Serial discontinuity along the Descoberto River Basin, Central Brazil

Abstract

AIM: The Descoberto Basin was studied as a discontinuous ecological system through one seasonal cycle (about one year), at 13 sampling sites; METHODS: The connectivity was analyzed in relation to environmental and limnological characteristics along the length of the Descoberto River, and the variables that most influenced the different sampling sites were determined; RESULTS: Sites K and L, located upstream and downstream of the entrance of the Melchior River, respectively, differed most in physical and chemical parameters. A Principal Components Analysis demonstrated that the system was more influenced spatially than temporally, with 74.57% of accumulated variance accounted for by the first two axes. High values of chloride, chlorophyll-a, BOD5, total phosphorus, and total organic carbon, as well as low dissolved-oxygen concentrations separated sites L and M from the others. Winter and spring were the seasons in which most parameters showed significant differences among the sites; CONCLUSIONS: The construction of the dam and waste discharge act as discontinuity factors affecting the referred system, mainly at middle region and lower patch, between the sites K and L. Besides the construction of the reservoir, the Melchior River, an extremely impacted system, affects the Descoberto River downstream from its entry. Important changes in water quality occur in the lower basin, especially downstream of the Descoberto Reservoir, with significant increases in nutrient concentrations, suspended solids, turbidity, and chlorophyll a, and therefore a decrease in water clarity.