Zooplankton Community Structure as a Function of Abiotic and Biotic Factors Prior to a Multiphased Restoration Effort

Abstract

Lake Taylorville, an impoundment on the South Fork of the Sangamon River, is located just south of Taylorville in Christian County, Illinois. The tributaries of this reservoir drain primarily agricultural areas and contribute to degradation of the reservoir through excessive sediment and nutrient loading. A restoration project is underway which involves construction of sediment basins and dry dams. Analysis of the crustacean zooplankton community has formed an integral part of an intensive limnological investigation of the reservoir during the initial stages of the restoration effort. Seasonal variation in the composition, and density of the major groups was observed. Rotifers (Brachionus and Polyarthra) were numerically dominant throughout the study period. Copepods (primarily nauplii) accounted for the second largest proportion of total zooplankton while cladocerans (Diaphanasoma and Daphnia) had the lowest relative density. Total zooplankton density increased significantly in late May before declining again in late August. Although many chemical, physical and biological factors potentially impact zooplankton community structure, I believe that an increase in temperature as well as algal units led to a significant increase in total zooplankton density in late May while decreased dissolved oxygen concentrations produced a sharp decline in late August. Predation by size selective planktivores probably does not control zooplankton density because of the limited light regime in Lake Taylorville.