Spatial variability of surface water quality in a large Brazilian semiarid reservoir and its main tributaries

Brazil has one of the greatest hydroelectric potential in the world with high number of reservoirs for the electricity generation. However, little is known about the influence of these environments on the water quality. The water quality monitoring data from 14 stations distributed throughout the Irapé HPP reservoir (lentic environment), and its main tributaries (lotic environment), between the years 2008 and 2018, were evaluated and compared to assess the spatial variability of water quality. The analyzed parameters included total alkalinity, thermotolerant coliforms, electric conductivity, biochemical oxygen demand, dissolved iron, total phosphorus, nitrate, total ammoniacal nitrogen, dissolved oxygen, pH, total dissolved solids, sulfate, water temperature, and turbidity. Cluster analysis (CA), Kruskal–Wallis (KW) tests, Spearman rank-order correlation, and principal component analysis (PCA) were applied to identify and compare the relationship between the main parameters in the lotic and lentic environments. The CA resulted in four clusters according to proximity and the environment type (lotic or lentic). In general, the water quality showed better conditions in the reservoir and in the lotic stations on the immediate surround. The results may be associated with the greater sedimentation in the lentic environment. The analyses indicated that agricultural activities and the geochemical characteristics of the region are the main responsible for changes in the water quality.