Abstract
Lipids of phytoplankton were examined in two freshwater lakes to determine their role as indicators of algal biomass and composition. An initial laboratory study on known cultures of algae proved useful in identifying differences in carbon and lipid concentrations among classes, and indicated the use of fatty acids and sterols as qualitative markers. Shifts in dominant algal classes were observed in Onondaga Lake and Lake Erie, with a large makeup of diatoms and cryptophytes in the spring, and chlorophytes and cyanobacteria in the summer. Differences in the trophic status of these two freshwater lakes suggest that fatty acids can be utilized as biomarkers in several different aquatic environments. Stable carbon isotopes were combined with lipid analysis to determine the fate of seston following stratification in Onondaga Lake, and the effect of changing algal classes on zooplankton grazing in Lake Erie.