Response of the benthic macroinvertebrate assemblage in a river affected by anthropogenic activity in the Extra-Andean Patagonia (Santa Cruz Province, Argentina)

Abstract

The purpose of this study was to analyze changes in the assemblage of benthic macroinvertebrates, as a response to anthropogenic environmental alterations in a river of the Extra-Andean Patagonia. Four sampling surveys were carried out between March 2017 and March 2019, in contrasting seasons on the middle course of the Chico River (Santa Cruz). Six sampling stations were established: two reference stations upstream of Gobernador Gregores town and four downstream at increasing distances from the locality. At each station, physic-chemical variables were measured and four macrobenthos samples were collected using a manual Surber-type net with a 500-µm mesh. The abundance of taxa and functional feeding groups (GFA) were analyzed using univariate and multivariate statistical methods. Twenty-six taxa were identified; the best represented were oligochaetes, hirudineans, gastropods and Chironomidae, Baetidae and Glossosomatidae insects. The reference stations and those further from the town presented higher values of diversity and richness of taxa and GFA; Chilinidae and Lymnaeidae molluscs were more important together with Baetidae, Glossosomatidae and Gripopterygidae insects. At the downstream stations, closer to the town, Naididae oligochaetes and Chironomidae insects dominated the macroinvertebrate assemblage with lower values of diversity and richness of taxa and GFA. The collectors-gatherers were the dominant feeding groups in these stations, where the contribution of urban effluents favored the detrituseating pathway and the opportunistic feeding strategy. Changes in composition and trophic structure of the macroinvertebrate assemblage provide relevant information to understand ecological modifications due to environmental alteration, and are of fundamental importance to interpret the biotic indices used to evaluate water body quality.