Composition of epilithic diatom and soft-algal assemblages in infralittoral zones of Tennessee reservoirs and correlations of composition to trophic state

Abstract

Assemblages of infralittoral periphytic algae are understudied due partially to the historical emphasis on phytoplankton and other water-column characteristics to evaluate the integrity of lentic systems. We tested the null hypothesis that characteristics of epilithic algal assemblages at infralittoral sites in reservoirs of Middle and East Tennessee do not infer trophic state. One infralittoral site in five mesotrophic and five eutrophic reservoirs in Middle and East Tennessee was sampled to determine the relative abundance of the most common epilithic diatoms and soft algae, concentrations of epilithic chlorophyll (chl) a, and water concentrations of chl a, total phosphorus (TP), and total nitrogen (TN). The concentration of epilithic chl a correlates significantly to the concentration of TP but not to TN as determined by the probability values for Pearson’s correlation coefficients. The water concentration of chl a does not correlate significantly to concentrations of TP, TN, or epilithic chl a. Trophic-state indicator values for 162 epilithic diatom taxa and 102 epilithic soft-algal taxa are calculated as the abundance-weighted average of the concentration of epilithic chl a normalized between 0 and 100. The trophic-state indicator values indicate the relationship of the abundance of algal taxa to trophic state and contribute to our limited knowledge of the effects of eutrophication on infralittoral algal taxa. Trophic-state indices are calculated as the mean abundance-weighted average of trophic-state indicator values for algal taxa of an assemblage. The index values infer the trophic state of the sites and are the first to use epilithic concentrations of chl a as opposed to water-column characteristics to indicate trophic-state optima for periphytic algae of lentic systems. The indices are easy to calculate and provide novel tools to help evaluate and monitor the trophic state of infralittoral sites in reservoirs of Middle and East Tennessee.