Ecologia do fitoplâncton no reservatório Arcoverde:estudo nictemeral e sazonal

Abstract

The aim of the present study was to analyze the phytoplankton in the Arcoverde-PE reservoir, during the nictemeral cycle in two distinct seasonal periods. Collections were made at two depths during the rainy and dry periods in 2007. The phytoplankton was identified and the density determinated. Concomitantly, analyses were carried out for the characterization of the system. In the rainy season, water was oxygenated, neutral pH, turbid and warmer, and in the dry season, the water ranged to oxygenated to anoxic, alkaline pH and turbity at surface. In both seasons, there was limited nitrogen and high concentrations of phosphorus. Thirtyeight infraspecific taxa were identified. Chlorophyta and Cyanophyta had the greatest number of species. Cyanophyta generally had higher densities in both seasons, at both depths and at different hours. It was observed a perennial bloom of Cylindrospermospis raciborskii. There was significant variations among hours and depths for abiotic variables in both season and it was observed significant differences for densities of phytoplankton for seasonal analysis. This indicates that environmental changes in the concentration of nutrients, pH and turbidity of the water are factors that facilitate the occurrence of Cyanophyta.