Analysis of the phytoplankton community emphasizing cyanobacteria in four cascade reservoirs system of the Iguazu River, Paraná, Brazil

Abstract

ABSTRACT Knowing the ecological changes in a reservoir is of great relevance to study environmental impacts and assess water quality. Among these studies, the knowledge about the structure of the phytoplankton community is essential, once they represent a fundamental component of aquatic ecosystems, responding immediately to physical and chemical alterations in water. The objective of this work was to analyze the phytoplankton community and the influence of abiotic factors, along the longitudinal axis in four cascade reservoirs system of the Iguazu River, Paraná, Brazil, emphasizing the importance of cyanobacteria. Foz do Areia, Salto Segredo, Salto Santiago and Salto Caxias reservoirs were the objects of this study. The phytoplankton counting was made tubular sedimentation chamber using an inverted microscope. The results showed that the four reservoirs are under eutrophication processes, presenting intense cyanobacteria blooms, dominated mainly by Microcystis aeruginosa and Sphaerocavum brasiliense. There was no evident longitudinal gradient related to phytoplankton, as expected for reservoirs in a cascade system. The dominance of cyanobacteria shows that the Iguazu River is undergoing an intense process of environmental degradation, threatening the integrity of biological communities and causing serious damage to the ecosystem as a whole.