Using a diversity index to establish water quality in lotic systems

Abstract

The results of the sequential comparison index (ICS) applied to a benthic macroinvertebrate community in La Antigua River Basin are presented. Benthic macroinvertebrates are organisms living embedded or on the bed surface of the water bodies and have been used to assess water quality. The results belong to two sampling sites, one in the Sordo river and the other one in the Hueyapan river, both affluents of La Antigua river. Biological and chemical samples were taken during the rainy season. According to ISC results and due to the presence of dominant organisms, mainly tolerant to organic pollution (Chironomidae, Annelidae), Sordo river is considered as polluted. On the contrary, Hueyapan river was classified as unpolluted since sensible organisms were found (Ephemeroptera, Coleoptera, etc.). Chemical anylisis results, compared with the ecological criteria for water quality, lead to consider both rivers as adequate for development and protection of aquatic life, and their use is only restricted by the presence of ammonia, which exceeds the limit of 0.06 mg/L. By the application of this biotic index, as well as by the  dentification of water quality bioindicators, it was determined that there are water quality differences in both rivers that can not be detected by the sole chemical analysis.