Phytoplankton assemblages and limnological characteristics in lotic
systems of the Paranapanema Basin (Southeast Brazil)
FERRAREZE1, M. & NOGUEIRA1, M.G.
1 Departamento de Zoologia, Instituto de Biociências – UNESP, Campus de Botucatu. C.P. 510, CEP 18618-000, Botucatu – SP
e-mail: mferrareze@ibb.unesp.br; nogueira@ibb.unesp.br
ABSTRACT: The main aim of this study was to analyze, comparatively, distinct stretches of the Paranapanema River and its tributaries based on the structure of the phytoplankton assemblages (composition, richness, diversity and abundance) and biomass (chlorophyll a). Such as the other large rivers of the Southeast Brazil, the Paranapanema has a series of reservoirs (eleven) constructed for electrical generation purpose. The reservoirs were not directly sampled in this study, although their influence in the results was evident. The sampling points were located in fluvial stretches of the basin – before the first reservoir, in the downstream zones of 9 reservoirs and in the inferior stretch of 10 tributaries. The data were obtained during the winter (August/2002) and summer (January/2003), corresponding to the dry and rainy periods, respectively. The total number of taxa identified was of 205. The richness and diversity, for both periods, were higher in the stretchs located downstream the dams when compared to the tributaries. The phytoplankton abundance was higher in the downstream zones of the reservoirs during the winter and in the tributaries during the summer. In the winter there was the predominance of the classes Bacillariophyceae, Chlorophyceae and Cryptophyceae. In the summer predominated Cyanophyceae and Cryptophyceae. Mean values for chlorophyll concentration were higher during winter. In general, considering the abundance of phytoplankton per classe, there was better similarity among the sampling points during the summer. This fact indicates the effect of homogenization due to the strong rains, typical of this period. The data of the limnological characteristics showed that the tributary rivers have more deteriorated conditions when compared to the main river of the basin, especially seen during the rainy season. During this period there was a remarkable increase in the concentration of suspended solids and nutrients (watershed runoff). The variables that better indicated the differences in the water quality were conductivity, dissolved oxygen and transparency. The study showed that phytoplankton assemblages respond quickly to the environmental changes in the basin, spatial and temporally. The data also demonstrated the importance of considering the lateral dimension, in addition to the longitudinal one, in the limnological studies carried out in large hydrographic basins.
Key-words: Paranapanema River, tributaries, reservoirs, phytoplankton, physical and chemical variables.