Biogeochemical Cycles

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Chapter 3

• Biogeochemical Cycles

Big Question Why Are Biogeochemical Cycles
Essential to Long-Term Life on Earth?
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• A biogeochemical cycle is the complete path a
  chemical takes through the Earths four major
  reservoirs
• atmosphere
• hydrosphere (oceans, rivers, lakes, groundwaters,
  and glaciers)
• lithosphere (rocks and soils)
• biosphere (plants and animals).

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• Chemicals enter storage compartments - sinks
• Amount that moves between compartments is the flux

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• net sink - when input exceeds output
• net source - if output exceeds input.

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Essential Elements

• 24 elements are required for life
• Macronutrients are required in large quantities
• carbon, hydrogen, nitrogen, oxygen, phosphorus,
  and sulfur.
• Micronutrients are required in small/medium
  quantities, or not at all in some organisms
• Copper, sodium, iodine

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Geological Cycle

• The formation and change of Earth materials
  through physical, chemical, and biological
  processes

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The Tectonic Cycle

• Lithosphere is comprised of several plates
  floating on denser material
• Plates move slowly relative to each other plate
  tectonics

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• Divergent plate boundaries occur at spreading
  ocean ridges
• Convergent plate boundaries occur when plates
  collide

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• Plate movements change the location of continents
  and alter atmospheric and ocean circulation
  patterns
• Plate boundaries are geologically active,
  producing volcanoes and earthquakes

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Hydrologic Cycle

• Evaporation
• Precipitation
• Runoff
• Groundwater

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• 97 of water is stored in oceans, 2 in glaciers
  and ice caps, 1 as freshwater on land or
  atmosphere
• Drainage basins or watersheds are the area
  contributing runoff to a stream or river
• Vary in size from a hectare to millions of square
  miles (e.g. Mississipi River drainage basin)
• Human impacts include dam construction,
  irrigation, stormwater runoff

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Rock Cycle

• Igneous rocks form from molten material such as
  lava. Broken down by physical and chemical
  weathering

• Sedimentary rocks form from accumulation of
  weathered material in depositional basins

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• Metamorphic rocks are formed from sedimentary
  rocks exposed to heat, pressure or chemically
  active fluids

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Rock Cycle
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Biogeochemical Cycles in Ecosytems

• Begins with inputs from reservoirs such as
  atmosphere, volcanic ash, stream runoff, ocean
  currents, submarine vents
• Chemicals cycle through physical transport and
  chemical reactions (e.g. decomposition)
• All ecosystems leak chemicals to other
  ecosystems.

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Annual Calcium Cycle in a Forest Ecosystem

• Soluble in water and easily lost through runoff

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Annual Sulfur Cycle In a Forest Ecosystem

• Includes gaseous forms (sulfur dioxide and
  hydrogen sulfide) and cycles much faster than
  calcium

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Carbon Cycle

• Carbon is vital for life but is not abundant
• Enters biological cycles through photosynthesis
  to produce organic forms of carbon

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Carbon Cycle in a Pond
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• Large inorganic carbon reservoir in oceans
• Dissolved CO2 is converted to carbonate and
  bicarbonate
• Transferred from land by rivers and wind

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Fossil Fuels

• Decomposition of dead organisms may be prevented
  by lack of oxygen or low temperatures
• Burial in sediments over thousands or millions of
  years transforms the stored organic carbon into
  coal, oil or natural gas

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Global Carbon Cycle
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Global Carbon Cycle
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• Case of the missing carbon!
• Analysis shows contribution of 8 .5 bill. tons
  into the atmosphere but less than ½ stays
  therewhere does it go?
• 7 billion from fossil fuels and 1.5 billion from
  deforestation

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Case of the missing carbon!

• Appears oceans are acting as carbon sinks as are
  forests and grasslands.
• But which area is more critical, and which one
  dominates.
• Will these blessings last?
• If they stop functioning we could face drastic
  changes even before 2050.

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Case of the missing carbon!

• Global tests of CO2 show less in the north than
  the south despite larger northern outputs
• Why is this the case?
• If land plants are doing the work then there
  should be a corresponding oxygen increase.
• If it is dissolving in the oceans then there
  should be no added oxygen.

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Case of the missing carbon!

• Results (best guess)
• Ocean is soaking up 2.4 billion tons globally
• Land plants do the most work in the northern
  hemisphere
• Forests literally breath in the carbon but
  appetite changes dramatically due to season,
  amount of sunlight, rainfall, and age of forests
• Marine organisms undergo photosynthesis as well
• So that leaves about 2.9 units unaccounted for
  between these groups.

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Case of the missing carbon!

• Biggest threats
• Decline in forest growth
• Killing of ocean phytoplankton due to rising sea
  temperatures
• Death of forests due to spread of disease and
  insects
• Melting permafrost layer
• Land clearing for development and agriculture
• Ofcourse continued output of carbon from fossil
  fuel burning

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Nitrogen Cycle

• Essential for manufacturing proteins and DNA
• Although 80 of atmosphere is molecular nitrogen,
  it is unreactive and cannot be used directly
• Nitrogen fixation converts nitrogen to ammonia or
  nitrate

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Nitrogen Fixation

• Some organisms have a symbiotic relationship with
  nitrogen fixing bacteria
• Found in root nodules in some plants, or in the
  stomach of some herbivores
• Nitrogen fixation also occurs through lightning
  and industrial processes

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Denitrification

• When organisms die, denitrifying bacteria
  convert organic nitrogen to ammonia, nitrate, or
  molecular nitrogen

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Global Nitrogen Cycle
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Phosphorus Cycle

• No gaseous phase
• Slow rate of transfer
• Released by erosion of exposed rock
• Absorbed by plants, algae, and some bacteria
• Exported from terrestrial ecosystems by runoff to
  oceans
• May be returned through seabird guano

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Global Phosphorus Cycle
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Phosphate Mining

• Impact on landscape by open-pit mining