Inorganic Carbon Cycle

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Inorganic Carbon Cycle

• 14 Feb 2007
• AWER 4500

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Acidity

• Measured by pH
• Disassociation of water

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pH Scale
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DIC Dissolved Inorganic Carbon

• Source of C for photosynthesis
• The amount of DIC determines the pH of most
  natural waters
• Determines the BUFFERING CAPACITY (ability to
  resist change in pH)

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Dissolved Inorganic Carbon

• CO2 - Carbon dioxide
• H2CO3 - Carbonic acid
• HCO3- - Bicarbonate
• CO3-2 - Carbonate

Forms
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Sources of DIC in lakes

• Rainwater
• Subterranean and river water
• Carbonaceaous rocks, i.e. limestone

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Air-Water Equilibrium Reactions
Therefore, a solution of CO2 in water is a weak
acid
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Overall equilibrium

• Adding acid moves the equilibrium to the left
• Removing acid moves the equilibrium to the right

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Limestone-Water-CO2 reactions
Overall Reaction
Breakdown
Therefore, a solution of water, CO2 and carbonate
is a weak base
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Overall distribution of DIC determined by pH
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Buffering capacity

• Definition
• Alkalinity, Acid Neutralizing Capacity
• Hardness

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An overall equilibrium involving calcium and
carbonate species gives
Travertine benches Havasu Canyon, AZ
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Marl Formation

• In water with lots of Ca and H2CO3 and high
  rates of photosynthesis
• Causes calcium carbonate to precipitate
• Marl

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Lake Erie Whiting Event
http//earthobservatory.nasa.gov/NaturalHazards
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