How do ecosystems recycle materials

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How do ecosystems recycle materials?
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Biogeochemical cycles

• Unlike energy that flows one-way through an
  ecosystem
• Nutrients are continously recycled
• Main cycles are of water, carbon, and nitrogen
• Humans have impacted all of these cycles

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Water cycle

• Water is evaporated from ocean
• Falls over water and land
• Returns to ocean through runoff
• Surface waters, ground water
• Returns to atmosphere by transpiration by plants

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Carbon cycle

• Photosynthesis removes it from atmosphere
• Respiration, burning returns it
• Only trace amounts in atmosphere (lt0.01)
• Most carbon stored in living organisms or in dead
  material
• Forms gas, coal, and oil deposits

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Human impacts on carbon cycle

• Increased carbon dioxide levels linked to global
  warming
• Due to burning fossil fuels and forests
• Solutions-reduce fossil fuel use, plant forests,
  other methods

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Global Temperature Record
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Temperature and CO2
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Nitrogen cycle

• Most abundant element of atmosphere (73)
• Unusable as molecular nitrogen
• Plants need fixed nitrogen
• an ion of nitrogen (nitrate or ammonia)
• Fixation comes from lightning or nitrifying
  bacteria
• Bacteria are free-living or symbiotic with plant
  roots

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Nitrogen cycle continued

• Some bacteria convert ammonium to nitrate
• Some convert nitrate back to molecular nitrogen
  (denitrifying bacteria)
• Nitrate can leach out of soil
• Animals consume excess nitrogen, release it in
  urea or uric acid
• Decomposers convert this back to ammonia
  (ammoniafication)

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Nitrogen Cycle
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Human impacts on nitrogen cycle

• Industrial manufacture of fertilizers
• Types of plants grown (legumes)
• Too much nitrogen can leach other nutrients from
  soil
• can lead to lowered biodiversity
• Can also cause algal blooms in aquatic
  environments
• can lead to oxygen depletion when algae die
• Excess nitrates in water are human health problem

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Fixed Nitrogen Sources
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Oxygen depletion from nitrogen runoff
Dead Zone in Gulf of Mexico