Limnology of a lateral lagoon system connected to a Neotropical reservoir (Rosana reservoir, São Paulo/Paraná, Brazil)

Resumo

The aim of this work was to perform a comparative analysis of four lateral lagoons and of the main channel of the Rosana Reservoir (Paranapanema river), southeast Brazil. The fieldwork was conducted during dry and rainy periods of 2004 and 2005. The analyzed variables were chlorophyll a, turbidity, total phosphorus, total nitrogen, dissolved nutrients (ammonium, nitrate, nitrite, phosphate and silicate), Secchi disk transparency, suspended solids, temperature, pH, dissolved oxygen and electrical conductivity. Intense summer rainfall provided a high input of allochthonous material into the system, resulting in conspicuous changes - high turbidity and nutrient concentrations and low transparency, especially in the reservoir channel. The cluster analysis showed a clear segregation between the reservoir sampling site and the lagoons. The results evidenced the strong influence of regional factors on the limnological structure and functioning of these environments. The alternation between dry and rainy periods changes significantly the characteristics of the main channel and lagoons, mainly due to the contribution of tributaries. Spatially, the system exhibited a remarkable limnological variability. This shows the need to consider these distinct habitats in regional conservation strategy, presently focused on terrestrial habitats.