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 EC_w, SAR and the pH, besides the concentrations of Cl^-, HCO₃^-, CO₃^2-, Na⁺ and Ca²⁺. The largest values of EC_w (0.26 dS m^-1) and the SAR (1.90 mmol_c 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 mmol_cL^-1).