AVALIAÇÃO DO ESTADO TRÓFICO ATUAL DO RESERVATÓRIO DA USINA HIDRELÉTRICA DE CURUÁ-UNA, A MAIS ANTIGA REPRESA CONSTRUÍDA NA AMAZÔNIA CENTRAL

Abstract

The Hydroelectric Plant reservoir of Curua-Una was the first hydroelectric power plant built in the Central Amazon. That reservoir can be an example of impacts projection caused by these ventures on aquatic habitats. The research objective was to classify the water from the Curua-Una reservoir by means of the trophic degree determination using the trophic state index. The samples were carried out monthly in the period from May 2016 to April 2017 in eight collection stations in the reservoir totaling 96 samples in 12 months. The following variables were measured: depth, transparency, total phosphorus, chlorophyll-A and rainfall. And then the Trophic Status Index (TSI) for reservoirs was evaluated. To analyze the significant spatiotemporal differences of the TSI, a two-way ANOVA was performed. The highest concentrations of total phosphorus were recorded at points 14,7 µg.L -1 near the main tributary, this region presents a geochemically richer soil. For the chlorophyll-a, in the closer human site from water dam, maximum observed was 20,94 µg.L -1 . The Trophic Status Index mean (TSIm) floated from ultraoligotrophic to mesotrophic, being observed both in the vicinity of the water dam and in the outermost area of the reservoir. Although it did not found significant spatial and temporal variables differences, it was possible to notice that the total phosphorus TSI did not coincide with chlorophyll-A TSI, which indicates that the eutrophication process is not fully established in the reservoir, and may be limited by factors that were not measured in this study, such as the effect of agricultural expansion. Keywords: Index of trophic; Mesotrophic; Curua-Una Hydroelectric Plant; Spatio-temporal variation; limnology.