The influence of whole lake aeration on the limnology of a hypereutrophic lake in central Florida

Abstract

To determine the influence of a multiple inversion aeration system upon the limnology of a small sinkhole lake, we monitored physical-chemical and biological parameters for 15 months prior to starting aeration and for 24 months thereafter. Aeration eliminated thermal stratification and dissolved oxygen concentrations of bottom waters increased significantly. Secchi disk transparency increased during aeration while turbidity, pH, alkalinity, total nitrogen, hydrogen sulfide and iron concentrations decreased significantly. Primary production and mean chlorophyll a did not change significantly during aeration but total phytoplankton cell volume decreased 2-fold. This decrease was caused by a marked reduction in blue-green algae which appears to be attributable to rapid mixing of the lake and to decreases in the pH. Cell volumes of green algae remained constant but numbers of taxa increased 70%. Densities of crustacean zooplankton were reduced markedly by aeration while densities of rotifers increased significantly during the first year but then returned to preaeration levels during the second year. Large-bodied cladocerans were replaced by small-bodied forms during aeration, and copepod populations became dominated by nauplii (97%). Densities of benthic macroinvertebrates declined 2-fold during aeration due to to a marked reduction (10-fold) in the Chaoborus population which correlated strongly with decreases in crustacean zooplankton abundance. The total number of taxa collected on individual sample dates increased throughout the two year aeration period (from 12 to 25) and chironomids became the predominant group (70%).