A comparison of selected diversity, similarity, and biotic indices for detecting changes in benthic-invertebrate community structure and stream quality

Implementation of advanced wastewater treatment at the two municipal wastew ater-treatment plants for Indianapolis, Indiana, resulted in substantial im provement in the quality of the receiving stream and significant changes in the benthic-invertebrate community. Diversity, similarity, and biotic indi ces were compared to determine which indices best reflected changes in the composition of the biota in the river. None of the indices perfectly reflec ted the changes in river quality or community structure. Similarity indices , especially percentage similarity, exhibit the most promise of the three c lasses of indices. Diversity indices were least useful, wrongly indicating that water quality deteriorated after the upgrade of the wastewater-treatme nt plants. The most descriptive tool in analyzing the data was the percenta ge of Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa present. Using a mixture of indices and other analytical tools, such as EPT, in the analys is of biological data will ensure the most effective investigations of wate r quality.