Hydrogeochemical Characteristics and Controlling Factors of Groundwater in a Typical Oasis in Arid Regions

In arid regions, oases are critical to human survival and development, relying heavily on groundwater to sustain ecological balance and support socio-economic growth. This study focuses on a representative oasis city, where 198 groundwater samples were systematically collected in September 2022. A suite of analytical methods—including statistical analysis, Piper and Gibbs diagrams, ion-ratio analysis, and hydrogeochemical modeling—was used to characterize groundwater chemistry and identify its controlling factors. The results indicate that groundwater in the area is slightly alkaline. Unconfined groundwater is dominated by HCO₃·SO₄–Ca and HCO₃·SO₄–Na·Ca types, whereas confined groundwater is mainly HCO₃·SO₄–Na·Ca and HCO₃·SO₄·Cl–Na·Ca. Groundwater ion composition is influenced by water–rock interaction, with major ions primarily derived from the dissolution of halite, evaporites, and carbonates; cation exchange processes further affect confined groundwater. Halite and gypsum dissolve, while calcite and dolomite are near dissolution–precipitation equilibrium; overall dissolution propensity is higher in unconfined than in confined groundwater. Hydrogeochemical modeling quantitatively corroborates the primary water–rock interactions inferred from qualitative analyses of groundwater flow. These findings improve understanding of hydrogeochemical evolution in oasis groundwater within arid regions.