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Download Nutrient Cycles in Ecosystems
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Nutrient Cycles in Ecosystems 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 Main nutrient reservoirs in the environment fraction of nutrient available to ecosystem geochemical cycle primary producers herbivores, carnivores, parasites detritivores, decomposers Fig. 47-14, p.852 Three Categories Hydrologic cycle Water Atmospheric Nitrogen and carbon Sedimentary cycles cycles Phosphorus and sulfur Hydrologic Cycle Atmosphere wind-driven water vapor 40,000 evaporation precipitation from ocean into ocean 425,000 385,000 precipitation onto land 111,000 evaporation from land plants (evapotranspiration) 71,000 surface and groundwater flow 40,000 Ocean Land Figure 47-15 Page 853 EVAPORATION PRECIPITATION TRANSPIRATION interception by plants dripping, trickling down along stems falling through to ground surface pooling, etc. infiltration of soil moisture in soil overland flow lateral flow seepage, percolation groundwater storage DEEP OUTFLOW base flow STREAM OUTFLOW Fig. 47-16, p.853 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 Fig. 47-18, p.855 Negative Effects of Irrigation Salinization, Elevation mineral buildup in soil of the water table and waterlogging Depletion of aquifers Aquifer Problems Figure 47-19 Page 855 Carbon Cycle Carbon moves through the atmosphere and food webs on its way to and from the ocean, sediments, and rocks Sediments reservoir and rocks are the main diffusion between atmosphere and ocean bicarbonate and carbonate in ocean water photosynthesis combustion of fossil fuels aerobic respiration marine food webs death, incorporation sedimentation into sediments uplifting sedimentation marine sediments Carbon Cycle - Marine Figure 47-20 Page 856 atmosphere combustion of fossil fuels volcanic action terrestrial rocks weathering photosynthesis aerobic combustion respiration of wood sedimentation land food webs soil water leaching, runoff death, burial, compaction over geologic time Carbon Cycle - Land peat, fossil fuels Figure 47-20 Page 856 Carbon in the Oceans Most carbon in the ocean is dissolved carbonate and bicarbonate Ocean currents carry dissolved carbon 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 Nitrogen Cycle Nitrogen is used in amino acids and nucleic acids Main reservoir is nitrogen gas in the atmosphere Nitrogen Cycle gaseous nitrogen (N2) in atmosphere nitrogen fixation by industry food webs on land uptake by excretion, death, uptake by fertilizers autotrophs decomposition autotrophs nitrogen fixation NH3-,NH4+ in soil leaching nitrogenous wastes, remains NO3in soil dentrification ammonification 2. Nitrification 1. Nitrification NO2in soil leaching Figure 47-25 Page 860 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 Ammonification & Nitrification Bacteria and fungi carry out ammonification conversion of nitrogenous wastes to ammonia Nitrifying bacteria convert ammonium to nitrites and nitrates 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 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 mining fertilizer guano excretion uptake by agriculture autotrophs uptake by weathering producers marine food webs dissolved in seawater leaching, runoff death, decomposition sedimentation land food webs death, decomposition settling out marine sediments dissolved in soil water, lakes, rivers weathering uplifting over geologic time terrestrial rocks Phosphorus cycle Fig. 47-27, p.862 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 Phosphorus Cycle mining FERTILIZER GUANO excretion agriculture uptake by autotrophs MARINE FOOD WEBS weathering DISSOLVED IN OCEAN WATER uptake by autotrophs weathering DISSOLVED IN SOILWATER, LAKES, RIVERS death, decomposition sedimentation LAND FOOD WEBS death, decomposition settling out leaching, runoff uplifting TERRESTRIAL ROCKS MARINE SEDIMENTS over geologic time Figure 47-27, Page 862 Human Effects In tropical countries, clearing lands for agriculture may deplete phosphoruspoor soils In developed countries, phosphorus runoff is causing eutrophication of waterways
