Effects of sewage on the chemical composition of Piracicaba River, Brazil

Water samples were collected from 7 locations dong major rivers of Piracica ba River basin for 22 months. The 4 upstream points represent non-polluted sites and the 3 downriver points represent polluted sites. Due to sewage in put, concentrations of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), major conservative cations and anions increased significantly in the polluted sites. The major increases were observed for sodium, chlor ide and sulfate, Nitrate was an exception for this pattern, with similar co ncentrations between polluted and non-polluted sites. The probable cause wa s reduction of nitrate to ammonium in the polluted sites, where anoxic cond itions prevail. Most of the variables had an inverse correlation with water discharge, especially in the polluted points. The sewage load was diluted by precipitation and surface waters.