Predicting DO Variations Caused by Algae

Eutrophic environments are often dominated by planktonic algal populations (phytoplankton) which can cause diurnal variations in DO concentrations through respiratory activity and photosynthesis. Photo synthetic oxygenation and respiratory deoxygenation rates of estuarine phytoplankton were measured at various standing crop (chlorophyll) levels. Oxygen production and consumption rates for actively growing phytoplankton populations were related to standing crop at 20○C and non-limiting light. Variations in algal photo synthetic production rate, as related to light adaption, age of cells, nutrition, temperature and algal type, are considered. The Streeter-Phelps equation was modified to include phytoplankton production and respiration rates in formulations designed to predict DO concentrations over a 24-hr period. An example is given, and the resulting predictions are compared with field measurements from a tidal reach of the San Joaquin River, California.