Investigating zooplankton abundance and composition within a Louisiana river and adjacent tributaries

Zooplankton is an ecologically important component of aquatic systems, facilitating the transport of nutrients and energy from phytoplankton to higher trophic levels. In addition to predator density and food levels, water velocity and physicochemistry can significantly influencing zooplankton abundance and community composition. We investigated the influence of habitat type (river channel, tributary creek, floodplain lake), physicochemistry, distance from the main channel, and time of year on zooplankton abundance and community composition in an Ouachita River / floodplain system downstream of Felsenthal Dam, Arkansas. This section of river is extremely flashy, with tributaries exhibiting 8-m depth fluctuations over a 1-month period. We used push nets and funnel traps to collect monthly zooplankton samples for one year from seven spatially distinct habitats in this river-floodplain system. Analyses of the factors influencing zooplankton community dynamics incorporated habitat as well as water quality variables, including nutrients, chlorophyll a and water depth. Preliminary results indicate temporal changes in both abundance and community composition among months, but few differences among sites within months, likely due to homogenizing influence of unusually high river stages that have characterized this section of the Ouachita River over the last year.