Dynamics of Ecosystems Chapter 57

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Dynamics of EcosystemsChapter 57
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Biogeochemical Cycles

• Biogeochemical cycles chemicals moving through
  ecosystems biotic and abiotic
• Can cross the boundaries of ecosystems (one
  ecosystem might import or export chemicals to
  another)

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Biogeochemical Cycles

• Water Cycle
• All life depends on the presence of water
• Amount of water available determines the nature
  and abundance of organisms present
• It can be synthesized and broken down
• Synthesized during cellular respiration
• Broken down during photosynthesis

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Biogeochemical Cycles

• Basic water cycle
• Evaporation
• Transpiration 90 of evaporation is through
  plants
• Condensation
• Precipitation
• Groundwater
• Aquifers provide 95 fresh water used in US

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Biogeochemical Cycles

• Water cycle

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Biogeochemical Cycles

• Changes in the supply of water to an ecosystem
  can radically alter the nature of the ecosystem
• Deforestation disrupts the local water cycle

• Water that falls as rain drains away

• Tropical rain forest ? semiarid desert

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Biogeochemical Cycles

• Nitrogen Cycle
• component of proteins and nucleic acids
• Usually the element in shortest supply
• Availability
• Most cannot use N2 (gas)
• Use NH3, and NO3-

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Biogeochemical Cycles

• Nitrogen fixation synthesis of nitrogen
  containing compounds from N2
• Nitrification N2 --gt NH3 --gt NO3-
• Denitrification NO3- --gt N2
• carried out by microbes free or living on plant
  roots
• Nitrogenous wastes and fertilizer use radically
  alter the global nitrogen cycle

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Biogeochemical Cycles

• Nitrogen Cycle

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Biogeochemical Cycles

• Phosphorus cycle
• Occurs in nucleic acids, membranes, ATP
• Exists as PO43- in ecosystems
• Plants and algae use free inorganic phosphorus,
  animals eat plants to obtain their phosphorus

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Biogeochemical Cycles

• Phosphorus cycle

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Biogeochemical Cycles

• carbon cycle (important component of bodies 20
  of human body weight)

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Biogeochemical Cycles

• Respiration/photosynthesis
• Methane producers anaerobic cellular respiration
  releases CH4
• Decomposition releases CO2
• Combustion burning fossil fuels produces CO2

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Biogeochemical Cycles

• Over time, globally, the carbon cycle may proceed
  faster in one direction
• Human burning of fossil fuels is creating large
  imbalances in the carbon cycle
• The concentration of CO2 in the atmosphere is
  going up year by year

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Biogeochemical Cycles

• Limiting nutrient weak link in an ecosystem
  shortest supply relative to the needs of
  organisms
• Fe for algal populations
• N and P for both terrestrial and aquatic
  ecosystems

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Biogeochemical Cycles

• Biogeochemical cycling in a forest ecosystem--
  Hubbard Brook Experiment
• Undisturbed forests are efficient at retaining
  nutrients
• Disturbed (cut trees down) amount of water runoff
  increased by 40
• Loss of Ca increased nine fold
• Loss of Phosphorus did not increase
• Loss of NO3- 53kg/hectare/yr

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Biogeochemical Cycles

• The Hubbard Brook Experiment
• 38-acre watershed. Orange curve shows nitrate
  concentration in the runoff water from the
  deforested watershed. Green curve shows the
  nitrate concentration in runoff from an
  undisturbed watershed