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Biol 121- 2010.01.20- Ecology- Community Ecology- Biogeochemical Cycles. Human Impact (Ch. 54).docx

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BIOL 121
Carol Pollock

Biol 121 225 Freeman 123042Jan 20 10 Biogeochemical cycle energy is not the only thing transferred in a food webchain ingested matter also contain carbon nitrogen phosphorus calcium and other elements that act as nutrients atoms are constantly reused as they cycle through trophic levels and air water and soil path element takes as it moves from abiotic systems through organisms biotic and back again is the biogeochemical lifeEarthchemical cyclehumans disturb biogeochemical cycles on massive scale so research is exploding What kinds of questions are posed 1 What are the nature and size of the reservoirs or areas where elements are about biogeochemical cycles stored for a period of timeeg C is stored in biomass of organisms also sediments soils coal and oil2 How fast does the element move between reservoirs and what factors influence these rates3 How does a biogeochemical cycle interact with other cycles General terrestrial nutrient cycle cycle starts when nutrients taken up from soil by plants and assimilated into plant tissue if plant eaten nutrients pass to animal members of ecosystems consumer food web if plant dies then nutrients enter decomposer food web once consumed by animal nutrients excreted and taken up by parasite or predator or added to the dead biomass reservoir when the animal dies nutrients in plant litter animal excretions dead bodies are used by primary composers like bacteria the combo of microscopic decomposers and ionsmcules released form the soil organic matter soil organic matter is a complex mixture of partially and completely decomposed detritus completely decayed organic material is humus bc it is rich in family of Ccontaining mcules called humic acids eventually nutrients in soil organic matter converted to an inorganic form eg cell resp by bacteria converts nitrogen in AA found in detritus to NH4 and NO3 ionsnutrients are available for uptake by plants Reuse of nutrients in the general terrestrial nutrient cycle described above nutrients are reusedhowever reuse is not complete nutrients leave ecosystem whenever plantanimal biomass leaves eg plant biomass is removed if herbivore enters ecosystem eats plant and migrates out of ecosystem before excreting nutrients or dying also flowing water or wind removes particlesinorganic ions to deposit somewhere else soil erosion removes nutrients rapidly and in potentially large quantities What are factors of rate of nutrient decomposition of detritus most often limits overall rate at which nutrients move cycling through ecosystem until decomp occurs nutrients stay tied up in intact tissuesdecomposition rate in turn is influenced by two types of factors abiotic conditions T ppt and quality of the detritus as a nutrient source for the decomposers
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