Lecture 13 - Carbon

Two main forms of Carbon

Organic and Inorganic

Inorganic Carbon

• Main reservoir is in atmosphere in form of Carbon Dioxide (CO2)

• Dissolving CO2 gas in water can result in a variety of forms • Carbon dioxide, carbonic acid, bicarbonate and carbonate

  • Bicarbonate Equilibrium

Inorganic Carbon - pH

Amount of carbon forms depends on pH (H+ ions) • Determines acid neutralizing or buffering capacity • Greater dissolved bicarbonate = greater buffering capacity

• Increase in CO2 in atmosphere is increasing acidity of aquatic ecosystems

Organic Carbon

Carbon chains bonded with other elements • Usually hydrogen and oxygen • Can be particulate or dissolved

Particulate Organic Carbon

• Particulate further divided into fine particulate (FPOM) and coarse particulate (CPOM)

• Particulate can be living or dead organic material

• Key source of food for heterotrophic organisms

Dissolved Organic Carbon

• Two major classes • Humic vs Non-humic

• Humic – by-products of breakdown of cellulose, tannins and lignins

• Non-humic – sugars, carbohydrates, amino acids, etc. → broken down by heterotrophs to yield humic compounds

Transformation of Carbon

Cycling of carbon dominated by photosynthesis and respiration

• Formation of Organic Carbon

Photosynthesis - CO2 + H2O + light energy → CH2O + O2

• Breakdown of Organic Carbon • Respiration - CH2O + O2 → CO2 + H2O + chemical energy

• involves oxidation of large organic molecules (most efficient)

• Carbon cycling can also involve •Anaerobic processes

• Oxidation with other molecules (e.g., nitrate and sulfate)

• Fermentation

• Methanogenesis