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Data of Thesis

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Author: Maria Isabel de Almeida Rocha

Title:.Seasonal variation of phytoplankton and zooplankton and the concentration of microcystins in these two trophic levels in the Reservoir Funil (Resende-RJ)

Year: 2007.    Full text (in Portuguese)

Abstract

The increase of nutrients input in lakes and reservoirs linked to different environmental factors accelerates the eutrophication process and establishes ideal conditions for cyanobacterial blooms. Funil Reservoir located between São Paulo and Rio de Janeiro States, formed by Paraíba do Sul River, was built in an industrial and agricultural region, with propitious characteristics for development of potentially toxic cyanobacterial bloom. The aim of this work was to evaluate the occurrence and transference of microcystins in the phytoplanktonic and zooplanktonic community of this reservoir, considering the composition and variation of both. Moreover, physical and chemical analyses of water were done monthly, throughout two consecutive years. Phytoplankton and zooplankton communities were previously separated, freeze-dried and, for the microcystins extraction, solubilized in acidified methanol. The extract was cleaned-up and analyzed by ELISA. Physical and chemical analyses demonstrated that the temperature of water varied approximately from 20 – 30ºC, pH had neutral-alkaline characteristics, the average of the dissolved oxygen concentration was 6.82 mg l-1 and the conductivity was 96.9 μS cm-1. These values, together with raised values of nutrients that arrive to Funil Reservoir, give adequate conditions to formation of a cyanobacterial bloom, causing reduction of the transparency of the water. The phytoplanktonic community was dominated by cyanobacteria, which reached more than 90% of the density in almost every month of study. The predominant genus was Microcystis, as in colonial or unicellular forms. Zooplankton varied monthly in density and composition of species. The copepods group had the highest densities and the rotifers group contributed with the highest variety of species. The population of cladocerans was reduced, with the dominance of the smallest one. These alterations in the zooplanktonic community can be associated to the constant presence of cyanobacterial bloom, which favors species already adapted to survive in these conditions. During all period microcystins were found in phytoplankton samples, reaching the maximum of 3.789 μg g-1, in December, 2004. These microcystins have been transferred to zooplankton communities, with values two orders of magnitude lower than phytoplankton approximately, with maximum of 63.15 μg g-1, in October, 2004. In accordance to these microcystins concentration results, it was observed three distinct phases: the first one with low microcystins concentration and low phytoplankton density; the second one with variation in microcystins concentration and in Microcystis density, and the third one with microcystins concentrations close to the first phase, but with an increase in phytoplanktonic population density. This is indicating, probably, the occurrence of three distinct populations. Considering these conclusions, the zooplanktonic community of the Funil Reservoir cannot be considered as a good vector of microcystins for higher trophic levels.

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