Qualitative aspects of the water from Poty River at Teresina, Piaui State, Brazil

Abstract The water quality of the Poty River was evaluated to agricultural purposes at Teresina, Piaui State, Brazil in periods of extreme temperatures and precipitation. Samples of water were collected in the river in 10 georeference points, at the São Paulo Residential curve (southeast zone) until the mouth in the Parnaíba River (north zone), in an approximate course of 23.7 km, from June to December 2004. Were determined the physicochemical variable ECw, SAR and the pH, besides the concentrations of Cl-, HCO3 -, CO3 2-, Na+ and Ca2+. The largest values of ECw (0.26 dS m-1) and the SAR (1.90 mmolc L-1)0,5 were registered in the month of October, due to the low index of rains, dry period and eventual human pollution. The Kruskal-Wallis test verified oscillations in the concentrations of HCO3- (1.68 to 1.91 mmolc L-1) along the sampled points. The RSC indicated that the water is adequate for agricultural purposes (<1.25 mmolcL-1).