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

• These consumers are:– Decomposers (bacteria & fungi)– Microbivores (tiny animals feeding on detritus, bacteria & fungi– Detritivores (larger generalized feeders)

Organisms of the Terrestrial Decomposer Food Web:

- Classification by Size

- Invertebrate decomposers are very diverse

Plant decomposition depends on mutualisms for cellulose digestion with either gut microflora

(bacteria) or microfauna (protozoa in termite guts)

- Interactions between species are important and increase overall levels of decomposition, indicating some “facilitation”

(e.g., Alder leaf loss increased as more stonefly species participated)

Stoneflies are bioindicators of stream health

Consuming carrion & feces

- Carnivores scavenge & digest animal bodies with high efficiency (80%)

- Herbivore feces is less digestible but specialists recycle

isopods speed breakdown & recycling of caterpillar feces

African dung beetles were deliberated imported into Australia in 1963 to solve problem of massive accumulations of bovine feces or “cow pies”

- 300 million pies/day generated with loss of 2.5 million ha/yr under dung!

- now 20 spp introduced

Nutrient budgets• Weathering of rock & soil:

– source of calcium, magnesium, iron, phosphorus & potassium– uptake through roots

• Atmosphere– source of carbon– uptake through leaves (& stems) and fixed through photosymthesis

• Atmosphere– Source of nitrogen– Uptake through roots by N- converting bacteria & algae to ammonium ions

• Atmosphere: wetfall & dryfall– Trace gases (sulfur & nitrogen)– Aerosols: oceanic water droplets (chlorine, sodium, etc.)– Dust particles: fires, wind, volcanoes (many mineral elements)

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

3) Supporting services

Primary production, nutrient cycling, soil formation

4) Cultural services

Spiritual, esthetic fulfillment, scientific, recreational

Valuation of lost services: Indonesian forest fires of 1997: 50,000 km2 burned

1) Replacement cost

Lost forest and agricultural products, clean water, tourism income, health care from smoke pollution

Increased greenhouse gas emissions 2) Contingent valuation

Public willingness to pay for different forest use scenarios

Total estimated loss of 4.5 billion $$ from 1997 Indonesian fires

Costanza: 38 $trillion worldwide (1997)

…. So why doesn’t this lead to government investment in protecting ecosystem services?

Agricultural Pollution: runoff of nitrates, insecticides and herbicides (ex.: nitrate leaching from soils and fertilizer; Germany)

Agricultural Pollution: managing agricultural runoff by restoring wetlands

148 wetlands under construction in Sweden to capture 40% of N before entering Baltic Sea

Managing eutrophication through biomanipulation

Objective: reduce plankton bloom due to N & P runoff in Lake Mendota, Wisconsin

- 1987: introduced two piscivorous fish spp

- zooplankton increase as predatory fish reduced by piscivores

- Larger zooplankton species became dominant, efficiently grazing on phytoplankton and improving water clarity

Pesticide Pollution

Biomagnification of two classes of pesticides in the Barents Sea:chlordanes & PCBs

- transport to the Arctic is from river runoff, and oceanic and atmospheric circulation

- chlordanes are biomagnified

less than PCBs

The Mauna Loa Observatory data tracking CO2 & the earth’s seasonal respiration

(from 280 ppm to 380 today, to 700 by 2100?)

Fossil Fuels & the Atmosphere

Net change- Earth’s surface temperature: - extremes in temp & rainfall to increase- map of 1951 to 1997 changes in temp

Predicted changes in the distribution of the Argentine ant by 2050

Red= improved conditions, blue = worse

CO2 emissions are from fossil fuels in the temperate developed world, but more from deforestation & burning in the tropical/underdeveloped world