Major ions chemistry of groundwater in the arid region of Zhangye Basin, northwestern China

Abstract

As one of the most arid regions in the world, the study area, Zhangye Basin is located in the middle reaches of the Heihe River, northwest China. Besides aridity, rapid social and economic development also stimulates greater demand for water, which is gradually fulfilled by groundwater extraction. In this study, the conventional hydrochemical techniques and statistical analyses were applied to examine the major ions chemistry and hydrochemical processes of groundwater in the Zhangye Basin. The results of chemical analysis indicate that no one pair of cations and anions proportions is more than 50% in the groundwater samples of the study area. High-positive correlations were obtained among the following ions: HCO₃ ⁻–Mg²⁺, SO₄ ²⁻–Mg²⁺, SO₄ ²⁻–Na⁺ and Cl⁻–Na⁺. TDS depends mainly on the concentration of major ions such as HCO₃ ⁻, SO₄ ²⁻, Cl⁻, Mg²⁺ and Na⁺. The hydrochemical types in the area can be divided into two major groups: the first group includes Mg²⁺–Na⁺–HCO₃ ⁻, Mg²⁺–Na⁺–Ca²⁺–HCO₃ ⁻–SO₄ ²⁻ and Mg²⁺–Ca²⁺–Na⁺–SO₄ ²⁻–HCO₃ ⁻ types. The second group comprises Mg²⁺–Ca²⁺–SO₄ ²⁻ type, Mg²⁺–Ca²⁺–SO₄ ²⁻–Cl⁻ type and Mg²⁺–Na⁺–SO₄ ²⁻–Cl⁻ type. The ionic ratio plot and saturation index calculation suggests that the silicate weathering, to some extent, and evaporation are dominant factors that determine the major ionic composition in the study area.