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

Ohio River zooplankton were collected monthly or quarterly for 1 yr from littoral and pelagic (main channel) areas in three navigation pools (constricted and floodplain) with four intrapool locations (lower pool and above, below, and within major tributaries). Total densities were minimal (1.64/L) when discharge and turbidities peaked (December-April) but were relatively high otherwise (21.63/L). Seasonal rises in rotifer 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 turbidity. Density was positively linked with temperature and negatively correlated with river velocity and turbidity. Diversities in littoral and pelagic areas were not different, but densities were higher nearshore (mostly copepods and cladocerans); rotifers were usually more common in the main channel. Neither proximity to low-head navigation dams nor channel morphology had detectable effects on zooplankton. Although total diversity and density were similar in tributaries and the main channel, rotifers were more abundant in tributaries, and the Ohio contained more cladocerans and copepods. Densities in the Ohio were greater below than above tributaries for rotifers and cladocerans but lower for copepods, primarily because of nauplii.