Identification of determinant ions of surface water electric conductivity in the Curu Basin, Ceará State

Abstract

This work was carried out to identify the major contribution of ions to the surface water salinity to the upper and down perennialized segments of the Curu river watershed. Water samples were collected, monthly, from oct./2004 to sept./2005, in nine points spread out along the Curu river, totalizing 85 samples. Analyses were carried out in the Soil and Water Laboratory at the Federal University of Ceará State and the following parameters were appraised: Water Electric Conductivity (ECw), Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^- and Cl^-. Multiple regression models were considered to identify the relationship between EC and the studied ions. Willmontt’s index was used to validate the calibrated models. Developed models to the upland and low land regions showed a good agreement; pointing out that the developed models are good for prediction of Electric Conductivity. Results showed that both models were sensible to Cl-. The ionic composition of EC in the upland region was defined by Na⁺, Ca²⁺, Mg²⁺ e Cl^-, while in the low land region Cl^- e HCO₃^- ions were statistically significant (5%). According to the applied index, the calibrated models presented excellent precision, with the performance index (c) up to 0.90 and Willmott’s index (id) higher than 0.98.