3. Results
During the study period, water transparency remained low, pH ranged from slightly acid to neutral, electrical
conductivity and nutrients concentrations, especially nitrogen and phosphorus were high (Table 1). Thermal
stratification occurred in the rainy season (October/2007-March/2008) and more pronounced from December/
2007 to February/2008, and the mixing of the water column occurred in April and May/2008, during the dry
period (April-September/2008) (Figure 1(a)). Pronounced dissolved oxygen stratification occurred almost over
the entire study period, leading to extended periods of oxygen depletion at the bottom layers (Figure 1(b)). Algal
biomass (chlorophyll a) remained high, with annual mean of 119.4 μg/L (Table 1).