Limnology of reservoirs in the Southeastern part of São Paulo State, Brazil. III. Water quality.

Abstract

This research was based on quarterly determinations made along the water column, at one station in each one of 17 reservoirs. Among the studied parameters, suspended matter, electric conductivity, pH and alkalinity, did not show high variation among the four sampling values. The ionic concentration of magnesium, iron, potassium, and chloride showed higher values in the 1^st and 4^th samplings (warm and raining season, October-March). It was observed that calcium, sulphate and sodium reached higher values in the 2^nd and 3^rd samplings (cold and dry season, April-September). Most of the studied parameters showed a vertical variation, frequently observed for the values of pH and rarely in relation to electric conductivity, alkalinity, calcium, magnesium, iron, sodium, potassium, sulphate and chloride. The ion manganese was rarely found in detectable concentrations. The salinity of the 17 reservoirs as a whole was 0.580 meq/L (sum of the medians of the concentrations of the main ions sodium, potassium, calcium, magnesium, sulphate, chloride and bicarbonate), while 0.319 meq/L is cation concentration. The dominant order finded was: Na > Ca > Mg > K and HCO₃ > Cl > SO₄.These reservoirs showed also the following median values: 34 µS/cm electrical conductivity; 0.206 meq/L alkalinity; 6.9 pH and 3.7 mg/L suspended matter.