Effects of Exposure Time, Season, Substrate Type, and Planktonic Populations on the Taxonomic Composition of Algal Periphyton on Artificial Substrates in the Ohio and Little Miami Rivers, Ohio

Abstract

Standard glass microscope slides were exposed at the surfaces of the Ohio and Little Miami Rivers at Cincinnati, Ohio, for 1, 2, 4, and 8-week periods in June through November 1966. The maximum cell densities were attained in samples from the Little Miami River after an exposure of 1 or 2 weeks, except in November. In the Ohio River, the maximum counts were observed after exposures of 4 weeks in June and July, and 1 week in August and September. In October and November, the cell density continued to increase with increasing periods of exposure. Distinct successional patterns in the composition of the periphyton populations were not found. The changes in the composition of the periphyton with increased substrate exposure time resulted principally from seasonal changes in environmental conditions and phytoplankton populations. The maximum algal cell density, 29 000/mm2, was observed in a 1-week sample collected in the Ohio River. The periphyton populations in both rivers were generally dominated by diatoms, which averaged 68 percent of the cell count. The most important genera were Achnanthes. Cyclotella, Gomphonema, Melosira, Navicula, Nitzschia, Stephanodiscus, and Synedra. Other important groups were the green flagellates and filamentous blue-green, coccoid green, and filamentous green algae. The biomasses on five sets of glass and Plexiglas slides exposed for 2 weeks in the Little Miami River during the period of August through November did not differ significantly.