Area IIE: The Living World Natural Biogeochemical Cycles

Biogeochemical Cycles Biogeochemical cycles: how nutrients cycle through biotic and abiotic components of ecosystems  involve soil, atmosphere, and organisms  examples: C and N cycles

Fig Hydrologic cycle Precipitation to land Transpiration from plants Runoff Surface runoff (rapid) Evaporation from land Evaporation from ocean Precipitation to ocean Ocean storage Surface runoff (rapid) Groundwater movement (slow) Rain clouds Condensation Transpiration Evaporation Precipitation Infiltration and Percolation

4-7 Matter Cycling in Ecosystems Water cycles chemically unchanged  natural renewal of water quality  human interference  1. we use of large amounts of fresh water  2. we increase runoff  3. we modify water quality  4. we are speeding the water cycle (?) by increasing global temperatures (?)

Water cycle

Diffusion between atmosphere and ocean Carbon dioxide dissolved in ocean water Marine food webs Producers, consumers, decomposers, detritivores Marine sediments, including formations with fossil fuels Combustion of fossil fuels incorporatio n into sediments death, sedimentation uplifting over geologic time sedimentation photosynthesi s aerobic respiration Fig. 4-29a Carbon cycle

Figure 4-29b Carbon cycle photosynthesis aerobic respiration Terrestrial rocks Soil water (dissolved carbon) Land food webs producers, consumers, decomposers, detritivores Atmosphere (most carbon is in carbon dioxide) Peat, fossil fuels combustion of wood (for clearing land; or for fuel sedimentation volcanic action death, burial, compaction over geologic time leaching runoff weathering Combustion of fossil fuels

Biogeochemical Cycles The carbon cycle is based on CO 2 in the atmosphere  CO 2 in atmosphere  plants make organic matter through photosynthesis  autotrophs and heterotrophs use organic matter through respiration and release CO 2  if respiration exceeds photosynthesis, CO 2 increases: greenhouse effect  human interference  1. we clear trees and plants  2. we add large amounts of CO 2 to atmosphere

Carbon cycle

Fig Human interference in C cycle Year CO 2 emissions from fossil fuel (billion metric tons of carbon equivalent) 1 High projection Low projection

Fig Nitrogen cycle NO 3 – in soil Nitrogen Fixation by industry for agriculture Fertilizers Food Webs On Land NH 3, NH 4 + in soil 1. Nitrification bacteria convert NH 4 + to nitrate (NO 2 – ) loss by leaching uptake by autotrophs excretion, death, decomposition uptake by autotrophs Nitrogen Fixation bacteria convert N 2 to ammonia (NH 3 ) ; this dissolves to form ammonium (NH 4 + ) loss by leaching Ammonification bacteria, fungi convert the residues to NH 3, this dissolves to form NH Nitrification bacteria convert NO 2 - to nitrate (NO 3 - ) Denitrification by bacteria Nitrogenous Wastes, Remains In Soil Gaseous Nitrogen (N 2 ) in Atmosphere NO 2 – in soil © 2004 Brooks/Cole – Thomson Learning

Biogeochemical Cycles The nitrogen cycle depends largely on bacteria  N 2  NH 3  NO 2 - and NO 3 - ammonia nitrite nitrate  human interference  1. we add NO to the air when we burn fuel it can become NO 2 and then HNO 3, causing acid rain  2. we add N 2 O to the atmosphere indirectly through the action of bacteria on livestock waste and fertilizers

Biogeochemical Cycles  human interference, cont.  3. we release nitrogen stored in soils and plants into atmosphere by removing trees  4. we upset aquatic ecosystems by adding excess nitrates in agricultural runoff and sewage systems  5. remove nitrogen from topsoil when harvesting, irrigating, or burn or clear grasslands or crops  6. we are affecting biodiversity

Fig Human interference in N cycle Global nitrogen (N) fixation (trillion grams) Year Nitrogen fixation by natural processes

Nitrogen cycle

Fig Phosphorus cycle GUANO FERTILIZER ROCKS LAND FOOD WEBS DISSOLVED IN OCEAN WATER MARINE FOOD WEBS MARINE SEDIMENTS weathering agriculture uptake by autotrophs death, decomposition sedimentation settling out weathering leaching, runoff DISSOLVED IN SOIL WATER, LAKES, RIVERS uptake by autotrophs death, decomposition mining excretion uplifting over geologic time

Biogeochemical Cycles The phosphorus cycle does not move through the atmosphere  human interference  1. we mine phosphate rock to make fertilizer  2. we reduce phosphate availability in tropics by cutting tropical forests  3. we add phosphates to runoff and disrupt aquatic systems

Phosphorus cycle

Fig Sulfur cycle Sulfur Hydrogen sulfide Sulfate salts Plants Acidic fog and precipitation Ammonium sulfate Animals Decaying matter Metallic sulfide deposits Ocean Dimethyl sulfide Sulfur dioxide Hydrogen sulfide Sulfur trioxide Sulfuric acid Water Ammonia Oxygen Volcano Industries

Biogeochemical Cycles The sulfur cycle  human interference  we add sulfur dioxide (SO 2 ) to the atmosphere by:  1. burning coal and oil to generate electricity  2. refining oil to make gasoline and other petroleum products  3. converting sulfur-containing ores into free metals