Relationships Among Substrate, Flow, and Benthic Microalgal Pigment Density in the Mechums River, Virginia

Measurements of photosynthetic pigments have been used to estimate the biomass of benthic microalgae on soft and hard substrates in a small river in the Virginia Piedmont. The irregular distribution of periphyton was partially related to substrate distribution and is explained as a result of spatial variations in the current regime in the river. High flow due to unpredictable and heavy rainfall is shown to be the main factor controlling algal biomass. Deterministic predictions of algal crop are therefore not possible in rivers of this type.