Impacto de uma barragem hidrelétrica sobre a biodiversidade bentônica em ambiente tropical

Abstract

The demand for water resources with quality and quantity has increased actions that aim at the conservation and restoration of aquatic ecosystems and their watersheds. The Conservation Units of the Pandeiros river basin were created with the objective of protecting this important tributary of the São Francisco river. Pandeiros Small Hydroelectric Power Plant (SHP), installed in the middle stretch of the river, was deactivated in 2008 due to the non-renewal of its environmental license. Since then, it has aroused the concern of several sectors of society regarding its possible decommissioning, which could restore the course of the river and avoid environmental risks and accidental disruption. This study was developed with the objective of evaluating the impact of the Pandeiros SHP dam on the benthic communities comparing upstream and downstream sections. The hypothesis of studies was the dam influenced the distribution of benthic macroinvertebrates along the river, with distinct benthic communities in three habitats upstream and downstream (river channel, semi-lentic and lagoon), with greater abundance of invasive species and tolerant species to hydraulic changes in the reservoir due to the dam. The influences of dam and abiotic water column and sediment variables on the composition and structure of benthic communities and the indicator taxa in the three habitats were evaluated. Water and sediment samples were collected in the rainy and dry seasons of 2014-2015 (N = 6), four sediment samples were collected in each at the eight sample sites using kicking-net, totaling 192 samples. No point sources of pollution were observed in the river, being its waters of excellent quality in all habitats. A total of 43,493 benthic macroinvertebrates were identified in 67 taxa, with higher abundances of Melanoides tuberculata (34%), Bivalvia (21%), Chironomidae (13%), Baetidae (6%) and Leptohyphidae (6%). The granulometric composition of the sediments was the abiotic variable that most influenced the benthic communities, with predominance of sands. In the reservoir, the dominance of the exotic species M. tuberculata was observed, with a density of 6.244 ± 1621 ind/m², and the exotic species Corbicula fluminea was indicator for this habitat. The results indicate composition and structure benthic community changes in the reservoir area, where the dam favored the establishment of exotic species and the reduction of the abundance of sensitive taxa of Ephemeroptera and Trichoptera. These results show the impact of the Pandeiros SHP dam on benthic biodiversity and will be useful to support the elaboration of proposals for environmental management and proposition of future measures for the decommissioning of the dam, contributing to the restoration and conservation of the Pandeiros river basin.