A comunidade de macroinvertebrados aquáticos e avaliação da qualidade da água dos arroios encantado e Santa Bárbara, no Município de Cerro Largo, Rs, Brasil

Abstract

The benthic macroinvertebrates are considered bioindicators because react to any change that might occur in the aquatic environment. The use of these organisms in research has been essential to capture aspects of environment. The present research used the methodology of biomonitoring to assess the environmental impacts through the diversity and composition of macroinvertebrates in Arroyos Encantado and Santa Barbara, in the municipality of Cerro Largo - RS, the first being situated in urban and rural areas and the second fully located in the rural area. The investigations have been carried out in the period April to September 2015, with samplings of benthic organisms on three stretches on the longitudinal gradient of the two creeks. A total of 1.518 specimens of macroinvertebrates were collected distributed in 25 families of insects, four families of crustaceans, molluscs from class Gastropoda, in addition to representatives of Annelida, classes Hirudinea and Oligochaeta. The most abundant families were: Hydropsychidae, Caenidae, Aeglidae, Beatidae, Gerridae, Chironomidae, Vellidae, Gyrinidae and Gomphidae, who summed together represent 84% of the collected individuals. The biotic index of families of Hilsenhoff (IBFs) indicated the following values and classes of water quality for the points assessed: Arroyo Encantado - P1 (between 4.80 to 4.98) with quality water good; P2 (between 5.29 to 5.64) with acceptable water quality; P3 (between 5,16 to 7,27) with water quality of acceptable to too bad; Arroyo Santa Bárbara - P1 (between 5.28 to 5.75), with water of acceptable quality; P2 (from 5,13 to 5,83), also with water of acceptable quality; and P3 (between 4.85 to 5.44) contribute with good quality water to acceptable. These results show that these arroyos contributed to the pollution of the waters of the River Ijuí.