Water quality in the lotic area of the Antas river before and after the construction of the Monte Claro hydroelectric plant, south Brazil Qualidade da água nos trechos lóticos do rio das Antas antes e após a constru o da usina hidrelétrica Monte Claro, sul do Brasil

AIM: This study characterized the water quality of the lotic areas of the Rio das Antas (Antas River)influenced by the construction of the Monte Claro hydroelectric plant (South Brazil), a run-of-the-river reservoir. METHODS: To assess the water quality, we selected four sampling points based on the results obtained in the water-quality monitoring program performed by CERAN (the Rio das Antas Energetic Company) in the pre-filling (2002-2004) and post-filling (2005-2008) periods. The river flow was monitored during both of the periods. Seasonal samplings were conducted, and alkalinity, chlorophyll a, total and fecal coliforms, conductivity, color, BOD, COD, total phosphorus, nitrate, nitrite, ammoniacal nitrogen, dissolved oxygen, pH, total dissolved solids, suspended solids, sulfates, temperature and turbidity were evaluated. The results were interpreted according to the Brazilian Environmental Council's Water Quality Index, Trophic State Index and CONAMA Resolution 357/05. To verify the occurrence of alterations before and after the plant operation, t-tests were performed. RESULTS: Significant changes in water quality were not observed after the impoundment. The permanence of the characteristics of the natural hydrography was important for maintaining the water quality. The decline of the water quality in a stretch with reduced flow was caused by Burati stream, a tributary containing high concentrations of nutrients and fecal coliforms. CONCLUSIONS:The Monte Claro hydroelectric plant did not alter the water quality of the Antas River. The small reservoir resulting from the plant project favors the maintenance of the water quality of the river and does not favor eutrophication. Attention should be given to Burati stream, a tributary of the Antas River, regarding its high nutrient and coliform content. OBJETIVOS: Este estudo caracterizou a qualidade da água nos trechos lóticos do rio das Antas influenciados pela constru o da usina hidrelétrica Monte Claro, com reservatório tipo fio d'água. MéTODO: Foram selecionados quatro pontos do programa de monitoramento da qualidade da água executado pela CERAN - Companhia Energética rio das Antas, nos períodos pré-enchimento (2002-2004) e pós-enchimento (2005 a 2008). Foi monitorada a vaz o do rio pré e pós-enchimento do reservatório. As amostragens foram sazonais, e utilizadas as variáveis alcalinidade, clorofila a, coliformes totais e fecais, condutividade, cor, DBO, DQO, fósforo total, nitrato, nitrito, nitrogênio amoniacal, oxigênio dissolvido, pH, sólidos dissolvidos totais, sólidos suspensos, sulfatos, temper