The assessment of phytoplankton functional groups may help water resource management, considering the multiple uses of this resource type. This research investigated the seasonal variation of these groups in the Itupararanga Reservoir (SP, Brazil). Four arms of the reservoir were sampled to determine the water temperature, pH, underwater Photosynthetically Active Radiation (PAR), turbidity, total phosphorus, nitrate and total suspended solids (TSS), besides qualitative and quantitative aspects of the phytoplankton community and meteorological data. The study was carried out in August and October 2009, and in February 2010, and suggested there is seasonal variation of phytoplankton groups (p*<0.05), with the predominance of organisms Sn, X1, M and F (winter), X1, Y, F and K (spring) and X1, J, K and W2 (summer). The main variables that influenced the abundance of groups in the winter and in the spring were TSS (7.4 to 48.1 mg L-1) and turbidity (7 to 96 UT). Temperature (27.8 to 29.1 ºC), pH (from 7.7 to 9.8) and PAR (>1000 µE m-2 s-1) were relevant in the summer. Considering the environmental variability of the arms of the reservoir (derived from the influence of tributaries), and the dominance of phytoplankton groups typical of eutrophic environments, we recommend continuous monitoring of this area so that different water uses can continue, particularly for supply and recreation.
Sorocaba River watershed; phytoplankton community; eutrophication; water resources; lentic systems
