Bio geochemical cycles

• What are the main forms of carbon in the atmosphere ?

  Carbon dioxide, methane, and carbon monoxide.
• What are the main forms of carbon in the hydrosphere?

  Hydrogen carbonate ions and dissolved carbon dioxide
• Carbon cycle

  
• What are the main forms of carbon in the biosphere ?

  Carbohydrates, proteins and lipids
• What are the main forms of carbon in the Lithosphere ?

  Carbonaceous rocks such as limestone, Fossil fuels
• What is dynamic equilibrium in the carbon cycle?

  When the natural rates of movement in and out of a reservoir balance then there is dynamic equilibrium, the processes should cancel each other out
• What Is it called when the negative feedback mechanisms of the earth produce a self regulating system that resists change?

  Global Homeostasis
• Negative feedback methods:

  • Faster/slower photosynthesis due to more/less CO2
  • Faster/slower photosynthesis due to increased/lowered temperature
  • More/less CO2 removed from atmosphere = more/less CO2 in atmosphere
• What is the Gaia hypothesis? The idea that the Earth is a self-regulating system
• Photosynthesis:

  Carbon dioxide + water -> Glucose + Oxygen
• What is respiration?


  Respiration releases the energy that was captured during photosynthesis which is used to drive metabolic processes. Aerobic respiration returns the carbon to the atmosphere as carbon dioxide. Anaerobic respiration usually returns carbon as methane
• What is fossilisation?

  The incomplete decomposition of dead organic matter, and often under anaerobic conditions, can produce long term carbon stores such as fossil fuels
• Some organisms such as molluscs, corals and planktons produce exo-sketons that include calcium carbonate. This produces rocks such as limestone which contain most of the carbon in the lithosphere
• What is natural combustion?


  The burning of organic materials releases carbon dioxide, natural fires in forests may be caused by lightning
• Atmospheric concentration of CO2

  
• Human affects on carbon cycle

  
• Changes in photosynthesis:

  • Deforestation - reduces carbon from atmosphere -> biomass
  • Afforestation - increases the movement of carbon from atmosphere -> biomass
  • Toxic marine pollution - Toxic marine pollution that kills phytoplankton can lead to higher atmospheric CO2 levels
• Changes in aerobic respiration:

  Ploughing increases the oxygen supply to decomposers living in the soil so aerobic decomposition takes place more rapidly. The amount of carbon in the soil DOM store is reduced and the amount in the atmosphere is increased
• Changes in Anaerobic respiration:

  • In the absence of oxygen, respiration by anaerobic soil organisms releases methane.
  • Anaerobic environments produced by human activities: Rice padi fields, Landfill sites, Anaerobic sediments in reservoirs
  • Anaerobic environments destroyed by drainage: Waterlogged fields, Marshland and Peatbogs
• Carbonic acid concentration in the sea:

  • Dissolved CO2 is in equilibrium with carbonic acid which dissociates to form hydrogen carbonate ions
  • The concentration of hydrogen ions affects the pH of the sea so an increase in dissolved CO2 will reduce the pH of the water.
  • So as atmospheric CO2 concentrations rise, dissolved CO2 concentrations increases, which therefore increases hydrogen ion concentrations and makes the sea more acidic
• Methane may be released into the atmosphere during fossil fuel extraction
• The combustion of fossil fuels and wood releases large amounts of CO2 into the atmosphere
• Biomass movements caused by humans:

  • Addition of compost/mulch to improve soil fertility
  • Deforestation and crop harvesting
  • Sewage discharged into the sea
  • Fishing/aquaculture
• How to sustainably manage the carbon cycle:

  • Conservation of biomass carbon stores
  • Alternatives to fossil fuels
  • Carbon sequestration
  • Carbon, capture and storage
• Conservation of biomass carbon stores:

  • Habitats such as peat bogs and mangroves contain huge amounts of carbon, protecting these from exploitation or damage is important to prevent even higher CO2 releases
• Fossil fuel alternatives:

  Renewable energy resources and nuclear power produce lower CO2 emissions
• Carbon sequestration - It could remove a lot of the CO2 from the atmosphere and slow down or reverse the rising CO2 concentrations.
• Carbon capture and storage:

  • Precombustion tech - Carbon captured before used so it releases no CO2 when burnt
  • Gasification - converts fuel such as coal into gaseous hydrogen and CO2
  • Oxy-fuel combustion systems - they use pure oxygen so that only CO2 and water vapour are produced, the water can be removed through condensation and the CO2 can be captured more easily due to it not being mixed with other gasses
  • Post combustion technology - dissolving it in a solvent, high pressure membrane filtration etc
  • Storage - After carbon is captured it can be stored in: depleted aquifers, oil reservoirs
• Nitrogen Cycle

  
• What is the Haber process?

  The conversion of hydrogen and nitrogen into ammonia which is converted into nitrates in the soil
• Land drainage increases nitrogen fixation and reduces denitrification - Aeration increases aerobic nitrogen fixing bacteria and decreases anaerobic denitrifying bacteria
• The growth of legume crops increases nitrogen fixation in plant proteins - this is due to the presence of symbiotic nitrogen-fixing bacteria in root nodules
• Consequences of changes in nitrogen reservoirs:

  - Eutrophication - algal blooms kills aquatic plants that de-oxygenate the water when they die which causes dead zones in the water

  - Global climate change - Nitrous oxides caused by fertiliser denitrification is a greenhouse gas

  - NOx toxicity - NOx, mainly from fossil fuel combustion can produce nitric acid causing acid rain

  - Photochemical smogs - NOx reacts with UV light and unburnt hydrocarbons to produce photochemical smogs
• Sustainable management of the nitrogen cycle:

  • Reduced combustion processes - Use alternatives to fossil fuels, control NOx releases
  • Natural nitrogen fixation processes instead of Haber process - Grow legume crops, Maintain aerobic soils to increase aerobic nitrogen fixing bacteria/reduce denitrifying bacteria
  • Management of biological wastes - return wastes to farm land to add nutrients/ reduce need for artificial fertilisers
  • Reduce soil nitrate leaching - Reduced ploughing, Low-solubility nitrogen fertilisers e.g urea, cultivation of cover crops to absorb and retain nitrates
• Aerobic soils increase good nitrogen fixing bacteria and decreases bad denitrifying bacteria, anaerobic environments such as rice paddi fields and waterlogged fields denitrify the soils
• Phosphorus cycle

  
• Phosphorous has several important biological functions, it is an important component of bones, DNA, RNA, cell membranes and proteins
• Most compounds of phosphorous have a low solubility and there is no gaseous reservoir of phosphorous
• Main processes in Phosphorous cycle:

  • Absorption by roots (Mycorrhizal fungi)
  • Decomposition
  • Sedimentation (Dead planktonic organisms)
  • Mountain building and weathering
  • Mining of phosphate rocks (Calcium phosphates on Nauru)
  • Fertiliser use (increases crop production but can contribute to eutrophication)
• Phosphate shortages is the limiting factor on crop productivity for large areas of farm land. The availability of phosphates is reduced by the removal of biomass during harvesting and the loss of phosphates with the eroded soil