Ionic structure modeling of water in Acaraú basin, Ceará.

Abstract

This work was carried out to identify and predict the relationship between electrical conductivity (EC) and the ionic load of surface water from Acaraú basin, Ceará State, Brazil. Data set used was sampled in eleven station every two months from April/2002 to Mar/2003, pooling a total of 77 samples. Stepwise regression equations were developed using EC as independent variables with ions: Na⁺, Cl^-, Ca⁺⁺, Mg⁺⁺, HCO₃^-, and K as dependent variables. Results showed that HCO3 - presented the highest contribution to EC variability in the up side, as well as the down side, of the Acaraú basin. Order of ion importance to the model was: HCO₃^-, Na⁺, Cl^-, Ca⁺⁺, and K⁺ to the up side; while to the down side was: HCO₃^-, Cl^-, and K⁺. The higher salinity was registered in the down side of the river due to the chloride water coming from the semiarid zone of the basin. All evaluated models showed excellent performance index (c > 0.90), with coefficient of determination (r²) and Willmontt’s index (id) higher than 0.98. Computed EC values showed a good agreement with observed values for both sides; suggesting that the selected ions explain well the EC variability.