Restoration of Heavily Oiled Tidal Flats and Salt Marshes ...

Restoration of Heavily Oiled Tidal Flats and Salt Marshes 18

Years After The Gulf War Oil Spill Linos Cotsapas

Jason Hale, Christopher Cormack, Thomas Minter, and Jacqueline Michel

Research Planning, Inc. and Pandion

Outline

• Introduction/Restoration Goals • Indicators of Stress • Remediation Activities • Results

The Event and The Program

• Largest marine spill in history • Less than 10% of estimated spill volume

recovered • UN-sponsored; KSA-implemented

program governed by UN-set guidelines

Guiding Principles • Decision 258 and F4 panel principles:

– Avoid techniques that pose unacceptable risks – Facilitate natural recovery to the extent possible – Rely on proven techniques – Utilize adaptive management – Be cost effective – Consider short- and long-term effects and

landscape connectivity – Result in more positive than negative results

The Approach

• Target “Ecological Restoration” • Methods must:

– Understand and characterize conditions and site

– Identify stressors – Design appropriate remediation activities – Test and monitor effects of remediation

activities – Adaptively manage

Heavily Impacted Tidal

Channels

Healthy Tidal Channels

Achieving Restoration Goals

• Promote ecological restoration in contrast to “removal of contaminants”

– Ecological structure, what we see – Ecological function, the “jobs” that are done

Achieving Restoration Goals

• Promote ecological restoration in contrast to “removal of contaminants”

• Ecological restoration and natural recovery – Remediation activities must promote or

accelerate rate of natural recovery – Remediation activities must conserve areas

exhibiting natural recovery

Achieving Restoration Goals

• Promote ecological restoration in contrast to “removal of contaminants”

• Ecological restoration and natural recovery • “Removal of contaminants” implies oil is

the principle stressor – But is this the case after 20 years?

Indicators of Stress • Ponding of upper marsh and channels at low tide • Widespread laminated algal mat • Widespread oil residues, surface and sub-surface • Tidal channel bank and bottom habitat degradation • Limited abundance and distribution of halophytes

(annual and perennial) • Limited abundance and distribution of key benthic

fauna

How to Speed up Recovery

• Build on proven methods and adaptively manage to local conditions

• Practical methods that are readily implementable

• Assess results and adapt

The Setting

Salt marshes and tidal flats: • Make up over 95%

of intertidal habitats between Jubail and Kuwait border

• Severely impacted by the spill

Salt Marshes–Remediation Objectives

• Re-establish tidal channel function • Eliminate ponding - promote drying of part

of marsh surface between tidal cycles • Reduce total petroleum hydrocarbon levels • Remove/till barriers • Provide improved channel bank and bottom

substrate

Salt Marshes – Techniques

• Channel excavation/refreshment • Tilling to break up algal mat and cohesive oiled

sediments • Removal/disposal of surface and cohesive

subsurface oiled layers • Microhabitat creation • Planting of marsh vegetation

Tidal Flats–Remediation Objectives

• Increase suitable habitat for grazers and burrowing infauna

• Reduce total petroleum hydrocarbon levels • Improve drainage and reduce ponding

between tidal cycles • Tilling to break up algal mat and cohesive

oiled sediments

Tidal Flats – Techniques

• “Dry” tilling of sediments followed by manual removal of remaining surface oil

• “Wet” tilling of sediments within constructed berms while flooded to liberate oil; and recovery by skimming/vacuuming

• Removal/disposal of surface and cohesive subsurface oiled layers

Excavation of Tidal Channels

• Routing always follows natural cues – Priority - existing channels in salt marsh

habitat – Additional “straight” channels added to areas

with persistent ponding during low tide and where density was below average

• Rules of connectivity determined stream order

• Fixed dimensions for channel types

After Excavation Before Excavation (line indicates location)

Excavation of Tidal Channels

Excavation of Tidal Channels

Channel Development

Channel Development

Point Bar Morphology

Point Bar Micro-Habitat

Pool Morphology

Microhabitat Creation

Mangrove Transplants

Tilling and Mixing

Wet Tilling

Oil Liberation and Removal

Results

Project Site Plan

Restoration Progress-Ecology

• Abundance and distribution of key benthic taxa that perform critical ecosystem functions:

– Grazing of microalgae substrate to keep channel bottom free from algal mat build-up

– Bioturbation for nutrient and carbon cycling; continued release/remediation of remaining residues

Restoration Progress-Ecology

Early Colonizers - Channel Bottom Habitat

• Grandidierella amphipod

Early Colonizers - Channel Bottom Habitat

• Grandidierella amphipod

• Potamides mud snail

• Polychaete and other benthic infauna

Nasima Burrowing Activity

Monitoring Results

• Robust monitoring program established measuring physical, chemical, and ecological variables

• Monitoring program data indicate that remediation methods have increased rate of ecological recovery in both salt marshes and tidal flats

Amphipods Snails

Nasima

South Channel North Channel

CRC1 Colonization – Two months post excavation

CRC1 Colonization – Five months post excavation

Amphipods Snails

Nasima

South Channel North Channel

CRC1 Colonization – 30 months post excavation

Amphipods Snails

Nasima

South Channel North Channel

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Average TPH Levels Before and After “Wet” Tilling

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Program Achievements • Excavated +160 km of existing and new tidal

channels • Tilled +300 ha of marsh and unvegetated tidal

flats • Off-site disposal of 110,000 m3 oil-contaminated

substrate • On-site re-use of 45,000 m3 of “No” or “low”

contaminated substrate as micro-habitat • Transplanted 105,000 mangroves • Remediated 1,800 ha of salt marsh and tidal flat

habitat

Conclusion Even after total devastation, with little if any natural recovery occurring 18 years after the spill, restoration of salt marshes and salt flats by re-establishing hydrological functioning and removal of physical barriers is possible with significant and quantifiable positive effects in the recovery of intertidal habitat functions