Phytoplankton dynamics in the main channel and embayments of a mainstream reservoir

Phytoplankton dynamics and related environmental factors at 10 main channel sites and 17 different embayments of a mainstream Tennessee River reservoir were studied for 6 months. Dynamics of 6 main divisions (Chlorophyta, Chrysophyta, Cryptophyta, Cyanophyta, Euglenophyta, and Pyrrophyta) were studied. Main channel phytoplankton productivity and community relationships developed on a continuum from riverine (hydraulic mixing) through transition (available light and nutrients) to lucustrine (nutrient competition) ecosystems. Embayment productivity and composition were highly influenced by nutrient availability (nitrogen and phosphorus). Strong associations among embayment divisions and environmental factors were: 1) cyanophytes, chlorophytes, pyrrophytes and total densities; low NO₂ and PO₄; watersheds with greater cropland composition; and fish with better health, 2) cryptophytes and euglenophytes; high nutrients; watersheds with greater pastureland composition; lower macrophyte coverage; and lower fish densities; 3) chyrsophytes and high total phosphorus; and 4) forestland; lower nutrients; lower phytoplankton productions; increased macrophytes; and higher fish densities. Urban land-use showed no strong association with any other variables.