Lecture 4

• How does the Biosphere function?

  • energy flow
  • nutrient/biogeochemical cycling
• Biogeochemical cycles: the movement of nutrients such as carbon, nitrogen and phosphorus through both abiotic and biotic components of ecosystems
• Nutrients are stored in compartments (reservoirs/stocks) in the different spheres
• Phosphorus cycle: phosphates move slowly through the soil and ocean, one of the slowest biogeochemical cycles
• Nitrogen Cycle:

  • Nitrogen fixation: microbes convert atmospheric N2 to NH3
  • Nitrogen fixation: lightning converts N2 to N03
  • NH4 - formed by consumption and decomposition
  • NH4 to NO3 - by Nitrification
  • NO3 to N2 - by Denitrification
• 3 processes through which Nitrogen is fixed: - produces reactive form that can be used by organisms

  • Nitrogen fixation
  • Nitrification
  • Decomposition
• Phosphorus cycle is the slowest:

  • P attaches itself to soil particles so the processes needed for it to move through soil and ocean is very slow
  • P only moves quickly through plants and animals
• Human Activities altering P and N cycles:

  • industrial and intentional biological fixation of N and mining of P - lead to increase in reactive N and speeds up release of P in env.
  • farmland runoff/industrial/municipal sewage discharges - lead to eutrophication
• Excess Nitrogen:

  • fast growing plants (e.g. algae)out-compete other plants which kills them
  • affects drinking water
  • eutrophication when they decompose - dead zones
  • impacts human and animal health
• Eutrophication: excess of nutrients in a body of water which leads to dense growth of certain plants e.g. algae - compete with other plants - when they die and decompose they use up oxygen - death of animals due to hypoxia
• Control measurements/Solutions:

  • sewage treatment plants
  • maintenance/restoration of wetlands
  • humans eating less meat - less fertiliser used - less manure produced
  • decreased use of fertilisers