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Nutrient Cycles in Ecosystems
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Biogeochemical Cycle The flow of a nutrient from the environment to living organisms and back to the environment Main reservoir for the nutrient is in the environment
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geochemical cycle Fig. 47-14, p.852
Main nutrient reservoirs in the environment geochemical cycle fraction of nutrient available to ecosystem herbivores, carnivores, parasites primary producers detritivores, decomposers Fig , p.852
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Three Categories Hydrologic cycle Atmospheric cycles
Water Atmospheric cycles Nitrogen and carbon Sedimentary cycles Phosphorus and sulfur
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Hydrologic Cycle Atmosphere precipitation onto land 111,000
wind-driven water vapor 40,000 evaporation from ocean 425,000 precipitation into ocean 385,000 evaporation from land plants (evapotranspiration) 71,000 surface and groundwater flow 40,000 Ocean Land Figure 47-15 Page 853
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EVAPORATION PRECIPITATION TRANSPIRATION interception by plants dripping, trickling down along stems falling through to ground surface pooling, etc. infiltration of soil overland flow moisture in soil lateral flow seepage, percolation groundwater storage base flow DEEP OUTFLOW STREAM OUTFLOW Fig , p.853
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Water Use and Scarcity Most of Earth’s water is too salty for human consumption Desalinization is expensive and requires large energy inputs Irrigation of crops is the main use of freshwater
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Fig , p.855
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Negative Effects of Irrigation
Salinization, mineral buildup in soil Elevation of the water table and waterlogging Depletion of aquifers
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Aquifer Problems Figure 47-19 Page 855
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Carbon Cycle Carbon moves through the atmosphere and food webs on its way to and from the ocean, sediments, and rocks Sediments and rocks are the main reservoir
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bicarbonate and carbonate in ocean water
diffusion between atmosphere and ocean combustion of fossil fuels bicarbonate and carbonate in ocean water photosynthesis aerobic respiration marine food webs death, sedimentation incorporation into sediments uplifting sedimentation marine sediments Carbon Cycle - Marine Figure 47-20 Page 856
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combustion of fossil fuels
atmosphere volcanic action combustion of fossil fuels photosynthesis aerobic respiration combustion of wood terrestrial rocks sedimentation weathering land food webs soil water peat, fossil fuels death, burial, compaction over geologic time leaching, runoff Carbon Cycle - Land Figure 47-20 Page 856
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Carbon in the Oceans Most carbon in the ocean is dissolved carbonate and bicarbonate Ocean currents carry dissolved carbon
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Carbon in Atmosphere Atmospheric carbon is mainly carbon dioxide
Carbon dioxide is added to atmosphere Aerobic respiration, volcanic action, burning fossil fuels Removed by photosynthesis
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Nitrogen Cycle Nitrogen is used in amino acids and nucleic acids
Main reservoir is nitrogen gas in the atmosphere
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excretion, death, decomposition nitrogenous wastes, remains
Nitrogen Cycle gaseous nitrogen (N2) in atmosphere nitrogen fixation by industry food webs on land uptake by autotrophs excretion, death, decomposition uptake by autotrophs fertilizers nitrogenous wastes, remains NO3- in soil nitrogen fixation dentrification NH3-,NH4+ in soil ammonification 2. Nitrification NO2- in soil leaching 1. Nitrification leaching Figure 47-25 Page 860
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Nitrogen Fixation Plants cannot use nitrogen gas
Nitrogen-fixing bacteria convert nitrogen gas into ammonia (NH3) Ammonia and ammonium can be taken up by plants
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Ammonification & Nitrification
Bacteria and fungi carry out ammonification conversion of nitrogenous wastes to ammonia Nitrifying bacteria convert ammonium to nitrites and nitrates
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Nitrogen Loss Nitrogen is often a limiting factor in ecosystems
Nitrogen is lost from soils via leaching and runoff Denitrifying bacteria convert nitrates and nitrites to nitrogen gas
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Human Effects Humans increase rate of nitrogen loss by clearing forests and grasslands Humans increase nitrogen in water and air by using fertilizers and by burning fossil fuels Too much or too little nitrogen can compromise plant health
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dissolved in soil water, lakes, rivers uplifting over geologic time
mining fertilizer excretion guano agriculture uptake by autotrophs uptake by producers weathering leaching, runoff dissolved in soil water, lakes, rivers marine food webs dissolved in seawater land food webs death, decomposition death, decomposition sedimentation settling out weathering uplifting over geologic time terrestrial rocks marine sediments Phosphorus cycle Fig , p.862
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Phosphorus Cycle Phosphorus is part of phospholipids and all nucleotides It is the most prevalent limiting factor in ecosystems Main reservoir is Earth’s crust; no gaseous phase
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DISSOLVED IN OCEAN WATER DISSOLVED IN SOILWATER, LAKES, RIVERS
Phosphorus Cycle GUANO FERTILIZER TERRESTRIAL ROCKS LAND FOOD WEBS DISSOLVED IN OCEAN WATER MARINE FOOD WEBS MARINE SEDIMENTS excretion weathering mining agriculture uptake by autotrophs death, decomposition sedimentation settling out leaching, runoff uplifting over geologic time DISSOLVED IN SOILWATER, LAKES, RIVERS Figure 47-27, Page 862
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Human Effects In tropical countries, clearing lands for agriculture may deplete phosphorus-poor soils In developed countries, phosphorus runoff is causing eutrophication of waterways
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