A culture model for phytoplankton succession in the Potomac River near Washington, D.C. (U.S.A.)

Abstract

The phytoplankton in the Potomac River near Washington, D.C., was monitored from May 1978 through February 1980. Because of difficulties in relating the abundance of the major groups of planktonic algae (chlorococcalean green algae, pennate and centric diatoms) to observed environmental conditions, a method for simulating the community in culture was developed. Cultures started with river samples collected at different times of the year showed a similar sequence of increase: centric diatoms, chlorococcalean green algae, pennate diatoms, filamentous blue-green algae. Since nutrient levels were maintained by periodic replacement of medium, succession was probably not determined by nutrient limitation. Inhibition of diatoms with germanium dioxide showed that growths of green algae and probably blue-green algae were unaffected by the initial peak of centric diatoms. The results suggest that succession in the river results from different growth rates of the algal groups as they are carried downriver. The cultures provide a system for testing the effects of different environmental conditions on phytoplankton composition.