

FAO (United Nations Food andAgriculture Organization) 1992.“Protect and Produce: Putting thePieces Together,” Rome.

Garten, C. T., and S. D. Wullschleger.In review. “Soil Carbon InventoriesUnder a Bioenergy Crop (Panicumvirgatum): Limits to Measurements ofSoil Carbon Storage” (submitted toJ. Env. Quality).

Goulden, M. L., S. C. Wofsy, J. W.Harden, S. E. Trumbore, P. M. Crill,S. T. Gower, T. Fries, B. C. Daube, S. M.Fan, D. J. Sutton, A. Bazzaz, and J. W.Munger 1998. “Sensitivity of BorealForest Carbon Balance to Soil Thaw,”Science 279:214–17.

Greenhouse Related Emissions, PNNL-11155, Pacific Northwest NationalLaboratories.

Gutknecht, K. 1998. “Can Carbon Be aNew Cash Crop?” Farmer-Stockman,(August): 28–30.

Lal, R., H. M. Hassan, and J. Dumanski1998. “Desertification Control toSequester Carbon and Mitigate theGreenhouse Effect,” presented at theworkshop “Carbon Sequestration inSoils: Science, Monitoring and

Beyond,” St. Michaels, Md., December3–5, 1998. Proceedings forthcoming.

Lal, R., J. Kimble, R. Follett, andC. Cole 1998. The Potential for U.S.Cropland to Sequester Carbon andMitigate the Greenhouse Effect, AnnArbor Press, Chelsea, Mich.

Lal, R., J. M. Kimble, E. Levine, andB. A. Stewart 1995. Soils and GlobalChange, CRC/Lewis Publishers, BocaRaton, Fla.

Marland, G., B. A. McCarl, andU. Schneider 1998. “Soil Carbon:Policy and Economics,” presented atthe workshop “Carbon Sequestration inSoils: Science, Monitoring andBeyond,” St. Michaels, Md., December3–5, 1998. Proceedings forthcoming.

Metting, F. B., J. L. Smith, and J. S.Amthor 1998. “Science Needs and NewTechnology for Soil CarbonSequestration,” presented at theworkshop “Carbon Sequestration inSoils: Science, Monitoring andBeyond,” St. Michaels, Md., December3–5, 1998. Proceedings forthcoming.

Mosier, A. R., W. J. Parton, D. W.Valentine, D. S. Ojima, D. S. Schimel,and O. Heinemeyer 1997. CH

4 and N

2O

fluxes in the Colorado ShortgrassSteppe: II. Long-Term Impact of Land UseChange, Global Biogeochemical Cycles,11: 29–42.

Oechel, W.C., S. J. Hastings,M. Jenkins, G. Reichers, N. Grulke,and G. Vourlitis 1993. “Recent Changeof Arctic Tundra Ecosystems from a NetCarbon Sink to a Source,” Nature 361:520–26.

Post, W. M., R. C. Izurralde, L. K. Mann,and N. Bliss 1998. “Monitoring andVerification of Soil Organic CarbonSequestration,” presented at the



workshop “Carbon Sequestration inSoils: Science, Monitoring andBeyond,” St, Michaels, Md., December3–5, 1998. Proceedings forthcoming.

Sohngen, B., R. Sedjo, andR. Mendelsohn 1998. “Timber Supplyand Forest Carbon in a World ofClimate Change: Some ModelingApproaches and Results,” in Herzog,H. J., ed., Proceedings of theStakeholders’ Workshop on CarbonSequestration, MIT EL 98-002,Massachusetts Institute of TechnologyEnergy Laboratory, June.

Stallard, R. F. 1998. “TerrestrialSedimentation and the Carbon Cycle:Coupling Weathering and Erosion toCarbon Burial,” Global BiogeochemicalCycles 12(2): 231–57.

Stone, R. 1998. “A Bold Plan to Re-create a Long-Lost SiberianEcosystem,” Science 282: 31–4.

Trexler, M. 1998. “Forestry As aClimate Change Mitigation Option,” inHerzog, H. J., ed., Proceedings of theStakeholders’ Workshop on CarbonSequestration, MIT EL 98-002,Massachusetts Institute of TechnologyEnergy Laboratory, June.

Watson, R. T., M. C. Zinyowera, andR. H. Moss 1996. Climate Change 1995:Impacts, Adaptations and Mitigation ofClimate Change: Scientific-TechnicalAnalyses, the Contribution of WorkingGroup II to the Second AssessmentReport of the Intergovernmental Panelon Climate Change, CambridgeUniversity Press, Cambridge, UK.

Zimov, S. A. and F. S. Chapin, III 1998.“Proposal on Creation of a PleistocenePark.”

Sequestration of CO 2 in Geologic Formations 5-1


SEQUESTRATION OF CARBONDIOXIDE IN GEOLOGICFORMATIONS

5.1 SEQUESTRATION IN GEOLOGICFORMATIONS BUILDS ON A STRONGEXPERIENCE BASE

Geologic formations, such as oil fields, coal beds,and aquifers, are likely to provide the first large-scale opportunity for concentrated sequestration ofCO2. In fact, CO2 sequestration is already takingplace at Sleipner West off the coast of Norway,where approximately one million tonnes of CO

2 are

sequestered annually as part of an off-shorenatural gas production project (see sidebar on theStatoil Project). Developers of technologies forsequestration of CO2 in geologic formations candraw from related experience gained over nearly acentury of oil and gas production, groundwaterresource management, and, more recently, naturalgas storage and groundwater remediation. In somecases, sequestration may even be accompanied byeconomic benefits such as enhanced oil recovery(EOR), enhanced methane production from coalbeds, enhanced production of natural gas fromdepleted fields, and improved natural gas storageefficiency through the use of CO2 as a “cushiongas” to displace methane from the reservoir.

5.1.1 Sequestration Mechanisms

CO2 can be sequestered in geologic formations bythree principal mechanisms (Hitchon 1996; DOE1993). First, CO2 can be trapped as a gas orsupercritical fluid under a low-permeabilitycaprock, similar to the way that natural gas istrapped in gas reservoirs or stored in aquifers. Thismechanism, commonly called hydrodynamictrapping, will likely be, in the short term, the mostimportant for sequestration. Finding bettermethods to increase the fraction of pore space


55555

By the year2025, effective,safe, and cost-competitiveoptions forgeologicsequestration ofall of the CO

2

generated fromcoal, oil, and gaspower plants andgenerated by H

2

production fromfossil fuels willbe availablewithin 500 km ofeach powerplant.

5-2 Sequestration of CO 2 in Geologic Formations


occupied by trapped gas will enablemaximum use of the sequestrationcapacity of a geologic formation.Second, CO2 can dissolve into the fluidphase. This mechanism of dissolvingthe gas in a liquid such as petroleum iscalled solubility trapping. In oilreservoirs, dissolved CO2 lowers theviscosity of the residual oil so it swellsand flows more readily, providing thebasis for one of the more common EORtechniques. The relative importance ofsolubility trapping depends on a largenumber of factors, such as the sweepefficiency (efficiency of displacement ofoil or water) of CO2 injection, theformation of fingers (preferred flowpaths), and the effects of formationheterogeneity. Efficient solubilitytrapping will reduce the likelihood thatCO

2 gas will quickly return to the

atmosphere.

Finally, CO2 can react either directly

or indirectly with the minerals and

organic matter in the geologicformations to become part of the solidmineral matrix. In most geologicformations, formation of calcium,magnesium, and iron carbonates isexpected to be the primary mineral-trapping processes. However,precipitation of these stable mineralphases is a relatively slow process withpoorly understood kinetics. In coalformations, trapping is achieved bypreferential adsorption of CO

2 to the

solid matrix. Developing methods forincreasing the rate and capacity formineral trapping will create stablerepositories of carbon that are unlikelyto return to the biosphere and willdecrease unexpected leakage of CO

2 to

the surface.

Finding ways to optimize hydro-dynamic trapping, while increasingthe rate at which the other trappingmechanisms convert CO

2 to less mobile

and stable forms, is one of the major

Statoil Sequesters CO2 from Off-Shore Gas Production

Natural gas produced from theSleipner West field in the North Seacontains nearly 10% by volume CO2.To meet the sales specification ofonly 2.5% CO2, most of the CO2 mustbe removed from the natural gasbefore delivery. Statoil uses anamine solvent to absorb the excessCO2. The separated CO2 is injectedinto an aquifer 1000 m under theNorth Sea. Approximately onemillion tonnes of CO2 are separatedand sequestered annually. Over theproject lifetime, 20 million tonnes ofCO2 are expected to be sequestered(Korbol and Kaddour 1995).



challenges that must be addressed byan R&D program.

5.1.2 Sources and Forms of CO 2

For the purposes of this assessment, weassumed that CO2 would be producedeither by combustion of fossil fuels togenerate electricity or by decarbon-ization of fossil fuels to producehydrogen. Following generation, CO

2

would be separated from the wastestream to a purity of at least 90%. CO2

would be transported as a supercriticalfluid by pipeline to the nearestgeologic formation suitable forsequestration. The technology, cost,and safety issues for transportationwere not considered.

5.1.3 Capacity of GeologicFormations Suitable forSequestration

Three principal types of geologicformations are widespread and havethe potential to sequester largeamounts of CO2:

• active and depleted oil and gasreservoirs

• deep aqueous formations,including saline formations

• deep coal seams and coal-bedmethane formations

Other geologic formations such asmarine and arctic hydrates, CO

2

reservoirs, mined cavities in saltdomes, and oil shales may increasesequestration capacity or provide site-specific opportunities but are likely tobe developed only after othersequestration targets are explored.

Maps showing the location of activeand abandoned oil and gas fields,deep-saline aquifers, and coal

formations are provided in Figs. 5.1through 5.3. Figure 5.3 also shows thelocation of fossil-fuel-fired powerplants. As illustrated, one or more ofthese formations is located within500 km of each of the fossil-fuel-burning power plants in the UnitedStates.

Estimates of sequestration capacity foreach of these types of geologicformations are provided in Table 5.1.While the range and uncertainty inthese estimates are large, and in somecases costs were not considered whenthey were developed, they suggest thata significant opportunity exists for CO

2

sequestration in geologic formations.More specifically, in the near term, theUnited States has sufficient capacity,diversity, and broad geographicdistribution of geological formations topursue geologic sequestrationconfidently as a major component of anational carbon management strategy.What is less certain is the ultimatecapacity that geologic formations cancontribute, over the centuries ahead, tosequestration of CO

2. Only through

experience and application ofsystematic screening criteria will wegain enough knowledge to assess theultimate sequestration capacity ofgeologic formations.

5.1.4 Drivers for R&D

Although the potential for CO2 seques-

tration in geologic formations ispromising, new knowledge, enhancedtechnology, and operational exper-ience must be gained in a number ofcritical areas. The primary drivers forR&D include

• developing reliable and cost-effective systems for monitoring CO

2

migration in the subsurface



Fig. 5.1. Location of gas-producing areas in the United States.

Fig. 5.2. Location of deep saline aquifers in the United States.



• assessing and ensuring long-termstability of sequestered CO

2 (<100

years)• reducing the cost and energy

requirements of CO2 sequestration

in geologic formations• gaining public acceptance for

geologic sequestration

This chapter outlines R&D needs toaddress these issues and provides acomprehensive road map of the criticalelements needed to achieve the

potential of geologic sequestration ofCO

2.

5.2 ASSESSMENT OF CURRENTCAPABILITIES AND R&DNEEDS

The current capabilities and needswere evaluated in the following contextfor each major type of geologicformation.

Fig. 5.3. Location of coal-producing areas in the United States and power plants.

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Industrial experience: What relatedindustrial experience provides thescientific, technological, andeconomic basis for evaluatingsequestration in geologic formations?

Beneficial uses of CO2: Are therebeneficial uses of CO

2 that may offset

the cost of sequestration or provide anadditional incentive for developing CO2

sequestration technology?

Regulatory, cost, and safety: What isknown about the regulatory framework,cost, and safety aspects of CO2 seques-tration in geologic formations?

Operational drivers: What are theoperational aspects that must beunderstood to enable cost-effective andsafe sequestration of CO2? Theseinclude

• CO2 trapping mechanisms: Which of

the trapping mechanisms is mostimportant? How much do weunderstand about them? What arethe key unresolved issues?

• CO2 waste stream characteristics:

What are the requirements for theCO2 waste stream? How pure shouldit be? What are the effects of impuri-ties on sequestration efficiency,cost, safety, and risk? Whattemperature and pressure areneeded at the wellhead? What arethe unresolved issues?

• Formation characterization: How cansequestration capacity and caprockintegrity be assessed? What attri-butes are most important forassessing capacity and integrity?

• Injection, drilling, and well comple-tion technology: How will CO

2 be

injected into geologic formations?How will the wells be drilled andcompleted? Are there specialmaterial-handing issues forsequestration of CO2?

• Performance assessment: Whatmethods can be used to design,predict, and optimize sequestrationof CO2 in geologic formations? Whatnew issues must to be addressed ornew approaches will be required?

• Monitoring: How can migration ofCO

2 in the subsurface be moni-

tored? How can leakage be detectedand quantified? How can we detectand monitor solubility and mineraltrapping?

In the following sections, we firstaddress these questions in the contextof issues unique to each type ofgeologic formation. Next we addresscross-cutting issues that are commonto all formations.

5.2.1 Opportunities for CO 2Sequestration in Oil and GasFormations

Oil and gas reservoirs are promisingtargets for CO

2 sequestration for a

number of reasons. First, oil and gasare present within structural orstratigraphic traps, and the oil and gasthat originally accumulated in thesetraps did not escape over geologicaltime. Thus these reservoirs should alsocontain CO2, as long as pathways to thesurface or to adjacent formations arenot created by overpressuring of thereservoir, by fracturing out of thereservoir at wells, or by leaks aroundwells. Second, the geologic structureand physical properties of most oil andgas fields have been characterizedextensively. While additionalcharacterization—particularly of theintegrity and extent of the caprock—may be needed, the availability ofexisting data will lower the cost ofimplementing CO2 sequestrationprojects. Finally, very sophisticatedcomputer models have been developedin the oil and gas industry to predict



displacement behavior and trapping ofCO

2 for EOR. These models take into

account the flow of oil, gas, and brinein three dimensions; phase behaviorand CO

2 solubility in oil and brine;

and the spatial variation of reservoirproperties, to the extent it is known.These same processes are responsiblefor hydrodynamic and solubilitytrapping of CO2 (see sidebar on naturalgas storage).

The first and most viable option for CO2

sequestration is to build upon theenormous experience of the oil and gasindustry in EOR. Currently, about 80%of commercially used CO

2 is for EOR

purposes. The technology for CO2

injection is commercially proven andcan be implemented without muchdifficulty (see sidebar on auxiliarybenefits of CO2 sequestration). EOR hasthe benefit of sequestering CO

2 while

increasing production from active oilfields. In the long term, the volume ofCO

2 sequestered as part of EOR projects

may not be comparatively large, butvaluable operational experience can begained that will benefit geologicsequestration in other types offormations.

CO2 could be sequestered in two typesof natural gas fields: (1) abandonedfields and (2) depleted but still activefields where gas recovery could beenhanced by CO2 injection. The map inFig. 5.1 suggests that, except for theNorth Central and Atlantic Coastalstates, abandoned gas fields arepresent in many parts of the UnitedStates. Deciding which abandoned gasfields could best be used in a CO2

sequestration program would require acomprehensive review of the currentconditions in abandoned fields andthe economics of their rehabilitation.This would be a major program ofinvestigation, but the necessary

technology to carry out such a reviewis available and well known to the gasindustry. Locating and sealingabandoned wells may be an ongoingchallenge for sequestration inabandoned gas fields.

In nearly depleted gas fields, it ispossible that injection could prolongthe economic life of the field bymaintaining reservoir pressures longerthan would otherwise be possible.However, enhancing gas productionthrough injection of another kind ofgas (e.g., CO

2) while the field continues

to operate has not been pursued in the

Natural Gas Storagein Geologic Formations

Daily and seasonal variability indemand for natural gas requires thestorage of large volumes of natural gasthat can be tapped as needed. Geologicformations are used to store naturalgas. Currently, they provide3 trillion ft3 of working gas capacity.Most gas is stored in depleted gasfields, but aquifers and mined cavernsin salt also contribute significantly tothe existing capacity. Natural gasstorage provides experience in anddemonstrates the feasibility of thehydrodynamic trapping mechanismfor use in sequestering CO2

(Beckman and Determeyer 1995).



United States. Therefore, pilot testsaugmented with laboratory andmodeling studies will be needed todevelop this technology. Someexperience may be gained from Gaz deFrance, which for the past 10 to 15years has been converting gas storageprojects to operate with two kinds ofgas: natural gas that is cyclicallyinjected and withdrawn as needed anda low-cost cushion gas. A similarconcept may be developed forcombining CO2 sequestration withenhanced natural gas production fromdepleted fields.

Table 5.2 lists the specific R&D needsfor advancing the technology andacceptability of CO2 sequestration inoil and gas reservoirs. Needs aredivided into near-, mid-, and long-term efforts that together provide acomprehensive set of actions that willcreate a set of sequestration options.

5.2.2 CO2 Sequestration in AqueousFormations

Aqueous formations are the mostcommon fluid reservoirs in thesubsurface, and large-volumeformations are available practicallyanywhere. For sequestration, deep(>2000 ft) formations that are not incurrent use are the most logicaltargets. As shown in Fig. 5.2, suitabledeep formations, which are usuallyfilled with brackish or saline water, arelocated across most of the UnitedStates.

Although there is little practicalexperience with CO2 sequestration inaqueous formations, aquifer storage ofnatural gas provides a foundation ofexperience for identifying importanttechnical issues. In addition, CO2

sequestration in aquifers has beendiscussed in the technical literaturesince the early 1990s. Operational

CO2 Sequestration in Geological FormationsCan Have Auxiliary Benefits

Recovering residual oil through the injection of CO2 into oil reservoirs began ona large scale in 1972 in Texas. Carbon dioxide enhances oil production by twoprimary mechanisms. First, CO2 gas displaces oil and brine, which aresubsequently pumped from the wells. Second, injected CO2 dissolves in the oil,leading to a reduction in viscosity and swelling of the oil, making it flow moreeasily and leading to enhanced production. The CO2 used for EOR usually comesfrom naturally occurring CO2-filled reservoirs. Pipelines carry CO2 from its naturalreservoirs to the oil field, where it is injected. Eventually, some of the injected CO2

is produced along with the oil. At the surface, it is separated and injected back intothe oil reservoir. EOR through CO2 injection provides one example of the beneficialuses of CO2 and operational experience to guide CO2 sequestration.

In the future, CO2 sequestered from power plants can be used to enhance coal-bed methane production. A pilot program of CO2-assisted coal-bed methaneproduction in the San Juan Basin, New Mexico, has been under way since 1996.This project, the Allison Unit Pilot run by Burlington Resources, is injecting4 million ft3/day of pipeline-fed CO2 from a natural source into a system of nineinjection wells located in the San Juan Basin. Preliminary results indicate thatfull-field development of this process could boost recovery of in-place methane byabout 75%.



experience from aquifer gas storageand these studies indicate that from anengineering perspective, the mainissues for CO2 disposal in aquifersrelate to (1) the disposal rate of CO2;(2) the available storage capacity(ultimate CO2 inventory); (3) thepresence of a caprock of lowpermeability, and potential CO2

leakage through imperfect confine-ment; (4) identification andcharacterization of suitable aquiferformations and caprock structures;

(5) uncertainty due to incompleteknowledge of subsurface conditionsand processes; and (6) corrosionresistance of materials to be used ininjection wells and associatedfacilities.

The main trapping process affectingCO2 sequestration in aquifers is wellunderstood, at least in a generic sense.Injection of CO2 into a water-filledformation results in immiscibledisplacement of an aqueous phase by a

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less dense and less viscous gas phase.Because CO

2 is soluble in water, some

of the CO2 will dissolve in the water.The thermophysical properties of waterand CO

2 that determine flow behavior—

such as density, viscosity, andsolubility—are well known, as is theirdependence on pressure, temperature,and salinity. Equilibrium solubility ofCO2 in water decreases by about afactor of 6 between 10 and 150°C, andit decreases with aquifer salinity(“salting out”). The rate at whichgaseous CO

2 will dissolve in water

depends on size and shape of the gas-water interfaces and may be subject toconsiderable uncertainty.

Uptake of CO2 by water may beincreased beyond what can beattributed to physical solubility byinteractions with carbonate minerals.Minerals such as calcite would bedissolved in response to CO2 injection.A considerably larger increase in

storage capacity is possible fromheterogeneous reactions withaluminosilicates (“mineral trapping”).There are indications that kinetics ofreactions with carbonates may be fast,while kinetics of silicate interactionsappear to be very slow, requiring tensor perhaps hundreds of years forsubstantial reaction progress.

Because CO2 is considerably less

dense and viscose than water, CO2

injection into aquifers will be prone tohydrodynamic instabilities. Theviscosity contrasts will lead to viscousfingering, and the density contrast willlead to gravity segregation. Thespecifics of each will depend on thespatial distribution of permeability atthe actual site and on injection rates(Fig. 5.4). The effect of these complexi-ties may be important in controllingthe relative importance of the threeprimary trapping mechanisms.Detailed characterization of these

Fig. 5.4. Gravity segregation, viscous fingering,heterogeneity, and preferential flow through faulted cap rockscould influence CO2 migration in the subsurface.



complexities will be difficult, but itmay not be necessary for achievingengineering objectives.

Two key issues distinguish CO2

sequestration in aquifers fromsequestration in oil and gas reservoirs.First, oil and gas reservoirs occur byvirtue of the presence of a structural orstratigraphic trap. This same trap islikely to retain CO

2. Identification of

such effective traps may be moredifficult in aqueous formations andmay require new approaches forestablishing the integrity and extent ofa caprock. Second, injection of CO2

into an aqueous formation is unlikelyto be accompanied by removal of waterfrom the formation. (In the case of EOR,oil is simultaneously withdrawn whileCO2 is injected.) Injection will thereforelead to an increase in formationpressure over a large area. Whether orto what extent large-scale pressuriza-tion will affect caprock integrity, causeland surface deformation, and induceseismicity must be better understoodto design safe and effectivesequestration.

A final issue concerning sequestrationin aqueous formations is the accep-table leakage rate from the formation tooverlying strata. Leakage of CO2 maynot pose a safety hazard and may, insome cases, be desirable if leakage tooverlying units increases theopportunity for enhanced solubility ormineral trapping. Evaluating generaland site-specific acceptable leakagerates should be part of a long-termstrategy for CO2 sequestration inaqueous formations.

Table 5.3 lists the specific R&D needsfor advancing the technology andacceptability of CO

2 sequestration in

aqueous formations. Needs are dividedinto near-, mid-, and long-term effortsthat together provide a comprehensive

set of actions that will create a set ofsequestration options.

5.2.3 Opportunities for CO 2Sequestration in CoalFormations

Coal formations provide an opportunityto simultaneously sequester CO2 andincrease the production of natural gas.Methane production from deepunmineable coal beds can beenhanced by injecting CO

2 into coal

formations, where the adsorption of CO2

causes the desorption of methane. Thisprocess has the potential to sequesterlarge volumes of CO2 while improvingthe efficiency and profitability ofcommercial natural gas operations (seesidebar on auxiliary benefits of CO2

sequestration).

This method for enhancing coal-bedmethane production is currently beingtested at two pilot demonstration sitesin North America. At one pilot produc-tion field in the San Juan Basin (NewMexico and Colorado), the operator hasinjected 3 million ft3/day of CO2

through four injection wells during a3-year period. Preliminary resultsindicate that full-field development ofthis process could boost recovery of in-place methane by about 75%. The keytechnical and commercial criteria forsuccessful application of this conceptinclude (1) favorable geology such asthick, gas-saturated coal seams, buriedat suitable depths and located insimple structural settings, which havesufficient permeability; (2) CO2

availability, such as low-cost potentialsupplies of CO

2, either from naturally

occurring reservoirs or fromanthropogenic sources such as power-plant flue gas; and (3) gas demand,which includes an efficient market forutilization of methane, includingadequate pipeline infrastructure, long-



term end-users, and favorablewellhead gas prices.

A second pilot demonstration of thisconcept is located in Alberta, Canada.The Alberta project is testing a processof injecting CO2 into one of Alberta’sdeep unmineable coal beds. Many ofAlberta’s coal deposits are rich in

methane. Preliminary computermodeling suggests that selectedtechniques for fracturing the coalsaround wells could be improved with asubstantial increase in primarymethane. The initial field activitiesconsist of a single well test, designedto measure reservoir properties,increase primary production by an

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effective fracturing technique, andevaluate CO

2-enhanced methane

recovery. A detailed technicalassessment will follow the field test inearly 1999.

Coal-bearing strata include both thinand thick coal seams and interlayeredsandstones, siltstones, and shales; andthey are usually saturated with water.This complex interlayered formationdefines the coal-bed reservoir interval.Coal-bed stratigraphy and thestructure/porosity/permeability ofinterlayered and overlying strata aresite-specific and will need to beindividually characterized. Unlike inoil and gas reservoirs, however, themethane in coal beds is retained byadsorption rather than by trappingbeneath an impermeable overlying/lateral seal. Therefore, the nature ofoverlying and adjacent strata becomesan important issue for retention of theCO2 within the coal-bed reservoirinterval until it is adsorbed, and forretention of the displaced methaneuntil it can be withdrawn. Techniquesto verify the capacity, stability, andpermanence of CO2 storage in coal-bedreservoir intervals are needed.

Table 5.4 lists the specific R&D needsfor advancing the technology andacceptability of CO

2 sequestration in

coal formations. Needs are divided intonear-, mid-, and long-term efforts thattogether provide a comprehensive set ofactions that will create a set of seques-tration options.

5.3 CROSS-CUTTING R&D NEEDSFOR GEOLOGIC FORMATIONS

Operational requirements and R&Dneeds for sequestration in each of thethree types of geologic formations wereassessed independently. Not unex-pectedly, needs common to all

formations emerged and aresummarized in this section. There aresignificant differences, however, in thematurity of technology and scientificunderstanding of the processesunderpinning CO2 sequestration indifferent types of geologic formations.Figure 5.5 highlights these similaritiesand differences.

5.3.1 CO2 Trapping Mechanisms

Hydrodynamic and solubilityprocesses responsible for trapping CO

2

in geologic formations are reasonablywell understood, especially over thetime frame associated with EOR(<20 years). Mineral trapping (i.e.,reactions relying on the chemicalreactions between the gas/liquid andsolid phases) is less well understood,particularly with regard to how fastthese reactions occur. Reactionsbetween CO2 and the microbialcommunities present in deep geologicformations are also poorly understood.Needs for new knowledge include

• hydrodynamics of CO2 migration in

heterogeneous formations (e.g.,sweep efficiency, preferential flow,and leakage rates)

• CO2 dissolution kinetics• mineral trapping kinetics• microbial interactions with CO

2

• influence of stress changes oncaprock and formation integrity

• nonlinear feedback processesaffecting confinement (e.g., mineraldissolution and precipitation thatchange rock permeability)

• CO2–methane adsorption/exchangebehavior on organic substrates

5.3.2 CO2 Waste StreamCharacteristics

A high-purity (>90% CO2), dry wastestream is the most desirable forsequestration in geological formations,



based largely on considerations aboutvolume reduction, costs for gascompression, and CO2 handling issues(e.g., corrosion). Scoping studies areneeded to evaluate beneficial ordetrimental effects of waste streamcharacteristics on trapping efficiency,economics, and safety of CO

2 seques-

tration. Examples of research needsinclude

• analysis of the effect of wastestream characteristics onhydrodynamic, solubility, and

mineral trapping/adsorptionefficiency

• cost/benefit analysis for deter-mining optimal CO2 purity

• evaluation of the influence of other“contaminants” (e.g., mercury) onthe safety and regulatory con-straints on CO

2 sequestration

5.3.3 Formation Characterization

Ongoing efforts related to oil and gasproduction and groundwaterremediation have led to development of

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hydraulic, geophysical imaging, andgeostatistical techniques forcharacterizing the heterogeneity ofsedimentary and fractured geologicalformations. These will be needed topredict the sweep efficiency in

aqueous formations. Additional needsspecific to sequestration include

• caprock characterization• identification of leakage paths and

rates

Fig. 5.5. Comparative evaluation of the technological and scientific maturityof operational requirements for sequestering CO2 in geologic formations. Graysignifies that the technology and scientific understanding are mature and ready to go.White indicates that some experience base is available but more experience is neededto evaluate and improve sequestration options. Black signifies that key processes,parameters, technologies, and an understanding of fundamental processes mustimprove significantly to achieve our vision for geological sequestration.



• evaluation of hydrologic isolationthrough the use of isotopic andother chemical analyses

• identification of mineral assem-blages that influence mineraltrapping and caprock integrity

• water encroachment in dewateredformations

• reservoir compartmentalization• initial conditions and evolution of

joints and fracture networks fromstress and chemically induceddeformation

5.3.4 Injection, Drilling, and WellCompletion Technology

Injection, drilling, and completiontechnology for the oil and gas industryhas evolved to a highly sophisticatedstate so that it is possible to drill andcomplete vertical, slanted, andhorizontal wells in deep formationsand wells with multiple completions,as well as to handle corrosive fluids.Optimization of these for CO

2

sequestration may require methodsoptimizing sequestration efficiency.Potential needs include

• methods of injecting additives forcontrolling the mobility of CO

2

• advanced well completion tech-nology for enhancing sweepefficiency

• addition of chemical or biologicaladditives for enhancing mineraltrapping

• development and emplacement ofin situ sensors for monitoring CO2

migration• injection technologies to limit CO2

migration beyond “spill-points” andthrough leaks in the caprock

5.3.5 Performance Assessment

Multiphase, multicomponent computersimulators of subsurface fluid flowhave been developed for oil and gas

reservoirs, natural gas storage,groundwater resource management,and groundwater remediation. Theaccuracy of these simulators dependsheavily on site- and project-specificcalibration and improves by continualparameter adjustment over the projectlifetime. Developing reliable tools forpredicting, assessing, and optimizingCO2 sequestration will require asimilar level of experience underactual operating conditions.Additional needs specific to CO2

sequestration include

• reactive chemical transport codeswith precipitation-dissolution andadsorption-desorption kinetics and

• coupled H-C-M (hydrological-chemical-mechanical) models forlong-term behavior and assessmentof induced micro-seismicity.

5.3.6 Monitoring

Monitoring of CO2 migration in the

subsurface is needed for large-scalesequestration of CO2. Tracking of thedistribution of trapped CO

2 in the

gaseous, dissolved, and solid phases isneeded for performance confirmation,leak detection, and regulatoryoversight. Existing monitoring methodsinclude well testing and pressuremonitoring; tracers and chemicalsampling; and surface and boreholeseismic, electromagnetic, andgeomechanical methods such astiltmeters. The spatial and temporalresolution of these methods is unlikelyto be sufficient for performanceconfirmation and leak detection.Needs include

• high-resolution mapping tech-niques for tracking migration ofsequestered CO

2 and its byproducts

• deformation and microseismicitymonitoring



• remote sensing for CO2 leaks andland surface deformation

5.3.7 Cross-Cutting FundamentalResearch Needs

As the individual road maps for thesegeologic formations were developed,several cross-cutting fundamentalresearch needs emerged. New andimproved understanding of theseissues will lead to safer and more cost-effective CO2 sequestration. Anexpanded discussion of fundamentalresearch needs can be found in Doveet al.

Multiphase transport in hetero-geneous and deformable media:Gravity segregation, viscous fingering,and preferential flow along high-permeability pathways will play adominant role in CO

2 migration in the

subsurface. These difficulties will becompounded by deformation accom-panying adsorption-desorptionprocesses and precipitation-dissolution processes. A betterfundamental understanding is neededto predict migration of CO2 and tooptimize sweep efficiency in geologicformations.

Phase behavior of CO2/petroleum/water/solid systems: The partitioningof CO2 between the aqueous, oil, gas,and solid phases is critical to under-standing trapping mechanisms, as wellas to predicting CO2-enhanced oilrecovery from petroleum formationsand enhanced gas recovery from coalformations. Better understanding ofthe solid/fluid partitioning, partic-ularly, is needed for optimizingenhanced gas recovery from coal-bedmethane projects.

CO2 dissolution and reaction kinetics:Although the principal reaction path-ways between CO

2 and sedimentary

formations are relatively wellunderstood (e.g., reactions of feldsparswith acid to form calcite, dolomite,siderite and clay; dissolution ofcarbonate minerals), the kinetics ofCO2 dissolution in the liquid phaseand subsequent rock-water reactionsare slow and poorly understood. Ifconversion of CO2 to these stablemineral phases is to be an importantcomponent of sequestration inaqueous formations, understanding ofthe kinetics of these reactions and theprocesses controlling them isessential.

Micromechanics and deformationmodeling: Production of oil and gasfrom geologic formations and subse-quent sequestration of CO

2 into

geologic formations will beaccompanied by deformation of thereservoir formation. The influence ofdeformation on the hydraulicproperties of the formation andintegrity of the caprock must be betterunderstood. In aqueous formations,unlike in oil and gas reservoirs whereinjection of CO

2 is accompanied by

withdrawal of fluids, deformation islikely to be widespread as the pressurebuilds in the formation. The effects ofdeformation on the integrity of thecaprock and its ability to induceseismic events must be betterunderstood to ensure the long-termstability and safety of CO2

sequestration.

Coupled H-M-C-T (hydrologic-mechanical-chemical-thermal)processes and modeling: Accuratelypredicting, assessing, optimizing, andconfirming the performance of asequestration project requires anaccurate coupled model of all of theprocesses that influence repositoryperformance and safety. While muchexperience in subsurface simulationhas been gained from the oil and gas



industry and from the groundwatermanagement and remediationindustries, other experience shows thatthe quality of our predictions dependsstrongly on having a simulator gearedtoward the specific application.Simulators tailored to the specificphysical and chemical processesimportant for CO2 sequestration mustbe developed, tested, calibrated, andrefined through operationalexperience.

High-resolution geophysical imaging:High-resolution geophysical imagingoffers the best potential for cost-effective monitoring of the migrationand byproduct formation of CO2 insubsurface environments. Three-dimensional and four-dimensional(time-lapse) images of geologicstructures and pore fluids can becreated with surface, surface-to-borehole, and cross-boreholetechniques. The resolution needs to beimproved if these methods are to berelied on to detect caprock leakage,formation of viscous fingers, andpreferential pathways.

5.4 ADVANCED CONCEPTS FORSEQUESTRATION INGEOLOGIC FORMATIONS

The sequestration techniquesdescribed draw heavily from currentapproaches used by industry forproduction of oil, gas, and coal-bedmethane and for storage of natural gas.Although these techniques providereasonable near-term options forsequestration of CO2, enhancedtechnology for CO

2 sequestration in

geologic formations may significantlydecrease costs, increase capacity,enhance safety, or increase thebeneficial uses of CO2 injection. Such

enhanced technologies include thefollowing:

• Enhanced mineral trapping withcatalysts or other chemicaladditives. Conversion of CO2 tostable carbonate minerals isexpected to be very slow under thecurrent scenarios envisioned forsequestration in geologicformations. Identification ofchemical or biological additivesthat increase reaction rates couldenhance the effectiveness ofmineral trapping.

• Sequestration in compositeformations. Multilayer formations,all with imperfect caprocks, mayresult in highly dispersed plumes ofCO2. The greater the degree ofdispersion, the greater theopportunity for efficient solubilityand mineral trapping. Developingdesign criteria that account foracceptable leakage acrossmultilayer formations couldincrease the geographicdistribution and capacity ofgeologic formations forsequestering CO2.

• Microbial conversion of CO2 tomethane. Microorganisms thatgenerate methane from CO

2

(methanogens) are known to existin a wide variety of oxygen-depleted natural environments. Ifsequestration sites could be chosento take advantage of this naturallyoccurring process, an underground“methane factory” could be created.Alternatively, additives thatstimulate methanogenesis could beinjected along with CO2 to promotemethane formation.



• Rejuvenation of depleted oilreservoirs. Injection of CO

2 into

active oil reservoirs is a widelypracticed EOR technique. However,even after the EOR process is nolonger economically feasible, asmuch as 50% of the original oil inplace may be left underground. CO

2

injection, followed by a quiescentperiod during which gravitydrainage and gas cap formationredistribute the gas and liquidphases, may rejuvenate an oilformation that can no longerproduce economically.

• CO2-enhanced production ofmethane hydrates: Methanehydrates in ocean sediments andpermafrost hold tremendousreserves of natural gas. Producinggas from these formations remains achallenge because of their complexstructure, mechanical properties,and the thermodynamic behavior ofhydrates. CO

2 injection into

methane hydrate formations mayenhance production while simul-taneously sequestering CO2.

5.5 OVERALL R&D PRIORITIES

Geologic sequestration is uniqueamong the options for sequestration ofCO

2 because of the extensive exper-

ience from related industries: oil andgas production, groundwater resourcemanagement, and groundwaterremediation. Nevertheless, a number ofcritical needs must be addressed tomake geologic formation a cost-competitive and safe option forsequestration of CO2. These have beenaddressed in detail in the previoussections of the report. Figure 5.6provides synthesis and a timeline for akey set of actions needed to acceleratedevelopment of a set of options for CO2

sequestration in geologic formations.Short-term needs feed into longer termprojects. Together these will provide a

Fig. 5.6. Key elements of the R&D road map for sequestration of CO2in geologic formations.



realistic assessment and cost andperformance data for large-scalesequestration of CO2 in geologicformations. The paragraphs belowelaborate on these key actions.

1. There must be a reliable assess-ment of geologic formationsavailable for sequestration of CO2

from each of the major power-generating regions of the UnitedStates. Screening criteria forchoosing suitable options must bedeveloped in partnership withindustry, the scientific community,the public, and regulatory oversightagencies.

2. Pilot tests of geologic sequestrationconducted early would helpdevelop cost and performance dataand help prioritize future R&Dneeds. These pilot tests should bedesigned and conducted withsufficient monitoring, modeling,and performance assessment toenable quantitative evaluation ofthe processes responsible forgeologic sequestration.

3. Geologic analogues, such as CO2

reservoirs and CO2-rich aquifers,should be studied to determine thefactors leading to caprock integrityand mineral-trapping mechanisms.

4. Fundamental research is needed toaid understanding of criticalprocesses and parameters that willcontribute to safe and effective CO2

sequestration.5. Advanced technologies are needed

for (1) increasing the volume of thegeologic formation filled by CO

2,

(2) creating stable long-term sinks(stable mineral assemblages), (3)increasing solubility and perhapsdiluting CO2 to acceptable levels,and (4) tracking migration of CO2 inthe subsurface.

6. Full-scale demonstration projects,performed in partnership with

industry, that integrate CO2

separation and transportation withgeologic sequestration are neededto provide cost, safety, andperformance data on geologicsequestration of CO2.

5.6 WORKS CONSULTED

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Eddy, G. E., C. T. Rightmire, and C. W.Byrer 1982. “Relationship of MethaneContent of Coal Rank and Depth:Theoretical Versus Observed,” SPE /DOE Paper 10800, in Proceedings of1982 SPE/DOE Unconventional GasRecovery Symposium, Pittsburgh, Pa.,May 16–18.

Fulton, P. F., B. Rogers, N. Shah, andA. A. Reznik 1980. “Study of theEffectiveness of Increasing MethaneProduction,” Chemical and PetroleumEngineering Department, University ofPittsburgh, Pittsburgh, Pa. (Workperformed for DOE under contractDE-FG-21- 79MC1083.

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of the Third International Conference onCarbon Dioxide Removal, Cambridge,Mass., September 9–11, 1996.

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2-

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Advanced Biological Processes 6-1


Advanced biologicalprocesses will bedeveloped anddeployed to enablepractices tosequester carbon innatural systems,remove or convertcarbon from fossilenergy systems intouseful andrefractory products,and recycle carbonthrough biologicalprocesses into endproducts thatsubstitute for fossilcarbon sources.


ADVANCED BIOLOGICALPROCESSES

6.1 BACKGROUND AND RATIONALE FORADVANCED BIOLOGICAL PROCESSESTO SEQUESTER CARBON

By 2025, the goal is to implement advancedbiological processes that would help limitemissions and sequester carbon fromconcentrated utility and industrial combustiongases and dispersed point sources. Advancedbiological technologies will augment or improvenatural biological processes for carbonsequestration from the atmosphere in terrestrialplants, aquatic photosynthetic species, and soiland other microbial communities. Thesetechnologies encompass the use of novelorganisms, designed biological systems, andgenetic improvements in metabolic networks interrestrial and marine microbial, plant, andanimal species. This strategy can be accomplishedby developing

• faster-growing, healthier, and more stress-resistant crop and plants

• a better understanding of biological diversity,genetics, and processes

• ways to enhance or maximize geologicalcarbon sequestration by use of microorganisms

• ways to enhance carbon sequestration inocean systems through transgenic and geneticmanipulation of members of the food chain

• alternative microbial polymers or geneticallyimproved plants as durable materials

Enhanced biological carbon fixation significantlyincreases carbon sequestration without incurringcosts for separation, capture, and compression.Higher ambient CO2 concentrations increasebiological carbon fixation. But the resultingbiomass generally has a higher carbohydrate andlower lignin content. Thus increased photo-synthate is trapped into readily degraded material.

66666

6-2 Advanced Biological Processes


Photosynthesis is a well-understoodprocess. It is responsible for virtuallyall CO2 fixation in nature. Naturallyoccurring non-photosyntheticmicrobial processes are also capable ofconverting CO2 to useful forms such asmethane and acetate. Although muchremains to be learned about naturalprocesses, we predict that focusedresearch will create new opportunitiesto significantly enhance carbonsequestration by advanced biologicalprocesses.

Genetic engineering could increasecarbon sequestration by developingdurable new products that would notbe consumed with release of CO2. Inaddition, soil sequestration could beincreased by altering the structure ofplants to enhance carbonsequestration in soils. New plantspecies would have a higherpercentage of biomass below ground,be resistant to decay, promote theformation of carbonate minerals, andinteract with soil microbes to optimizethe recycling of plant nutrients.Alternately, the structure and/orcomposition of aboveground plantstructure biomass, including cellwalls, could be altered to facilitateplant bioconversion processes and torender non-harvested biomass lessdegradable in the environment. Themetabolic networks of plants and algaealso could be altered to direct anincreased share of photosynthate todesired products.

The four topic areas that compriseadvanced biological technologies forcarbon sequestration are carboncapture technology, sequestration inreduced carbon compounds,increasing plant productivity, andalternative durable materials. Thesehave cross-disciplinary applications interrestrial, geological subsurface, andocean environments.

6.2 CARBON CAPTURETECHNOLOGY SUPPORT


The prospects of using advancedbiological processes to capture andreduce or sequester carbon fromindustrial processes are largelytheoretical. However, the incentives fordeveloping these processes aresubstantial because they are based onnaturally occurring biologicalprocesses that do not require purified(or concentrated) CO2 streams to beimplemented effectively. Additionalresearch will be required to determinethe technical and economic feasibilityof these approaches for terrestrial,geological, and ocean systems.Advanced biological processes have thepotential to lower energy expenditures,reduce the need for chemicalprocessing, increase recycling ofcarbon, and reduce the use of fossilfuels.

Sewage plants today are being affectedby changes in community dynamicsdue to generation of new types ofwastes from biotechnology facilitiesand “chip technology.” Engineers arejust now beginning to work moreclosely with microbial ecologists,physiologists, and molecular biologiststo better monitor the changes in themicrobial diversity and metabolismthat are requiring new paradigms formore effectively treating wastewater.

Subsurface microbiology andgeomicrobiology researchers have seenan increase in funding for thecharacterization and monitoring of“rock”-inhabiting microorganisms.Through the use of molecular probes,polymerase chain reactionamplification, and even synchrotron



technology, scientists are beginning tounderstand how these populationsfunction in a world where there may belimited sources of carbon for energy.Through these studies, researchershave genetically identified and, insome cases, isolated newmicroorganisms that depend uponnon-carbon sources of energy. Thesestudies are laying the foundation forstudies of microbial carbonsequestration and alternative energysources.


6.2.2.1 Energyplexes

Because of the high energy costsassociated with current technologiesfor capture and separation atcombustion sources with low-concentration CO2 streams, the jointconsideration of energy productionand carbon capture might significantlylower costs. This may best be achievedby expanding the concept of“energyplexes” with integration ofbiological processes (NationalLaboratory Directors 1997). Biologicalprocesses integrated into energyplexeswould produce energy, treat waste,sequester carbon, and produce usefulend products. The integration at onesite would minimize transportationcosts, minimize the potential forenvironmental damage, and maximizeyields. These concepts need furtherdevelopment, but some aspects, whichinclude biological components, havebeen put into place on a limited scale

Waste treatment associated withlandfills, sewage treatment facilities, oreven release of sewage into waterbodies produces significant CO2 andother greenhouse gases (especiallymethane) from fixed carbon. Thiscarbon represents a potential source of

renewable energy. Molecular biologymethods could be employed to slow thedecomposition rates of solid wastes inlandfills. In addition, thebioengineering technology to trap,separate, and recycle CO2 and methanedecomposition products at landfillsand sewage treatment facilities needsto be improved.

Sewage treatment is designed tosanitize wastes and to reduce thecarbon burden before discharge. Thusan implicit goal of sewage treatment isthe production of CO2. Most CO2 isproduced by the aerobic treatmentstage. A shift to complete anaerobicfermentation could lower emissions. Amodification of sewage treatment inthis manner, via integration ofphysiological and genetic regulation,could generate more methane to meetthe fuel demand of plant operation andcould generate a higher-carbon endproduct for use in soil building andagriculture. Knowledge aboutphysiological processes and endproducts must be expanded to designthese plants.

Reductions in CO2 emission couldderive from more efficient operation ofsewage treatment plants and landfillsand integration of managed wetlandsinto waste treatment processes. Basicunderstanding of these biologicalprocesses must be expanded to allowmore effective implementation of theseoptions. Consideration should be givento the integration of these facilities intoenergyplexes to provide carbon andnutrients for other biological processes(e.g., production of carbonate rocks bymetal-reducing organisms, productionof biomass by algae).

6.2.2.2 Geological systems

Biological conversion of CO2 intoinsoluble carbonate rocks, such as



siderite (FeCO3)—using metal-reducing bacteria and metal-containing fly ash or other low-valueproducts—is technically feasible. Ifiron is abundant and available as abioreductant, siderite can be formed.These materials could be used inroadbeds, as composite materials, or asfill. In any case, solid carbonate rocksignificantly simplifies storage anddisposal of CO

2 by enormously

increasing the density of the materialto be handled. Either metal-reducingorganisms or algae could be applied toprecipitate carbonate rocks. Metalscould be reduced by bacteria andprecipitated as carbonates. Recentresearch on metal-reducingthermophilic bacteria hasdemonstrated that siderite productionby these bacteria can be substantial.

6.2.3 Research Implementation

6.2.3.1 Energyplexes

The energyplex concept involvesrecycling CO2 in waste flue gases froma power generation facility viaphotosynthesis to generate a store ofreduced carbon in the form of algalbiomass. Storage can take the form ofpolysaccharides or triglycerides, bothof which are readily usable fuels, or ofchemical feedstocks for downstream

bioconversion processes. Althoughadditional concepts will undoubtedlybe developed and should be sought,initial efforts are likely to focus onseveral research areas, includingintegration of primary productionusing waste CO2 and heat. Theseenergyplexes could benefit fromintegration of sewage or other wastetreatment because the nutrients andcarbon could be used in biologicalprocesses at the site. Because ofseasonal, land, and water limitations,this alternative may be applicable onlyin certain localities or specializedsituations.

One area that has been the focus ofconsiderable research in the past isgrowth of algae for fuel production.Previous research focused on dieselreplacements (“biodiesel”). In addition,the production of hydrogen and otherchemical feedstocks using algae isworth additional investment inresearch. Some algae can be cultivatedin saline or alkaline waters, which areavailable in the southwestern deserts,where land is relatively plentiful. Thisalternative might be limited by thecosts of pond preparation, CO2

injection, or algal harvest.

6.2.3.2 Geological systems

Microbial processes can probably beengineered to greatly accelerate theformation of carbonates from naturalsilicate minerals such as serpentinite(see Chap. 7). While it is known that therelease of magnesium ions fromcrushed serpentinite is greatlyenhanced in the presence of nitrifyingbacteria (Lebedeva, Lyalikova, andBugel’skii 1978), geneticmanipulations, use of otherchemotrophic organisms, andexploitation of microbial acid formationcan be expected to further acceleratethe decomposition of silicate minerals.

Energyplexes forConventional Crops

An additional potential option is touse the CO2 and the waste heat topromote the growth of more conven-tional agricultural crops. Use of CO2

can lead to increases in productivityof plant growth in hydroponics orwetlands applications. Pilot projectsare under way to capitalize on thisconcept.



Knowledge about the factors thatinhibit plant growth in serpentine soils(serpentine barrens, where littlevegetation is found) can be used todesign microorganisms that toleratehigh magnesium concentrations andlow calcium/magnesium ratios andresist heavy metal toxicity. Geneticengineering has the potential as wellto endow these organisms with thecapacity to use metal sulfide mineralsas energy sources and CO2 as thecarbon source for growth. Carbondioxide would be sequestered asmagnesium carbonate and asmicrobial biomass.

Additional advanced concepts includethe utilization of enzyme systems andcatalysts for CO

2 capture. The goals of

the research would be to achieveshorter residence times and higherthroughput. A more innovativeapproach may be to develop biologicalcatalysts for removal of CO2. These mayinclude “artificial photosynthesis”(microbial or self-assembly)applications with molecular devicesthat mimic photosynthesis. As some ofthe solvent-based CO2 absorbentscurrently in use are organiccompounds, biological production ofsolvents for CO2 scrubbing is feasible.

6.3 SEQUESTRATION INREDUCED CARBONCOMPOUNDS


The feasibility of a significant midtermimpact on global climate change byincreasing the size of forests is firmlyestablished. Algal biomass schemes fortrapping CO

2 have advanced in recent

years and should be explored as apossible supplement to forest

management and advancedagricultural biotechnologies.

The surface area of the planet isdominated by oceans (75%), wherebioproductivity is often limited bynutrient availability. As discussed inChap. 3, nutritional enrichment couldenhance ocean algal growth andmarine productivity and mightincrease net oceanic CO

2 fixation.

Advanced biological techniques couldbe used to increase phytoplanktonproductivity or to alter the competitivecapacities of organisms that feed onalgae. Marine algal production is notlimited by water availability and affordsgreater opportunities to controlnutrient delivery.

Algae are amenable to relatively simplegenetic manipulations aimed atincreasing photosynthetic efficiency,maximizing yields of desirable energystorage products, and optimizingconversion of photosynthetic productsto fuels or chemical feedstocks. Suchstrategies could also be applied toterrestrial plant species.


The goal is to have a mix of biologicalsystems that will provide incrementalbut significant contributions to overallcarbon management.

Research on using algae in pondsystems for renewable energy is likelyto have spin-offs for open-ocean carbonmanagement schemes and couldeventually lead to ocean harvesting–based renewable energy technologies.Recovery of other products fromfermented algal biomass—for example,fertilizers for terrestrial crops or foropen-ocean fertilization, or single-cellprotein for animal nutrition—wouldimprove overall economics.



Plant and microbial genomics projectscurrently under way will eventuallyprovide detailed knowledge aboutorganismal metabolic networks andinterrelationships among differentcells in a plant and different organismsin an ecosystem. Such knowledge willenable a better understanding ofecosystems and how to manage theirproductivities. We need moreinformation about

• the function of genes beingsequenced and computerizedmethods to manipulate and storethe huge quantities of data pouringforth from genomics efforts

• how to introduce individual genesand pathways into a wide variety ofplants and microbes

• gene replacement strategies forplant species

• artificial chromosomes for theintroduction of large segments ofgenetic material into plants

• more rapid and reliable methods forscreening candidate geneticallyengineered plants and for clonalpropagation of engineered plants


Most renewable energy schemesgenerate considerable recalcitrantbiomass and therefore offer theopportunity for significant net carbonfixation in addition to their value inreducing the demand for fossil energy.Compared with the difficulties of CO2

sequestration by separation,compression, and transport, thehandling and storage of recalcitrantbiomass is straightforward.

6.3.3.1 Sequestration of biologicalcarbon in ocean sediments

Chapter 3 discusses enhancing thenatural biological carbon cycle in theoceans. Research topics in advanced

biology regarding this carbonmitigation option include thefollowing:

• To what extent can biomassconcentration and disposition begenetically manipulated?

• Are there feasible geneticmanipulations of biomass thatwould alter the decreasing rate ofbiomass production in the openocean?

• Can we develop an organism thatwill rapidly and costeffectivelyassess the ecological impacts ofvarious nutrient stimulationscenarios?

• Can organisms be engineered sothat deposition of biological carbonoutweighs the adverse pH effects ofcarbonate deposition?

• Are there advanced biologicalapproaches to increasingphytoplankton accumulationspecifically in upwelling, nutrient-rich waters?

• Can genetic biomarkers bedeveloped to monitor and assessthe ultimate fate of biomass in deepocean sediments? (In particular, weneed a better understanding of theconversion of biomass to methaneclathrates.)

An intriguing aspect of accumulatingbiomass in ocean sediments is thepotential that this process couldbecome an energy resource in thelong-term. It is plausible that futureenergy scenarios would includemethane recovery from clathrateslocated in well-defined deposits.

6.3.3.2 Alkaline ponds for carbonsequestration

The capacity of some blue-green algaeto thrive essentially as monoculturesin waters of high alkalinity creates thepossibility of much more effective CO2



sequestration than would be possiblewith other photosynthetic systems. Thechemical hydration rate of CO2

increases with pH, as does the amountof inorganic carbon that can bedissolved in aqueous solution.Alkaline ponds have the potential totrap virtually all of the smokestack CO

2

emissions as well as the majorpollutant gases SO2 and NOx.Accumulation of biomass can beoptimized by pH manipulations thatsuppress the biomass-consumingactivities of respiring organisms. Withappropriate mass culturing of suitableblue-green algae, photosyntheticactivity can maintain alkaline pHwhile providing a renewable energyresource. The feasibility of massculturing of microalgae in alkalineseawater has been established,demonstrating the potential fordeveloping much larger mass culturesystems than could be contemplatedwith freshwater ponds.

6.3.3.3 Schemes for producingrefractory biomass fromterrestrial plants

Two possibilities for fixing CO2 intomaterials with recycle times much

longer than wood can be considered:polymeric materials that are relativelyrefractory to biological degradationand inorganics (carbonates).

A large number of plant speciessynthesize diterpenoid resins ornatural rubber, two materials that arerelatively stable in the environment.Although few of these species are ofeconomic significance, they arewidespread and adaptable to a range ofclimates, could be grown on a largescale, and could be engineered forimproved efficiency for conversion ofCO2 to product. These end products ofplant metabolism could be deposited assuch or cross-linked to minimize thepossibility of biological degradation(e.g., vulcanized rubber).

The development of new materials (e.g.,novel biomass-derived plastics), thatwould increase the use of reducedcarbon compounds in the economycould be a significant element incarbon management. Another approachcould be directed toward eliminatingthe irreversible conversion ofpetroleum to CO2 by substituting“recyclable” plant products for fine andintermediate-scale chemicals and

Aquaculture in the Desert

In 1987, during Eritea’s war of independence from Ethiopia, simple ponds weredug along the shore to a depth of about 0.5 m below the low tide line and about200 m2 in area. The ponds were filled with sea water and chemical fertilizers togrow algae and inoculated with mullet fingerlings at a rate of one fingerling persquare meter. After 4 months, each fish weighed about 1 lb. Less than 1% mortalitywas detected among these algae-eating fish, which are famous for their hardinessin resisting disease and coping with low oxygen concentrations. This is equivalentto a rate of production of about 15 tons/ha per year and demonstrated that desertshores could produce enough food to justify cultivation on a large scale. This wasnot surprising. In southeast Asia, freshwater ponds have been fertilized to growalgae and inoculated with algae-eating fishes for centuries. Their only variation onthis time-proven practice was to substitute seawater for fresh water and marinefish and algae for freshwater fish and algae. (www.ibt.tamu.edu/invitro/guested.htmhttp)



even transport fuels. These couldinclude the plant essential oils, fixedoils, resins, and even heptane, which isa major component of turpentine andan excellent transport fuel. Geneticengineering of plants to improve theavailability of these products is entirelyfeasible.

Lignin is relatively resistant tobiodegradation, and increasing thelignin content of plants would slow thedecay of biomass in soils. Plantgeneticists have discovered mutationsthat decrease the lignin content ofplants to increase nutritional value forruminants. Moreover, as thebiochemical pathways for ligninbiosynthesis in plants becameelucidated, the genes encoding ligninpathway enzymes were cloned andhave recently been employed to alterthe quantity and quality of lignin inpoplar and aspen tree species. Thetechnology of lignin manipulationcould be applied to plants that arecurrently being considered forreforestation with the objective ofincreasing net carbon transfer.

It has been estimated that only 3% ofthe carbon in solid wood in landfills isconverted to CO2 or methane (Skog andNicholson 1998). This limiteddecomposition of wood is attributed tothe recalcitrance of lignin in anaerobicenvironments. Although anaerobicbacteria can degrade cellulose, muchof the cellulose in solid wood issequestered from bacterial action by alignin barrier and therefore cannot bebiodegraded. Even paper productsundergo only partial decomposition inlandfills. Currently, most of the woodand wood products in landfills issequestered carbon. However,alterations in the structure of wood bydecreasing lignin content couldincrease its biodegradability. It is

likely that significant lignin wouldremain even in genetically modifiedwoody plants and that landfillscontaining such plants would stillsequester carbon. However, increasingbiodegradability could increasemethane yields from landfills, and theenergy value of buried wood and woodproducts could provide an economicincentive for using woody materials forcarbon sequestration. In contrast toreforestation or high-productivityagricultural schemes, there is anunlimited amount of carbon that couldbe sequestered in landfills.

6.4 INCREASING PLANTPRODUCTIVITY

Research would improve the ability togenetically manipulate plants toincrease phototosynthetic activity andfix CO

2 and nitrogen more efficiently.

Manipulation of plant genomes toobtain the desired effects is still apoorly developed field. Much moreattention needs to be given to thefundamental mechanisms of celldevelopment, cell wall biochemistry,plant photosynthetic processes, andprimary and secondary metabolicprocesses.

More rapidly growing herbaceousagricultural plant species will enhancethe removal of CO2 from the atmosphereand trap it in photosynthate that can bereadily converted into renewable fuels,chemicals, polymer precursors andfoodstuffs. Rapidly growing woodyspecies will trap CO

2 in durable timber

that can be used for a wide variety ofstructures. Other fast-growingherbaceous and woody species willprovide easily delignified fiber forpaper, composites, and blockcopolymers.




The advent of modern molecularbiology has enabled strategies forimprovement of many differentorganisms through genetic engi-neering, including many agriculturaland timber crop species. Our currentunderstanding of the processes ofphotosynthesis, photorespiration, plantpathology, and wood structure andfunction, among others, suggests manystrategies for increasing the rate ofbiological carbon sequestration. The25-year time frame of the proposedR&D program would permit advancesin several of these areas to be success-fully deployed on a large commercialscale, which could have a significantimpact on U.S. carbon emissions.

Plants get their carbon from CO2, which

makes up only 0.03% of the present-day atmosphere. Microscopic floatingplants, phytoplankton, and other algaetake up CO2 dissolved in water. Bothterrestrial and water plants requiresolar energy to reduce CO

2 to biomass.

Photosynthesis is responsible forconversion of sunlight into chemicalenergy by essentially all primaryproducers in nearly all ecosystems. Itprovides the foundation of the foodchain for life on Earth and is also thesource of the oxygen in ouratmosphere.

Sunlight provides the energy for theprimary mechanism of carbon fixationfrom the atmosphere. The theoreticalmaximum efficiency of light energycapture and conversion into usablechemical energy is approximately 5%(expressed as a fraction of visible lightenergy available at the earth’s surface).Plant photosystems seldom operate atanywhere near this efficiency, a factthat provides us with an excellentopportunity for carbon sequestration.Photosynthetic efficiency varies widelywith the ecosystem and time of year.The efficiency of some forests can be aslow as 0.1 to 0.05%, while that ofmarsh grasses can be as high as 2 to4% in the early spring. The photo-synthetic efficiency of corn and sugarcane can be as high as 3.5 to 4%.

Engineering Rubisco for Speed

Plants fix carbon by taking CO2 from the air and adding it to small precursorsugars in plants. This step is carried out by an enzyme known as Rubisco. Rubiscois the most abundant protein in the world, making up 50% of all plant proteins. TheRubisco enzyme is slow and inefficient. It not only fixes carbon but, in an alternatereaction, adds oxygen to the precursor sugars and degrades them, diverting theenzyme from productive activity. It may be possible to engineer into Rubisco moreefficient carbon-fixation mechanisms or to discover more efficient, naturallyoccurring forms of Rubisco in as yet poorly characterized or undiscoveredorganisms.

The activity of Rubisco is regulated by another enzyme called Rubisco activase.Rubisco activase controls the overall process of photosynthesis by making Rubiscoactivity responsive to light intensity. Researchers are currently changing aspecific part of the Rubisco activase enzyme by genetic engineering to analyze itsfunction. Information about the mechanism and structure of Rubisco activaseeventually can be used to make changes that improve the activity of the enzymeand increase photosynthetic efficiency. (www.photoscience.la.asu.edu/Photosyn/faculty/salvucci.html)



Environmental conditions stronglyaffect photosynthetic efficiency, but thebiochemistry of the photon capture andenergy conversion system could beimproved as well.

Photosynthetic carbon fixation islimited by the efficiency of two veryimportant processes—conversion ofincident light energy to capturedchemical energy and the primarycarbon fixation reaction catalyzed bythe enzyme Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase),the most abundant protein on Earth.Either or both of these processes maybe limiting in terms of carbon seques-tration rates, and it is thought that theycould be enhanced significantly viaadvanced biological approaches.

Rubisco is not only a very slow en-zyme, but is also inefficient because itcan react with molecular oxygen in aprocess known as photorespiration.This results in a futile (nonproductive)metabolic cycle. As the ratio of CO2 toO2 in the atmosphere increases, theproductive carboxylation efficiencywill naturally increase. However, itmay also be possible to discover moreefficient, naturally occurring forms ofRubisco in as yet poorly characterizedor undiscovered organisms, or toengineer into Rubisco an exaggeratedpreference for CO2 over O2 usingmodern molecular biologicaltechniques (Mann 1999).

Some plant species have alreadydeveloped a solution to the problempresented by Rubisco. A group ofwarm-climate grass species known asC

4 grasses (including corn, sorghum,

and sugar cane) evolved a specializedleaf anatomy (Krantz anatomy; contrastC

3 and C

4 anatomy in Figs. 6.1 and 6.2,

respectively). These plants show littleor no photorespiration and areconsiderably more efficient because

Fig. 6.1: Typical leaf anatomy in a C3plant. (www.biology.arizona.edu/181/rick/photosynthesis/C4.html)

Fig. 6.2: Typical leaf anatomy in a C4plant. (www.cme.msu.edu/WIT/Doc/mj_recon.html)



CO2 is carried to sites of photo-synthesis. This trapping of CO

2 is

carried out via the Hatch-Slackpathway (Fig. 6.3), which is notaffected by oxygen. Geneticmanipulation, to optimize pathwaysfor trapping CO2, comprises significantresearch opportunities.

Although 78% of our atmosphereconsists of nitrogen, plants are notcapable of converting it into formsthey can use. Certain bacteria,however, produce enzymes thatfacilitate the transformation ofnitrogen gas into ammonia and othernitrogen-containing compounds thatcan readily be absorbed by plant rootsand used by the plant. In nature, thenatural decay of dead biomass releasesnitrogen in forms that can often beabsorbed by plants. This occurs both interrestrial systems and in the oceans.Nitrogen availability is often growth-limiting and is routinelysupplemented with fertilizers inagricultural practice. Some plantspecies, notably the legumes, do notrequire nitrogen fertilization becausetheir roots are colonized by nitrogen-fixing microorganisms. Ammonia canbe readily assimilated by plants andincorporated into other nitrogen-containing compounds, such as aminoacids, which are essential for proteinsynthesis. The critical enzyme innitrogen fixation is called nitrogenase,and it breaks the very strong triplebond of N2. These complex and poorlyunderstood enzymes require largeamounts of energy to accomplish thisreaction. In addition, nitrogenasescontain an assortment of complex,iron-containing co-factors, which areessential for activity. Thus, iron isoften rate-limiting for nitrogen fixationin the ocean.

When photosynthetic light capture, CO2

fixation, and nitrogen availability no

longer limit plant metabolism, one canimprove regulation of and/or redesignsecondary metabolic pathways forconversion and sequestration of theprimary products. It is thus veryimportant to understand both thespatial and temporal linkages amongmetabolic pathways in an organism, aswell as modes of long-term storage ofthe sequestered products. Elucidationof these linkages and carbon storagecapabilities will be best addressed bystructural biology, plant and microbialmolecular genetics, and computationalsimulation and theory.

Other environmental factors affectingcarbon sequestration are predation byinsects and microbial pathogens,which decrease global crop and forestyields. In addition, other stresses, suchas drought, saline soils, heat and cold,pH, and the presence of heavy metalsand other pollutants, limit plant growthrates and biomass accumulation.Ameliorating such stresses has been atarget for improvement by agricultureand silviculture over the centuries.Modern plant science has mitigatedcrop losses, but there is still plenty ofroom for improvement, as evidenced by

Fig. 6.3: Carbon fixation as it occurs viathe Hatch-Slack pathway in C4 plants.(www.biology.arizona.edu/181/rick/photosynthesis/C4.html)



the prolific activity and investment inplant biotechnology.

It is advantageous to increasedeposition of carbon in soils. Thismight be accomplished most effectivelyby increasing the transfer ofphotosynthate to root systems and byincreasing the accumulation ofrecalcitrant bioproducts (such aslignin) in forest litter. Deposition ofcarbon in soil by agricultural andsilvicultural systems might beincreased by shifting photosynthatepartitioning from aboveground tobelowground organs via geneticmeans. Increasing the recalcitrance ofroot tissues should also be explored asa possibility. Root deposition might beparticularly important in therestoration of degraded soils orcultivation of plants in marginalecosystems.

Nitrogen fixation could also increaseroot deposition and stimulate rootexudates. Soil microbes play animportant but incompletely understoodrole in enabling nutrient uptake byplants. Microbes associated with plantroots are an essential component ofbiological nitrogen fixation. Carbo-hydrates and other nutrients secretedby plant roots foster microbial growth,and the associated bacteria and fungimobilize minerals (such as phosphate)and fix nitrogen for plant use. Byincreasing secretion of photosynthateby roots, it might be possible toincrease biological nitrogen fixationand the cultivation of crops inmarginal lands. For example, specificplant-associated fungi are essential forthe cultivation of softwood species ontopsoil-deficient lands reclaimed fromopen pit mining. It seems likely thatsimilar relationships might beimportant in other degradedenvironments.

Several significant non-photosyntheticCO

2 fixation reactions occur in nature

(University of Chicago 1998). As muchas 10% of the cellulose andhemicellulose in plant biomass mightbe converted in the anaerobicenvironment to methane and CO2 byconsortia of anaerobic bacteria.Acetogenic bacteria appear to play amajor role in this process. At the globallevel, approximately 10 GT of acetate ismetabolized annually in the anaerobicenvironment, and about 10% of thismay be derived from CO

2 fixation via

the acetyl-CoA pathway. Potentiallyimportant niches for acetogens includetermites, monogastric and ruminantanimal digestive systems, and forestsoils.

If a source of hydrogen can be providedin a CO2-rich, O2-free environment, CO2

can be fixed efficiently into nonvolatilecarbon compounds. Interestingly, ithas recently been discovered that thestrictly chemical action of water onbasaltic rock formations deep below thesurface of the earth serves as a sourceof hydrogen for microbial ecosystems(Gollin et al. 1998). These reactionsmay be important for biosequestrationin geologic formations, such as spentoil and gas wells.

The advent of genetic engineering hasimproved crop productivity byincreasing disease resistance andimproving the ability of engineeredcrops to compete with undesired plantspecies. Plant products, especiallyoilseed crops, have been altered toincrease the production of marketableoils, and these engineered varieties arebeing grown commercially. Additionalengineering could increase oilproduction or other desirable products.Several genetically engineered cropspecies are currently being grown inthe United States and other countries



and are rapidly capturing marketshare. For example, 40% of the Canolacrops in Canada and 33% of thesoybean crops in the United States aregenetically engineered.

Research is under way to examineplant-insect interactions. The researchusually focuses on combating aspecific insect pest by producingtransgenic plants (plants with genesfrom other species) that synthesizecompounds that inhibit insectmetabolism. Producing a disease-resistant transgenic plant requires thatthe molecular mechanisms involved inhost plant resistance be elucidated.Unfortunately, these mechanisms varygreatly among plant pathogens.

Advances in gene technology haveoffered various novel routes to improvethe disease resistance of crops.Resistance to a number of insectspecies has been created by use ofgenes encoding protease inhibitorsand the d-endotoxin of Bacillusthuringiensis. Resistance against anumber of viruses was obtained byexpressing genes encoding for the viralcoat protein, applying the principle ofcross-protection.


In order to realize the maximumbenefit from biological fixation, weneed more basic knowledge about whatprocesses limit plant growth in manyspecialized crops for food, feed, fiber,fuel and structural uses. We also needmore information about optimalcultivation and harvest methods,particularly in marginal environmentswhere water or soil quality is limiting.Other growth-limiting factors such asdisease and insect pests also requirebetter understanding. Biotechnology

and plant genomics will play largeroles in reaching these goals.


Plant productivity can be increased by

• improving photosynthetic efficiencyby increasing light-trapping re-action efficiency and decreasingphotorespiration (C4 pathway; engi-neering Rubisco efficiency andreaction rate)

• developing rapid methods for ge-netic manipulation of agricultural,tree, and nontraditional specieswith CO

2 sequestering potential

(transformation and regenerationsystems)

• developing new tools formanipulating fast-growingherbaceous and woody species(artificial chromosomes; genereplacement techniques)

• reducing the time required tocreate transgenic plants in thelaboratory

• enhancing non-photosyntheticmechanisms for CO

2 fixation

(bacterial methanogenesis andacetogenesis)

• genetically engineering the cellwalls of agricultural species so thatthey can be more easily andeconomically converted to fuelsand chemicals

• developing crops or processes thatwill biosynthesize functionalfeedstock chemicals for thesynthesis of recalcitrant products(e.g., non-biodegradable plastics)

• improving nitrogen fixation inmicrobial symbionts of plants and/or by cloning genes into plants

• developing simplified nitrogenasesthat bypass the current mechanisticcomplexity, iron-dependence andenergy intensity issues



• improving insect and diseaseresistance via transgenics andprotein engineering

6.5 ALTERNATIVE DURABLEMATERIALS


6.5.1.1 Biopolymers

The past several years have seendramatic growth in the use of enzymesfor synthetic applications. This hasbeen particularly apparent in theincreased use of enzymes for polymerdesign and modification. Enzymes offersignificant advantages over chemicalcatalysts in the synthesis of materialswith highly specialized properties—including biodegradability,biocompatibility, inherent selectivity(e.g., enantio-, regio-, and chemo-),and easily tailored functionalities—allproduced under conditions thatminimize the formation of by-productsand the avoidance of unwantedpollutants (Dorkick 1998).

The development of carbon feedstocksfor chemical applications will reduceCO2 emissions by displacing fossilhydrocarbons. Primary examples arethe use of polymers derived fromrenewable agricultural resources, suchas corn or sugar beets. Thesecompounds are also commonly knownas “bioplastics.” For many applications,the plastic “peanuts” used as packingmaterial have been replaced bybioplastics. These bioplastics aredisplacing petrochemical-basedpolymers, such as polyethylene,polystyrene, and polypropylene. Oneclass of bioplastics, the PLA resins, arecomposed of chains of lactic acidderived from conversion of starch tosugar followed by fermentation tolactic acid. Dow Chemical and Cargillhave recently formed a joint venture tocommercialize PLA on a large scale.Polyhydroxyalkanoates (PHAs), achemically distinct family ofbiodegradable bioplastics, are beinginvestigated by Monsanto and Proctor& Gamble for use as petro-plasticsubstitutes. Monsanto is looking atproducing PHAs in crop plants insteadof fermentation vats.

Turning Sugar into Better Polymers

The polymer polytrimethylene terephthalate (3GT) has enhanced propertiescompared with traditional polyester (2GT). Yet commercialization has been slowbecause of the high cost of making trimethylene glycol (3G), one of 3GT’smonomers; it is a two-step process. However, recently, through recombinant DNAtechnology, an alliance of scientists from DuPont and Genencor International hascreated a single microorganism with all of the enzymes required to turn sugar into3G. This breakthrough is opening the door to low-cost, environmentally sound,large-scale production of 3G. The eventual cost of 3G produced by this process isexpected to approach that of ethylene glycol (2G).

The 3GT that is created by a fermentation process requires no heavy metals,petroleum, or toxic chemicals. The primary material comes from agriculture—glucose from cornstarch. Rather than releasing CO2 to the atmosphere, the processactually captures it because corn absorbs CO2 as it grows and all liquid effluent iseasily and harmlessly biodegradable. 3GT can also be subjected to methanolysis, aprocess that reduces polyesters to their original monomers. Used polyesters can berecycled indefinitely by being repolymerized. (www.dupont.com/corp/science/bionylon.html)



Bioplastics and biofuels are promisingemerging technologies, but othertechnologies may have a greater long-range impact in terms of carbonsequestration. Bioplastics are expectedto compete with petro-plastics on acost/performance basis. If the carbonused in the process is fromatmospheric sources (e.g., frombiomass) the net result is carbonsequestration. The market for thesematerials may limit the carbonsequestration potential; however, otherbiological processes, especially whenpart of an integrated sequestrationstrategy, could have greatersequestration potential.

6.5.1.2 Microbial production ofcellulose

Acetobacter xylinium, a non-photosynthetic bacterium mostcommonly used in the production ofvinegar, can use glucose, sugar,glycerol, or other organic substratesand convert them into pure cellulose(Brown 1979). Weyerhaeuser, alongwith the now defunct CetusCorporation, spent 7 years optimizingthe production of bacterial cellulose,which has unique structural andabsorption properties. Several patentshave been filed on the applications ofbacterial cellulose.

Microbial cellulose has beeninvestigated as a binder in papers.Because it consists of extremely smallclusters of cellulose microfibrils, itadds greatly to the strength anddurability of pulp when integrated intopaper. Ajinomoto Company andMitsubishi Paper Mills in Japan arecurrently active in developingmicrobial cellulose for paper products(see patent JP 63295793 at www.botany.utexas.edu/facstaff/facpages/mbrown/position1.htm). Thisbiopolymer is just one example of the

many microbial polymers that havepotential for use as alternative durablematerials.


Unfortunately, the plastic nowproduced by plants and bacteria isbrittle and decomposes rapidly.Research into ways to improve thequality of bioplastics to enhance theirusefulness in consumer goods isneeded. Alteration of the biosyntheticpathways via gene shuffling, proteinengineering, and improvedfermentation technology at extremetemperatures must be integrated toachieve these improved bioplastics.

To overcome the drawbacks tosuccessful commercialization ofbacterial cellulose, efforts havecentered on understanding thebiosynthetic process itself, then tryingto optimize the fermentation process toproduce more cells and cellulosebiosynthesis. Further genetic study ofthe operon-controlling cellulose

CelluloseFactories

Acetobacter xylinumis nature’s most prolific

cellulose-producing bac-terium. As many as a million

cells can be packed into a largeliquid droplet, and if each one ofthese “factories” can convert up to108 glucose molecules per hourinto cellulose, the productshould virtually be madebefore one’s eyes. (www.botany.utexas.edu/facstaff/facpages/mbrown/position1.htm)



synthesis is needed. Gene shufflingmay have some applications also withrespect to strain “quilting of genes”and selection of improved transformats.

Because microbial cellulose is anextracellular product that is excretedinto the culture medium, special careand handling is necessary to maintainoptimal production. The cellulosemembrane itself can become a barrierfor substrates and oxygen necessary forthe cells to produce cellulose. Novelfermentation approaches have beendeveloped to overcome some of theintrinsic difficulties for mass culture ofAcetobacter, and a vigorous program ofbacterial strain selection from regionsall over the world has provided a stockresource of stable, efficient cellulose-producing strains.

What is needed at the present is a wayto convert bench-scale fermentation toan efficient, large-scale fermentationtechnology. This research need for newdevelopment technology can beachieved through a combination ofgenetic engineering and a betterunderstanding of microbial physiologyin submerged culture.


6.5.3.1 Biopolymers

Research to improve the desiredcharacteristics of bioplastics includesthe following:

• advances in elucidating structuralbiology

• genetic altering of enzymaticpathways

• improved protein crystallography• computational biology to simulate

structure and properties at extremetemperatures

• genetic engineering to improvedurability and elasticity

6.5.3.2 Microbial cellulose

The recent success with cloning andsequencing the genes for bacterialcellulose synthesis (Saxena, Lin, andBrown 1990, 1991) plus functionalgenomic information (Saxena et al.1994) will result in new ways to furtheroptimize bacterial cellulose productionby Acetobacter xylinium as well as otherbacteria and algae that synthesizecellulose.

Continued efforts in integrating thephysiology and molecular biology ofbacterial polymers combined withstructural and functional analysis viacrystallography and synchrotroncharacterization should make thesebacterial polymers even more attractiveand affordable.

6.6 SUMMARY ANDCONCLUSIONS

R&D efforts leading to sustainedsequestration of gigatonnes of carbonper year from the atmosphere are primesequestration options. Large-scalebiological sequestration opportunitieswill require significant time andresources for deployment, so weenvision successive technologydeployments over 25 years (Fig. 6.4).Near-term measures (before 2005) havelow technical risk and will havelimited carbon sequestration effects atfirst, but they may become increasinglylarge sinks with time. Medium-termoptions will use more advancedstrategies involving significantlyhigher technical risk but may permithigher carbon sequestration capacitywith fewer resources. Long-termoptions are characterized as high-riskbut may offer remarkable potential forcarbon sequestration.



Table 6.1 ranks the strategiesdiscussed in this chapter by technicalfeasibility, timeliness, and potentialeffects. Rankings would probably differif other relevant factors, such aseconomics, public policy, and risks(health and environmental), were alsoconsidered. Some rankings aresubjective because of the ill-definedscope of some options. For example,

Fig. 6.4. Key elements of the R&D road map for advanced biological processes.

genetic engineering of crop plants fordisease and pest resistance ispracticed commercially today; hence,this level of engineering is deemed tobe highly feasible. On the other hand,targeted genetic manipulation ofgrowth and durability characteristics ofconifers is likely to prove difficult andis deemed less feasible.



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6.7 REFERENCES

Brown, R. M., Jr. 1979. “Biogenesis ofNatural Polymer Systems, with SpecialReference to Cellulose Assembly andDeposition,” pp. 50–123 in Proceedingsof the Third Phillip Morris ScienceSymposium, Ellen Walk, ed., Richmond,Va., November 9, 1978.

Brown, R. M., Jr., J. H. M. Willison, andC. L. Richardson 1976. “CelluloseBiosynthesis in Acetobacter Xylinum:1. Visualization of the Site of Synthesisand Direct Measurement of the In VivoProcess,” Proc Nat Acad Sci U.S.A.73(12):4565–69.

Dorkick, J. 1998. “Biocatalysis onAgricultural Materials: A NaturalAlternative,” Abstract, Tenth CIFARConference, University of California—Davis, Davis, Calif., October 9.

Gollin. D., X. L. Li, S. M. Liu, E. T.Davies, and L. G. Ljungdahl 1998.“Acetogenesis and the PrimaryStructure of the NADP-DependentFormate Dehydrogenase of Clostridiumthermoaceticum, a Tungsten-Selenium-Iron Protein,” pp. 303–8 in Advances inChemical Conversions for MitigatingCarbon Dioxide: Studies in SurfaceScience and Catalysis, Vol. 114, T. Inui,M. Anpo, K. Izui, S. Yanagida, andT. Yamaguchi, eds., Elsevier ScienceB.V.

Herzog, H., E. Drake, and E. Adams1997. CO

2 Capture, Reuse, and Storage

Technologies for Mitigating GlobalClimate Change: A White Paper,Massachusetts Institute of TechnologyEnergy Laboratory.

Lal, R., J. M. Kimble, R. F. Follett, andB. A. Stewart, eds. 1998. Soil Processesand the Carbon Cycle, CRC/LewisPublishers, Boca Raton, Fla.

Lebedeva, E. V., N. N. Lyalikova, andYu Yu Bugel’skii 1978. “Participationof Nitrifying Bacteria in the Weatheringof Serpentinized Ultrabasic Rocks” (inRussian), Mikrobiolobiya 47:1101–7.

Mann, C. 1999. “Genetic EngineersAim to Soup Up Crop Photosynthesis,”Science 283 (January 15) 314–16.

National Laboratory Directors 1997.Technology Opportunities to Reduce U.S.Greenhouse Gas Emissions, Oak RidgeNational Laboratory.

Ralph J., J. J. MacKay, R. D. Hatfield,D. M. O’Malley, R. W. Whetten, andR. R. Sederoff 1997. “Abnormal Ligninin a Loblolly Pine Mutant,” Science277:235–9.

Ralph, J., R. D. Hatfield, J. Piquemal,N. Yahiaoui, M. Pean, C. Lapierre, andA. M. Boudet 1998. “NMRCharacterization of Altered LigninsExtracted from Tobacco Plants Down-Regulated for Lignification EnzymesCinnamylalcohol Dehydrogenase andCinnamoyl-CoA Reductase,” Proc NatlAcad Sci U.S.A. 95:12803–8.

Saxena, I. M., F. C. Lin, and R. M.Brown, Jr. 1990. “Cloning andSequencing of the Cellulose SynthaseCatalytic Subunit Gene of AcetobacterXylinum,” Plant Molecular Biology15:673–83.

Saxena, I. M., F. C. Lin, and R. M.Brown, Jr. 1991. “Identification of aNew Gene in an Operon for CelluloseBiosynthesis in Acetobacter Xylinum,”Plant Molecular Biology 16:947–54.

Saxena, I. M., K. Kudlicka, K. Okuda,and R. M. Brown, Jr. 1994.“Characterization of Genes in theCellulose Synthesizing Operon (AcsOperon) of Acetobacter Xylinum:



Implications for CelluloseCrystallization,” J. Bacteriology176:5735–52.

Skog, K. E., and G. A. Nicholson 1998.“Carbon Cycling through WoodProducts: The Role of Wood and PaperProducts in Carbon Sequestration,”Forest Products Journal 48:75–83.

Stevens, T. O., and J. P. McKinley1995. “Lithoautotrophic MicrobialEcosystems in Deep Basalt Aquifers,”Science 270:450–4.

Stevens, T. O., and J. P. McKinley1995. “Lithoautotrophic MicrobialEcosystems in Deep Basalt Aquifers,”Science 270: 450–4.

University of Chicago 1998. “ISAM ‘J’Carbon Cycle Model: Modify the CO2

Emissions,” University of Chicago,Department of the GeophysicalSciences, available atwww.geosci.uchicago.edu/~archer/cgimodels/isam.d.html.

Advanced Chemical Approaches to Sequestration 7-1



77777 ADVANCED CHEMICALAPPROACHES TOSEQUESTRATION

7.1 INTRODUCTION

Advanced chemical processes might lead tounique sequestration technologies or toimprovements in our understanding of chemistrythat will enhance the performance of otherapproaches to sequestration. Chemistry is acrosscutting discipline that will interact withvirtually all aspects of the sequestration problem.This chapter discusses R&D topics for options notcovered in the previous chapters on sequestrationtechnologies but that require advances in ourunderstanding of chemistry.

Advanced chemistry shares significant commonground with separation and capture. Improvedmethods of separation, transport, and storage willbenefit from research into advanced chemicaltechniques necessary to address sequestration viachemical transformation. Because anysequestration technique will involve storing vastamounts of carbon-rich materials, environmentalchemistry is an important cross-linkingtechnology to most of the approaches mentionedin this report. The fate of CO

2 in geological

underground storage sites is in part determinedby the chemical interaction of the CO2 with thesurrounding matrix, whether it is coal in coal bedsor the mineral rock that caps saline aquifers deepunderground where brines of carbonic acid caninteract. Many issues pertaining to aqueouscarbonate/bicarbonate chemistry are relevant toocean disposal or underground disposal.Carbonate chemistry in very basic solutions mayoffer potential for extracting CO2 from air. Becauseclathrates may be used to separate CO2 fromhigh-pressure systems, knowledge of theirproperties may be important to understandingapproaches to ocean disposal. Subsurface arctic or

Advances inchemical sciencesand the resultingtechnologies allowgaseous CO

2 or its

constituent carbonto be transformedinto materials thatare benign, areinert, are long-livedand contained inthe earth or waterof our planet, orhave commercialvalue. Thesetransformationsrepresenteconomical ways tosequester CO

2 or

its constituentcarbon.

7-2 Advanced Chemical Approaches to Sequestration


marine hydrate formations may also beevaluated as geologic disposal options.Enhancing soil carbon combinesbiological and environmentalchemistry. Similarly, oceanfertilization generates biomass carbonthat may interact with oceanchemistry.

7.1.1 Introduction to the Problem andSolutions

Most anthropogenic emissions of CO2

result from the combustion of fossilfuels. Advanced technologies are beingdeveloped to use fossil fuels forco-production of chemicals along withpower, including approaches todecarbonizing methane or coal toproduce hydrogen. Hybrid approachesmay be developed that are analternative energy source to createhydrogen, making it reasonable to usethe hydrogen and captured CO2 toproduce transportation fuels. Anumber of web sites containinformation on the developmentaltechnologies alluded to. Seewww.nire.go.ip/NIRE/ andwww.fe.gov.doe/coal_power/.

The advanced chemical technologiesenvisioned for the future would workwith the technologies now beingdeveloped to convert recovered CO

2

economically to benign, inert,long-lived materials that can becontained in the earth or water of ourplanet or that have commercial value.Most of the advanced chemicalapproaches identified in this chapterassume that separation and captureprocesses will make availablepressurized CO

2 with minimal (and

defined) impurity levels at ambienttemperature (i.e., pipeline CO2).Decarbonization technologies willproduce particulate carbon at the siteof the process, while advanced powergeneration technologies may produce

a separate stream of carbon monoxide(CO) for use as a feedstock at the plantsite. Enhanced chemical processesmay also play a role in indirect captureof CO

2 via terrestrial sinks or through

ocean fertilization.

7.1.2 Potential Chemical Approachesto Sequestration

One potential approach tosequestration is to transform CO2 intonon-commercial materials that areinert and long-lived, such asmagnesium carbonate (MgCO3).Because they have no commercialvalue, such materials would need to besequestered in a relatively inexpensiveway, such as refilling the mining pitsthat first provided the magnesium andassociated material. After beingincorporated in MgCO3, the wholeworld’s 1990 output of carbon could becontained in a space 10 km ´ 10 km ´150 m (see sidebar “The Volume ofCarbon Sequestration”).

The ocean also may provide aninexpensive site for sequestration ofcarbon. Carbon dioxide can beincorporated in an ice-like material,called CO

2 clathrate, that is long-lived

when located at a sufficient depthbelow the ocean surface. After beingincorporated in CO

2 clathrate, the

whole world’s 1990 output of carboncould be contained in a space with avolume of approximately 80 km3.

Carbon dioxide, CO, or carbon fromenergy production also could berecovered and transformed intocommercial products (e.g., plastics andrubber) that are inert and long-lived. In1996, the world’s total output of allsuch products required approximately206 ́ 106 tonnes of carbon or 3.5% ofthe anthropogenic carbon emittedduring that year (SRI 1997).Alternately, bulk commodities for use



Comparison Between the Road Map Goal andLarge Industrial Activities

A comparison of the amount of material in sequestered carbon and other largeearthmoving activities

• The stated goal of this report is to have the capacity to sequester gigatonnes ofcarbon by the middle of the next century.

• In 1996, U.S. mines shipped approximately 1 gigatonne of sand and gravel.• In 1996, U.S. mines shipped approximately 1 gigatonne of coal.• The Iron and Steel Bureau estimates that the productive capacity of the world

steel industry is 1 gigatonne per year.• According to the Chemical Economics Handbook, the world petrochemical

industry bases all of its products on seven precursors. Combined, in 1996 theseseven precursors embodied approximately 0.2 gigatonnes of carbon.

The Volume Required for Mineral Sequestration

The aerial photograph shows the Bingham Canyon copper mine on the left-hand side. The town of Copperton, Utah, is located to the right of the mine and tothe left of the identification number 242 along the top (1 in. = 1.08 miles).Kennecott Copper extracts some 250,000 tons of rock every day from this mine.Kennecott has been mining this deposit for 90 years. The pit is currently half amile deep and 2.5 miles wide. If it were a stadium, it could seat nine millionpeople. An average sized power plant, operating at 33% efficiency when firing12,500 Btu/lb coal, would require approximately 35,000 tons of silicate rock perday to capture the CO2 produced based on the carbonate reaction shown inTable 7.1. To sequester a full year’s carbon emissions—based on typical unitavailability and capacity factors—would require space equivalent to 35 days ofproduction from this mine.



in construction, for example, mayrepresent larger target markets (see thesidebar on potential of sequestrationsites and technologies).

In addition, as detailed knowledge isdeveloped, the demands of varioussequestration methods may drive thecreation of techniques to capture theessence of natural processes. Forexample, it has been suggested thatCO2 could be sequestered in coalseams. Some of the research needed toinvestigate that possibility also willbear upon the potential for absorbingCO2 into other materials that couldprovide temporary storage; suchmaterials might be used to recover CO2

from automobile exhaust or directlyfrom the atmosphere. As anotherexample, knowledge of biomimeticchemical techniques—which areessentially models or abstractions ofbiological processes—might allow us toduplicate these processes undercontrolled conditions and improvethem to enhance reaction rates or

reduce the creation of unwanted orhazardous by-products.

7.2 CHEMICAL PROCESSES FORSEQUESTRATION

Carbon chemistry is very flexible andhas helped to create an impressivearray of products. Many chemicalprocess options exist for capture andsequestration or reuse of carbon.However, some require as much energyor consume as much raw material asdid the original process that emittedthe carbon. Such options may havevalue in a particular niche market, butthey are unlikely to representsignificant options for long-termsequestration of large quantities ofcarbon. Whether a process represents adesirable option varies with theeconomic circumstances and withthe attitudes of society; thus it isimportant to identify a number ofapproaches that offer a flexible mix of

Table 7.1 Thermodynamics of chemical/physical transformations involving CO2

Chemical/physical transformation DH298°K (Kcal/mole)

Energy productionCoal combustion C + O2 ® CO2 –94.05a

Natural gas CH4 + 2O2 ® CO2 + 2H2O –191.76a

combustionSequestration

Bicarbonate CO2 + 1/2CaSiO3 + 1/2H2O ® 1/2Ca2+ + HCO3– + 1/2SiO2 –15.70a

Carbonate CO2 + 1/3Mg3Si2O5(OH)4 ® MgCO3 + 2/3SiO2 + 2/3H2O –3.45a

Oxalate CO2 + CO + CaSiO3 ® CaC2O4 + SiO2 –31.34a

Clathrate CO2 + 6H2O ® CO2•6H2O –5.68(at 121•K)b

Liquification CO2(g) ® CO2(l) –1.27(at 298•K, 63.5atm)c

Utilization

Methanol synthesis CO2 + 3H2 ® CH3OH + H2O –31.30a

(Hydrogen production) (3H2O ® 3H2 + 3/2O2) (+205.05)a

Cyclic organic CO2 + PhCH+CH2 + 1/2O2 ® PhCHO(C+O)OCH2 –55.3d

carbonate aR. C. Weast, M. J. Astle, and W. H. Beyer. CRC Handbook of Chemistry and Physics. CRC Press,Boca Roton, Fla., 1988–1989. bS. L. Miller and W. D. Smythe. “Carbon Dioxide Clathrate in the Martian Ice Cap,” Science, 170(1970): 531–532. cW. M. Braker and L. Allen. Matheson Gas Data Book, 6th Ed. Matheson, Lyndhurst, N.J., 1980,p. 26. dN. Cohen and S. W. Benson. Chem. Rev. 93 (1993):2419–38.



options. Options selected must meetthese criteria:

• A process must be environmentallybenign.

• It must be stable and sustainablefor long-duration storage ordisposal.

• It must be safe.• It must be cost-competitive with

alternative approaches tosequestration or avoidance.

• Sufficient knowledge of the process,such as thermodynamics andkinetics, must be developed to allowcomprehensive analysis.

• It must be prima facie reasonable,particularly in terms of the energybalance.

This chapter identifies two groups ofchemical processes: (1) those thatproduce materials for sequestrationand (2) those that yield useful productsof potential commercial value. Weexamined the knowledge required todetermine whether these conceptsrepresent viable options. We alsoevaluated the current state ofknowledge for each process. For eachconcept, significant R&D needsincluded (1) an understanding of thebasic chemistry and chemicalengineering requirements; (2) processdevelopment, optimization, scale-up,and environmental control; and(3) systems issues of environmentaland ecological impact and economicacceptability. In most cases, the basicchemical reactions have beenidentified, the basic thermochemicalproperties have been tabulated, andsome process concepts have beenestablished. However, substantial gapsremain.

7.2.1 Inert Benign Long-TermStorage Forms

One goal of this effort is to designchemistry-based processes that can

convert separated and captured CO2 toproducts appropriate for long-term,environmentally acceptable, andunmonitored storage. It is essentialthat these options be economicallycompetitive with other approaches tosequestration when performed on themassive scale required to make asignificant impact compared with CO2

production rates. This approach isbased on mimicry of natural chemicaltransformations of CO2, such asweathering of rocks to form calcium ormagnesium carbonates and thedissolution of CO2 in seawater to yieldbicarbonate ions. These twoexothermic reactions occurspontaneously in nature. Examples ofproducts for disposal includecarbonate (CaCO

3/MgCO

3), bicarbonate

(HCO3–), clathrate (CO2•nH2O), and

oxalate (CaC2O4/MgC2O4). Table 7.1presents data on key chemicalreactions—some at the heart of theconcepts discussed in this section andothers that serve as points of reference.Note that schemes to produce fuels,such as methanol, require hydrogengas. Combining the methanol synthesisreaction and the hydrogen productionreaction shows that the combinedprocess would require a large netenergy input.

Four possible approaches to theseprocess are discussed and theknowledge gaps are presented for each.

1. The conversion of natural silicateminerals by CO2 to producegeologically stable carbonateminerals and silica,

(Mg, Ca)xSi

yO

x+2y + x CO

2 ® x (Mg,

Ca)CO3 + y SiO2 ,

is thermodynamically favorable, asis demonstrated by the naturalweathering of silicates, albeit at ageologic pace. Current knowledge



of this reaction indicates that it isexothermic, that it can be carriedout in several steps, and thatsufficient raw materials areavailable to supply the silicatesneeded. The challenge is to designconditions of temperature, reactionmedium, and reactor configurationthat will allow this transformationto be carried out at sufficientlyrapid rates. An example currentlybeing studied is the use of ahydrous MgCl2 molten salt with aserpentine mineral feed in whichHCl/Cl– appears to play a catalyticrole. R&D will need to addressnovel concepts that allow the keytransformations to proceed in asingle step, at a faster rate and ataffordable cost. Topics requiringstudy include (1) the mechanismand kinetics for this gas-solidreaction, as well as catalysts and/or reaction media to promote it;(2) thermodynamics and kinetics ofthe gas-molten salt reactions andthe chloride chemistry; (3) designsfor solids-consuming, solids-producing reactors, control of thephysical form of the solid productsto optimize processing, andcorrosion control; and (4) theeconomic and environmentalimpacts of mining of the silicates,surface disposal of the carbonate/silica product, and the trace metalproducts that may offer collateraleconomic benefits.

2. A second chemical system isdissolution of CO

2 in the oceans (or

other natural waters) as solublebicarbonate,

CO2 + 2H2O ® H3O+ + HCO3

– ,

coupled with the need for a sourceof added alkali to avoid loweringthe pH of the body of water. Thispathway is important both for

sequestration in geologicformations and for ocean disposal.The CO2 might simply be put in theocean, where most of it wouldpersist as dissolved gas, carbonicacid, and the bicarbonate ion if theCO2 were injected far enough belowthe surface. The bicarbonate ionmight be created throughdevelopment of biomimeticpathways in man-made systemsand disposed of near the shore inshallow waters, assuming theneeded cations could be provided.The current level of understandingof the process of dissolution andreaction is inadequate to allowdevelopment of a process with thepotential to sequester CO2 at therate at which it is currentlyproduced in power plants. R&D onusing bicarbonate to sequester CO2

should address (1) ocean and freshwater and electrolyte chemistry, theinfluence of solid surfaces, and theprecipitation of carbonates;(2) design of reactors and injectorsto facilitate efficient mixing ofreactants; (3) the effects ofenhanced bicarbonate levels onaquatic life and ecology and on theformation of carbonate deposits byadvanced biological approaches;(4) rates of transportation from theatmosphere to the ocean; (5) rates ofstimulated growth of candidateorganisms to capture and hold CO2;and, (6) biomimetic pathways toform calcium carbonate, includingthe process to make the necessarycalcium available to the reaction.

3. The clathrate of CO2 and H2O (seeFig. 7.1), structurally analogous tothe better known methane hydrate,may offer potential as a form forlarge-scale storage in the coldoceans or in man-made systemsthat mimic the requisite conditions.Clathrates may be used in CO

2



separation from high-pressuresystems, and their properties maybe important to understanding bothapproaches to ocean disposal and

geologic disposal options. Formingclathrates as a separation step in anintegrated gasification combinedcycle power plant could beattractive. Preliminary estimates ofthe energy required indicate that3 to 4% of the total plant energywould be needed. This is animprovement over techniquesavailable today. Based on what isnow known, additional R&D will berequired to (1) improve thedefinition of the phase diagram,thermodynamics, and physicalproperties of the CO2–H2O system athigh pressure in the presence of theelectrolytes and impurities foundin the ocean, as well as improve thedefinition of the kinetics offormation and long-term stability ofthe clathrates; (2) identify practicalmethods for deep-ocean injectionand mixing; and (3) assess the localecological impacts of hydrateformation. Further explorationwould be necessary to determinewhether, in the longer term, CO2

disposal via clathrate formationcould be coupled with recovery ofmethane fuel from the methanehydrate deposits in the oceans.

4. In addition to these processconcepts, exploratory R&D iswarranted on defining additionallow-energy disposal states ofcarbon that would meet the guidingprinciples for this topic; examplesmight include formates andoxalates. Because CO2 is an acidicgas, it can be captured by using analkaline substance to form stablecompounds with it. A procedurethat uses one mole of alkali totransform two moles of CO2—suchas in the transformation of CO2 tolow-energy-state poly-carboncompounds such as calcium/magnesium oxalate (CaC2O4/MgC

2O

4)—is desirable because of

Fig. 7.1. Mixtures of gas clathrateshave been found near coasts around theworld. These gas hydrates may bemixtures of methane clathrates and CO2

clathrates. If so, their presence promptsfurther investigation of the possibilitythat CO2 clathrates could be sequesteredin the same places. The photos show theformation of a gas clathrate during anexperiment.



the greater CO2-to-alkaline ratio.Research needs include(1) development of methods forsynthesis of regenerable alkalinecompounds and for effective use ofalkaline; (2) use of molecularmodeling to identify newcompounds in which one mole ofan alkaline species would tie upseveral moles of CO2 (Zeissel 1998);(3) exploration of total energyrequirements—which include thosefor chemical reactions as well asthose for chemical processing—forboth exothermic reactions involvingCO2 and endothermic reactionsrequiring a small amount ofenthalpy input; (4) research intocatalysis reactions, processoptimization, surface disposalissues, and environmentalconcerns. Finally, engineeringstudies and system evaluations ofthe types described would beneeded.

7.2.2 Products from Carbon DioxideUtilization

The goal of CO2 utilization is to designchemical processes that can convertseparated and captured CO2 to usefuland durable products that havereasonable lifetimes (tens to hundredsof years). Carbon dioxide either inwhole or in part can participate inmany chemical reactions (Fig. 7.2).

Such utilization strategies, whenexamined from the perspectives of thecurrent petrochemical industry, willnot have the capacity to handle thebulk of emitted CO

2. However, the

products and durable goods that areproduced may have greater value andstorage lifetimes and lesserenvironmental impacts than existingmeans to produce these same products.Additional markets might be developedif R&D were directed toward creation ofproducts with large annual uses, such

Fig. 7.2. Paths to utilize CO2 in synthetic chemistry. Source: Aresta1998.



as construction materials or parts forautomobile bodies (see sidebar on useof carbon in ultralight vehicles).However, widespread use of carbon-based products would require largeshifts in infrastructure and would facestiff competition from the industriesmanufacturing the products theysought to displace.

Four end-uses that could be viewed assupporting the need for a particulartechnology are described in thefollowing paragraphs, and gaps inknowledge are identified. This list isnot comprehensive because of the greatvariety of organic synthesis routes thatexist, but it provides a sense of theopportunity and scope of this approachto carbon sequestration. (See alsoElsevier 1998 and ACS et al. 1996).

• Particulate carbon, perhaps frommethane decarbonization, could beconverted into new compositematerials and used in durableconstruction materials such asconcrete. The challenge is findingeconomically viable methods ofconverting solid carbon intodurable goods and new composites.An associated issue is the physicalcharacteristics of the suppliedcarbon, assuming that the carboncomes from fuel decarbonizationprocesses. Scientific andtechnological capabilities areneeded to define the chemicalpathways from hydrocarbons tosolid carbon, discover newcomposite chemistry, andunderstand how to incorporatecarbon into new building materials.

Use of Carbon in Ultralight Vehicles

The Rocky Mountain Institute has performed a number of analyses ondevelopment of ultralite vehicles. In December 1996, it published a report titled“Costing the Ultralite in Volume Production: Can Advanced-Composite Bodies-in-White be Affordable?” (Mascarin et al. 1996) that examines the use of a carbon-fiber-composite monocoque body-in-white in an ultralite vehicle or hypercar. Thebody of the car would be made of parts molded from advanced polymer compositesand assembled with adhesives. The composites could be formed from carbon fibersembedded in an epoxy or other resin. The carbon fibers could representapproximately 50% of the total weight.

The typical hypercar prepared from these materials would have a curb weightof 637 kg, of which approximately 190 kg is the weight of the monocoque body. Ifcarbon from the fuel cycle were used to create the products needed forconstruction of such a vehicle, each body shell might contain 100–150 kg of carbon(the report does not list the actual percentage of carbon in the monocoque body).The report discusses the cost of carbon fiber in terms of the size of the marketneeded to ensure a low cost for the needed material–a market of approximately0.6 to 0.9 million carbon-fiber cars per year.

Assume that all the needed carbon from such a car body could be derived fromeither fuel decarbonization or from products made from CO or CO2 captured aftersome or all of the chemical energy had been used for energy production. Then thismarket might require carbon sufficient to make approximately 750,000 cars/year,each car requiring 125 kilograms of carbon. This usage represents approximately100,000 tonnes of carbon per year. A total of 750,000 cars per year would representapproximately 10% of the current U.S. new car market.



Specific needs includeidentification of (1) thermochemicalprocesses, (2) new catalysts andreactors, and (3) alternative fuelsources. The lifetime of the productor material is a key variable to beconsidered in performing life cycleand system cost and performanceanalyses.

• Many studies have addressed theneed to identify ways to use CO2 asa carbon feedstock for production ofplastics or other similarcommodities. Needed scientific andtechnological capabilities include(1) definition of chemical reactionpathways, (2) catalyst development,and (3) process development andoptimization. A significantenvironmental driver is thesubstitution of CO2 for toxicsubstances such as phosgene,which is used as a feedstock toproduce isocyanates,polycarbonates, and other productsused in industrial processes.Research has uncovered thepathway for this substitution tooccur exothermically, implying thatmore benign processing may be aneconomic driver as well. Productlifetimes need to be assessed, butwe assume that they will be on theorder of decades to centuries.Another approach might be partialoxidation (via gasification) toproduce energy and some CO thatcould serve as a feedstock forchemical processes.

• Alternately, it might be possible touse the carbon either from the fuelor from products of the combustionprocess to create soil amendmentsto enhance sequestering carbon innatural systems. Similar technicalconcerns exist about, for example,how to optimize these products fortheir desired end use. However, the

requirements for achieving productpurity and for avoiding potentialenvironmental impacts differ.

• Finally, much attention has beenfocused on carbon-neutralprocesses in which fuels andchemicals are formed from CO

2

feedstocks via pathways that woulduse renewable energy sources.Scientific and technologicalcapabilities will be needed toidentify new catalysts,electrocatalysts, and efficientreactors. However, this approachrequires a source of cheaphydrogen to react with CO

2.

Schemes have been proposed tosplit water to provide a source ofhydrogen. Direct use of H

2 as a fuel,

as an alternative to reactinghydrogen with CO2, should beaddressed through a systemsevaluation of costs and benefits. Ingeneral, the question ofsequestration or avoidance needsto be addressed with respect tocarbon neutral processing.

7.3 ENABLING CHEMICALTECHNOLOGIES

Previous sections of this chapterdescribed the chemical aspects ofsequestering CO

2 for ocean storage of

bicarbonates and clathrates; landstorage as solid alkaline carbonates;cross-compounds in which a simplecation ties up a number of CO2

molecules; and storage in durablematerials such as plastics, composites,and chemicals. Significantdevelopments in enabling science andassociated technologies are needed tosupport these concepts (see Fig. 7.3).Some processes will be greatly aided byimproving computational capabilitiesrelated to molecular modeling fornovel synthesis routes to make carbon-



based products, or for development ofimproved solvents such as stericallyhindered amines to capture carbonfrom flue gases. Many of thesecapabilities are already underdevelopment to support creation of newenergy and environmentaltechnologies. A partial list of theenabling technologies neededincludes

• Develop catalysts needed toenhance geologic sequestration,use of the carbon in CO2, anddecarbonization (e.g., mimicphotosynthesis; use Ti02 andsunlight to split CO2)

Fig 7.3. A road map of needed research into advanced chemical approaches. The science andtechnology capabilities address needs of both advanced chemical processes and the other focusareas. These capabilities are topics that need attention in the near term, as are the componenttechnologies that support the carbonate rock option and biomimetic processing (the latter wouldenhance the chances for success of sequestration in oceans and geologic formations).

• Develop new solvents and sorbentsfor gas separations (O2 from air orCO2 from flue gas)

• Develop a thorough understandingof the chemistry key to CO2

adsorption and methane desorptionfrom coal seams

• Explore novel formulations forfertilizers to be applied to enhanceterrestrial or oceanic sequestrationconcepts

• Create membranes and thin filmsfor advanced separations (e.g., high-temperature ceramic membranes toenable air separation)

• Develop agglomerating agents,binding agents (e.g., coal andlithium zirconate), and coatings



• Improve high-temperaturematerials, particularly metal oxides(e.g., BaO and BaO3 cycles for high-temperature separation or NiO orCoO mixed with Yttria-stabilizedzirconia for chemical loopingcombustion)

• Explore novel reactor concepts andthe requisite sensors and controls

The development of improved catalystsand other new materials is particularlyimportant.

Catalysis. Developing effectivecatalysts capable of multiple electronreduction chemistry is the majorchallenge for creating an effectivetechnology for reducing CO2 to high-energy intermediates. Considerablesuccess has been achieved in thedesign, synthesis, and analyses ofdonor and acceptor assemblies capableof light-driven, one-electron chargeseparation processes. Current researchdemonstrates that remarkablyenhanced catalytic efficiencies areachieved in natural and artificialphotochemical systems by inducingredox chemistry on surfaces inconstrained, structured environments.

Novel structured catalytic assembliescapable of initiating single-step,multiple-electron, reductive chemistryare needed. Redox assemblies capableof cooperative charge accumulationmimic the biological process of CO

2

reduction in photosynthesis and wouldprovide a photoelectrochemical systemthat could use CO

2 as a chemical

feedstock for synthesis of carbon-basedchemicals.

New catalysts will be required toenhance the rates of formation ofalkaline carbonates and oxalatesAdditives that could enhance geologicsequestration of CO2 also are needed.

These materials would be injected withCO

2 early in the period of use to coat

the cap rock or features toward theboundary of the reservoir. Over time,say after 5 years, they would begin toreact with the injected CO2 to seal thereservoir and reduce the potential forleakage.

New materials. New materials areneeded to handle the extreme processconditions of molten salt chemistry.Chemical approaches (e.g., bariumoxide and barium peroxide) to airseparation or chemical loopingcombustion (nickel oxide or cobaltoxide mixed with yttria-stabilizedzirconia) should be studied becausethey can take advantage of the hightemperatures available at power plants.Binding and agglomeration processesmust be defined both for the fabricationof products from particulate carbonand for other uses, such as the captureof CO2 from vehicles. For example,materials like lithium zirconate mightbe good CO2 absorbers and thus enablethe capture of some CO2 from vehicleemissions, a hitherto overlookedapproach that merits long-rangehigh-risk research. As anotherexample, composite materials thatmight result from adding carbon toplastics, polymers, glasses, cementsand ceramics should be studied.

7.4 SUMMARY

This chapter explored three approachesto carbon sequestration usingadvanced chemical technologies:

1. Develop benign by-products fordisposal. This avenue may offer thepotential to sequester large(gigatonne) amounts ofanthropogenic carbon.



2. Produce commercial products. Thistopic probably represents a lesserpotential (millions of tonnes) butmay result in collateral benefitstied to pollution prevention.

3. Conduct enabling studies that mayimpact the ability of technologiesunder development in other focusareas to meet their potential.

Based on our review of advancedchemical concepts, and recognizingneeds identified in other focus areas,priority should be placed on obtainingthe chemical knowledge required to

• Absorb/adsorb CO2 in coal seams.• Create magnesium carbonate as

described in the carbonate reactionin Table 7.1. The product is inertand benign.

• Understand and exploit CO2

clathrates, ice-like materials thatprecipitate out of mixtures of waterand CO

2 under the proper

conditions.• Form and dispose of aqueous

solutions of carbonates, thebicarbonate ion being the mostprominent, in the ocean or otherappropriate bodies of water.

• Develop commercial products madefrom CO2, CO (from advanced power

system concepts), or carbon createdvia decarbonization.

Table 7.2 provides more informationabout these approaches.

The materials above the double line(that is, oxalates, etc.) have virtuallyunlimited carbon sequestrationpotential. The ones below the line areless likely to play a major role based onboth thermodynamic considerationsand the potential size of target markets.Given current consumption patterns,only a small percentage of fossil carbonfeedstocks is used for producingcarbon-based goods. The rest goestoward energy production. Reducedcarbon will be of interest in nichemarkets that are driven by the value ofthe products they generate. Thechemical industry could use newchemical processes for producingvaluable chemicals and materials, aswell as avoid potential environmentalpenalties for continued CO2 emissions.The economic benefits of newprocesses might provide increasedtechnological competitiveness forindustry and the ability to use CO2 as afeedstock for chemical production inaddition to current petroleum-basedfeedstocks. However, the overall effectof product development on carbon

Table 7.2 Approaches to sequestration using chemical processes and examples of their use

Chemical form of carbon Examples of implementation

Aqueous carbonate ions: CO3* *, HCO3

* Ocean disposal, deep saline aquifersSolid carbonates: CaCO3, MgCO3 Terrestrial, ocean floor, underground disposal

Clathrates: CO2•nH2O, n ~ 6 Ocean, ocean floor disposalCarbon adsorption of CO2 Coal bed methane extractionOther low-energy states of carbon, Novel disposal technologies such as oxalates

Solid carbon Underground disposal, feedstock for composite materials

Carbon-based fuels (e.g., methanol) CO2-based fuel cycles, alternative energyCarbon bound in durable commercial goods Long-lived construction materials (e.g., plastics)



sequestration is likely to be smallunless new products that are used inlarge quantities can be developed,such as building materials or materialsfor automobile bodies. Based on thescale of sequestration that may beneeded, our analysis favors researchinto those chemical options that offerthe greater sequestration potential.Thus we consider stable and benignend products for disposal a morepromising approach to the problem. Inaddition, enabling studies should bepursued that benefit both othersequestration methods and thedevelopment of chemical means tomimic natural processes undercontrolled conditions.

7.5 END NOTES

1. In hydrate-clathrate, the maximumratio of guest molecules (e.g., CO

2)

to water molecules is approximately1/7. (See E. Denude, Sloan, Jr.,1998. Clathrate Hydrates of NaturalGases, Marcel Dekker, New York, p.53.) The density of ice isapproximately 0.9 grams/cm3. Toestablish the needed order ofmagnitude, we assume that onegram-mole of ice (18 grams)occupies 20 cm3 and that at most1/7 gram-moles of CO2

(44/7 grams) occupies the same20 cm3. Thus 1/7 gram-mole ofcarbon occupies at least 20 cm3,probably more. Hence we estimatethe maximum effective density to be12/7 grams of carbon per 20 cm3,which is 0.085 grams carbon percm3. Thus after 109 tonnes ofcarbon was incorporated in CO2

clathrate, this clathrate wouldoccupy a volume of at least 1.2 ´1011 m3 or 12 km3.

2. The ratio of the mass of MgCO3 tothe mass of carbon, incorporated

therein, is 7. It follows that109 tonnes of carbon would bebound within 7 ́ 109 tonnes ofMgCO

3. The density of crystalline

magnesium carbonate is 3 grams/cm3. In practice, powdered materialwith a bulk density of somewhatless would be sequestered. Perhapsabout 10% more space would beneeded for powder than for crystal(e.g., 2.7 grams/cm3). If so, 7 ´109 tonnes of MgCO3 would occupy2.6 ́ 109 m3 which is the volume ofa box whose sides are 10 km by10 km and whose height is 26 m.

7.6 REFERENCES

SRI International 1997. The ChemicalEconomics Handbook, Menlo Park,Calif., 350.0000E.

EIA (Energy InformationAdministration) 1998. InternationalEnergy Outlook, 1998, DOE/EIA-0484,Washington, D.C., April.

EIA (Energy InformationAdministration) 1997. Emissions ofGreenhouse Gases in the United States1996, DOE/EIA-0573, U.S. Departmentof Energy, Washington, D.C., October.

Aresta, Michele, “Perspectives ofCarbon Dioxide Utilization in theSynthesis of Chemicals. CouplingChemistry with Biotechnology,” inT. Inui, M. Anpo, K Izui, S. Yanagida,T. Yamaguchi, eds. 1998. Advances inChemical Conversions for MitigatingCarbon Dioxide, Studies in SurfaceScience and Catalysis, Vol. 114,Elsevier Science B.V.

T. Inui, M. Anpo, K Izui, S. Yanagida,T. Yamaguchi, eds. 1998. Advances inChemical Conversions for MitigatingCarbon Dioxide: Proceedings of theFourth International Conference on



Carbon Dioxide Utilization, Kyoto,Japan, September 7–11, 1997,Vol. 114, Elsevier Science B.V.

ACS (American Chemical Society),American Institute of ChemicalEngineers, Chemical ManufacturersAssociation, Council for ChemicalResearch, and Synthetic OrganicChemical Manufacturers Association1996. Technology Vision 2020: The U.S.Chemical Industry, Washington, D.C.,available at http://www.chem.purdue.edu/ccr/v2020/ (accessed 12/21/98).

Mascarin, A. E., J. R. Dieffenbach,M. M. Brylawski, D. R. Cramer, andA. B. Lovins 1996. Costing the Ultralightin Volume Production: Can Advanced-

Composite Bodies-in-White beAffordable?” (December 1996 revision),available at http://www.rmi.org/hypercars/b_i_w/T95_35.html(accessed 12/21/98).

Zeissel, R. 1998. “Molecular Tailoringof Organometallic Polymers forEfficient Catalytic CO2 Reduction:Mode of Formation of Active Species,”in T. Inui, M. Anpo, K. Izui,S. Yanagida, T. Yamaguchi, eds.,Advances in Chemical Conversions forMitigating Carbon Dioxide: Proceedingsof the Fourth International Conferenceon Carbon Dioxide Utilization, Kyoto,Japan, September 7–11, 1997,Vol. 114, Elsevier Science B.V.

Technology Road Map for Carbon Capture and Sequestration 8-1


88888 DEVELOPING AN EMERGINGTECHNOLOGY ROAD MAP FORCARBON CAPTURE ANDSEQUESTRATION

8.1 INTRODUCTION

Road-mapping techniques are being used bynumerous industrial firms, industry collaborativegroups, and government agencies in theirplanning processes. The term “road mapping” hasbeen broadly applied to many kinds of activities,and there are many types of road maps.

The purpose of an emerging technology road mapis to provide—and encourage the use of—astructured scientific R&D planning process.Emerging technology road maps furnish aframework for managing and reviewing thecomplex, dynamic R&D process needed to achieveimportant strategic goals. These road maps showgraphically how specific R&D activities can createthe integrated technical capabilities needed toachieve strategic objectives. This chapter describesthe creation of an emerging technology road mapfor the capture and sequestration of CO2.

8.2 A CARBON CAPTURE ANDSEQUESTRATION SYSTEM

An emerging technology road map seeks toidentify the scientific and technologicaldevelopments needed to achieve a specifictechnology goal. The process of identifying theneeded science and technology must be focusedby developing a concept of the technologicalsystem that would enable achievement of that goal.This task is particularly difficult in the case ofcarbon capture and sequestration because there isno paradigm for such a system.

Emergingtechnology roadmaps furnish aframework formanaging andreviewing thecomplex, dynamicR&D processneeded to achieveimportant strategicgoals.


8-2 Technology Road Map for Carbon Capture and Sequestration


Today, carbon is emitted to theatmosphere from energy technologiesthat were not designed to capture, letalone sequester, these emissions.There are many ideas for, and evendemonstrations of, technology tocapture and sequester carbon fromfossil fuel combustion. However, wemust consider that the current energysystem could be modified significantlyto make an economical capture andsequestration system possible. Thusthe emerging technology road map forcarbon capture and sequestrationcannot be constructed apart fromconsideration of current and emergingenergy technologies. It will involve aniterative process to connect this roadmap with others being developed byDOE for various parts of the energytechnology system.

Figure 8.1 gives a top-level picture of acarbon capture and sequestrationsystem and its linkages to the energysystem. Within the current fossilenergy system, carbon is processed inseveral forms by different fossil fueltechnologies in many different parts ofthe energy system. To keep it frombeing emitted to the atmosphere, thiscarbon must be captured, processed insome way to separate or purify it, andchanged to a solid, liquid, or gaseousform that is convenient for transport. Itcan then be transported in anengineered system to a site forsequestration or for transformation intoa long-lived end product. Alternatively,the carbon could be emitted as CO2

and transmitted through theatmosphere if sequestration by bio-absorption can be assured in some partof the natural carbon cycle.

This report has concentratedprincipally on the new scientificunderstanding and technology (shownin white in Fig. 8.1) that are needed forspecific capture and sequestration

functions. Transportation technologies(shown in gray) have not beenaddressed. However, particularly inChaps. 2 and 7, reference is also madeto specific changes in components ofthe existing energy system (shown inblack) that would simplify and/or lowerthe cost of capture and sequestration.

The close relationship between fueltransformation—from naturalhydrocarbons to refined fuels fortransportation and/or dispersedenergy technology—is of particularimportance in this regard. Changes inthe carbon content of refined fuels canalter the flow of carbon through thecapture and sequestration system.Lowering the carbon contents oftransportation fuels can change thebalance between carbon transportedthrough the atmosphere and that whichmust be handled in potentially moreexpensive engineered systems. Theform of fossil-fueled electricity-generating technology also plays animportant role in determining the formand cost of capture and sequestrationtechnology. The cost and applicabilityof the individual capture andsequestration technologies showndepends fundamentally on theparticular fossil-fueled electricity-generation technology employed.These are two areas for particularemphasis in coordinating this roadmap with other DOE transportation andfossil energy technology road-mappingefforts.

The major capture and sequestrationtechnologies are listed in Fig. 8.1 andare discussed in detail in Chaps. 2–7.Each can be developed and improvedindividually. However, the economiccost and effectiveness of the overallcarbon capture and sequestrationsystem depend on the effectivecombination of many technologies.



Their relative importance must finallybe judged in the context of theintegrated technology system. Thesystem shown in Fig. 8.1 is adequatefor taking the first steps in developing acarbon capture and sequestrationemerging technology road map, but amore detailed system engineeringeffort will be required to add economicand engineering substance to thissketch before the requirements neededto plan an R&D program can begenerated.

8.3 BUILDING AN EMERGINGTECHNOLOGY ROAD MAP

After identifying the technology goalsand the integrated technology systemneeded to satisfy those goals, the nextstep in developing an emergingtechnology road map is to assess thealternative technological pathways that

might lead to achieving the integratedtechnology system. The approach is toconstruct these pathways within atechnological hierarchy. The highestlevel of the hierarchy is the integratedtechnology system—in this case, thecarbon capture and sequestrationsystem. The hierarchy ends with thescience and technology capabilitiesthat are needed to develop thetechnologies that make the systemeconomical and effective.

Analyzing the integrated technologysystem in terms of its componentfunctions and the performancerequired to meet the strategic goalconnects these extremes. First, weidentify the critical technologyplatforms that might provide high valuein the operation of the integratedtechnology system. The technologicalcomponents that make up thetechnology platforms can also

Fig. 8.1. The top-level diagram of a carbon capture and sequestration technologysystem showing the relationship to the fossil energy system.



frequently be identified within theintegrated technology system.However, the performance ordevelopment requirements of thesecomponents must be determined fromthe needs of the technology platforms,which are aimed at increasing theeconomic performance of the wholesystem.

As applied to emerging technologies,the hierarchy includes technology indifferent stages of development. In fact,not all of the science or technology inan emerging technology road map iswell defined. Some elements may wellbe represented by little more thanfunctional requirements and atechnical intelligence–gathering planto identify scientific or technologicalapproaches. Thus after assembling theframework of the road map by workingdownward through the hierarchy frompolicy goals to capabilities, one mustalso work upward from the capabilitylevel to identify possible pathways andto map a course of development.

8.4 BUILDING THE CARBONCAPTURE ANDSEQUESTRATION ROAD MAP

Chapters 2–7 are organized by relatedareas of scientific expertise. Thesechapters were prepared by experts ineach science and technology area thatwould be needed to develop a carboncapture and sequestration system suchas that shown in Fig. 8.1. The materialprovided by these expert groups is thefoundation for developing a carboncapture and sequestration road map.

To develop the outline of an emergingtechnology road map from thismaterial, the carbon capture andsequestration system outlined inFig. 8.1 was broken down into itsfunctional components. The result isshown graphically as the capture andsequestration technology system inFig. 8.2.

Then, using the Graphical ModelingSystem (GMS), an integration groupasked each of the working groups toidentify technology platforms that theybelieved would be critical for theefficient performance of these systemfunctions and that were particularlydependent on the group’s science andtechnology. Within these technologyplatforms, the groups were asked toidentify specific components, againwithin their science and technologyareas, that they believed could beimportant to the development of thesetechnology platforms. Finally, eachgroup was asked to identify the scienceand technology capabilities that wouldbe essential for the successfuldevelopment of the technology thatthey had identified. They also specifiedthe relationships between the scienceand technology at each level withinthis science and technology hierarchy.This exercise enabled each of theworking groups to better perceive the

Definitions of the TechnologyHierarchy

Technology platform: Acombination of components;intellectual property; and market,business, and technical know-howthat can be applied to a family ofprocess needs.

Component: A technology orspecific knowledge that performs, orallows the performance of, a unitfunction supporting one or moretechnology platforms.

S&T Capability: General science,engineering, and managementknowledge and skills that enabledevelopment of components andtechnology platforms.



relationship of its particular technicalarea to the overall carbon capture andsequestration system. Each of theworking groups also adapted thisgeneral approach to better illuminatethe technical discussion in its chapter.

The integration group assembled all ofthis expert input into a system-leveloutline of an emerging technologyroad map (Fig. 8.2). The outlineillustrates the complex inter-dependence of the science andtechnology described in the precedingsix chapters. To achieve the capabilityto capture and sequester a significantfraction of anthropogenic carbon by2025, development is required at eachlevel of this hierarchy supporting afully functional carbon capture andsequestration system. Even at thisstage in the development of a road map,

the need for a coordinated science andtechnology development program isevident from the many science andtechnology relationships shown inFig. 8.2.

The science and technologyunderlying the nodes at each level ofthe hierarchy in Fig. 8.2 is discussedin more depth in Chaps. 2–7. Each ofthese items is also shown in summaryfashion in Tables 8.1–8.3. Workingfrom the bottom to the top of Fig. 8.2, tosupport the carbon capture goal, thenext step is to assemble thecapabilities, develop criticalcomponents, create new technologyplatforms, and integrate them with oldtechnology to form a new carboncapture and sequestration system.From the capability to the systemslevel, technology becomes increasingly

Fig. 8.2. The structure of an emerging technology road map for carbon capture andsequestration. The boxes (nodes) contain the science and technology needs developed by expertworking groups in Chaps. 2–7. The lines represent the relationships and performance requirementsamong technologies.



integrated as it moves from theresearch laboratory to commercialapplication. In the past, these stages ofdevelopment were often sequential.Today, they are more often overlappingin time and involve extensiveinteraction through the developmentand commercialization process.Exploring the path from science tosystem application consists ofidentifying the expected technologyneeds and performance requirementsat each level of integration andmapping the relationships betweenthem.

8.5 BUILDING THE R&D CAPACITY

The road mapping presented in thischapter leads to a three-prongedapproach to R&D:

• Specific fundamental scientificbreakthroughs in chemistry,geology, and biology that arenecessary to achieve the visionpresented in Chap. 1 are describedbelow and in Chaps. 2–7.

• Large-scale field experimentswould help scientists understandthe efficacy, stability, and impact ofstored carbon, as well as itsconsequences on humans and the

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environment. These might beaccomplished by piggy-backing onprojects being conducted for otherpurposes in collaboration withindustry, other federal agencies,and/or international programs.

• A coordinated program would takeadvantage of advances in basicresearch and findings from fieldstudies. These data andconclusions should be

coordinated, communicated, andintegrated to better targetadditional scientific research andthe design of future fieldexperiments.

8.5.1 Advanced Sensors andMonitoring Systems

This three-pronged approach issupported by three system technology

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platforms and one system componenttechnology that cuts across all focusareas.

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ensure that data are available in realtime and the overall measurementsystems will operate under a variety ofconditions. The need for advancedsensors and monitoring systems isimportant for four reasons: (1) Thenature of separation, capture, storage,and removal of CO

2 from the

atmosphere needs to be quantified inorder to measure the efficacy of thetechnology. Without suchcharacterization, it will be difficult tounderstand the underlying processes.(2) The stability of the sequestrationmethods must be validated. We need toknow how long the carbon will stay.This will be particularly necessary foroceanic, terrestrial, and geologicalsequestration. New sensors will needto be developed to measure carbonspeciation in soils and CO2 chemicaland physical behavior in geologicalformations. (3) We must havemeasurement systems to evaluateimpacts due to carbon sequestration.These impacts will need to be sharedwith the public. This will requiredevelopment of sensors andmonitoring systems for measurementof possible impacts in ocean, geologic,and terrestrial reservoirs. (4) Carbonsequestration will need to bemonitored and verifiable if it is to playa role in international agreements.

8.5.2 Carbon Processing Platforms

The first technology platform is carbonprocessing. The focus of this platform isthe development of advanced chemicaltechnologies, which are in turnplatforms for capture and separationand the development of technologieswith collateral benefits. Theeffectiveness of capture and separationtechnologies in isolating relativelypure CO

2 for transport and

sequestration will also determine thepotential efficacy of geological andocean sequestration options. The

technology platforms that will berequired include:

• Chemical/physical absorption,such as the synthesis of novelabsorbents

• Chemical/physical adsorption• Advances in membrane

technologies, such as thedevelopment of polymericmembranes for increasingdissolution/diffusion rates

• Mineralization/biomineralization,such as developing better reactionpaths for formation of carbonatesand bicarbonates for geologic andocean dissolution andsequestration

• Low-temperature distillationsystems

• Novel concepts, such as bettermethods for producing CO2

clathrates and use of algalbioscrubbers on emissions streams

Capture and separation technologiescan also be developed based onengineering and/or chemistryadvances of existing technologiesalready being used in industries suchas oil and gas refineries. An importantside benefit can be the capture andseparation of hydrogen to be used as aclean fuel.

Advances in chemistry research canspecifically support oceans andgeological sequestration. Geologicalsequestration will require a betterunderstanding of corrosion, as well asof silicate/carbonate complexinteractions. Research will be neededin chemistry and materials sciences tosupport these geological options.Chemical research in biomimeticprocessing and the production ofclathrates can enhance theeffectiveness of engineered solutionsfor the sequestration of CO2 in theoceans. In particular, the ability to



sequester carbon as bicarbonates orcarbonates cost-, resource-, andenergy-efficiently will markedlyincrease the time for which carbon iseffectively sequestered.

Chemistry research also has the bestpotential for developing collateralbenefits. Carbon species can bemanufactured into commercialcommodities, thus giving sequestrationan additional economic driver forcommercialization. Two problems existwith this approach. First, removingcarbon prior to combustion mayincrease its economic potential butwill reduce its energy content. Second,the current market cannot properlyuse the potentially large amounts ofcarbon-containing materials producedas part of these processes. New marketsand uses will need to be created. Someof these may be in the development ofdurable materials that could be usedfor construction materials or soilamendments. Other enablingtechnologies that would be developedas part of this research would includenew catalysts, chemical sensors, andmanufacturing process chemicals.

It is important to note that, while thereis a huge amount of information on theinorganic and organic chemistry ofcarbon dioxide, sequestration needswill require new breakthroughs.

8.5.3 Biological Absorption Platforms

Biological absorption is the secondsystem technology platform. Scientificresearch in this area will be necessaryto enhance the ability of terrestrial andsoil sinks to sequester CO

2, which will

be based on advanced biologicalresearch. Plant sciences must developnew rapid-growing species and new,commercially viable woody species.Genetic engineering and molecularbiology advances must be used to

create new plant species and enhancemicrobial rhizospheres to increaseplant productivity. Research must bedone to increase understanding of soilbiogeochemistry to enhance carbonuptake and sequestration in soils. As isthe case with ocean sequestration,ecosystem dynamics must be betterunderstood to evaluate potentialimpacts of new farming methods,introduction of new species, control ofpests, and increased carbon content insoils. Finally, a potential way ofenhancing ocean sequestration may becoupled with advanced biologicalresearch. Bioengineered solutions forincreasing the primary productivity ofoceans will allow for improvedbiological mechanisms of increasedCO

2 uptake. Additionally, the

development of algal scrubbers for CO2

separation and capture may enhancetechnologies in this area.

8.5.4 Engineered Injection Platforms

The third key system technologyplatform is engineered systems. Theemphasis for sequestration in oceansand geological sinks is similar:although progress has been made inthe geological arena, improvedinjection systems must be developed toenhance the delivery of CO2 to thesesinks. In addition, many researchadvances in chemistry will requireinnovative engineered systems toeffectively implement newtechnologies.

All of these findings are interrelated.For example, ocean and geologicalsequestration will not be effectiveunless efficient capture, separation,storage, and transportationtechnologies are developed to deliverCO

2 to sink locations. Capture and

separation technologies in turn mustrely on advances in chemistry andconcomitant engineered solutions to



make these technologies efficient andcost-effective.

It is clear from Tables 8.1–8.3 that thetechnology platforms are not allequally developed. One of theseplatforms, short-term storage, has notbeen examined at all because thecarbon capture and sequestrationsystem has not yet been sufficientlyspecified. It is included simplybecause the current natural gastransmission system, although smallby comparison to an eventual CO

2

transmission system in terms of gasvolume, requires large short-termstorage capacity to operate.

Other platforms, such as integratedcarbon generation and recovery, arebridges to other road-mapping efforts.For instance, the road map supportingVision 21 (a proposed description of thefuture evolution of fossil fueltechnology) is consideringmodifications to fossil power systemsthat could significantly simplify thecapture of CO2. Some platforms, such asCO

2 transportation or engineered

injection, are brief because of anassumption that a great deal ofexperience has already beenaccumulated in these areas. Thisassumption will require furtherexamination after a more detailedsystem engineering picture of a carboncapture and sequestration system isdeveloped.

The most elaborated platforms arecarbon processing and biologicalabsorption. This is natural for thecarbon processing platform because ofthe wealth of known chemicalengineering techniques that might beadapted to this problem. This platformwill become more focused as theconditions under which carbon mustbe captured and processed becomemore clear from system analysis and

other energy and fossil fueltransformation road maps.

On the other hand, one might expectthe elements within the biologicalabsorption platform to expand evenfurther as the wealth of possibilitiespresented by progress in the biologicalsciences is further explored. Thisrichness is also reflected in thetechnology components supportingthis platform.

The inclusion of the biologicalabsorption platform is a genuinedeparture from traditional lines ofenergy technology development. Itbrings with it ties to agricultural andecological research that have beentenuous at best in the history of energydevelopment. Once carbon capture andsequestration become a feature ofenergy planning, scientific andtechnological progress in these fieldsassumes a key role in future energydevelopment.

Recognizing linkages betweendisparate fields of knowledge such asthese is a key feature of the road-mapping process. Developing andexploiting these linkages requiresfurther effort.

8.6 NEXT STEPS

This chapter has described the firststage in developing an emergingtechnology road map for carboncapture and sequestration. Startingfrom a potential DOE policy goal, thetechnology system to achieve that goalhas been sketched out. The areas ofscientific and technologicaldevelopment needed to support thisgeneral technology system have beenidentified, including new areas foreignto traditional energy technologydevelopment.



Although mutual relationships anddependencies of scientific andtechnological development in all ofthese fields have been identified andare indicated by the links in Fig. 8.2,the corresponding performancerequirements have not yet beendeveloped. Nor has the phasing ofpotential R&D schedules beenconsidered. Overlaps have beeneliminated to some extent, butpriorities and gaps in the technologyneeds have not been examined. Morework needs to be done on specifyingthe economic constraints andtechnology needs of the integratedcarbon capture and sequestrationsystem illustrated in Fig. 8.1. Thiswork can be done in parallel with thesteps outlined in the followingparagraphs, but it must be done toprovide substance to the final roadmap.

The road map outline described is avaluable product. It should be used asa framework for Phase II of the CarbonSequestration Road Map in developinga quantitative evaluation of the scienceand technology requirements for acarbon sequestration system. This isan essential aspect of building ausable road map with all of therequisite characteristics.

Road maps should integrate planningand implementation. The road mapshould consider all the plans of theorganization, such as mission andvisioning, market analysis, andportfolio analysis. But it goes beyondmere vision to develop a general planfor developing capabilities. Actionableitems should naturally flow from theroad map. The primary purpose of theemerging technology road map is toinfluence future events, not to predictthem. Program objectives set for thefuture should, of course, be based on

realistic expectations about market,policy, and technical trends. However,no one can predict the future. Thevalue of emerging technology roadmaps derives from the fact that thefuture can be shaped by newtechnological developments. Roadmaps are intended for revision. A roadmap is not a plan for the future that isunchangeable when it is completed. Asevents unfold and new researchresults emerge, the plan must bechanged to address the most currentstate of knowledge—and to buildbeyond the new frontier. The road mapshould provide a mechanism foraccommodating serendipity—externalevents and new research results thatshould be incorporated into thetechnology development plans. Theprocess of reaching a consensus is asimportant as the product. To be trulyeffective, the road map should be avision of the future reached byconsensus among all parties who haveresponsibility for the R&D—thefunders, developers/deliverers, andimplementers/users of technology.

Thus, the process of road mapping is asimportant as the final product of theprocess—the road map itself. Frequentcommunication with uppermanagement along the way,involvement of all layers and functionsof the DOE organization, andstakeholder participation are keys tosuccess. Based on the results obtainedso far, the stakeholders include othergovernment agencies and theagricultural industry in addition to theenergy industry. Many different viewsand priorities must be considered andsynthesized into a coherent plan tocarry out R&D on carbon capture andsequestration. This will develop thesupport needed as DOE attempts toimplement the emerging technologyroad map.

Findings and Recommendations 9-1


99999 FINDINGS ANDRECOMMENDATIONS

The options for sequestering carbon are diverse.Some are being implemented already, and otherswill require advances in scientific andengineering disciplines. Many options will requirelong lead times prior to implementation. In thischapter we identify issues central to thedevelopment of an R&D program that would enableus to make viable carbon sequestration optionsavailable for the 2025 to 2050 time frame.

The existing R&D program should be expandedsoon. If carbon sequestration is to have asignificant impact, it will necessarily involvechanges of a large magnitude. Decisions madetoday about the energy infrastructure are likely tobe with us for the greater part of a century. Newinformation will help us develop an infrastructurewith the flexibility to operate in tandem withcarbon sequestration options. Therefore, researchshould anticipate substantially any necessarycarbon reduction efforts.

For carbon capture and sequestration to become aviable large-scale option, it must be cost-competitive, safe, and acceptable. The R&Dprogram should be oriented toward understandingmore fully the fate of sequestered CO2 and theimpacts it will have on the environment and onhuman safety, and toward developing options toensure a flexible response.

Given the federal government’s role in supportinghigh-risk R&D in the long-term national interest, acarbon sequestration research and technologydevelopment program should be significantlyexpanded on the strength of the eventuality thatsuch technology will be needed in the energymarketplace some time in the first quarter of thenext century. This message is consistent with arecent report of the President’s Council of Advisorson Science and Technology and other

“To protect theclimate cost-effectively,technologybreakthroughs,technologyincentives, and theelimination ofbarriers for thedeployment ofexistingtechnologies areneeded. Broad-based cooperativeprograms tostimulate marketsand develop anddisseminate newand existingtechnology toindustrialized anddevelopingcountries must be ahigh priority” (WorldResources Institute,British Petroleum,General Motors,Monsanto 1998).


9-2 Findings and Recommendations


investigations. We should begin thisR&D now, because the optionsavailable in 2025 and beyond will bedetermined by research beingconducted today.

The first section of this chapterdiscusses overarching issues thatbecame apparent during thedevelopment of this preliminary roadmap. They are key aspects of carbonsequestration that must beacknowledged and addressed in theplanning and implementation of anexpanded R&D program. The secondsection presents our recommendationsresulting from an analysis of the focusareas discussed in the previouschapters and from discussions duringthe workshops.

The implementation of carbon captureand sequestration science andtechnology must be based on publicacceptance. Even though somestrategies seem inherently beneficial(e.g., planting more forests andprotecting wetlands), it may be achallenge to gain public acceptance ofsome sequestration options because oftheir large scale, the fact that they arenew and may be viewed as addingcosts without adding value, anduncertainties about theirenvironmental consequences.Although some current sequestrationactivities are presumably safe andbenign, such as the Sleipner WestProject in the North Sea, other optionshave largely unknown consequences.

Some sequestration options withpotentially large environmentalimpacts may evoke strong concernsfrom the public. Whether asequestration option is successful willdepend not only on predictedconsequences but also on publicacceptance, based uponunderstanding of benefits and costs.

9.1 FINDINGS

• Carbon sequestration is a broadtopic with many internal linkages;combining processes often canprovide ancillary benefits

The ancillary benefits of many carbonsequestration options are appealing.Thus one of the ways to improve theprospects for carbon sequestration is tocombine different processes andbenefits so that the larger system ismore attractive than individual parts.One example is the increasedproduction of oil that would result fromthe use of CO2 for enhanced oilrecovery or the enhanced production ofmethane from injecting CO

2 into coal

beds—sequestering CO2 whileextracting fossil resources. Anotherexample discussed in Chap. 6 onadvanced biological processes is theenergyplex, referred to by DOE as the“Vision 21 Plant,” which is a series ofmodular plants (an industrialecosystem) that integrate theproduction of power, heat, chemicals,and fuels to maximize the use ofavailable energy while capturing andsequestering carbon emissions.Another example of combiningprocesses would be using capturedcarbon to make construction materialsor soil enhancements that wouldotherwise be unavailable.

As Fig. 8.1 in Chap. 8 illustrates,carbon sequestration involves manytechnological paths and connectionsor feedbacks. The need to connectprocesses is evident. Costs andcapacities of alternative sequestrationoptions must be based upon consistentassumptions. For instance, thecharacteristics of a particular CO

2

stream—its location, temperature,pressure, concentration, orimpurities—may make it more suitablefor sequestration in one type of sink,



such as a geological formation, than inanother, such as an ocean.

The number of disciplines involved incarbon sequestration R&D is large.Much can be gained by coordinatingresearch programs with relatedscientific and engineering activities;for example, scientists studying theoceanic carbon cycle and deep seainjection may need to collaborate withthe offshore energy companiesdeveloping deep-sea technology.

We found that many research topicsinvolve critical links in several of thefocus areas. The development ofmonitoring systems is important acrossall the focus areas, and advancedbiological and advanced chemicaltopics have potential impacts in severalfocus areas. In addition, forsequestration options that cannot relyon taking CO2 directly from theatmosphere, efficient CO2 capture,separation, and transportation methodsare critical. If the cost of capture is veryhigh or the delivery system cannotaccommodate the large amount ofcarbon that must be sequestered, nodegree of cost reduction or efficiencyimprovement for any sequestrationoption would be sufficient for it tocompete with other carbon reductionefforts.

• Many carbon sequestrationoptions can work within theexisting infrastructure; otherscenarios would require a newdistribution system

A primary benefit of manysequestration options is that they usethe existing infrastructure; indeed,sequestration may allow for continueduse of fossil fuels and may be basedupon current infrastructure.Sequestration also is consistent with

the development of new advancedfossil-fuel-fired generation plants.Sequestration is likely to start with theeasiest opportunities, which mayrequire few infrastructure changes,such as the Sleipner West project inthe North Sea or improved agriculturaland forestry practices.

Other scenarios might requiresignificant infrastructure changes. Forinstance, shifting to hydrogen-poweredtransportation to reduce carbonemissions would require a newhydrogen distribution system. Theissues in developing a newdistribution system, perhaps by makingit cost-competitive before it reaches acritical size, are outside the purview ofthis report, but they are significant.

• Carbon sequestration is anappropriate topic for government-sponsored R&D, which will becritical to successfulimplementation

The prior findings suggest carbonsequestration is not a trivial challenge.The integration required to obtainindustrial participation, addressenvironmental issues, and gain publicacceptance suggests that an expandedgovernment initiative is needed. Inaddition, unlike for clean energy andenergy efficiency, no economic orregulatory incentives exist at this timefor carbon sequestration, suggestingthe need for more governmental thanprivate responsibility for support ofresearch and technology developmentprograms. This conclusion was alsoreached by the DOE-sponsoredStakeholders’ Workshop on CarbonSequestration held in June 1998(Herzog 1998), at which industry sent astrong message that “the researchagenda for the moment must be led,and funded, by government.”



Most possibilities for carbonsequestration involve immaturetechnologies and ideas. The carbonsequestration options include topicsthat are inadequately investigatedcompared with many other energyresearch areas, making theopportunities for significantbreakthroughs high. Government-sponsored R&D could result insurprising advances that might changethe rules of the game. Although littleprivate sector R&D is under way at thistime, there is evidence (witness recentannouncements by British Petroleumand others) that the private sector willattempt to implement carbonmitigation approaches that are knownto be technically and economicallyfeasible. Domestic and internationalforest projects also are beingconducted by the electric utilityindustry. These may offer uniqueopportunities for an R&D program toidentify complementary links toindustrial practices that could lead toearly demonstration opportunities.

• Some carbon sequestration optionscould be used as near-termmeasures until other carbonmanagement technologies,including other carbonsequestration technologies,can be implemented

There is much we cannot predict withconfidence about the reaction of thenatural system to increases in atmos-pheric CO2 concentrations. There maybe “nonlinear” responses derived frompositive feedbacks. An altered climatecould bring an increased release ofgreenhouse gases through, forinstance, more rapid mineralization ofsoil organic material, altered oceancurrents, or offgassing of CO

2 and/or

methane from permafrost regions.

If scientists were to predict with somedegree of reliability that there would bea nonlinear response in the nearfuture, it might result in the need toemphasize development and imple-mentation of near-term sequestrationalternatives even though the lifetime ofthe sequestered carbon might be lesspermanent than is desirable. In thiscase, one sequestration option mighttarget R&D to provide techniques andtechnologies to stall the nonlinearresponse until some other morepermanent solution could beimplemented.

9.2 RECOMMENDATIONS

9.2.1 Beginning the R&D Program

The following recommendationsshould apply to the carbonsequestration research program.

• Ensure that the carbonsequestration research programdevelops technologies andpractices that are cost-effectiveand benign. For carbonsequestration to be a viable option,it must compete favorably withother carbon managementprograms with respect to cost andeffectiveness. Carbon sequestrationshould be safe, predictable, reliable,measurable, and verifiable.Research programs should lead tothese ends. To be cost-effective, theresearch program will need toreduce costs associated with thecurrent separation andsequestration technologies andprocesses and support thedevelopment of new, innovativetechnologies and processes.

• Ensure that the research isintegrated with other, related



research programs. The researchprogram will be linked to related,ongoing research programs so as toleverage the efforts. For instance,results from biomass or carboncycle research could help indeveloping the biologicalunderstanding needed forterrestrial sequestration.

The research program should beconducted collaboratively amongthe offices in DOE and with othergovernment agencies. Ties to othercountries through researchprograms or through scientificbodies, such as IEA’s GreenhouseGas R&D Programme, should bemade. The research program shouldalso collaborate with the researchand other activities undertaken bythe private sector.

• Ensure that the research programis flexible and targets a widevariety of approaches. Carbonsequestration is an immature field,so multiple approaches and scalesare warranted. There are manyprospects for significant advances.An expanded R&D program shouldbe broad-based, including bothbasic and applied, theoretical,laboratory, and field-basedresearch, and all sources andsinks. A robust R&D program isneeded that has the flexibility toevolve over time as new scientificadvances are incorporated into theoverall energy system. For example,deregulation of utility companiesmay lead to market penetration byhighly distributed power systemswhose individual emissions wouldbe difficult to capture, aggregate,and sequester. Changes in theavailability of oil and in the use ofnuclear power because ofgeopolitical reasons could alter the

energy mix and the accompanyingCO

2 emissions. Future demand for

materials made from CO2, such asacetate or bioplastics, may increasedramatically. Changes in otherrelated technologies, such asbatteries and fuel cells, willinfluence the effectiveness ofvarious technology pathways. Ourunderstanding of the safety andpotential environmentalconsequences of varioussequestration options will evolve.An approach is needed that has along-term goal but has theflexibility to respond to changes inpublic policy and energy systems,as well as to the successes andfailures of its own researchactivities.

• Initiate field-scale investigationsto help guide other carbonsequestration research andincrease understanding ofprocesses at the field scale. Animportant facet of any carbonsequestration R&D program will beto include some early field-scaleinvestigations. Some sequestrationoptions may be sufficiently readyfor pilot- or field-scale research,such as sequestering CO2 in soilsand vegetation, geologicalformations, or in deep coal bedsfrom which methane is extracted.Selection of these investigationsshould be based on existinginformation and the opportunitiesfor early results that could providerapid assessment and feedback tofundamental R&D needs. Large-scale long-term field studiesshould test research concepts andreduce economic, environmental,and operational uncertaintiesassociated with the newtechnologies.



• Ensure that the research programdevelops an integrated approachto setting R&D priorities andevaluating the probability ofsuccess for different sequestrationoptions. One potential researchtopic is the development of anintegrated framework for carbonsequestration. A context for theoverall research program would beuseful because so many of theissues cross disciplines and relatedactivities. The integrative modelingwould include investigations intolife-cycle analysis, risk,uncertainty, and, to the extentpossible, economics. One goalwould be to generate a clear modelof the carbon flows, including theform that the carbon takes (gaseous,compressed liquid, elemental,carbonate, clathrate, etc.). A secondgoal would be to keep track of theupstream “costs” associated withthe carbon in the form in which it isfound. It is important to measurethe energy penalties associatedwith providing carbon in aparticular form at any particularplace in the system. This researchwould precede actual economicanalysis of many of the morecomplicated sequestration options.

• Ensure that the results of the R&Dprogram are provided topolicymakers to aid them indeveloping policy and selectingthe most efficient and effectivesolutions to the issues of climatechange. This report is not intendedto modify the policy process thatdetermines what, if anything,should be done about climatechange. But those policy processesshould be informed about theavailability, costs, and ancillarybenefits of various sequestrationoptions. Research and reporting onmonitoring, verification,

effectiveness, and environmentalconsequences of carbonsequestration technologies andpractices are an essential elementin an iterative process, the goal ofwhich is to help policymakersdesign more efficient and effectivesolutions to carbon management.

9.2.2 Developing the Road Map

The following recommendationsshould apply to the continuation of thisroad map.

• Criteria for setting researchpriorities should include themagnitude of the impact of thecarbon sequestration option.Further development andrefinement of this road map couldinclude setting priorities for theresearch. Many priorities anddiscussions of staging—that is,which research topics should beconducted first and which shouldcome later—are included in thefocus area chapters 2–7. Chapter 8offers further general criteria thatcould be used in setting priorities.Although sequestration will likelybe achieved through the use of anumber of technologies, only thoseresearch topics should be targetedthat have the potential forsignificantly reducing CO2

emissions with acceptableenvironmental impacts and costs(in either real dollars or energylosses). Longer-term researchshould focus on the benefits ofsequestration mechanisms that willbe effective on scales from multipledecades to millennia. Thoseapproaches with shortersequestration time horizons willprovide important relief in the shortterm, but they must be augmentedwith more substantial solutions inthe longer term.



• This roadmap should be developedfurther and refined. This report isonly a first step and should beenhanced by engaging a broadercommunity in discussions of thevarious sequestration pathwaysoutlined in the roadmap. Theunderstanding of carbonsequestration is still in its earlystages, and R&D pathways are stillbeing formulated. Technologypathways are outlined in this roadmap, but more explicit pathwayscan be generated for some of thefocus areas. Some explicitrecommendations are made in thefocus area chapters, but phasing ofpotential R&D schedules has notbeen done. The next step shouldinclude more intense participationby stakeholders, such as the privatesector and non-governmentalorganizations.

9.3 PRINCIPAL FOCUS AREARECOMMENDATIONS

9.3.1 Separation and Capture of CO 2

There are numerous options for theseparation and capture of CO2, andmany of these are commerciallyavailable. However, none has beenapplied at the scale required as part ofa CO

2 emissions mitigation strategy,

nor has any method beendemonstrated for all the anthropogenicsources considered in this R&D map.Many issues remain regarding theability to separate and capture CO2

from anthropogenic sources on thescale required, and to meet the cost,safety, and environmentalrequirements for separation andcapture. In our assessment of thescientific and technological gapsbetween the requirements for CO

2

separation and capture and thecapabilities to meet these

requirements, many explicit andspecific R&D needs were identified.

• Geologic or ocean storagesequestration options that use aconcentrated source of CO2 requirelow-cost carbon separation andcapture techniques to be viableoptions. The scale of the industrialsystem required to processgigatonnes of carbon warrantsinvestigation into new solvents,adsorbents, and membraneseparation devices for either pre- orpost-combustion separation.

• A science-based and applications-oriented R&D program is needed toestablish the efficacy of current andnovel CO

2 separation processes as

important contributors to carbonemissions mitigation. Importantelements of such a program includethe evaluation, improvement, anddevelopment of chemical andphysical absorption solvents,chemical and physical adsorbents,membrane separation devices withselectivity and specificity for CO

2-

containing streams, molecular andkinetic modeling of the materialsand processes, and laboratory-scaletesting of the selected processes.

• Field tests are needed of promisingnew CO2 separation and captureoptions in small bypass streams atlarge point sources of CO

2, such as

natural gas wells and hydrogenproduction plants.

9.3.2 Ocean Sequestration

• The ocean provides a largepotential reservoir. Activeexperiments are already under wayin iron fertilization and other testsof enhanced marine biologicalsequestration, as well as deep CO2

injection. Improvements in



understanding marine systems willbe needed before implementation ofmajor marine sequestrationcampaigns.

• Field experiments of CO2 injectioninto the ocean are needed to studythe physical/chemical behavior ofthe released CO2 and its potentialfor ecological impact.

• Ocean general circulation modelsneed to be improved and used todetermine the best locations anddepths for CO2 injection and todetermine the long-term fate of CO2

injected into the ocean.

• The effect of fertilization of surfacewaters on the increase of carbonsequestered in the deep oceanneeds to be determined, and thepotential ecological consequenceson the structure and function ofmarine ecosystems and on naturalbiogeochemical cycling in theocean need to be monitored.

• New innovative concepts forsequestering CO2 in the ocean needto be identified and developed.

9.3.3 Carbon Sequestration inTerrestrial Ecosystems

• The terrestrial biosphere is a largeand accessible reservoir forsequestering CO

2 that is already

present in the atmosphere. Naturalcarbon fluxes are huge, so that evensmall forced changes resulting fromR&D advances would be verysignificant. It will be important toaddress the consequences ofaltering the natural flux.

• The terrestrial ecosystem is a majorbiological scrubber for atmosphericCO2 (present net carbon

sequestration is ~2 GtC/year) thatcan be significantly increased bycareful manipulation over the next25 years to provide a critical“bridging technology” while othercarbon management options aredeveloped. An increase in carbonsequestration to perhaps as muchas 5 to 10 GtC/year may beachieved as a result of directedR&D. Ecosystem protection isimportant and may reduce orprevent loss of carbon currentlystored in the terrestrial biosphere.The focus for research, however,should be on increasing the rate oflong-term storage in soils inmanaged systems.

• Research on three key interrelatedR&D topics is needed to meet goalsfor carbon sequestration interrestrial ecosystems:

— Increase understanding ofecosystem structure andfunction directed towardnutrient cycling, plant andmicrobial biotechnology,molecular genetics, andfunctional genomics.

— Improve measurement of grosscarbon fluxes and dynamiccarbon inventories throughimprovements to existingmethods and throughdevelopment of newinstrumentation for in situ,nondestructive belowgroundobservation and remote sensingfor aboveground biomassmeasurement, verification, andmonitoring of carbon stocks.

— Implement scientific principlesinto tools such as irrigationmethods, efficient nutrientdelivery systems, increasedenergy efficiency in agriculture



and forestry, and increasedbyproduct use.

• Field-scale experiments in large-scale ecosystems will be necessaryto understanding bothphysiological and geochemicalprocesses regulating carbonsequestration based uponintegrative ecosystem models. Suchcarbon sequestration experimentsare needed to provide proof-of-principle testing of newsequestration concepts andintegration of sequestrationscience and engineeringprinciples.

9.3.4 Sequestration in GeologicalFormations

Although there is extensive industrialexperience in geologic sequestration ofCO2, many important issues must beaddressed to reduce costs, ensuresafety, and gain public acceptance.Implementation of therecommendations outlined willprovide the information andoperational experience needed toaddress these issues.

• Limited geological sequestration isbeing practiced today, but it is notyet possible to predict withconfidence storage volumes andintegrity over long time periods.Many important issues must beaddressed to reduce costs, ensuresafety, and gain public acceptance.

• Fundamental and applied researchis needed to improve the ability topredict, optimize, and monitor theperformance of sequestration in oil,gas, aqueous, and coal formations.Elements of such a programinclude multiphase flow inheterogeneous and deformablemedia; phase behavior; CO

2

dissolution and reaction kinetics,micromechanics and deformationmodeling; coupled hydrologic-chemical-mechanical-thermalmodeling; and high-resolutiongeophysical imaging. Advancedconcepts should be included, suchas enhancement of mineraltrapping with catalysts or otherchemical additives, sequestrationin composite geologic formations,microbial conversion of CO2 tomethane, rejuvenation of depletedoil reservoirs, and CO

2-enhanced

methane hydrate production.

• A nationwide assessment is neededto determine the location andcapacity of the geologic formationsavailable for sequestration of CO

2

from each of the major power-generating regions of the UnitedStates. Screening criteria forchoosing suitable options andassessing capacity must bedeveloped in partnership withindustry, the scientific community,and public and regulatory oversightagencies.

• Pilot-scale field tests of CO2

sequestration should be initiated todevelop cost and performance dataand to help prioritize future R&Dneeds. The tests must be designedand conducted with sufficientmonitoring, modeling, andperformance assessment to enablequantitative evaluation of theprocesses responsible for geologicsequestration. Pilot testing will laythe groundwork for collaborationwith industrial partners on full-scale demonstration projects.

9.3.5 Advanced Biological Processes

The 21st Century has been referred toas the “Century for Biology.” Indeed,many new molecular tools have been



developed that will aid in newdiscoveries and assist in providingsolutions to key problems facinghumankind and the planet. Thedifference that advanced biologicaltechniques can make will be evidentwhen they are integrated with land,subsurface, and ocean managementpractices. The followingrecommendations will promote cost-effective and stable biological solutionsto carbon sequestration.

• Advanced biological techniquesmay produce improvements tooradical to predict. Biologicprocesses can yield sequesteredcarbon products at the least cost.New carbon sequestration optionscould become feasible and otherscould be improved using advancedbiological techniques.

• Research should be initiated on thegenetic and protein engineering ofplants, animals, andmicroorganisms to addressimproved metabolic functions thatcan enhance, improve, or optimizecarbon management via carboncapture technology, sequestrationin reduced carbon compounds, usein alternative durable materials,and improved productivity.

• The objectives and goals of theadvanced biological researchshould be linked to those specificproblems and issues outlined forcarbon sequestration in geologicalformations, oceans, and soils andvegetation so that an integratedresearch approach can elucidatecarbon sequestration at themolecular, organism, andecosystem levels.

• Short-, mid-, and long-term goalsin advanced biological researchshould be insituted so that a

mimetic yardstick can be employedto assess scale-up issues, geneticstability in natural settings, andefficacy in the field.

9.3.6 Advanced Chemical Approaches

• Most carbon sequestration optionsrely on chemical reactions toachieve benign, stable, and inertproducts. Studies to enhance therelevant chemistry almost certainlywill reduce the costs or increasethe effectiveness of these options.Results from R&D on advancedchemical topics also may make itpossible to generate useful andmarketable byproducts.

• The proper focus of R&D intoadvanced chemical sciences andtechnologies is on transforminggaseous CO

2 or its constituent

carbon into materials that eitherare benign, inert, long-lived andcontained in the earth or water ofour planet, or have commercialvalue.

— Benign by-products forsequestration should bedeveloped. This avenuemay offer the potential tosequester large (gigatonne)amounts of anthropogeniccarbon.

— Commercial products need to bedeveloped. This topic probablyrepresents a lesser potential(millions of tonnes) but mayresult in collateral benefitstied to pollution prevention.

• The chemical sciences can fillcrucial gaps identified in the otherfocus areas. In particular,environmental chemistry is anessential link in determining theimpact and consequences of these



various approaches. Studies toaddress the specific gaps identifiedin Chap. 7 should be conducted toensure that other focus areas meettheir potential.

9.4 REFERENCES

Herzog, H. J., ed. 1998. Proceedings ofthe Stakeholders’ Workshop on Carbon

Sequestration, MIT EL 98-002,Massachusetts Institute of TechnologyEnergy Laboratory, June.

WRI (World Resources Institute) BritishPetroleum, General Motors, andMonsanto 1998. Climate ProtectionInitiative: Building A Safe Climate, SoundBusiness Future, Washington, D.C.

Contributors A-1


Appendix A

CARBON SEQUESTRATION WORKING PAPERCONTRIBUTORS AND WORKSHOP ATTENDEES

A-2 Contributors


Contributors A-3


Appendix A

CARBON SEQUESTRATION WORKING PAPERCONTRIBUTORS AND WORKSHOP ATTENDEES

Note: Bold text indicates attendees at October 28–29, 1998, workshop

Focus Areas Co-Leads

Sally BensonLawrence Berkeley National Laboratory1 Cyclotron RoadMail Stop 90-1110Berkeley, CA 94720Phone: 510/486-5878 or 510/486-7071Fax: 510/486-7714E-mail: [email protected]

John F. ClarkeBattelle Washington OperationsPacific Northwest National Laboratory9001 D Street, SW, Suite 900Washington, DC 20024-2115Phone: 202/646-5280Fax: 202/646-7824E-mail: [email protected]

James EkmannDeputy Associate DirectorOffice of Systems and Env’l. AnalysisFederal Energy Technology CenterP.O. Box 10940, MS 922-178CPittsburgh, Pennsylvania 15236Phone: 412/892-5716Fax: 412/892-4561E-mail: [email protected]

R. G. (Gil) Gilliland, Associate DirectorEnergy and Engineering SciencesOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6248Phone: 423/574-9920Fax: 423/576-6118E-mail: [email protected] or [email protected]

George R. HendreyDivision of Environmental Biology and InstrumentationBrookhaven National LaboratoryBldg. 318Upton, NY 11973Phone: 516/344-3262Fax: 516/344-2060E-mail [email protected]

Howard J. HerzogEnergy Lab, Massachusetts Institute ofTechnology77 Massachusetts Ave., E40-471Cambridge, MA 02139-4307Phone: 617/253-0688Fax: 617/253-8013E-mail: [email protected]

A-4 Contributors


John C. HoughtonEnvironmental Sciences DivisionDepartment of Energy, SC-7419901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-8288Fax: 301/903-8519E-mail: [email protected]

Jennie C. Hunter-CeveraLawrence Berkeley National Laboratory1 Cyclotron RoadMail Stop 70A-3317Berkeley, CA 94720Phone: 510/486-7359Fax: 510/486-7152E-mail: [email protected]

Gary K. JacobsEnvironmental Sciences DivisionOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6036Phone: 423/576-0567Fax: 423/574-7287E-mail: [email protected]

Roddie R. Judkins, ManagerFossil Energy ProgramOak Ridge National Laboratory1 Bethel Valley RoadOak Ridge, TN 37831-6084Phone: 423/574-4572Fax: 423/574-5812E-mail: [email protected] or [email protected]

Robert L. KaneOffice of Planning/Environment AnalysisDepartment of Energy, FE-261000 Independence Ave., S.W.Washington, DC 20585Phone: 202/586-4753Fax: 202/586-1188E-mail: [email protected]

Anna PalmisanoEnvironmental Sciences DivisionDepartment of Energy, SC-7419901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-9963Fax: 301/903-8519E-mail: [email protected]

David E. Reichle, Associate DirectorLife Sciences and Environmental TechnologiesOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6253Phone: 423/574-4333Fax: 423/574-9869E-mail: [email protected] or [email protected]

Robert H. SocolowEnergy and Environmental StudiesH104 Engr QuadPrinceton UniversityPrinceton, NJ 08544Phone: 609/258-5446Fax: 609/258-3661Email: [email protected]

John StringerExecutive Technical FellowEPRI3412 Hillview AvenuePalo Alto, CA 94304-1395Phone: 650/855-2472Fax: 650/855-2002E-mail: [email protected]

Alan M. WolskyEnergy Systems DivisionArgonne National Laboratory9700 South Cass Ave, ES/362Argonne, IL 60439-4815Phone: 630/252-3783Fax: 630/252-1677E-mail: [email protected]

Contributors A-5


Nicholas B. WoodwardEngineering and Geosciences DivisionDepartment of Energy, SC-1519901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-4061Fax: 301/903-0271E-mail: [email protected]

Michael T. YorkDepartment of Energy, FE-33Department of Energy, Headquarters1000 Independence Ave,. SWWashington, DC 20585Phone: 202/586-5669Fax: 202/586-4341E-mail: [email protected]

Separation and Capture

Roddie R. Judkins, ManagerFossil Energy ProgramOak Ridge National Laboratory1 Bethel Valley RoadOak Ridge, TN 37831-6084Phone: 423/574-4572Fax: 423/574-5812E-mail: [email protected] or [email protected]

John StringerExecutive Technical FellowEPRI3412 Hillview AvenuePalo Alto, CA 94304-1395Phone: 650/855-2472Fax: 650/855-2002E-mail: [email protected]

Joseph M. AbrardoGlobal Product ManagerAir Products & Chemicals5884 Krause RoadSchnecksvile, PA 18078Phone: 610/481-8902Fax: 610/481-7166E-mail: [email protected]

Allen G. Croff, Associate Division DirectorChemical Technology DivisionOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6178Phone: 423/574-7192Fax: 423/576-7468E-mail: [email protected]

Richard D. DoctorArgonne National LaboratoryRichard D. Doctor9700 South Cass Ave.Argonne, IL 60439Phone: 630/252-5913Fax: 630/252-5210E-mail: [email protected]

Thomas P. DorchakFederal Energy Technology CenterP.O. Box 10940, Mailstop C04Pittsburgh, Pennsylvania 15236Phone: 304/285-4305 or 304/285-4664E-mail: [email protected]

Douglas E. FainBechtel Jacobs Company LLCP.O. Box 4699, MS 7271Oak Ridge, TN 37831-7271Phone: 423/574-9932Fax: 423/576-2930E-mail: [email protected]

Robert GlassLawrence Livermore National Laboratory7000 East Ave., P.O. Box 808, Mail Code L-352Livermore, CA 94550Phone: 925/423-7140Fax: 925/422-0049E-mail: [email protected]

A-6 Contributors


Amitabh GuptaPraxair, Inc.175 East Park DriveP.O. Box 44Tonawanda, NY 14150Phone: 716/879-2194Fax: 716/879-7567E-mail: [email protected]

Soil/Vegetation

Rich Birdsey and John HomU.S. Forest ServicePhone: 610/975-4092Fax: 610/975-4095 or 4213E-mail: rbirdsey/[email protected] jhom/[email protected]

Marilyn A. BufordQuantitative Ecology ResearchNational Program LeaderVegetation Management and Protection Research StaffUSDA Forest ServiceP.O. Box 96090201 14th Street SWWashington, DC 10090-6090Phone: 202/205-1343Fax: 202/205-2497E-mail: mbuford/[email protected]

Roger C. DahlmanU.S. Department of EnergyEnvironmental Sciences Division, SC-7419901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-4951Fax: 301/903-5555E-mail: [email protected]

Mary K. Firestone333 HilgardUniversity of California, BerkeleyBerkeley, CA 94720-3110Phone: 510/642-3677Fax: 510/643-5098E-mail: mkfstone@nature. berkeley.edu

Charles N. FlaggBldg. 318Brookhaven National LaboratoryUpton, NY 11973Phone: 516/344-3128Fax: 516/344-3246 (fax)E-mail: [email protected]

Ron FollettColorado State University301 South Howes, #424Fort Collins, CO 80523Phone: 970/490-8220Fax: 970/490-8213E-mail: [email protected]

Inez Fung301 McCone HallUniversity of California, BerkeleyBerkeley, CA 94720-4767Phone: 510/643-9367Fax: 510/643-5098E-mail: [email protected]

George R. HendreyDivision of Environmental Biology and InstrumentationBrookhaven National LaboratoryBldg. 318Upton, NY 11973Phone: 516/344-3262Phone: 516/344-2060Fax: 516/344-2060E-mail: [email protected]

Gary K. JacobsEnvironmental Sciences DivisionOak Ridge National LaboratoryP.O. Box 2008, 1 Bethel Valley RoadOak Ridge, Tennessee 37831-6036Phone: 423/576-0567Fax: 423/576-7287E-mail: [email protected]

Contributors A-7


Julie D. JastrowEnvironmental Research DivisionBuilding 2039700 South Cass AvenueArgonne National LaboratoryArgonne, IL 60439Phone: 630/252-3226Fax: 630/252-8895E-mail: [email protected]

Dale W. JohnsonDesert Research Institute7010 Dandini Blvd.Reno, NV 89512Phone: 702/673-7379Fax: 702/673-7485E-mail: [email protected]

Dr. Rattan LalOhio State University422B Kottman Hall2021 Coffey RoadColumbus, OH 43210Phone: 614/292-9069Fax: 614/292-7432E-mail: [email protected]

Dr. Patrick MegonigalDepartment of Biology, MS-3E1George Mason UniversityFairfax, VA 22030-4444Phone: 703/993-1045Fax: 703/993-1046E-mail: [email protected]

Blaine MettingPacific Northwest National Laboratory902 Battelle Blvd.P.O. Box 999 P7-54Richland, WA 99352Phone: 509/372-0317Fax: 509/376-9650E-mail: [email protected]

Walter C. OechleGlobal Change Research GroupDepartment of Biology, PS-240San Diego State University5500 Campanile DriveSan Diego, CA 92182Phone: 619/594-6613Fax: 619/594-7831E-mail: [email protected]

Keith PaustianColorado State UniversityB248 Natural & Environmental SciencesFort Collins, CO 80523Phone: 970/491-1547Fax: 970/491-1965E-mail: [email protected]

Mac PostOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6335Phone: 423/576-3431Fax: 423/574-2232E-mail: [email protected]

Kenneth E. Skog, Project LeaderTimber Demand and Technology Assessment ResearchUSDA Forest Products LaboratoryOne Gifford Pinchot Dr.Madison, WI 53705Phone: 608/231-9360Fax: 608/231-9508E-mail: [email protected]

Ronald M. ThomBattelle Marine Sciences Laboratory1529 West Sequim Bay RoadSequim, WA 98382Phone: 360/681-3657Fax: 360/681-3681E-mail: [email protected]

A-8 Contributors


Margaret S. TornCenter for Isotope GeochemistryLawrence Berkeley National Laboratory1 Cyclotron Road, Bldg. 90, MS-1116Berkeley, CA 94720Phone: 510/528-6046Fax: 510/486-5686E-mail: [email protected]

Creighton D. WirickDepartment of Applied Science1 Technology StreetBrookhaven National LaboratoryUpton, NY 11973Phone: 516/344-3063Fax: 516/344-3246E-mail: [email protected]

Lynn L. WrightEcological Sciences SectionEnvironmental Sciences DivisionOak Ridge National LaboratoryP.O. Box 2008, Bethel Valley RoadOak Ridge, TN 37831-6422Phone: 423/ 574-7378Fax: 423/ 576-8143E-mail: [email protected]

Oceans

Anna PalmisanoEnvironmental Sciences DivisionDepartment of Energy, SC-7419901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-9963Fax: 301/903-8519E-mail: Anna.Palmisano@oer. doe.gov

Howard J. HerzogEnergy Lab, Massachusetts Institute of Technology77 Massachusetts Ave., E40-471Cambridge, MA 02139-4307Phone: 617/253-0688Fax: 617/253-8013E-mail: [email protected]

Peter BrewerSenior ScientistMonterey Bay Aquarium Research Institute (MBARI)P.O. Box 628Moss Landing, CA 95039-0628Phone: 408/775-1706Fax: 408/775-1645E-mail: [email protected]

Sallie W. Chisholm, ProfessorDept. of Civil & Env’l. Engr., & Biol.48-425 Massachusetts Institute of TechnologyCambridge, MA. 02139Phone: 617/253-1771Fax: 617/258-7009E-mail: [email protected]

Taro TakahashiLamont-Doherty Earth ObservatoryColumbia UniversityPalisades, NY 10964Phone: 914/365-8537E-mail: [email protected]

Jim BishopEarth SciencesLawrence Berkeley National Lab1 Cyclotron Road Mailstop 90-1106Berkeley, CA 94720Phone: 510/495-2457E-mail: [email protected]

Ken CaldeiraLawrence Livermore National Laboratory7000 East Ave., P.O. Box 808, Mail Code L-103Livermore, CA 94550Phone: 925/423-4191Fax: 925/423-6388E-mail: [email protected]

Contributors A-9


Geological Formations

Nicholas B. WoodwardEngineering and Geosciences DivisionDepartment of Energy, SC-1519901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-4061Fax:E-mail: [email protected]

Sally BensonLawrence Berkeley National Laboratory1 Cyclotron RoadMail Stop 90-1110Berkeley, CA 94720Phone: 510/486-5878 or 510/486-7071Fax: 510/486-7714E-mail: [email protected]

Robert E. SmithEnvironmental Protection Agency Headquarters401 M Street, S.W.Washington, DC 20460Phone: 202-260-5559E-mail: [email protected]

Robert BurrusU.S. Geological SurveyNational Center, Room 4C30212201 Sunrise Valley Drive, MS 956Reston, VA 20192Phone: 703/648-6144Fax: 703/648-6419E-mail to: [email protected]

Wolfgang R. WawersikSandia National Laboratories, New MexicoP.O. Box 5800Albuquerque, NM 87185-0751Phone: 505/845-8627Fax: 505/844-9449E-mail: [email protected]

Akhil Datta-GuptaDepartment of Petroleum EngineeringTexas A&M UniversityCollege Station, TX 77843-3116Phone:Fax:E-mail: datta-gupta@spindletop. tamu.edu

Kevin KnaussLawrence Livermore National Laboratory7000 East Ave., P.O. Box 808, Mail Code L-202Livermore, CA 94550Phone: 925/422-1372Fax: 925/422-0208E-mail: [email protected]

Fred StalkupAtlantic Richfield CorporationE-mail: [email protected]

Charles ByrerU.S. Department of EnergyFederal Energy Technology CenterP.O. Box 880Morgantown, WV 26507-0880Phone: 304/285-4547E-mail: [email protected]

Laura Pyrak-NolteDepartment of PhysicsPurdue University1396 Physics BuildingWest Lafayetta, IN 47907-1396E-mail: [email protected]

Paul WitherspoonEarth SciencesLawrence Berkeley National Laboratory1 Cyclotron Road, Mailstop 90-1116Phone: 510/486-5082 or 510/642-5390Fax: 510/527-1336E-mail: [email protected]

A-10 Contributors


Karsten PruessEarth SciencesLawrence Berkeley National Laboratory1 Cyclotron Road, Mailstop 90-1116Berkeley, CA 94720Phone: 510/486-6732 or 510/486-6696Fax: 510/486-5686E-mail: [email protected]

Michael YorkDepartment of Energy, FE-331000 Independence Ave., S.W.Washington, DC 20585Phone: 202/586-5669Fax: 202/586-4341E-mail: [email protected]

Advanced Biological

Jennie C. Hunter-CeveraLawrence Berkeley National Laboratory1 Cyclotron RoadMail Stop 70A-3317Berkeley, CA 94720Phone: 510/486-7359Fax: 510/486-7152E-mail: [email protected]

David E. Reichle, Associate DirectorLife Sciences and Environmental TechnologiesOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6253Phone: 423/574-4333Fax: 423/574-9869E-mail: [email protected] or [email protected]

Thomas W. Jeffries, DirectorInstitute for Microbial and BiochemicalTechnologyForest Products LaboratoryOne Gifford Pinchot DriveMadison, WI 53706Phone: 608/231-9453Fax: 608/231-9262E-mail: [email protected]

Al LucierNational Council for Air and Stream ImprovementP.O. Box 13318Research Triangle Park, NC 27709-3318Phone: 919/558-1993Fax: 919/558-1998E-mail: [email protected]

Norm G. LewisInstitute of Biological ChemistryWashington State UniversityP.O. Box 646340Pullman, WA 99163-6340Phone: 509/335-2682Fax: 509/335-7643E-mail: [email protected]

Rolf MelhornLawrence Berkeley National Laboratory1 Cyclotron RoadMail Stop: 70-108BBerkeley, CA 94720Phone: 510/486-5068Fax: 510/486-7303E-mail: [email protected]

Rick OrnsteinBattellePacific Northwest National LaboratoryP.O. Box 999Richland, WA 99352Phone: 509/375-2132Fax: 509/375-6904E-mail: [email protected]

Tony PalumboOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-8646Phone: 423/574-8002Fax: 423/576-8646E-mail: [email protected]

Contributors A-11


Sharon Shoemaker250 Cruess HallUniversity of California, DavisOne Shields Ave.Davis, CA 95616Phone: 530/752-2922Fax: 530/752-6578E-mail: [email protected]

Steven R. ThomasNational Renewable Energy Laboratory1617 Cole Blvd.Golden, CO 80401Phone; 303/275-3858Fax: 303/275-3799E-mail: [email protected]

Bob UffenSciCentral.com1125 North Utah StreetArlington, VA 22201E-mail: [email protected] [email protected]

Rodney DeGrootForest Products LaboratoryOne Gifford Pinchot Dr.Madison, Wisconsin 53705-2398Phone:Fax: 608/231 9592E-mail: DeGroot_Rodney_C/[email protected]

John ZerbeForest Products LaboratoryOne Gifford Pinchot Dr.Madison, Wisconsin 53705-2398Phone: 608/ 231-9353Fax: 608/231-9508E-mail: Zerbe_John_I/[email protected]

Robert J. FellowsPacific Northwest National LabP.O. Box 999 / MS K2-21Richland, WA 99352Phone: 509/375-2247Fax: 509/375-6666E-mail: [email protected]

Rodney CroteauWashington State UniversityClark 291P.O. Box 646340Pullman, WA 99164-6340Phone: 509-335-1790E-mail: [email protected]

Advanced Chemical

James EkmannDeputy Associate DirectorOffice of Systems and Environmental AnalysisFederal Energy Technology CenterP.O. Box 10940, MS 922-178CPittsburgh, Pennsylvania 15236Phone: 412/892-5716Fax: 412/892-6290E-mail: [email protected]

Alan M. WolskyEnergy Systems DivisionArgonne National Laboratory9700 South Cass Ave, ES/362Argonne, IL 60439-4815Phone: 630/252-3783

Shih-Ger ChangEnvironmental Energy TechLawrence Berkeley National Laboratory1 Cyclotron Road, Mailstop 70-108BBerkeley, CA 94720Phone: 510/486-5125Fax: 510/486-5401E-mail: [email protected]

Klaus LacknerALDSSR, MS B260Low Alamos National LaboratoryLos Alamos, NM 87545Phone: 505/667-5694Fax: 505/665-4361E-mail: [email protected]

A-12 Contributors


Kim MagriniNational Renewable Energy Laboratory1617 Cole Blvd., Mail Stop 1613Golden, CO 80401Phone: 303/275-3706Fax: 303/275-2905E-mail: [email protected]

Marvin Poutsma, DirectorChemical and Analytical Sciences DivisionOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6129Phone: 423/574-5028Fax: 423/574-4902E-mail: [email protected]

Cross-Cut/Integration

John C. HoughtonEnvironmental Sciences DivisionDepartment of Energy, SC-7419901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-8288Fax: 301/903-8519E-mail: [email protected]

Robert L. KaneOffice of Planning/Environment AnalysisDepartment of Energy, FE-26Department of Energy, Headquarters1000 Independence Ave., S.W.Washington, DC 20585Phone: 202/586-4753Fax: 202/586-1188E-mail: [email protected]

John F. ClarkeBattelle Washington Operations9001 D Street, SW, Suite 900Washington, DC 20024-2115Phone: 202/646-5280Fax: 202/646-7824E-mail: [email protected]

Robert H. SocolowEnergy and Environmental StudiesH104 Engr QuadPrinceton UniversityPrinceton, NJ 08544Phone: 609-258-5446Fax: 609-258-3661Email: [email protected]

Joan OgdenH113 Engrg QuadEnergy and Environmental StudiesPrinceton UniversityPrinceton, NJ 08544Phone: 609/258-5470Fax: 609/258-3661E-mail: [email protected]

Terry SurlesLawrence Livermore National Laboratory7000 East Ave., P.O. Box 808, MailCode L-640Livermore, CA 94550Phone: 925/423-1415Fax: 925/423-2395E-mail: [email protected]

Marylynn PlacetBattelle Washington OperationsPacific Northwest National Laboratory901 D Street, Suite 900Washington, DC 20024-2115Phone: 202/646-5249Fax: 202/646-7825E-mail: [email protected]

R. G. (Gil) Gilliland, Associate DirectorEnergy and Engineering SciencesOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6248Phone: 423/574-9920Fax: 423/576-6118E-mail: [email protected] [email protected]

Contributors A-13


David E. Reichle, Associate DirectorLife Sciences and Environmental TechnologiesOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6253Phone: 423/574-4333Fax: 423/574-9869E-mail: [email protected] [email protected]

DOE Headquarters

Martha Krebs, DirectorOffice of ScienceDepartment of Energy, SC-11000 Independence Ave., S.W.Washington, DC 20585Phone: 202/586-5430Fax: 202/586-4120E-mail: [email protected]

Robert KripowiczAssistant Secretary for Fossil EnergyDepartment of Energy, FE-11000 Independence Ave., SWWashington, DC 20585Phone: 202/586-4695Fax:E-mail: [email protected]

Michael L. KnotekOffice of the Secretary of EnergyDepartment of Energy, S1000 Independence Ave., SWWashington, DC 20585Phone: 202/586-3500Fax: 202/586-7210E-mail: [email protected]

Ari Patrinos, Associate DirectorOffice of Biological and Environmental ResearchDepartment of Energy, SC-7019901 Germantown RoadGermantown, MD 20874-1290Phone: 310/903-3251Fax: 301/903-5051E-mail: [email protected]

Michelle Broido, DirectorEnvironmental Sciences DivisionDepartment of Energy, SC-7419901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-3281Fax: 301/903-8519E-mail: [email protected]

Dr. Ehsan U. KhanOffice of Planning and AnalysisOffice of Energy ResearchDepartment of Energy, SC-51000 Independence Ave., SWWashington, DC 20585Phone: 202/586-4785Fax: 202/586-7719E-mail: [email protected]

Jeffrey S. SummersOffice of Fossil EnergyDepartment of Energy, FE-2319901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-4412Fax:E-Mail: [email protected]

Lawrence D. (Douglas) CarterOffice of Fossil EnergyDepartment of Energy, FE-261000 Independence Ave., SWWashington, DC 20585Phone: 202/586-9683Fax: 202/586-9684E-Mail: [email protected]

Frank M. Ferrell Jr.Office of Fossil EnergyDepartment of Energy, FE-2319901 Germantown RoadGermantown, MD 20874-1290Phone: 301/903-3768Fax:E-mail: [email protected]

A-14 Contributors


Support

Brenda W. CampbellLife Sciences and EnvironmentalTechnologiesOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6253Phone: 423/574-4333Fax: 423/574-9869E-mail: [email protected]

Carolyn H. KrausePublic AffairsOak Ridge National LaboratoryP.O. Box 2008Oak Ridge, TN 37831-6144Phone: 423/574-7183Fax: 423/574-1001E-mail: [email protected]

Rich ScheerEnergetics, Inc.501 School St SW # 500Washington, DC 20024-2754Phone: 202/479-2748, ext. 105Fax: 202/479-0229E-mail: [email protected]

Mindi FarberEnergetics, Inc.501 School St SW # 500Washington, DC 20024-2754Phone: 202/479-2748, ext. 107Fax: 202/479-0229E-mail: [email protected]

Publication Team

Computing, Information, and Networking DivisionOak Ridge National Laboratory

Deborah M. CouncePhone: 423/576-8785Fax: 423/574-1001E-mail: [email protected]

Sandi LyttlePhone: 423/574-6963E-mail: [email protected]

Vicki BeetsPhone: 423/574-6695E-mail: [email protected]

Judy Campbell, ORNL Publishing Services

Rosemary Adams, ORNL Graphic Services

Erica Atkin, CDI Engineering Group

Judy Benton, ORNL Publishing Services

Jane Parrot, ORNL Graphic Services

Jamie Payne, ORNL Graphic Services

Angela Wampler, ORNL Publishing Services

Carbon Sequestration: Detailed Description of Ecosystems and Specific Issues B-1


Appendix B

DETAILED DESCRIPTIONS OF ECOSYSTEMS ANDRESEARCH AND DEVELOPMENT NEEDS

B-2 Carbon Sequestration: Detailed Description of Ecosystems and Specific Issues




Appendix B

DETAILED DESCRIPTIONS OF ECOSYSTEMS ANDRESEARCH AND DEVELOPMENT NEEDS

1. Forests (Rich Birdsey, Mac Post, Marilyn Buford, Ken Skog)

Long-term baseline estimates show that increases in biomass and organic matteron U.S. forest lands from 1952–1992 added 281 MMTC/year of carbon to forestecosystems (25% of U.S. emissions for the period). Projections suggest continuingincreases averaging 177 MMTC through 2040. For the period 1990–92approximately 250 MMTC/year were sequestered in standing trees (~50%), andforest floor/coarse woody debris/ soils (~50%). The gain in forests is net of woodremoved for products, and net of mortality from all causes including fire, pests,and disease. Carbon in wood used for products in 1990 was added to the pool ofcarbon in products in use, and products in landfills—for an additional netincrease of carbon in products of about 60 MMTC/year.

Research on basic processes, measurement and monitoring, implementationmethods and risk assessment in the forestry sector can provide cost-effective,environmentally sound methods in which to sequester more carbon. But,evaluation of the most effective forestry sector methods requires life cycleanalyses that compare tradeoffs among alternate ways to use land area (forest andnonforest) for products for sequestration, and among alternate products (forest-and nonforest-based) to satisfy end use-needs. With that caveat, it is clear thatresearch in a number of areas can improve forest sector contributions tosequestration. Areas where research is needed to improve cost effectiveness andenvironmental effects knowledge include: afforestation of marginal cropland;reducing deforestation; reforestation and improved forest management forsequestration; substituting wood products for more energy intensive products;reducing energy use in timber growing, harvesting, product production, and inend use; reducing wildfires; use of biomass fuel in place of fossil fuel withregrowth of biomass; increasing the amount of carbon in durable wood productsand uses; increasing paper and wood recycling; planting trees in urban andsuburban areas; enhancing soil carbon through species selection andmanagement practices, including understory and ground cover management.

Current capabilitiesResearch is conducted in a broad range of forest sector disciplines that contributeto an understanding of, and means to alter, carbon accumulation in forests andforest products. These include soil science, tree physiology, tree genetics,ecological systems, forest pathology, forest entomology, forest mycology, firescience, forest mensuration, silviculture, forest management, forest economics,forest operations, wood products technology, and pulp and paper science.

Future needsResearch needs to be focused on (1) understanding basic biological, industrial,and socioeconomic processes that can increase sequestration in the forestry



sector, (2) measurement, monitoring, and modeling of ecosystem function and theforestry economic sector to evaluate the effectiveness of means to altersequestration, (3) evaluation of alternative combinations of alterations to theforestry sector to increase sequestration and compare them to other uses of landand use of nonwood products for end-use needs (life cycle assessment), and(4) evaluation of risks of unwanted changes to ecosystem functions.

Strategies and objectivesAfforestation of marginal cropland and pasture. Substantial gains in carbonstorage in biomass and soils on afforested lands are possible. This technology islimited primarily by the availability of suitable land (for ecological or economicreasons), nursery capacity, willingness of landowners to participate, andavailability of technical assistance. Size of program and cost estimates vary widelybecause of differences in how and where proposed programs would beimplemented and because of differences in carbon accounting. If the new forestland is managed for wood products, then the disposition of carbon in woodproducts, byproducts, and disposal must also be considered.

Improved forest management. There are opportunities to improve carbon storageby changing silvicultural practices on certain sites and forest conditions. Themagnitude of increased carbon storage may be difficult to quantify sincesilvicultural practices are usually developed and applied for another purpose,such as increasing timber growth, and will not necessarily increase biomassgrowth and soil carbon storage. Nevertheless, some forest stands may not begrowing at biologically potential rates because of suboptimal stocking levels.These stands offer the best opportunities for enhanced carbon storage. Also,silvicultural practices may be designed to maximize the amount of carboneventually stored in harvested wood products.

Reduce conversion of forest land to nonforest use (reduce deforestation).Conversion of forest land to nonforest use usually means permanent loss of all ora substantial part of live biomass and reduction of organic matter in soils and theforest floor. CO2 and other greenhouse gases are emitted when the removedbiomass and organic matter is burned or decomposes. Some carbon may besequestered in wood products if the removed biomass is utilized. Protecting andconserving forests should maintain or increase carbon pools in the short term, aslong as natural disturbance rates do not reach catastrophic levels.

Increase sequestration of carbon in wood and paper products. Wood harvestedfrom forests remains sequestered and is emitted to varying degrees depending onhow products are made, used, and disposed of. Sequestration in products anduses can be increased by altered processing methods, shifts in products used,shifts in end-use durability, and shifts in landfill management. Sequestration inforests and products can be increased by coordinated understanding of forestecosystems and products utilization.

ObjectivesAboveground• Increase and maintain area of forest cover.• Maximize biomass accumulation.



• Maximize average standing stock of biomass.• Increase carbon retention in wood products and landfills.

ObjectivesBelowground• Increase and maintain area of forest cover.• Increase soil organic matter on depleted soils.• Minimize soil and litter disturbance during forest operations.• Employ management techniques that increase soil organic matter in existing

forest.

Research and development needs understandingAboveground• Develop genetically improved plantation species to maximize growth and wood

density.• Develop silvicultural practices (e.g., stocking control, understory

management, and prescribed burning) that maximize biomass accumulation.• Enhance wood and paper products characteristics that increase sequestration

(e.g., durability, lignin, recyclability).• Improve understanding of the interactions between natural disturbances

(weather, fire, pests), management practices, and forest protection, with regardto impacts on long-term carbon storage.

• Determine socioeconomic causes (e.g., social institutions) of deforestation.

Belowground• Develop silvicultural practices and/or selections of species or genotypes that

result in a higher humification efficiency (i.e., increase the fraction of deadorganic matter that is converted into stable soil humus during decomposition).Much of the litter applied to the surface, including most wood, never entersthe soil as humus. Material that enters via the soil has a higher humificationefficiency. Material that has a higher lignin content has a higher humificationefficiency. Research is needed to assess species or management that affectsallocation and tissue composition on soil carbon accumulation.

• Litter and soil decomposition is affected by a number of physical, chemical,and biological factors. Physical factors amenable to management include soiltemperature and moisture. Chemical factors include nutrient content and pH.Biological factors include microorganisms, micro- and macro-invertebrates.Research to determine manipulations of these factors to decreasedecomposition rates without drastically affecting tree growth is required.Research to create deeper rooting zones would also be important.

MeasurementAboveground• For major ecoregions, quantify the potential biomass gains from converting

agricultural use to forest using different stand establishment techniques andspecies (comparative cross-sectional studies; existing long-term researchsites).

• Identify existing forest conditions that result in suboptimal biomassaccumulation.



• Compare carbon mitigation of burning wood, recycling wood/paper, shifting tolonger-lived uses, landfilling (with limited decay).

• For monitoring and verification of changes in aboveground carbon storage,improve and integrate use of data from forest inventory, remote sensing, andAmeriflux collection methods.

Belowground• For major ecoregions, quantify the potential soil carbon (including organic

layers) gains from converting agricultural use to forest using different standestablishment techniques and species (comparative cross-sectional studies;existing long-term research sites).

• For monitoring and verification of changes in below ground carbon storage,improve national forest inventory collection of periodic data on soil organicmatter, litter, and coarse woody debris.

ImplementationAboveground• Develop and use national models to identify high sequestration combinations

of genetically improved species, forest management intensities, productsutilization, and landfill management.

• Perform life cycle analyses for major tree species, silvicultural systems, andwood products. Note that this involves analysis of energy inputs throughoutthe life cycle.

Belowground• Develop methods to improve the efficiency of the humification process for

logging residue.

Assessment• Evaluate the impact of changes in forest growth/sequestration on essential

ecosystem functions.• Evaluate the risk that disturbances to forests (e.g., fire, pests) and climate

change induced changes in productivity or species viability may thwartvarious activities to increase sequestration.

General• Develop interagency coordination of research and interagency coordination of

strategies to increase sequestration.

Links to other ecosystems• Use comparative studies to evaluate carbon tradeoffs from converting

agricultural use to forest use.• Understand the socioeconomic tradeoffs of converting agricultural use to

forest use.• Determine the impacts of deforestation to agricultural or developed use on

major forest ecosystem carbon pools.



2. Agricultural and Grassland Ecosystems (Keith Paustian, Julie Jastrow,Margaret Torn, Ron Follett, Mary Firestone)

The carbon sequestration potential in agricultural and grassland ecosystems isprimarily centered in the soil. Standing stocks of aboveground biomass aremodest (typically < 10 Mg C/ha) compared to forests and, in the case of annualcrop systems, may be entirely absent for part of the year. In contrast, grasslandand agricultural soils may contain several hundred mg/ha of carbon, comparableto amounts aboveground in densely forested communities.

The high levels of carbon achievable in grassland and agricultural soils are theresult of the accumulation of plant and microbial-derived residues which becomeincreasingly recalcitrant through recurring cycles of decomposition by soilorganisms. In addition, association of organic matter with soil minerals, throughbinding to colloidal surfaces and occlusion within soil aggregate structures,reduces their accessibility to microbial decay, enhancing organic matteraccumulation.

Soil carbon levels are determined by the balance of carbon additions from rootsand aboveground litter and the decomposition rates of the organic matter presentin soils. Hence, carbon sequestration (i.e., increasing standing stocks of carbon)can be promoted by increasing carbon input rates, decreasing decompositionrates, or both. Carbon input rates are a function of the net productivity of plants,the allocation of that productivity between removals (i.e., harvest, fire) andresidues returned to soil, and organic matter imports (e.g., manure, sludge). Soilorganic matter decomposition rates depend on the composition and activity of soilorganisms, which are influenced by their abiotic environment (temperature,moisture, aeration, mineral nutrients, pH), the physiochemical quality of theorganic substrates (its chemical composition, particle size) and the accessibility ofthese substrates to soil organisms (influenced by soil texture and soil structurerelationships). Ecosystem management to increase carbon stocks will be based onthe manipulation of these controls on inputs and decomposition rates.

Current carbon sequestration capabilities of grassland and agriculturalecosystems

Cropland currently occupies about 150 Mha of land area in the U.S. (contiguous48 states) with an additional 14 Mha of formerly cultivated lands in grassland andforest set-asides (mainly Conservation Reserve Program Lands). Agricultural andset-aside lands represent about 20% of total land area of the U.S. Soil carbonstocks (0–1 m) under cropland are on the order of 15–20 Pg (based onextrapolations from surface soil estimates (0–30 cm) by Kern and Johnson 1993)),compared to the 60–80 Pg total for all ecosystems in the contiguous U.S. (Kern1994, Waltman and Bliss 1997). Historically, these lands have suffered a net lossof carbon, on the order of 5–6 Pg, following conversion of the native ecosystems tocropland. More recently, increased productivity and improved managementpractices have probably reversed this trend such that overall carbon levels havenow stabilized or begun to increase (Cole et al. 1993, Lal et al. 1998). Existingmanagement practices which are responsible for improving carbon levels includereduced tillage intensity, productivity increases through genetic improvements



and increased management inputs (fertilizer, pesticides, irrigation); intensifiedcrop rotations (e.g., reduced summer-fallow); and set asides of marginal croplandto perennial vegetation, mainly grasses (Paustian et al. 1997). Recent estimates ofthe potential for carbon sequestration in U.S. agricultural soils, using existingtechnologies, are on the order of 50–200 Tg/year over the next 2–3 decades(Bruce et al. 1998, Lal et al. 1998). The range of these estimates reflects bothuncertainties in carbon accumulation rates for different practices and soil/climate conditions and uncertainty in the projected rates and extent of adoptionof carbon conservation practices.

Grasslands include both extensively managed native rangelands as well asintensively managed pastures. In the lower 48 states, there are about 160 Mha ofnonfederal rangelands and 50 Mha of pastures (1992 National ResourceInventory). Conventional management factors that can impact soil carbon levelson grasslands include grazing management, burning, species selection, andproduction inputs (i.e., fertilizer, irrigation). Intensively-managed grasslands (i.e.,pastures), where productivity and management inputs are relatively high,probably have the greatest opportunities for increasing soil carbon throughimproved practices such as rotational grazing and application of fertilizers (Nyborget al. 1997). On rangelands, traditional management is largely restricted tomanipulating grazing intensity, which has variable impacts on soil carbon. Ingeneral, where vegetation cover and production of rangelands are not adverselyaffected by grazing, there is little change in SOM (Burke et al. 1997, Milchunasand Lauenroth 1993). Compared to agricultural lands, there is less field dataupon which to base estimates of current carbon sequestration potential ingrasslands. Bruce et al. (1998) estimated potential rates of sequestration for U.S.pastureland at 10 Tg/year. The greatest opportunities for carbon sequestration inrangelands involves rehabilitation of degraded areas. Unfortunately there is noexisting national data base from which to estimate rangeland conditions and thepotential for improvement of degraded rangelands. Widespread but slow rates ofcarbon sequestration may be occurring in many grasslands due to CO2

fertilization and increased anthropogenic nitrogen deposition, but reliableestimates are currently lacking.

Strategies and objectives for carbon sequestration in grassland and agriculturalecosystems

Strategies for increasing carbon stocks in these soils revolve around maximizingthe amount of carbon that can be delivered to the soil and subsequentlymaximizing its residence time in the soil (by reducing rates of decomposition).Ultimately nearly all carbon that enters the soil is recycled back to theatmosphere, but the amount of carbon in the soil will increase in direct proportionto its mean residence time. Since croplands and grasslands represent the primaryfood production systems for society, it’s important that carbon sequestrationstrategies be compatible with the maintenance of food and feedstock supplies.Fortunately, many measures to increase primary productivity also increase plantresidue production, and increasing soil carbon levels are generally beneficial formaintaining highly productive systems. However, tradeoffs do exist. For example,increasing the yield component of crop plants without increasing total netproductivity will come at the cost of reducing carbon inputs to soil, and



retirement of cropland to perennial grassland (or trees) may yield higher carbonsequestration rates but with a loss of food production capacity.

A variety of strategies can be conceived to increase net primary productivity andcarbon inputs to soil, through increased photosynthetic efficiency, increasednutrient and water use efficiency, and shifts in allocation of photosynthate to thebelowground component. For extensively managed grasslands (rangelands),strategies to increase carbon inputs would be based largely on restoringdegraded, poorly managed areas through control of invasive species, eliminationof severe overgrazing, and active restoration on severely degraded rangelands. Inpastures and croplands, a wider variety of more management-intensive strategiesexist, including improved grazing management (e.g., rotational grazing); fertilitymanagement; pest control; species selection; and genetic improvements,including plant bioengineering.

On the decomposition side, strategies include manipulating the abioticenvironment in favor of plant growth vs microbial (decomposer) activity, while stillmaintaining the function of the soil microbial community. For example,increasing water use efficiency of plant production (e.g., reduced summer-fallow,higher plant density, more efficient plant water extraction), reduces “excess”water, producing drier soils and reduced microbial activity. Many grass and cropspecies have lower temperature optima than the majority of microflora. Thussomewhat cooler temperatures (e.g., with use of surface mulches) may reducedecomposition rates while optimizing plant carbon inputs. Soil organic mattertypically shows a substantial increase in age with depth (e.g., Paul et al. 1997)due, in part, to lower rates of decay at depth, from lower temperatures, reducedaeration and other factors. Thus, developing and/or using deeper rooting plantscan place more carbon in locations where its residence time is increased. Thesusceptibility of plant residues to decay is influenced by their chemicalcomposition, so that increasing the amounts of recalcitrant substances (e.g.,lignin, polyphenols) in residues could enhance carbon storage. Decompositionrates in soils are inhibited by the close association of organic substances withmineral colloids (clays, oxides) and the occlusion of organic matter within soilaggregates. Tillage tends to reduce aggregate stability; thus reducing oreliminating tillage can help maintain the physical protection capacity of soils.Development of reduced and/or zero-tillage systems for a wider variety of cropsand environments is an important strategy. Increased use of perennial grassesand legumes, alone or in rotation with annual crops, is effective in building soilcarbon stocks. Other opportunities might include the use of artificial colloidalamendments to sorb and “protect” organic matter in soils. Finally, directmanipulation of microbial communities through bioengineering couldconceivably be used to reduce decomposition rates, although the unlikelihood ofsuccess (i.e., a reduced ability to metabolize organic matter would make for poorlycompetitive organisms) and the potential for undesirable side effects (i.e.,disruption of the biogeochemical cycling function of soils) argue against thedesirability of such strategies.

Strategies to sequester carbon in agricultural and grassland ecosystems alsoneed to factor in the carbon cost in terms of fossil fuel subsidies (e.g., fertilizerand herbicide production, farm machine use, irrigation pumping) for various



production practices, as well as the potential effects on other soil-emittedgreenhouse gases, chiefly N

2O and CH

4. Previously described strategies directed

at increasing primary production efficiency (i.e., increased nutrient and wateruse efficiency), increased use of nitrogen fixation by legumes in crop rotations (toreplace fertilizer nitrogen), increase dependence on mycorrhizae and adoption ofzero-tillage systems (Frye 1984) would reduce fossil carbon requirements.Agricultural ecosystems are usually net sources of N2O, particularly from soilswith high amounts of inorganic nitrogen. In addition, methane is generated byruminant livestock and also by waterlogged soils, notably rice paddies. While CO2

is much more abundant in the atmosphere, N2O and CH4 are, molecule formolecule, more potent greenhouse gases relative to CO

2. The impact of carbon-

sequestering practices on the potential emissions of these other gases, therefore,cannot be ignored. Although the secondary effects of carbon-conserving practicesare often difficult to quantify, any proposed practice should be carefully assessedto ensure that the benefits in carbon stored are not seriously reduced by theemission of other gases.

Research and development needs

Research is needed to promote a better understanding of key soil processes, inorder to assess how and to what degree they can be manipulated to promotecarbon sequestration. In addition, there are major R&D needs that relate to theestimation and quantification of current and future carbon stocks as a function ofenvironmental and management factors. These later needs cut across all themajor ecosystem types.

For specific R&D priorities related to understanding controls on primaryproductivity and plant allocation, we refer to the section under BiomassCroplands. R&D priorities related to soil processes and controls and inventories ofcurrent and future carbon stocks are outlined below:

Research needs for fundamental understanding of soil processes and controls

A. Increase depth of soil carbon1) Species-soil-climate interactions controlling root depth distribution2) Controls on decomposition at depth3) Deep movement of organic and inorganic carbon4) Effect of tillage systems on rooting depth

B. Increase root mass1) Controls on aboveground to belowground carbon allocation for different

plants2) Species selections that dramatically increase root mass3) Nutrient controls and feedback on productivity4) Adaptations to CO2 increases, temperature increases, and pH tolerance

C. Transform Labile carbon to Recalcitrant carbon1) Isolation and characterization of recalcitrant organic matter2) Controls on formation of recalcitrant SOM3) Role of soil structure in SOM physical protection4) Role of soil minerals and cations on chemical protection of SOM5) Effect of litter quality on decomposition rate



6) Effect of rhizodeposition and exudation on decomposition rate7) Effects of microbial community structure on SOM cycling and stabilization

D. Create less favorable abiotic environment1) Soil moisture-microbial community interactions affecting decomposition2) Community and biome variability in thermal responses of microorganisms3) Effect of nitrogen addition (as fertilizer, deposition, biological nitrogen-

fixation) on decomposition

Research needs for improving inventories of carbon stocks in agricultural andgrassland ecosystems

A. Dynamic inventories of land cover and land management system distributions1) Development of coverages with improved spatial resolution to differentiate

fragmented land covers2) Improved differentiation of crop and grassland species assemblages3) Remote sensing techniques to resolve different management regimes

within landcover/vegetation types (e.g., tillage management, cover crops,grazing intensity)

B. Survey data1) Global metadata compilation of national land use/management

information2) Standardization and/or cross comparison of survey/inventory approaches

and definitions3) Synthesis (within United States) and cross validation of national level

survey data (e.g., USDA/NRI, FS, BLM, USDA/ERS)C. Information on distribution and characteristics of soils

1) More information on soil carbon concentrations at depth2) Synthesis and integration of data from distributed pedon data holders (e.g.,

universities, state agencies)3) Standardization (international) of attributes (e.g., carbon analytical

methods, bulk density, texture, drainage, and depth) and techniquesneeded to estimate soil and litter carbon stocks and soil bulk density (e.g.,as part of USDA/NRCS and ISRIC collaboration).

4) In situ, nondestructive determinations of soil carbon

Needs for quantification and prediction of carbon sequestration

A. Development of modeling approaches1) Testing and refinement of models for less studied systems; for example,

flooded and poorly drained soils, highly weathered soils (e.g., Ultisols,Oxisols), volcanic-derived soils

2) Representation (in simulation models) of SOM fractions that areanalytically determined, concomitant with experimental science toimprove functionally meaningful characterization of SOM

B. Enhancement of SOM monitoring networks1) In field relocateable, resampling points designed to minimize spatial

variability, tied into existing monitoring systems (e.g., NRI). Measurechange under a variety of cropping/grassland systems (steady-state/aggrading/degrading) in a variety of climates and soil types

2) Increased deployment of ecosystem CO2 flux systems, coordinated so as to



leverage information from existing long-term experimental sites(e.g., establish new flux measurements for soil, crop and managementvariables where long-term experimental records exist) and intensified soilsresearch at existing CO2 flux tower facilities

C. Coordinate and synthesize spatially referenced data coverage for importantmodel driving variables.

References

Bruce, J. P., M. Frome, E. Haites, H. H. Janzen, R. Lal, and K. Paustian. 1998.Carbon Sequestration in Soil. Soil Water Conservations Society White Paper,23 p.

Burke, I. C., W. K. Lauenroth, and D. G. Milchunas. 1997. Biogeochemistry ofmanaged grasslands in central North America. In: E. A. Paul, K. Paustian, E. T.Elliott, and C. V. Cole (eds). Soil Organic Matter in Temperate Agroecosystems:Long-term Experiments in North America. pp. 85–102, CRC Press, Boca Raton,FL, USA.

Cole, C. V., K. Paustian, E. T. Elliott, A. K. Metherell, D. S. Ojima, and W. H. Parton.1993. Analysis of agroecosystem carbon pools. Water, Air and Soil Pollution,70:357–371.

Frye, W. W. 1984. Energy requirement in no-tillage. In: Phillips, R. E. and Phillips,S. H. (eds.). No Tillage Agricultural Principles and Practices. Van NostrandReinhold, New York, pp. 127–151.

Kern, J. S. 1994. Spatial patterns of soil organic carbon in the contiguous UnitedStates. Soil Sci. Soc. Am. J. 58: 439–455.

Kern, J. S. and M. G. Johnson (1993). Conservation tillage impacts on nationalsoil and atmospheric carbon levels. Soil Sci. Soc. Am. J. 57: 200–210.

Lal, R., J. M.Kimble, R. F. Follett, and C. V. Cole. 1998. The Potential of U.S.Cropland to Sequester Carbon and Mitigate the Greenhouse Effect. Ann ArborPress, Chelsea, MI, 128 p.

Milchunas, D. G. and W. K. Lauenroth. 1993. Quantitative effects of grazing onvegetation and soils over a global range of environments. Ecol. Monog.63:327–366.

Nyborg, M., M. Molina-Ayala, E. D. Solberg, R. C. Izaurralde, S. S. Malhi, and H. H.Janzen. 1997. Carbon storage in grassland soils as related to N and S fertilizer.pp. 421–432 In: Lal, R., J. Kimble, R. Follett, and B. A. Stewart (eds).Management of Carbon Sequestration in Soil. CRC Press, Boca Raton.

Paustian, K., H. P. Collins, and E. A. Paul. 1997. Management controls on soilcarbon. In: E. A. Paul, K. Paustian, E. T. Elliott, and C.V. Cole (eds). SoilOrganic Matter in Temperate Agroecosystems: Long-term Experiments in NorthAmerica. pp. 15–49, CRC Press, Boca Raton, FL, USA.

Paul, E. A., R. F. Follett, S. W. Leavitt, A. D. Halvorson, G. A. Peterson, and D. J.Lyon. 1997. Radiocarbon dating for determination of soil organic matter poolsizes and dynamics. Soil Sci. Soc. Am. J. 61:1058–1067.

Waltman, S.W. and N.B. Bliss. 1997. Estimates of SOC content for the U.S. USDA/NRCS, Lincoln, NE.



3. Biomass Crop Lands (Lynn Wright, Sandy McLaughlin, Jerry Tuskan, DonReimensneider, and Carl Trettin)

Biomass production and harvesting systems are being developed to optimizeaboveground plant productivity per unit area in a way that conserves andimproves soil resources, maintains or improves water quality and wildlife habitat,provides profit potential to the landowner, and supplies low-cost, uniformfeedstocks to energy providers as a means of displacing fossil fuel. The cropsunder development for this land use are primarily perennial crops, includingseveral grass and tree species worldwide. These crops are grown using agronomictechniques such as cultivation or herbicide use for site preparation, fertilization,pest and disease control for crop maintenance, and periodic removal of theaboveground portion of the crop. The grass species are harvested annually or morefrequently while the tree crops have 3–10 year harvest intervals. It is generallyassumed that the trees or grasses will be grown in relatively large blocks for easeof harvest, handling, and utilization. Alternative methods of biomass productioninclude mixing annual and perennial crops (agroforestry), using shelterbelts orriparian zones to produce biomass, and mixing species in production stands.

A critical assumption for carbon sequestration analysis is that these perennialcrops will be established on idled or surplus crop or pasture land, on croplandthat is occasionally flooded, or on lands marginally profitable for annual cropproduction because of poor soil quality, erosion sensitivity, nutrient degradation,or other reasons. The rate of conversion of agricultural cropland to biomasscropland will be economically and policy driven but is also dependent on thedevelopment of new, more efficient biomass production and bioenergy conversiontechnologies. In some areas of Europe, idled agricultural cropland is alreadybeing converted to biomass crop production for energy end-use. In other places,such as the United States, the biomass cropping systems described above arebeing used to produce fiber products with energy production as a by-product.

Current carbon sequestration capabilities of biomass croplandThe greatest carbon emission reduction gain from biomass cropland will beobtained when economic or policy conditions result in the use of biomasscropland to produce feedstocks that substitute for carbon emitting fossil fuelssuch as coal and oil. Since adequate economic and policy drivers are not yet inplace in most areas of the world, very little land currently is managed as biomasscropland. In the United States about 50,000 ha have been converted fromagricultural cropland to production of woody crops. Several million ha of croplandwere converted to switchgrass and other grass mixtures as part of theConservation Reserve Program in the United States from the mid-1980s to mid-1990s. However, those lands have not received fertilization or pest control andthus are not highly productive. Similar types of land conservation programs wereinstituted in Europe for similar reasons. In addition, many parts of the formerSoviet Union have large amounts of idled cropland reverting to naturalecosystems with the change from centrally managed to private managedagricultural systems. For purposes of a carbon sequestration analysis, somecombination of the current carbon sequestration capabilities of annual cropsystems and pastureland should be used as the biomass cropland baseline.



Strategies and objectives for biomass cropland carbon sequestrationSince biomass cropland systems are at a very early stage of development, theopportunity exists to select and develop perennial plant species and managementsystems that optimize both aboveground production and belowground carbonsequestration while providing profit to the landowner. The primary researchstrategy here is to increase the per unit land area rate of carbon fixation in theaboveground (economic) portion of the perennial plant biomass by 2 to 4 times. Apolicy/economic strategy is to develop markets for biomass crops to assureperiodic removal of the crops for sequestration in bioproducts (e.g., wood products,bioplastics, etc.) and bioenergy (fossil carbon substitution). Development of themarkets could be enhanced by genetically improving the characteristics ofperennial biomass crops for bioenergy or bioproduct utilization

One risk associated with biomass croplands is public acceptance of land usechange. Because of this, biomass croplands will have to provide more than justcarbon sequestration and energy benefits in order to be accepted. Some level ofoptimization of carbon sequestration and plant productivity may have to besacrificed in order to assure that water quality, soil conservation, and wildlifebenefits are provided as an inherent component of biomass cropland ecosystems.Thus realizing the high rates of carbon sequestration that deployment of biomassproduction systems can offer additionally requires; (1) land use policy thatfacilitates biomass cropland implementation without violating strongly held ideasabout land use, (2) multiple environmental benefits associated with the land usechange and, (3) achievement of high carbon fixation and storage rates with lowfossil carbon inputs.

The amount of carbon sequestration in biomass cropland will ultimately dependon the scale of land use conversion that occurs. Conversion of between 10 and15% of current crop and pasture land worldwide to biomass production appears tobe a feasible goal that would not substantially impact food and fiber productionand which could provide observable regional environmental benefits.

Research and development needsAll plant productivity research could benefit from improving our understanding ofplant and soil processes. Research on plant process understanding must integratewith genetic improvement and crop management activities focusing on carbonsequestration impact. Genetically improved stock should optimally combine high-yield potential, with disease and pest resistance, high water-use and nutrientefficiency and optimal feedstock properties for conversion. Genetic potentialneeds to be achieved in concert with crop management techniques that minimizecarbon inputs but assure sustainability of yields over time. Functional genomicswill use molecular genetics to identify and modify plant growth and developmentprocesses, including individual gene expression, host-microbial interactions, allphysiological responses, and plant assembly mechanisms. Integrated physiology,entomology, pathology, and agronomic studies are needed to elucidate plantgrowth and stress resistance mechanisms (i.e., studies focused on CO2 fixationand respiration processes, carbon allocation, efficiency of carbon capture per unitof nutrients and water available, and pest and disease resistance are required).The selection and deployment of improved planting stock and crop managementtechniques must be optimized for each soil type and climatic zone.



Similar to most plant ecosystems, process understanding is critical to improvingbelowground carbon sequestration in biomass croplands starting with improvingour understanding of the processes controlling the movement of abovegroundcarbon to soil carbon pools. Carbon storage process studies should include;(1) determination of how carbon fractionation influences labile and recalcitrantforms of carbon, (2) quantification of how existing carbon levels affect storagerates and, (3) determination of factors affecting the rate and form of downwardcarbon migration in soils. The process research should be supplemented withextensive surveys documenting how carbon forms vary with soil type, depth,temperature, physical properties, and chemistry as well as types of crops andcropping strategy. In evaluating crops and cropping approaches it will beimportant to link effects of nitrogen management and tillage practices to carbonstorage rates, stability of carbon gains over time, and the equilibrium conditions.Finally, a better understanding how climate change events (such as nitrogendeposition, regional ozone levels, changing precipitation patterns, and overallglobal warming) may feedback to affect carbon inputs and storage will addvaluable information for predicting long-term effects.

The measurement and quantification research that would non-destructivelydetermine carbon sequestration in the soil in biomass croplands would be verybeneficial. Remote sensing approaches could also improve our ability to surveylarge areas of land thus predicting levels of standing biomass. Research toimprove our understanding of the linkage between above- and belowgroundcarbon gains would be helpful in estimating soil carbon gains based on tons ofbiomass harvested annually.

Implementing the strategy for increasing carbon sequestration in biomasscropland requires the initiation of research that will lead to (1) technologies thatare economically viable and environmentally sound and (2) analytical techniquesthat will assist policy makers in determining optimal land use allocationstrategies for achieving carbon sequestration goals. Carbon sequestration will notincrease in any ecosystem unless there are appropriate economic and policydrivers.

One risk associated with biomass croplands is public acceptance of land usechange. This is part of the reason why biomass croplands will have to provide morethan just carbon sequestration and energy benefits in order to be accepted by thepublic. Thus some level of optimization of carbon sequestration and plantproductivity may have to be sacrificed in order to assure that water quality, soilconservation, and wildlife benefits are provided as an inherent component ofbiomass cropland ecosystems.

LinkagesBiomass cropland R&D will be similar to that proposed for traditional agriculturalcrops, intensively managed forests, and managed grasslands since in all cases, amajor goal is the production of biomass for removal from the site. Improvement ofplant growth on degraded ecosystems could also share some similarities inapproach with biomass croplands, since stress tolerance will be a component ofboth systems.



Biomass and agricultural cropland R&D will differ in that the former will focusprimarily on perennial plants and the latter on annual plants and that most of theproducts from biomass crops will have a longer sequestration residence time.Basic plant research may be able to address some topics common to both, butperennial and annual plants have very different requirements for survival, andthus many differences in basic plant mechanisms.

Biomass cropland and managed forest or grassland ecosystems will differ by thefact that biomass crops will likely be established on former agricultural lands thatare carbon depleted, while forest and grassland soils will likely have lessopportunity for soil carbon increases.

A major cross cutting issue is to develop appropriate decision models andanalytical techniques for optimizing land use allocation under various economicand policy scenarios. In the context of this report, consistent decisions have to bemade on accounting for carbon removed from sites, considering portions thatreturn to the atmosphere with no fossil substitution and portions that aresequestered or substitute for fossil carbon.



4. Wetlands (Carl Trettin, Ron Thom, Patrick Megonigal, Walter Oechel)

Global wetlands cover about 7% of the total land surface, and contribute about10% of the total global net primary productivity (NPP). Many systems have a highturnover rate (production:biomass) indicating loss and export rates are high. Inaddition, loss to sedimentation in deep portions of lakes and oceans may be great.Wetlands produce 40% of the global methane emissions. The degree to whichwetlands produce methane is intimately tied to the hydrology of the system.Systems, such as rice paddies, that are wet much of the time, have greatermethane emission rates. Marshes and some other wetland systems can benutrient limited. Wetlands have the highest carbon density among all terrestrialecosystems. Because of their low drought stress, high nutrient availability, andability to expand below ground biomass in enriched conditions, wetlands have arelatively great capacity to sequester additional carbon dioxide.

Wetlands sequester carbon through accretion of sediments and organic matter.Accretion is great in coastal systems where sediment input to estuaries is high.Marshes, in particular, form land through progradation. Very limited studies haveshown that coastal marshes under enriched CO

2 conditions, can sequester more

carbon in the below ground biomass. Carbon sequestration through peat formationis an active process especially in boreal systems. Because of their position at theinterface between land and water bodies, wetland export large quantities ofcarbon to deeper portions of lakes, estuaries and oceans, where carbon can besequestered through burial.

Wetland soils contain a significant proportion of the terrestrial soil carbon (20–25%), despite the relatively small proportion of the total land area occupied. InNorth America, approximately 50% of the wetlands are forested. They are animportant carbon sink, and a major source of atmospheric methane. Carbondynamics in wetland soils also affect non-point pollutants, ground and streamwater chemistry, and biogeochemical processes. Although soil carbon in wetlandsis recognized as being an important component of global carbon budgets andfuture climate change scenarios, relatively little work has been done to considerthe role of terrestrial ecosystems in managing carbon sequestration. Wetlands areamong the most productive ecosystems in the world. They also have propertiesthat reduce the rate of organic matter turnover from the ecosystem. Hencewetlands inherently have the two primary factors controlling carbonsequestration, (1) high rates of organic matter input, and (2) reduced rates ofdecomposition. There is considerable opportunity for managing that capability toaffect enhance carbon sequestration while sustaining the other valued ecosystemfunctions. However, considerable research is needed to provide the knowledgefoundation for the resource management decisions.

In the United States, 50% of wetlands have been lost or converted to other uses(e.g., crop and grazing lands). Globally the loss is undocumented, but could easilybe as great. Sea level rise is causing net loss of some coastal wetlands, and carbonsinks in temperate and boreal wetlands have decreased by 50% (from 0.2 to0.1 GtC year–1) due to development and resource extraction. Loss in tropicalsystems could likely exceed this amount. The leading causes of wetland loss areconversion, deforestation, development, and hydrological modifications.



Because of the global losses of wetlands, restoration of damaged, degraded andconverted ecosystems represents a major opportunity to improve sequestration inwetlands. We estimate that restoring 25% of the wetlands would result in anincrease in carbon sequestration. Hydrological controls could be effectively usedto produce a positive balance in favor of carbon sequestration vs methaneemission. Some wetland system are nutrient (nitrogen) limited to some degree.Hence, fertilization or other methods to introduce nitrogen into these systemscould increase primary productivity and enhance carbon storage. Reduction inthe rate of sea level rise would reduce the rate of conversion of intertidal wetlandsto subtidal mud bottom. Massive restoration efforts presently underway on theMississippi River delta through the Coastal Wetland Protection, Preservation andRestoration Act (CWWPRA) represent an excellent opportunity to evaluate theeffects of large scale restoration on carbon sequestration and comparison of forest,shrub, and herbaceous wetlands.

Strategies• Identify degraded wetlands and develop management/conservation strategies

to rehabilitate processes that sequester soil carbon. These lands have theinherent characteristics to sequester large amounts of carbon; reestablishinganaerobic processes and managing inputs have the potential for large amountsof long-term carbon storage. Especially important opportunities exist in prior-converted agricultural lands.

• Implement vegetation management strategies that sustain the soil carbonresources while producing woody crops.

• Increase soil carbon storage by identifying sites that have high productivitypotential through managing water and nutrient resources.

• Conserve wetland landscapes that are inherently effective at carbon storage.• Mitigate carbon loss through created wetland systems.

Objectives• Increase soil carbon sequestration in managed wetlands to rates above the

norm for natural or unmanaged systems.• Increase acreage of wetlands within selected landscapes thereby enhancing

both above and below ground carbon storage.• Increase the volume of wood products derived from the resource that enter

stable products classes.• Implement planning / decision systems that consider carbon sequestration at

the landscape level.• Consider the value of carbon sequestration in designing mitigation projects.

There may be inherent limits on the potential for any given wetland tosimultaneously have both very high productivity and extremely slowdecomposition rates. Such limits will be important to understand if we wish tomanipulate wetlands to enhance carbon sequestration. One limit that isincompletely understood in wetlands is the link between carbon and nitrogencycling. Plants require a substantial nitrogen supply to support highphotosynthesis rates. Most of the annual nitrogen demand in wetlands is suppliedby decomposition of soil organic matter, a process that produces both plantavailable nitrogen and CO2. Thus, wetlands cannot necessarily support high rates



of photosynthesis and low rates of decomposition simultaneously. A basicresearch needed in wetlands is understanding how nutrient inputs andhydrology can be managed to optimize net ecosystem production in wetlands.

Coastal marshes have high rates of primary production due to tidal subsidies ofwater and nutrients, and high rates of carbon sequestration in soils due to lowdecomposition rates and burial by sediments. Global sequestration in thesesystems is perhaps 0.025 to 0.05 Pg carbon per year. One of the largest coastalmarsh systems is the Mississippi River delta, which has an area of ~30,000 km2,roughly 10% of all coastal marshes. Both natural and artificial impacts arecausing annual losses of 66 km2 of freshwater and saltwater wetlands in thebasin, and efforts to slow these losses are underway. Halting the current losseswould save about 0.03 Tg y-1 in soil carbon sequestration. Restoring thesewetlands would increase this amount by perhaps 20-fold.

R&D NeedsAboveground• Improve the understanding of the processes controlling vegetative production

and community dynamics.• Improve the understanding of the hydrologic controls on above and

belowground carbon allocation and carbon uptake vs emission.• Develop a modeling framework to consider the role of wetlands in carbon

sequestration at the landscape scale.• Develop an understanding of how wetland plants (i.e., trees) will respond to

increased levels of atmospheric CO2.• Develop techniques to sustainably manage wetland ecosystems.• Determine the differences among forest and herbaceous communities in

carbon sequestration.

R&D NeedsBelowground• Improve the understanding of the processes controlling biomass allocation to

roots among different wetland species.• Develop an understanding of the role of mychorrizae in carbon fixation and

plant productivity.• Determine how different land management practices affect soil carbon storage.• Determine the feedback of changes in soil carbon storage on ecosystems

functions (e.g., habitat, water quality, hydrology).• Determine the interactions of nutrient levels, temperature, redox and organic

matter quality on carbon turnover and sequestration.• Determine the organic matter sources affecting soil carbon storage.• Role of fire in limiting carbon sequestration.• Explore opportunities for creating wetland/carbon storage systems as an

integral components of the landscape. Such a system would provideenvironmental benefits (e.g., water quality, habitat, recreation) and providelong-term carbon storage.

• Improve the understanding of the hydrologic controls on processes controllingcarbon sequestration.



LinkagesWetlands are inherent to most landscapes where soil carbon storage is important.Accordingly, whether the management system is on the upland, adjoining thewetland, or directly within the wetland, wetlands are probably involved inattempts to affect carbon sequestration on the land. The linkages are controlledprimarily by the movement of water. Hence understanding the functionallinkages among ecosystems or management zones is critical to developingsustainable management systems. Wetlands effect soil carbon storage primarily asa result of reduced rates of organic matter turnover caused by anoxia. Factorsaffecting hydrology or aeration may affect the processes controlling soil carbonstorage. Accordingly, there are direct linkages to land use (i.e., water use, wastedisposal, urbanization) that must be considered at the landscape scale. Alteredclimates factors including temperature, precipitation, and atmospheric CO2

should be expected to change wetland processes and carbon storage. Studies ofthe effects of climate change factors on wetlands have largely been ignored.Accordingly, there is a critical need to develop an understanding of climatechange influences on wetland processes so that those influences can beconsidered in conjunction with current and planned management approaches.

There is considerable interest in the United States in mitigating wetland lossthrough banking and project-specific approaches. The carbon sequestrationfunction is not currently considered as part of the wetland value. Hence, it islikely that carbon losses are occurring with questionable prospects for long-termparity. Accordingly, there is an opportunity to design mitigation systems toprovide, and perhaps enhance, carbon sequestration functions. Wetlands areproductive ecosystems. There is considerable opportunity to enhance thatproductivity while sustaining valued ecosystem functions at the landscape scale.However, development of integrated assessment systems based on knowledge ofecosystem processes is required.



5. Deserts and Degraded Lands (F. Blaine Metting and Rattan Lal)

Deserts and degraded lands are considered together because restoration of theseecosystems to sequester carbon can require highly manipulative strategies. Manyof the same strategies can be applied to both systems, with some modifications.

The definition and areal extent of degraded lands is somewhat difficult to assess.Included under different definitions are both “natural” and anthropogenicdegradation. Worldwide, there are approximately 1965 ´ 106 ha of degraded soils,4% from physical degradation, 56% from water erosion, 28% from wind erosionand 12% from chemical degradation. With proper management these soils havethe combined potential to sequester between 0.81 and 1.03 Gt C/year. Categoriesinclude saline, sodic, saline-sodic, mine spoils, and eroded or severely erodedsoils.

Erosive processes are as a consequence of overly intensive tillage often combinedwith climate change and other inappropriate practices, such as use of marginallands and steep topographies, and over grazing. One result is desertification.Estimates of land areas subject to degradation and desertification vary from~1–2.5 ´ 109 ha. Annual desertification rates vary from ~5–27 ´ 106 ha, half ofwhich is occurring on rangelands.

Depending on the basis for their definition (i.e., evapotranspiration or other aridityindices, vegetation, soil taxonomy), deserts account for between 11–12% of theEarth’s land surface. Estimates vary from 108-to-2+ ´ 109 ha and include hyper-arid regions receiving <200 mm annual precipitation (ppt.) and arid areas with<200 mm of winter ppt. or <400 mm total annual ppt. Addition of semi-arid areasreceiving 200-500 mm of winter ppt. or 400–600 mm of summer rainfall increasesthe areal extent of deserts to ~5 ´ 109 ha. The principal feature of these regions istheir negative water balance, which is reflected by generally sparse and oftenseasonal plant cover and low primary production. With open or absent plantcanopies, much of the soil surface of deserts is exposed to full sunlight. Oneresult is the evolution of unique microbial ecosystems dominated by autotrophicbacteria, microalgae and/or lichens known variously as cryptobiotic or algalcrusts and desert pavement. Organic carbon stocks are much smaller than otherecosystems, but desert soils (primarily in the Aridosol soil order) often containsignificant concentrations of inorganic carbon, principally as caliche. Otherfeatures of desert soils are:

• Aridosols occupy ~1.7 ´ 109 ha• Average carbon density of desert soils ~3–3.5 kg/m2/m depth• World wide desert soil stock ~59 Gt total C, 4.7 Gt N• Global caliche accretion rate ~0.05 Gt C/year

Strategies for enhanced carbon sequestration

Strategies for enhanced carbon sequestration have different objectives for desertsand degraded lands. For deserts, enhanced sequestration strategies are largelyinnovative uses of otherwise under utilized resources. Restoration of degradedlands and strategies to minimize or reverse desertification processes, on the other



hand, are as much aimed at reversing loss of carbon to the atmosphere as they areto enhancing sequestration. With the exceptions of the use of saline and brackishgroundwater resources for (1) crop irrigation or (2) microalgal mass culture,strategies for deserts and degraded lands largely focus on below groundsequestration. The greatest potential may be the discovery and application ofinnovative ways to enhance the accumulation of inorganic carbon stocks.

1. Control desertification (minimize, reverse) and restore degraded lands bymeans of improved land management practices

2. Delineate “bright” (trigger) spots for desert carbon sequestration. That is,identify area(s) to focus short-to-mid term desert carbon sequestration efforts.

3. Exploit under utilized desert resources to create wetlands and large-scaleaquaculture projects with saline and brackish surface and groundwaters

4. Use existing plant and microbial resources together with biotechnology andgenetic engineering:• Screen, identify and adapt C4 and CAM plants• Engineer enhanced water use efficiency, salt tolerance, high pH tolerance

into select species for desert regions• Engineer for desired root physiology/metabolism and architecture• Encourage and manipulate surface and rhizosphere microbial communities

to enhance sequestration5. Expand the use of land application of organic and inorganic soil amendments:

• Organic matter• Inorganic nutrients (e.g., Ca to enhance caliche development)• Microbial inocula to promote the development of desert crusts

Objectives

The objectives of the strategies for enhanced soil carbon sequestration in desertsand for restoration of degraded lands are to:

1. conserve soil and water, enhance water use efficiencies2. utilize neglected and underutilized resources3. strengthen/direct desired biogeochemical cycles/processes4. enhance vegetal cover and effective carbon sequestration by plants and

microbial communities

Research and development needs

Research and development needs for enhanced carbon sequestration in desertsand degraded lands falls within seven categories. These include research toestablish global databases in biotechnology and land management, and to betterunderstand natural plant, microbial, and soil processes and theirinterrelationships in arid and disturbed ecosystems. Specific research anddevelopment needs include:

1. Quantify and categorize the extent and severity of degraded lands on a globalscale. The availability and quality of this information is inadequate.Campaigns to collect, archive and make available data are required to better



understand the extent of degraded lands and for developing effective andprioritized international research programs.

2. Understand mechanisms and processes controlling carbon pools and fluxes indeserts and degraded lands. A number of basic biogeochemical mechanismsimportant to establishing a solid, fundamental understanding ofenvironmental and ecological processes in deserts and degraded lands arepoorly understood. Research is needed to better understand the following:• Aeolian/dry deposition processes and effects on carbon sequestration• Inorganic carbon formation and movement and the role of Ca• Influence(s) of soil physical properties on carbon sequestration in arid

regions, including the roles of texture, clay mineralogy, and soil structureand aggregation

• Biogeochemical cycles/controls of carbon sequestration and movement,including N, P, S, Fe, Ca and Cl

• The microbial ecology of desert soil surfaces and rhizosphere microbialcommunities

• Physical, mechanical, and species-mediated weathering of exposed subsoilor parent material on eroded sites

3. Management practices for desertification control and soil restorationDesert lands are, by definition, water limited. Thus, fewer than 10% of aridregions are cropped. Therefore, key management strategies for utilizingdeserts and reversing desertification must focus on minimizing the waterdeficit. Important objectives are:• The use of appropriate plant species. In particular, many arid land plants

have evolved special photosynthetic mechanisms for enhanced water useefficiency. These include the C4 photosynthetic fixation pathway and thecrassulacean acid metabolism (CAM) pathway. There are many advantages togrowing C4 and CAM plants in arid regions based on their improved waterand soil nutrient use efficiencies at high temperatures. Research is neededto improve understanding of global biodiversity of C4 and CAM plants thatcould be screened for innate carbon sequestration traits of interest and usedin field research projects.

• Supplementary irrigation and the use of under utilized saline and brackishsurface and ground waters. Growing crops or mass culturing microalgae thattolerate saline and alkaline water is another strategy for which expandedresearch efforts are required.

• Research focused on techniques for soil erosion control, particularly assuited to arid lands is required. This research needs to be integrated withmanagement efforts to optimize soil fertility, residue use, salinity controland the possible use of novel microbial and chemical amendments.

4. Molecular biology and plant genetic engineeringBiotechnology to improve plant performance in desert environments is neededand should focus on:• Development of genetic transformation tools and methods in new plant

species for desert growth and carbon sequestration, including C4 and CAMplants.

• Genetic engineering of desired traits into existing crop and forage plants,including salinity tolerance, water use efficiency, etc. One approach is toengineer desirable C4 and CAM metabolic traits into C3 crop plants.



5. Microbial biologyMicroorganisms and microbial communities in and on desert soils are uniquein comparison to agricultural and forest soils. In some arid and hyper-aridsettings, microbial communities are the only mechanism for biological CO2

fixation. They are also responsible for nitrogen input via biological N2 fixation

and for weathering of primary minerals and nutrient release. Fundamentalresearch is needed in desert plant rhizosphere microbial community functionand diversity of cryptobiotic communities (i.e., desert pavement, and lichenand microlagal crusts). In addition, applied research to develop anddemonstrate microbial inoculants for rhizosphere and soil crust manipulationand development is needed.

6. Desert ecologyEcosystem-scale research is required to better understand integratedecological roles of desert plant and animal communities, including the roleand global significance of arthropods in soil carbon cycling and sequestration.Ecological research is also needed to determine the appropriateness andextent of expansion or modification of grazing practices in arid and semi-aridregions.

7. Economic, social and policy researchIn all cases, research is required for cost-benefit and risk analysis for alltechnical and management options for enhanced soil carbon sequestration indeserts and degraded lands. This includes the need for life cycle analysis allapproaches to determine the overall energy and carbon budgets forimplementation.

Bibliography

Lal, R., H. M. Hassan, and J. Dumanski. 1998. Desertification control to sequestercarbon and mitigate the greenhouse effect. Contributed Discussion Paper,Workshop on Soil carbon Sequestration. Pacific Northwest NationalLaboratories, Oak Ridge National Laboratory, Council for Agricultural Science& Technology, December 3–5, 1998 (unpublished).

Metting, F. B. and J. L. Smith. 1998. Science needs and new technology for soilcarbon sequestration: a discussion paper. Contributed Discussion Paper,Workshop on Soil carbon Sequestration. Pacific Northwest National Laboratory,Oak Ridge National Laboratory, Council for Agricultural Science &Technology, December 3–5, 1998 (unpublished).

J. Skujins (Ed.). 1991. Semiarid Lands and Deserts. Soil Resource and Reclamation.Marcel Dekker, New York.

Schlesinger, W. H., G. M. Marion, and P. J. Fonteyn. 1989. Stable isotope ratiosand the dynamics of caliche in desert soils. In: Rundel, P. W., J. R. Ehleringer,and K. A. Nagy (Eds.). Stable Isotopes in Ecological research. Springer-Verlag,Inc., New York.



6. Urban and Suburban Forested Areas (John Hom, David Nowak, RichardPouyat, Marilyn Buford)

Carbon storage by urban forests nationally is estimated between 400–900 milliontons (aboveground tree and shrub biomass only, Nowak 1995). Within the urbanarea, the largest carbon tree storage is found in institutional lands dominated byvegetation (e.g., parks, preserves, cemeteries, golf courses), in residential land use(1–3 family residential buildings), multiresidental areas (apartments) and vacantlots. Small trees account for the majority of the trees in urban areas. Incomparison, U.S. forested ecosystems store approximately 52.5 billion tons ofcarbon (Birdsey 1992) and have 3–4 times higher live carbon/ha than urbanforests, due to the lower average percent tree cover in urban sites (~28%). Theestimates of suburban forest carbon storage are not well known, and aresometimes included in carbon estimates for urban forests, as they fall between theinventories of rural and urban forests.

Land use is one of the most significant factors affecting urban vegetation.Urbanization eliminated 10 million ha of agricultural and forested land in theUnited States between 1960 and 1980 (Alig and Healy 1987). It is estimated that80% of the U.S. population will live in urban areas by the year 2025, up from 74%in 1986 (Alig and Healy 1987). Urban areas account for less than 1% of the totalterrestrial life zones. The total amount of land dedicated to urban uses was26 million hectares in 1992 (World Resource 1996).

Soil carbon densities for urban soils are relatively high compared to other biometypes, higher than temperate forest soils, and comparable to wet boreal forest(17.5 and 23.7 kg/m2, Pouyat, personal communication). Data suggest that longterm urban forests soils may store more carbon than in rural forest soils with lesslabile carbon and greater passive carbon pools (Groffman et. al. 1995).

Urban forests are unique as they perform the dual function of directlysequestering atmospheric carbon and by indirectly conserving energy use ofstructures through shading, reducing the “heat island effect” by transpirationalcooling, and reducing turbulent transfer losses. It was estimated that planting10 million urban trees annually over the next 10 years would sequester and offsetthe production of 363 million tons of carbon over the next 50 years, with 20% dueto direct carbon sequestration and 80% due to avoided carbon emission fromenergy conservation under optimal tree location. The total sequestration andenergy offset of carbon reduction under this scenario is less than 1% of thecarbon emissions projected for the United States over the same 50 year period(Nowak 1995).

Strategies

Urban forest planning and management to direct urban forest structure to desiredoutcome of increasing forest cover, increase rate of carbon capture, and long-termmaintenance of standing stock within space and land-use limitations.

Sustain or enhance existing tree health to maximize sequestration whileminimizing losses due to tree mortality (hold on to existing carbon).



Establish properly selected and located urban trees in available planting areas.Planning to maximize building energy conservation will yield greatest relativecarbon benefit.

ObjectivesAboveground1. Increase and maintain area of urban and suburban forested areas2. Maximize biomass accumulation within space and land use limitations3. Minimize mortality losses under multiple stress conditions within urban

environment4. Increase net carbon retention in maintenance (pruning), landfill (disposal),

and recycling (leaf and chipping) practices.

R&D needsAboveground

Identify and select tree species and genotypes, for the urban and suburbanenvironment that meets objectives of increasing sequestering carbon andreducing emissions.

Evaluate physiological responses and carbon allocation of urban trees and shrubsto those in rural environments. Urban trees are exposed to elevated CO2 andtemperature gradients within an urban-suburban environment as well asmultiple stress interaction with ozone and atmospheric deposition of nitrogen andsulfur compounds.

Identify policy and management issues that would lead to preserving existingurban forests and increasing tree planting: energy conservation, economicdevelopment, natural resources planning, social-economic values.

Full life-cycle analysis on carbon budget of urban and suburban forests toincrease carbon sequestration and reduce emissions. Trees in the urbanenvironment require greater energy inputs in establishment, maintenance anddisposal (fertilizer, site prep, pruning, leaf litter, chipping, transport and disposal).Trees offset energy use by energy conservation on buildings through shading,reduction of heat island effect, and turbulent transfer losses.

ObjectivesBelowground1. Increase and maintain urban and suburban forest cover2. Increase soil carbon densities3. Employ planning and management practices to minimize soil, litter

disturbance and maximize soil carbon retention

R&D needsBelowground

Will urban land uses result in greater soil carbon storage? Soil carbon densitiesfor urban soils are relatively high compared to other biome types. Long term urbanforests soils may store more carbon than in rural forest soils.



Determine litter quality changes and soil decomposition rates in the urbanenvironment. The urban environment receives elevated chemical andatmospheric inputs. This can produce changes in litter quality by air pollution(ozone) or exotic plant species. Temperature increases in the urban environmentand greater nitrogen deposition will increase decomposition rates. Heavy metaland air pollution damage to plant tissue should decrease decomposition rates.Changes in microbial and soil invertebrate composition across urban to ruralenvironments may change rates of decomposition.

Develop urban land use management practices to increase soil carbon.Management practices, such as irrigation and fertilization make up for sitelimitations restricting plant and root growth.

Investigate effects of drastic soil disturbances that occur in urban areas on soilcarbon

Links to other ecosystems:

1. Determine the net conversion of land use (i.e., agricultural and forested landsto suburban and urban forested lands).

2. Determine extent of urban land uses in other vegetation life zones (e.g.,coastal areas, wetlands conversion to urban and suburban use).

References

Alig, R. J. and R. G. Healy. 1987. Urban and built-up land area changes in theUnited States: An empirical investigation of determinants. Land Economics:63:215–226.

Birdsey, R. A. 1992. Carbon storage and accumulation in U.S. forest ecosystems.Gen. Tech. Rep. WO-59. Washington, DC: USDA, Forest Service. 51 p.

Groffman, P. M., R. V. Pouyat, M. J. McDonnell, S. T. A. Pickett, and W. C. Zipper.1995. Carbon pools and trace gas fluxes in urban forest soils. In: Lal, R.,Kimble, J., Levine, E., Stewart, B. A. eds. Advances in soil science:SoilManagement and Greenhouse Effect. Boca Raton, FL: CRC press 147–158.

Nowak, D. J. 1995. Atmospheric carbon dioxide reduction by Chicago’s urbanforests. In: Chicago’s urban forest ecosystem: results of the Chicago UrbanForest climate Project. Gen. Tech. Rep. NE-186. Radnor, PA USDA, ForestService, Northeastern Forest Experiment Station:83–94.

World Resources Institute. World Resources (Oxford University Press, New York,1996).



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