The Effects of Agricultural Land Use on Periphyton Quality and Fatty Acid Composition in Midwestern Streams

Agricultural inputs of nitrogen (N) and phosphorus (P) to aquatic ecosystems stimulate the growth of algae. Although increased basal production has the potential to propagate to higher trophic levels, commensurate shifts in algal community composition have physiological implications for primary consumers. Taxonomic groups of algae differ in their concentrations of essential fatty acids (EFAs) and in digestibility. We characterized the eplithic algal communities in riffles of 12 Ohio streams along a gradient of agricultural land use by quantifying periphyton biomass, P content, C:N ratio, and chlorophyll-a. We also analyzed the fatty acid profiles of periphyton and primary consumers. There was a weak positive correlation between total epilithic biomass and % agricultural land in the watershed. However, % EFA in periphyton was negatively correlated with % agriculture. Three streams in predominantly agricultural areas, but with robust and extensive riparian buffers, had fatty acid profiles that were similar to those of more pristine streams.