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  1. 1. Biogeochemical Cycles Vivek Srivasatava
  2. 2. Energy/Matter Flow • Energy and matter flow through the biosphere • Sun >> autotroph >> heterotroph >> fossil fuel storage >> human fuel consumption • Biosphere < > lithosphere < > atmosphere < > hydrosphere • Elements cycle through both the biological and geological world, hence biogeochemical cycles
  3. 3. Elemental Cycles • H, O, and C make up > 99 % of the Earth’s biomass • N, Ca, K, Mg, S, and P are significant nutrients • Cycling of C, O, N, P, and S are discussed in this chapter
  4. 4. Concepts in Biogeo. Cycles • • • • Reservoir - where material or mass is stored Flux: rate of flow of material Steady state: inflow = outflow Dynamic state: fluxes are reservoirs are changing with time • Residence time: length of time a chemical stays in a reservoir • Feedback: positive and negative
  5. 5. Reservoirs of Carbon • • • • • • Carbon is found in all four spheres Biosphere - organic matter Atmosphere - CO2, CH4 Hydrosphere - H2CO3 ,HCO3 - , CO3 = Lithosphere - CaCO3 , coal, oil, and gas Processes: photosynthesis, formation of sediments, weathering, combustion, plate tectonics
  6. 6. Carbon Cycle
  7. 7. Human Interference • Human-induced processes – Extraction and combustion of fossil fuels (speeds up the medium-term cycling) – Cement manufacturing – Deforestation (biomass burning) • All of these processes release CO2 into the atmosphere and affect the natural cycling of carbon
  8. 8. Oxygen Cycle • Essential for aerobic life • Closely linked to carbon cycle • Very large reservoir (20% of gas in atm.), not susceptible to human interference • Also, not a greenhouse gas • Reservoirs: atmosphere, surface organic material (biosphere), and buried organic matter (lithosphere)
  9. 9. Nitrogen Cycle • Essential to life - important in forming amino acids >> proteins • Most abundant in the atmosphere (79%) • Flows continuously through the spheres • Reservoirs: atmosphere and biosphere (soil) • Processes: Nitrogen fixation/ nitrification and denitrification • Atmosphere => soil => plants => atmosphere (fig. 5.7)
  10. 10. Nitrogen Cycle • Nitrification/ nitrogen fixation: converts N 2 to forms usable by plants (NH3, and NO3-) • Denitrification: is the conversion of NO 3back to N2 in the atmosphere or in gases in the soil • Symbiotic relationship: bacteria supply the plant with usable nitrogen and feed off the sugars and starches made by the plant
  11. 11. Nitrogen Cycle • Human activities account for >50% of nitrogen fixation (fertilizers, cultivation of nitrogen fixing plants) • Denitrification - done mainly by bacteria not by humans. • Despite the huge size of the atmospheric reservoir of nitrogen, human activites profoundly affect the nitrogen cycle
  12. 12. Nitrogen Cycle
  13. 13. Eutrophication • Consequence of excess nutrients (nitrates, phosphates) entering bodies of water • Produces algal blooms (over productivity) • When these algae die they settle at the bottom of the water column • Decomposition process consumes oxygen and depletes it from water • This destroys the organisms that need oxygen (fish)- Lions Lake, Warrensburg, source of nutrient - goose droppings
  14. 14. Phosphorus Cycle (Phosphorus is required for the manufacture of ATP and all nucleic acids) 1. Reservoir – erosion transfers phosphorus to water and soil; sediments and rocks that accumulate on ocean floors return to the surface as a result of uplifting by geological processes 2. Assimilation – plants absorb inorganic PO43(phosphate) from soils; animals obtain organic phosphorus when they plants and other animals 3. Release – plants and animals release phosphorus when they decompose; animals excrete phosphorus in their waste products
  15. 15. Phosphorus Cycle • Long-term cycle: Burial of phosphate in sediments => uplift => weathering => phosphate in soil or ocean • Residence time ~108 yrs • Extraction (mining) short-circuits the longterm cycle
  16. 16. Phosphorus Cycle • Reservoirs: Hydrosphere (as phosphate ion), lithosphere (phosphate minerals), and biosphere (bones, teeth, shells) • Short-term cycle: PO43- in soil or ocean => assimilation by plants => consumption by animals => decay or excretion => recycled to soil or ocean, residence time 100s of yrs
  17. 17. Phosphorus Cycle • Atmosphere is not a source • As with nitrate, phosphate is an important nutrient in coastal upwelling zones • As with nitrate, humans are doubling the rate of transport of phosphate into the environment through the application of fertilizers
  18. 18. Nitrogen Cycle
  19. 19. Phosphorus Cycle