Ionic condition and input and output rates of some chemical solutes in Lavapés stream, Sorocaba, SP, Brasil

Abstract

This paper aimed to analyze the seasonal ionic condition and the input and output of nutrients of a watershed with urban land use in the municipality of Sorocaba to estimate the impacts in the Sorocaba river. Water samplings were taken at two sites in a period of twelve months between 2009 and 2010. The concentration of magnesium, calcium, alkalinity, sulfate, chloride, potassium, nitrate and total phosphorus had been determined in laboratory using the titrimetric and spectrophotometric methods, for each of one of the twenty four samples collected. The results were presented in the Maucha’s ionic diagram; nutrient input and output were calculated based on the results of nitrate and total phosphorus concentrations. Observed proportional variation was not significant during the study according to Maucha’s ionic diagrams. Cation dominance order was Ca2+ > Mg2+ > K+, and anion dominance order was Alcalinity > SO42- > Cl-. The input and output of nitrate and total phosphorus was larger in the rainy months, as expected. The watershed total estimated ion values shows low influence over the Sorocaba River watershed, with values close to 5,83 ton of nitrate and 0,14 ton of total phosphorus. According to modified Carlson trophic state classification, the study area has a medium eutrophication potencial, and the Lavapés stream can be considered as mesotrophic.