Environmental Quality Analysis Of A Sector Of The Chico River (Santa Cruz, Argentina) Based On Benthic Indicators

The Chico river, located in the center of Santa Cruz, runs 600 km from its source to its mouth. In its middle reaches, is the town of Gobernador Gregores (48 degrees 45' 3 '' S, 70 degrees 14' 54 '' W), which exerts influence on the river through agricultural activities and the discharge of urban sewages. In order to know the degree of impact on the water quality of the river, the analysis of the community of benthic macroinvertebrates was carried out and the Biotic Monitoring Patagonian Streams (BMPS) index was calculated. A first survey was performed in March 2017 at six sampling stations arranged in a gradient design, with two control stations upstream and four stations downstream of the town. At each station, water samples were taken for physicochemical analysis, environmental data were recorded with a multiparameter probe, and four samples of macrobenthos were collected using a Surber network with 0.5 mm mesh. The collected organisms were identified and counted under optic and stereoscopic microscopes. For each sample, species richness (S), total abundance (N), diversity (H') and evenness (J) were calculated, and the abundance data were analyzed using multivariate statistics. A total of 25 taxa were identified. The best represented were the oligochaetes Naididae, the hirudineans, the mollusks Chilinidae and Lymnaeidae, and the insects Chironomidae, Baetidae and Glossosomatidae. At the stations located downstream closest to the town the community was dominated by oligochaetes and chironomids, and presented the lowest values of S, H' and J. The values of BlViPS at these stations indicated the existence of polluted to heavily polluted water. At the control and the furthest downstream stations, the values of S, H' and J increased significantly, and the BlViPS index indicated better conditions in the environmental quality of the river.