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Guide 34 Ecosystem Ecology: Energy Flow and Nutrient Cycles tp://www.mordantorange.com/blog/archives/comics_by_mike_bannon/mordant_singles/0511/ • Overview: Ecosystems, Energy, and Matter • An ecosystem consists of all the organisms living in a community – As well as all the abiotic factors with which they interact Regardless of an ecosystem’s size Its dynamics involve two main processes: energy flow and chemical cycling Energy flows through ecosystems While matter cycles within them • Energy flows through an ecosystem – Entering as light and exiting as heat Tertiary consumers Microorganisms and other detritivores Detritus Secondary consumers Primary consumers Primary producers Heat Key Chemical cycling Energy flow Sun Material (Chemical) cycling in the environment involves TRANSFORMATION In the water cycle it is Transformation of State – gas-liquid-solid In chemical cycles (C, N, P, S) it is Transformation in Redox State http://www.wou.edu/las/physci/GS361/Energy_From_Fossil_Fuels.htm The major Chemical Transformations in the Environment are carried out by microorganisms – and on a global scale, very large amounts are transformed every year. Recent increases in anthropogenic N fixation in relation to “natural” N fixation. Modified from Vitousek, P. M. and P. A. Matson (1993) 1 Tg = 1 X 109 kg Microorganisms can make a “living” off of the energy available in the Electron Tower A General Model of Chemical Cycling • All elements – Cycle between organic and inorganic reservoirs • Gaseous forms of carbon, oxygen, sulfur, and nitrogen – Occur in the atmosphere and cycle globally • Less mobile elements, including phosphorous, potassium, and calcium – Cycle on a more local level • The carbon cycle – Reflects the reciprocal processes of photosynthesis and cellular respiration Decomposition and Nutrient Cycling Rates • Decomposers (detritivores) play a key role – In the general pattern of chemical cycling Consumers Producers Decomposers Nutrients available to producers Abiotic reservoir Geologic processes GtC – Giga Tons Carbon - One Billion Tons of Carbon In considering material flow through an environment Two Factors need to be considered: Pool Size (Compartment Size) BOXES Flux – gain or loss to the pool over some period of time ARROWS Gm N per day N in plants Kg/ha • Net primary production (NPP) – Is equal to Gross primary Production (GPP) minus the energy used by the primary producers for respiration • Only NPP – Is available to consumers • Different ecosystems vary considerably in their net primary production – And in their contribution to the total NPP on Earth Open ocean 125 65.0 Continental shelf 5.2 Estuary 24.4 360 5.6 1,500 0.3 Algal beds and reefs 0.1 Upwelling zones 0.1 2,500 4.7 3.0 Desert and semidesert scrub 3.5 3.3 90 Savanna 2.9 Cultivated land 2.7 Boreal forest (taiga) 2.4 Temperate grassland 1.8 Woodland and shrubland 1.7 Tundra Tropical seasonal forest 1.5 1.3 Temperate evergreen forest 1.0 Swamp and marsh 0.4 Lake and stream 0.4 0 10 0.1 0.04 0.9 2,200 22 900 7.9 9.1 600 9.6 800 600 5.4 700 1.6 Temperate deciduous forest 0.9 500 Extreme desert, rock, sand, ice Tropical rain forest 1.2 3.5 0.6 140 1,600 7.1 1,200 1,300 4.9 3.8 2,000 2.3 250 20 30 40 50 60 0 500 1,000 1,500 2,000 2,500 0.3 0 Key Marine Terrestrial Freshwater (on continents) (a) Percentage of Earth’s surface area (b) Average net primary production (g/m2/yr) (c) 5 10 15 20 Percentage of Earth’s net primary production 25 • Overall, terrestrial ecosystems – Contribute about two-thirds of global NPP and marine ecosystems about one-third North Pole 60N 30N Equator 30S 60S South Pole 180 120W 60W 0 60E 120E 180 Trophic Relationships • Energy and nutrients pass from primary producers (autotrophs) – To primary consumers (herbivores) and then to secondary consumers (carnivores) Trophic Efficiency and Ecological Pyramids • Trophic efficiency – Is the percentage of production transferred from one trophic level to the next – Usually ranges from 5% to 20% Pyramids of Production • This loss of energy with each transfer in a food chain – Can be represented by a pyramid of net production Tertiary consumers Secondary consumers Primary consumers Primary producers 10 J 100 J 1,000 J 10,000 J 1,000,000 J of sunlight • The dynamics of energy flow through ecosystems – Have important implications for the human population • Eating meat – Is a relatively inefficient way of tapping photosynthetic production • Worldwide agriculture could successfully feed many more people – If humans all fed more efficiently, eating only plant material Trophic level Secondary consumers Primary consumers Primary producers Food webs: complexes of feeding relationships A food web refers to all the trophic (feeding) connections among species within a community. http://www.sltec.com.au/sltec/products_liqfert_sustain_n_gro.html Biogeochemical Cycles THE CARBON CYCLE THE WATER CYCLE CO2 in atmosphere Transport over land Photosynthesis Solar energy Cellular respiration Net movement of water vapor by wind Precipitation over ocean Evaporation from ocean Precipitation over land Burning of fossil fuels and wood Evapotranspiration from land Percolation through soil Runoff and groundwater Carbon compounds in water Higher-level Primary consumers consumers Detritus Decomposition • Water moves in a global cycle – Driven by solar energy Water Movement is a major force in Geological Change Wadi Zin The nitrogen cycle and the phosphorous cycle THE PHOSPHORUS CYCLE THE NITROGEN CYCLE N2 in atmosphere Rain Geologic uplift Runoff Assimilation NO3 Nitrogen-fixing bacteria in root nodules of legumes Plants Weathering of rocks Denitrifying bacteria Consumption Sedimentation Decomposers Ammonification NH3 Nitrogen-fixing soil bacteria Nitrifying bacteria Nitrification Soil Plant uptake of PO43 Leaching NO2 NH4+ Nitrifying bacteria Decomposition http://www.mpi-bremen.de/Binaries/Binary135/figone.jpg Nitrogen Cycle http://www.physicalgeography.net/fundamentals/images/nitrogencycle.jpg The sulfur cycle http://www.scienceclarified.com/Oi-Ph/Oxygen-Family.html http://www.fos.su.se/~magnuss/SinNature.png The End
