Energy Flow 2

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Energy Flow 2

• BS 111
• Ecology Biodiversity

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Objectives

• describe the basic features of biogeochemical
  cycles and compare several different nutrient
  cycles

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Biogeochemical cycles

• Solar energy infinite
• Chemical elements limited
• Life on earth dep. on recycling of essential
  chemical elements
• While organism alive - nutrients absorbed waste
  products released
• When organism dies atoms in complex molecules
  returned in simpler compounds to atmos., soil,
  water by action of decomposers
• Decomposition replenishes pools of inorganic
  nutrients - plants and other autotrophs use to
  build new organic matter
• Nutrient cycles involve both biotic abiotic
  components biogeochemical

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A general model of nutrient recycling arrows
indicate the processes that move nutrients
between reservoirs
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Nutrients

• A nutrient is either element or compound
  necessary for or contributing to an organism's
  metabolism growth, or other functioning
• Carbohydrates are compounds made up of sugars
• Proteins are organic compounds consist of amino
  acids joined by peptide bonds
• Fats consist of a glycerine molecule with three
  fatty acids attached
• Inorganic chemical compounds such as minerals,
  water, O2 may also be considered nutrients.

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Water

• Essential to all orgs., availability influences
  rate of ecosystem processes, e.g. PP
  decomposition in terrestrial systems.
• Oceans 97, 2 glaciers/ice caps, 1 lakes,
  rivers, groundwater
• Evaporation of liquid by solar energy,
  condensation of water vapour into clouds,
  precipitation

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The water cycle
On a global scale, evaporation exceeds
precipitation over the oceans Net movement of
water vapour carried by winds from ocean to
land Excess precipitation over evaporation
formation of surface and ground water flow back
into sea Over sea, evaporation forms most water
vapour On land, 90 vaporisation due to plant
respiration
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Carbon

• Forms the framework of the organic molecules
  essential to all organisms
• Reservoirs fossil fuels, soils, sediments of
  aquatic ecosystems, oceans (dissolved carbon
  compounds) plant and animal biomass, atmosphere
  (CO2), sedimentary rocks, e.g. limestone but slow
  turnover
• Photosynthesis by plants and phytoplankton
  removes substantial atmospheric CO2 each yr
  approx. CO2 added to atmos. By cellular
  respiration by producer and consumers
• Photosynthesis cellular respiration provide
  link between terrestrial atmospheric envs.

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Photosynthesis and cellular respiration
responsible for major transformations and
movements of carbon Seasonal pulse in
atmospheric CO2 caused by decreased
photosynthetic activity during N. hemisphere
winter Global scale return of CO2 to atmosphere
by respiration closely balances
photosynthesis BUT burning of wood and fossil
fuel adds more
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Cont.

• Remove carbon for short-term re-cycling for
  millions yrs, e.g. organic litter accumulating
  quicker than broken down can form coal,
  petroleum locked away as unavailable organic
  nutrients
• CO2 lowest in N. hemis. Summer more land/veg. in
  north. Max. photosynthetic activity in summer
  thus reducing CO2 in atmos.
• Fossil fuels effectively return to the atmos.
  CO2 removed by photosynthesis long ago
• Meantime new equilibrium in global carbon cycle
  balance being disrupted

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Nitrogen

• N - colourless, odourless, tasteless gas
  constituting 78.08 atmos.
• constituent element of all living tissues amino
  acids
• Plant fertilizers often limiting plant nutrient
• Then in run off or wastewater discharges reaching
  streams, lakes, or seas will promote aquatic
  plant growth.

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Enters ecosystems atmospheric deposition added
to soil dissolved by rain Nitrogen fixation
soil bacteria/symbiotic bacteria in plants roots
own uses but produce excess ammonia Nitrification
nitrifying bacteria convert toxic ammonia to
less harmful nitrate Majority of N recycled
locally by decomposition reassimilation

Widths of arrows represent relative contribution
of each process variable across ecosystems
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Phosphorus

• P - non-metal of the N group, phosphorus commonly
  found in inorganic phosphate rocks and in all
  living cells
• Major constituent of nucleic acids, phospholipids
  and ATP (Adenosine triphosphate) energy storing
  molecules bones and teeth
• Largest reservoirs in sedimentary rocks of marine
  origin

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Weathering of rocks gradually adds phosphate to
soil, some may leech ground surface water into
sea Phosphate taken up by producers and
incorporated into biological molecules- may be
eaten by consumers and distributed through food
web Phosphate is returned to soil or water
through either decomposition of biomass or
excretion by consumers
No significant phosphorus containing gases , only
small amounts move through atmos. dust and spray
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Summary

• Life on earth dep. on recycling of essential
  chemical elements
• Nutrients
• The water cycle
• The carbon cycle
• The nitrogen cycle
• The phosphorus cycle

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Recommend Reading

• Campbell Reece, Chapter 55, pp 1231 - 1233