Spatio-temporal variation of the hydrogeochemical characteristics, formation mechanism, and pollution assessment of shallow groundwater in Karamay, China

Groundwater is an important water resource in the Karamay region, which is located in an arid area in northwestern China. A comprehensive understanding of groundwater chemistry and quality is essential for the sustainable development and effective management of water resources. However, the hydrogeochemical characteristics, formation mechanism, and pollution characteristics of groundwater in this region remain unclear. Hence, this study analyzed 274 groundwater samples, collected in the wet and dry seasons, using multivariate statistical analysis. Basic statistical results showed that groundwater was weakly alkaline to alkaline with high TDS, and the average cation and anion concentrations followed K⁺ <Mg²⁺<Ca²⁺<Na⁺ and CO₃^2-<HCO₃^-<SO₄^2-<Cl^-, respectively. High values of SO₄^2-, Cl^-, Na⁺, Ca²⁺, Mg²⁺, and K⁺ were mainly concentrated in Baijiantan District and the northern part of Karamay District. Groundwater was dominated by the NaCl type, which was mainly controlled by evaporation and rock weathering, and the control pattern remained stable between the wet and dry seasons. The major components of groundwater primarily originated from the dissolution of minerals, including unsaturated halite and gypsum, as well as saturated dolomite and calcite. Cation exchange played a significant role in groundwater evolution. The ratios of polluted areas to the total area were 63.19-70.72 % and 62.55-68.30 % in the wet and dry seasons, respectively, indicating very poor groundwater quality. These findings can provide insights into the evolution of the groundwater environment in arid regions, and guide water resources management and protection in ecologically fragile areas.