Respostas da qualidade da água e fitoplânctons à redução de vazão e recepção de cargas de sedimentos no reservatório de Xingó/AL

Abstract

In the semi-arid region of northeastern Brazil, the Xingo reservoir is the last of a series of cascading reservoirs in the Sao Francisco river basin. From the perspective of river flow, the sharp reduction of rainfall in 2012 promoted the program of average flow reduction from 2013, contextualized by the most severe reduction in flow over the last hundred years. In 2015 a bottom discharge was given to the Delmiro Gouveia reservoir for the Xingo reservoir, raising concern about the effects of these actions on the water quality of this reservoir. Given the complexity of water quality variations in aquatic ecosystems, it is necessary to expand the panorama of physical and chemical responses of reservoir waters inserted in cascade systems. This article aims to evaluate the effects of average flow reduction, in the period from 2010 to 2015 of the Sao Francisco River basin, and of bottom discharge on the quality of Xingo reservoir water, also used for human supply. For this purpose, secondary data on rainfall, flow and water quality were collected by CHESF at three monitoring points on the Lake, representative of the anterior, intermediate and posterior parts. The results showed that the event of flow reduction allied to upstream sediment discharge led to an increase in temperature and alteration in nutrient concentration with consequent proliferation of cyanobacteria.