Groundwater quality and its suitability for drinking and agricultural use in the Yanqi Basin of Xinjiang Province, Northwest China

Abstract

The Yanqi Basin in Xinjiang Province is an important agricultural area with a high population density. The extensive agricultural activities in the Yanqi Basin started in the 1950s with flood irrigation techniques. Since then, the groundwater table was raised because of the absence of an efficient drainage system. This obstacle is a crucial factor that restricts sustainable socioeconomic development. Hydrochemical investigations were conducted in the Yanqi Basin, Northwestern China, to determine the chemical composition of groundwater. Sixty groundwater samples were collected from different wells to monitor the water chemistry of various ions. The results of the chemical analysis indicate that the groundwater in the area is generally neutral to slightly alkaline and predominantly contains Na⁺ and Ca²⁺ cations as well as HCO₃ ⁻ and SO₄ ²⁺ anions. High positive correlations between HCO₃ ⁻–Mg²⁺ + Ca²⁺, SO ₄ ²⁻–Mg²⁺, SO₄ ²⁻–Na⁺ + K⁺, and Cl⁻–Na⁺ + K⁺ were obtained. The total dissolved solids (TDS) mainly depend on the concentration of major ions such as HCO₃ ⁻, SO₄ ²⁻, Cl⁻, Ca²⁺, Mg²⁺, and Na⁺ + K⁺. The dominant hydrochemical facies for groundwater are Ca²⁺–Mg²⁺–HCO₃ ⁻, Mg²⁺–Ca²⁺–SO₄ ²⁻–Cl⁻, Na⁺–K⁺–Cl⁻–SO₄ ²⁻, and Na⁺–K⁺–Mg²⁺–Cl⁻–HCO₃ ⁻ types. The hydrochemical processes are the main factors that determine the water quality of the groundwater system. These processes include silicate mineral weathering, dissolution, ion exchange, and, to a lesser extent, evaporation, which seem to be more pronounced downgradient of the flow system. The saturation index (SI), which is calculated according to the ionic ratio plot, indicates that the gypsum–halite dissolution reactions occur during a certain degree of rock weathering. SI also indicates that evaporation is the dominant factor that determines the major ionic composition in the study area. The assessment results of the water samples using various methods indicate that the groundwater in the study area is generally hard, fresh to brackish, high to very high saline, and low alkaline in nature. The high total hardness and TDS of the groundwater in several places indicate the unsuitability of the groundwater for drinking and irrigation. These areas require particular attention, particularly in the construction of adequate drainage as well as in the introduction of an alternative salt tolerance cropping.