Occurrence of toxic cyanobacterial blooms in San Roque Reservoir (Córdoba, Argentina): a field and chemometric study.

We evaluated the presence of cyanobacterial blooms in San Roque Reservoir (Córdoba, Argentina). Cyanobacterial blooms and water samples were collected over 4 years (1998-2002). We confirmed the presence of microcystin-LR and microcystin-RR in 97% of these blooms. The total amount of microcystin (MC) ranged between 5.8 and 2400.0 microg x g(-1) of freeze-dried bloom material. These values suggest that guidelines for safe water consumption and recreational use should be established for this reservoir. Twenty-eight physical and chemical parameters were measured in water samples and evaluated by discriminant analysis (DA). A first DA was used to evaluate the factors promoting cyanobacteria occurrence, identifying nine parameters following three patterns associated with cyanobacterial growth. Inorganic phosphorous was found to promote the presence of blooms, whereas the highest proliferation of cyanobacteria was observed in the presence of smaller amounts of carbonate, bicarbonate, sulfate, and fecal coliform bacteria. The results observed during our fieldwork, analyzed using DA, agreed with the results of other laboratory studies, thus confirming the usefulness of DA to help with the evaluation of a complicated environmental data matrix. A second DA, using only water samples collected during the presence of cyanobacteria blooms, identified another nine parameters. The analysis of these parameters allowed us to identify certain environmental factors that could lead to the dominance of toxic strains, thus increasing the amount of MC. The results showed that, in our case, an increase in the water temperature was associated with higher amounts of MC per dry weight unit, whereas an increase in the concentrations of ammonia-nitrogen and iron were associated with lower amounts of MC, thus disfavoring the dominance of toxic strains.