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BILD 3 July 21, 2010 Woodruff: biogeochemical cycles 1 BIOGEOCHEMICAL CYCLES SUN P H C NUTRIENT --------------- DECOMPOSERS POOL (reservoir) ATMOSPHERE SOIL LITHOSPHERE OCEANS Biogeochemical Cycles In studying cycling of water, carbon, nitrogen, and phosphorus, ecologists focus on five factors: 1. Each chemical’s biological importance 2. Forms in which each chemical is available or used by organisms 3. Major reservoirs for each chemical 4. Key processes driving movement of each chemical through its cycle 5. The living organisms responsible for key links in the cycle Fig. 55-14a Precipitation over land Transport over land Solar energy Net movement of water vapor by wind Evaporation from ocean Percolation through soil Evapotranspiration from land Runoff and groundwater Precipitation over ocean WATER CYCLE ATMOSPHERE 0.001% WATER CYCLE Approx. 500 g water are transpired for each gram of terrestrial primary productivity (>10 17 g/yr). Transpiration therefore accounts for 93% of terrestrial evapotranspiration Total precipitation: 378 x 10 18 g/yr Atmospheric pool: 13 x 10 18 g/yr Therefore water in atmospheric pool recycles 29 times/year (11-14 days) Fig. 55-14b Higher-level consumers Primary consumers Detritus Burning of fossil fuels and wood Phyto- plankton Cellular respiration Photo- synthesis Photosynthesis Carbon compounds in water Decomposition CO 2 in atmosphere CARBON CYCLE ATMOSPHERE 0.03% CARBON CYCLE Transit time of atmospheric C is approx 8 years CO 2 absorbs or reflects long wavelength infrared light It does not absorb or reflect the longer wave lengths entering the atmosphere but it does reflect back to earth the infrared radiant energy emanating from the surface of the sunlit earth. This energy warms the air. More atmospheric CO 2 will trap more energy and cause more warming. This is the so-called Greenhouse Effect.
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BILD 3 July 21, 2010 Woodruff: biogeochemical cycles 2 CARBON CYCLE For most of the •last million years CO 2 has varied between 200-240 ppm •the last 10,000 years it has varied between 260-280 ppm Since 1750 fossil fuel use & deforestation has increased atmospheric CO 2 >38% to 387 ppm and will double by 2100 LE 54-17c Assimilation N 2 in atmosphere Decomposers Nitrifying bacteria Nitrifying bacteria Nitrogen-fixing soil bacteria Denitrifying bacteria Nitrification Ammonification Nitrogen-fixing bacteria in root nodules of legumes NO 3 NO 2 NH 4 + NH 3 TERRESTRIAL NITROGEN CYCLE ATMOSPHERE 78% N 2 DENITRIFICATION NITROGEN (5) FIXATION (4) NO 3 - ORGANIC NITRIFICATION NH 2 - (3) NO 2 - UREA DECOMPOSITION
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