Análise da composição e abundância da comunidade fitoplanctônica em quatro reservatórios do rio Iguaçu

Abstract

Knowledge of ecological changes in a reservoir is of great relevance to the study environmental impact and of the water quality, especially the knowledge of phytoplankton community estructure, that has a role importante in aquatic ecosystems, which respond quickly to physical and chemical changes of the water, and markedly contribute to the production of organic matter. The objective of this work was to analyze the composition and abundance of phytoplankton under the influence of abiotic variables along a longitudinal axis in four reservoirs in a cascade system, emphasizing the importance of cyanobacteria populations. Located in the state of Parana, the reservoirs of hydroeletric stations of the Iguaçu River, namely, Foz do Areia, Salto Segredo, Salto Caxias and Salto Santiago, were chosen as the study area because they receive high nutrient load of anthropogenic origin, which contributes to increased concentrations of nitrogen and phosphorus, and consequently the formation of frequent blooms. To conduct this study were collected samples for analysis of abiotic and biotic variables in twelve points in the reservoir of Foz do Areia and nine points in the other reservoirs (Segredo, Santiago e Caxias), distributed as follows: three in river region, three in the intermediate region and three in the lake region, in November 2012, February 2013 and October 2013. Qualitative samples of phytoplankton were collected through a plankton net, and quantitative were collected directly from the environment. All samples were fixed immediately. The identification of the species was made with the aid of an common microscope, while the phytoplankton counting was made tubular sedimentation chamber using an inverted microscope. Analysis of physical and chemical parameters of water were made. During the study period, a total of 232 taxa were recorded that belonged to 10 classes. The cyanobacteria were dominant in the four reservoirs studied, being responsible for blooms occurred mainly under the influence of Microcystis aeruginosa and Sphaerocavum brasiliense densities in the reservoirs in Foz do Areia and Salto Segredo in November 2012 and February 2013. The dominance of cyanobacteria associated with high temperature and nutrient concentration in the reservoirs, show that the Iguazu River is undergoing an intense process of environmental degradation, which can threaten the integrity of biological communities and cause serious damage to the health of the ecosystem as a whole.