ZOOPLANKTON ASSEMBLAGES IN THE OHIO RIVER - SEASONAL, TRIBUTARY, AND NAVIGATION DAM EFFECTS

Ohio River zooplankton were collected monthly or quarterly for 1 yr fr om littoral and pelagic (main channel) areas in three navigation pools (constricted and floodplain) with four intrapool locations (lower poo l and above, below, and within major tributaries). Total densities wer e minimal (1.64/L) when discharge and turbidities peaked (December-Apr il) but were relatively high otherwise (21.63/L). Seasonal rises in ro tifer density preceded increases in cladocerans and copepods; rotifers were nearly twice as abundant as cladocerans and copepods. Diversity (species richness) was not correlated with temperature, velocity, or t urbidity. Density was positively linked with temperature and negativel y correlated with river velocity and turbidity. Diversities in littora l and pelagic areas were not different, but densities were higher near shore (mostly copepods and cladocerans); rotifers were usually more co mmon in the main channel. Neither proximity to low-head navigation dam s nor channel morphology had detectable effects on zooplankton. Althou gh total diversity and density were similar in tributaries and the mai n channel, rotifers were more abundant in tributaries, and the Ohio co ntained more cladocerans and copepods. Densities in the Ohio were grea ter below than above tributaries for rotifers and cladocerans but lowe r for copepods, primarily because of nauplii.