Cumulative changes in water quality caused by six cascading hydroelectric dams on the Jauru River, tributary of the Pantanal floodplain

ABSTRACT The present study examines the individual and cumulative environmental effects of the six cascading hydroelectric dams currently in operation on in the Jauru River, a direct tributary of the Paraguay River, the main river in the Pantanal, as well as presenting a general characterization of water quality in the Jauru River. Water quality was evaluated at eight sites along the longitudinal gradient of the Jauru River. A total of 339 water quality samples from between 1990 and 2013 were considered, including 72 samples collected prior to the installation of Hydropower plants, treated as natural, and 267 samples, treated as altered . Statistica 7 software was used for statistical treatment and for the Kruskal-Wallis nonparametric test; squared Pearson correlation (coefficient of determination, R 2) was also applied to evaluated the relationship between the morphological and hydraulic parameters of each reservoir and cumulatively, with the rate of change of water quality parameters in three stretches of the Jauru River. The water quality of the Jauru River in general was characterized by low concentrations of electrolytes and slightly acidic pH, oligotrophy, reduced values of color, turbidity and solids and good oxygenation. While these general conditions were maintained over the two phases studied, we verified the occurrence of change in the pattern of variation of the physical and chemical conditions evaluated, mainly between the second and the fifth hydroelectric reservoir. This change, which implies discontinuity in the longitudinal gradient, was indicated by nine out of the twelve parameters measured in this stretch of the Jauru River, downstream of each individual reservoir and/or cumulatively. The constructive characteristics of the hydropower plants, especially water inlet height, water retention time and flooded area, as well as the proximity between two or more impoundments, are factors that influenced the observed changes, which are important aspects in the processes of environmental licensing for these future plants, or even, in some cases, to avoid them from being built at all as planned. This research also indicated the need for studies that consider the basin in an integrated way, and for the collection of more consistent data before these impoundments are implemented.