The Chemical Properties and Formation Mechanisms of Shallow Groundwater in the Guohe River Basin, China

An investigation of the distribution and control factors of groundwater is significant for the rational exploitation and utilization of groundwater resources. This study analyzes the hydrogeochemical processes and control factors of shallow groundwater in the Guohe River Basin. A hydrogeological survey was conducted, and hydrochemical and hydrogen–oxygen isotopic data of 125 samples of surface water and groundwater were analyzed. The results showed that the total dissolved solid (TDS) content in shallow groundwater was 138–2967 mg/L, with an average of 831 mg/L. A decline in the TDS was observed from the upper to the lower reaches. The contents of the anions and cations in the shallow groundwater were in the order HCO₃⁻ > Cl⁻ > SO₄²⁻ and Na⁺ and K⁺ > Mg²⁺ > Ca²⁺, respectively. The cation exchange increased the aqueous concentrations of Na⁺ and K⁺, and the TDS content was highly correlated with the contents of Na⁺, Cl⁻, and SO₄²⁻ ions. The δD and δ¹⁸O values in shallow groundwater increased from the upper to the lower reaches, with the mean δD values being −59.72‰, −53.58‰, and −47.17‰ and the mean δ¹⁸O values being −8.33‰, −7.37‰, and −6.43‰. The contribution rates of the recharge source, evaporation, and water–rock interaction to the groundwater TDS concentration were 20.4%, 29.5%, and 50.1%, respectively. The water–rock interaction dominated the formation of shallow groundwater in the Guohe River Basin. The dissolution of salt rock and gypsum contributed to ion formation in shallow groundwater. The research findings can be used to improve the groundwater quality in the Guohe River Basin.