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CH3041
REDFIELD FORMULA
• Biotic life alters the chemical composition
of a water body significantly.
• Elemental proportions in algal biomass:
Redfield Formula  Protoplasm = C106H263O110N16P1
• A steady state approximation gives simple  stoichiometric reactions for Photosynthetic production & heterotrophic Respiration:
•
106CO2 + 16NH4+ + H2PO4- +106H2O D Protopl. + 106O2 + 15H+ 
 
R
P
106CO2 + 16NO3- + H2PO4- +122H2O + 17H+ D Protopl. + 138O2
• If NH4+ is used as a nitrogen source then
the pH will be lower than if NO3- is used.
Algae and aquatic plants prefer ammonium to nitrate. This is because the nitrogen is in a reduced state which the algae can directly utilize for the production of amino acids (the building blocks of proteins). Nitrate must first be reduced to nitrite and then ammonium in order for the algae and plants to utilize nitrogen in this state. This takes energy and, as a result, the plants and algae cannot grow with equal efficiencies given the same amount of nitrate nitrogen as they would on ammonium nitrogen.