The Flux of Energy & Matter through Ecosystems • These fluxes tie biological communities to the abiotic environment; both together are called ecosystems • Biomass is the standing crop of living organisms and is expressed as dry matter (kg) per unit area (or energy (joules)/area in case of energy flow) • Primary productivity (PP): rate at which biomass is produced • Net primary productivity (NPP): energy produced by plants minus energy lost as as community respiratory heat • Secondary productivity: rate of biomass production by heterotrophs (non-autotrophs or non-plants)
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The Flux of Energy & Matter through Ecosystems These fluxes tie biological communities to the abiotic environment; both together are called ecosystems.
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The Flux of Energy & Matter through Ecosystems
• These fluxes tie biological communities to the abiotic environment; both together are called ecosystems
• Biomass is the standing crop of living organisms and is expressed as dry matter (kg) per unit area (or energy (joules)/area in case of energy flow)
• Primary productivity (PP): rate at which biomass is produced
• Net primary productivity (NPP): energy produced by plants minus energy lost as as community respiratory heat
• Secondary productivity: rate of biomass production by heterotrophs (non-autotrophs or non-plants)
Total NPP summed for each of the Earth’s biomes- tropical rain forests & savannas highest- marine & terrestrial totals similar
Net PP from the biomass of different ecosystems- higher productivity for aquatic & non-forest for given biomass
Ultimately, the functioning and nature of biological communities depends on plant productivity
Plant net productivity varies with latitude- forests:boreal: 1025 gC/m2/yr temperate: 1400 gC/m2/yr tropical: >3000 gC/m2/yr
a) grasslands & tundra b) cultivated crops c) lakes
These relationships suggest that temperature & radiation limit NPP
What limits Primary Productivity?- for terrestrial communities, 4 possible resources and a condition (temperature)
1) Radiation from the sun …. not usually a limiting factor
Photosynthetic efficiency maxes out at only 1-3% of available radiation
…..although under optimal conditions, crop plants may achieve 3-10%
2) Carbon dioxide Some communities respond
to global increases in CO2 …..but concentration similar around earth, so can’t explain differences
….
3) Rainfall & 4) Temperature are critical factors that commonly limit primary productivitya) savannas (global sample) b) all ecosystems (Tibetan plateau)
5) Mineral nutrients (N & P especially, sometimes micronutrients) are often limiting factors where rainfall abundant
--- fertilization works!
-*limiting factors change seasonally in most ecosystems
- length of growing season & temp/water
NA broadleaf forests: Sandy soils are water- & N-limited
Aquatic systems
Mineral nutrients commonly limit production in aquatic ecosystems phytoplankton in Canadian lakes
upwelling zone (nutrient-rich)-shading effect
nutrient-poor marine area
b&c: Namibia ocean phytoplankton
Net PP rises, then declines during succession
- early successional pine vs. late successional fir
Managing a forest forCarbon sequestration?
Not surprisingly, secondary productivity is positively related to primary productivitya) zooplankton in lakes b) bacteria in water
c) Caterpillars on Daphne Island, Galapagos
Transfer efficiencies- only 10% of PP is converted in aquatic & terrestrial systems
1) Much primary productivity is not consumed by grazers and supports the decomposer community
CE= consumption efficiency
2) Not all consumed biomass is assimilated into consumer biomass
AE= assimilation efficiency
3) Some assimilated biomass is converted and lost as respiratory heat
PE= production efficiency
Trophic transfer efficiency (=CE x AE x PE) varies tremendously between trophic levels and communities (e.g., variation in 48 studies of TTE in aquatic communities)
General patterns of energy flow for different communities: - note major distinctions in % NPP flows to consumers vs. decomposers- plankton: “live consumer community”; terrestrial: low consumption
Dramatic differences in % NPP consumed by herbivoresvs. channeled into dead organic matter (DOM)
The Process of Decomposition
• release of energy and the mineralization of chemical nutrients (conversion of elements from organic back into inorganic form)
• gradual disintegration of dead bodies & other organic matter through biological and physical agents
• finally, breakdown into CO2, H2O & inorganic nutrients by consumers of dead organic matter
Flux of matter through ecosystems: Pools of chemical elements in atmosphere, lithosphere (rocks) & hydrosphere (water)
Biogeochemistry: Study of fluxes of elements between these three compartments Components of nutrient budgets of a terrestrial & aquatic system linked by streamflow
Annual carbon budget for a ponderosa pine (Oregon)
tree rootslitter
soil carbon
Respiratory heat loss From herbivores
Units: gC/m2 & gC/m2/yr
Pathways of carbon in the ocean
All water bodies receive inputs from land, so human activities critical
- vast amounts of methane ice trapped in continental shelf sediments (19x damaging re CO2 greenhouse gas)
- small & large phytoplankton most important
Global Biogeochemical Cycles: nutrients move
around globe by winds and water -the hydrological cycle showing fluxes & reservoirs of water(volumes in 106 km3)
Read about the major reservoirs & fluxes for these four key nutrient elements
Lowlights of Pollution
• Pollution: contamination of environment by human waste and by unwanted products of human activities
• Homo sapiens unique in:– using fire, fossil fuels and nuclear fission to do work & transform
landscapes
– mine, smelt & transform metals
– create new chemicals
– alter atmosphere and climate on large scale
• Our focus: pollution of natural systems
• Note that other courses deal with these issues in detail
Effect of 1947 DDT pesticide introduction on wild bird eggshell thicknesssome peregrine falcon populations dropped to 10% of former size; others went extinct
-Sparrowhawk eggshell thickness index -Correlated with DDT use
Environmental Economics: valuation of ecosystem services and net loss from human activities
1) Provisioning services
Wild foods, fibers, timber, water
2) Regulating services
Regulation of climate, floods, filtering of pollutants