Comunidade de macroinvertebrados bentônicos e qualidade da água nos principais riachos da sub-bacia hidrográfica do Rio Comandaí, mesorregião noroeste rio-grandense, Brasil

Abstract

Human activities have significantly altered natural environments. Currently, aquatic environments are among the most affected. Rivers suffer from natural and anthropogenic actions from their sources to their mouths, which alter the physical characteristics of the habitat and the quality of the water. Disturbed environments exert pressure on the structure of the benthic community of macroinvertebrates. Several methodologies for studying the composition of the community of biological organisms can be used to determine the water quality and the health of aquatic ecosystems. The organisms most commonly used in biomonitoring belong to the community of benthic macroinvertebrates. These organisms respond to environmental variations since all, or at least part of, their life cycles occupy the aquatic environment. The presence or absence of macroinvertebrates can tell us about the environmental integrity of a watercourse. In this context, the following research question of this study was presented: does anthropogenic action influence the reduction of taxonomic diversity of macroinvertebrates and decrease water quality in the Comandaí river subwatershed? The objective of this study was to evaluate and characterize the water quality in the main streams of the Comandaí river subwatershed, located in the northwest mesoregion of the state of Rio Grande do Sul, Brazil. The benthic macroinvertebrates were used to calculate the Family Biotic Index (FBI), Biological Monitoring Working Party (BMWP) score system, and Shannon-Wiener index in 27 sample sections of the streams. Nine streams were selected, based on the diagnosis of the watershed, and are considered the main contributors to the Comandaí river. Macroinvertebrate collections were carried out in the spring of 2016 and fall of 2017, using a dip net for a multi-habitat approach for a collection period of 40 minutes. A total of 11,982 benthic macroinvertebrates were collected from 63 families belonging to the taxa: Platyhelminthes, Annelida, Mollusca, Crustacea, and Insecta. The most abundant families were Hydropsychidae (15.2%), Simullidae (13.5%), Chironomidae (11.95%), and Baetidae (10.69%). The overall quality of water varied from clean water to water with moderate pollution effects. There was no difference in water quality between the sections of the streams. Among the regions of the subwatershed there was a significant difference in water quality only for the BMWP index (p-value≤0.01) in the fall of 2017, with the best water quality recorded in the spring. The analysis of the results allows us to conclude that the studied biotic indexes show a strong correlation with the water quality and reflect the changes caused due to anthropogenic actions in the longitudinal gradient of the Comandaí river subwatershed. Therefore, macroinvertebrates are important bioindicators and can provide information relevant to programs for the management and preservation of water resources.