Alteração dos níveis fluviométricos a jusante de barragens : influência da inversão de fluxo sobre a assembleia de peixes em tributários da planície de inundação do alto rio Paraná.

Abstract

Among the impacts imposed by dams on downstream basin stretches are those resulting from the changes in discharge, both natural, with increase of the minimum and decrease of the maximum, as the short-term resulting from the dam operation. The effects of this regulation are particularly relevant in floodplains, where in addition to affecting the connectivity between biotopes, can lead to reversal of flow in relevant stretches of tributaries, such as the Baía River in Upper Paraná River. It was verified the intensity and the extent to which the reversal of tributary flow modifies the limnological variables as well as the structure of fish assemblages associated with macrophytes. The reverse flow differed from normal flow by higher values of transparency, dissolved oxygen concentration, pH and conductivity. Changes to these variables were not, however, significant for different tributary stretches analyzed. There was no significant difference in the abundance and species richness. The evenness significantly differed only in relation to the position, with higher average value before Curutuba channel. The standard length showed higher average before Curutuba channel or when the flow was reversed, which may be indicative of larger fish from the Paraná River and the search for refuge from predators. The structure of fish assemblages differed significantly from the position of the points. Apparently, the differences were not accentuated by the fact that the species of the studied area is exposed to this impact for over 10 years and also by the presence of macrophyte that positively influence the diversity of fish. It is evident the need for more intensive studies of the impacts promoted by dams downstream, as a result of reverse flow, which has great influence for limnological variables and fish assemblage structure. It must be emphasized that this kind of impact is very little considered in the literature, but may be the mechanism to explain several processes, especially for the maintenance of biological diversity in the Upper Paraná River floodplain.