Water quality assessment of fifth-order tributaries of the reservoir at the Marechal Mascarenhas de Morais Hydroelectric Power Station in the Rio Grande watershed (State of Minas Gerais, Brazil)

Aim: This study assessed the water quality from the springs and river mouths of the fifth-order tributaries which compose the reservoir of Marechal Mascarenhas de Morais HPS in the middle Rio Grande watershed, Minas Gerais, Brazil. Methods: It has been studied 14 tributaries distributed in the reservoir, two points for tributary - spring and river mouth. Eighteen limnological variables added to the Rapid Assessment Protocol and Trophic Level Index were evaluated. The benthic macroinvertebrates had been collected by the use of a granulometric sieve and a Petersen-type sampler. Results: The cluster analysis of limnological data revealed the existence of two tributary groups. Group I consisted of eutrophic tributaries degraded by human activities, while group II exhibited good water quality and well-preserved environments. Group I was divided into two subgroups, Ia tributaries were characterized by being altered by human activities, while the Ib subgroup was composed of highly impacted tributaries. By ordering the PCA, it can be observed spatial segregation of groups, where the most polluted tributaries were separated from those which are better preserved. A total of 8,987 individuals belonging to 36 families of macroinvertebrates were identified. The family Chironomidae was the most abundant. There was no significant difference in total abundance and the richness of macroinvertebrates taxa inhabiting springs, by those who inhabiting the river mouths. Conclusions: It was noticed that most of the tributaries which supply and composes the reservoir are already degraded and have low quality water. It is observed that the human presence drastically affected water quality and faunal composition of tributaries. Thus, it is necessary a complementary study of the tributaries in working with issues related to reservoirs, as these components have direct influence on the water quality and composition of these lentic environments. Objetivos: O trabalho avaliou a qualidade da água das nascentes e fozes dos afluentes de quinta ordem que abastecem o reservatório da UHE Marechal Mascarenhas de Morais na bacia do médio rio Grande, Minas Gerais. Métodos: Avaliaram-se 14 afluentes distribuídos no reservatório, sendo dois pontos por afluente - nascente e foz. Dezoito variáveis limnológicas somadas ao Protocolo de Avaliação Rápida e o Índice de Estado Trófico foram avaliados. Os macroinvertebrados bentônicos foram coletados com peneira granulométrica e pegador de fundo Petersen.