[Hydrochemical and Isotopic Characteristics in the Surface Water of the Fenhe River Basin and Influence Factors].

The Fenhe River Basin is the mother river of Shanxi Province. Due to the over-exploitation of water resources and the impact of social and economic development, the ecological environment has deteriorated. After a series of treatment and protection measures, the water quality has since been improved. Mathematical statistics, Piper diagrams, Gibbs model, hydrogen and oxygen isotopes, and other methods were used to analyze the characteristics and sources of hydrochemistry in the surface water of the Fenhe River basin, which revealed the evolution process of surface water quality of the Fenhe River basin. The results showed that the content of the main hydrochemical components in the main stream surface water of Fenhe River basin increased gradually along the runoff path. The hydrochemical types of surface water of Fenhe River basin were mainly HCO ₃ ·SO ₄ ·Cl-Ca·Na·Mg and SO ₄ ·HCO ₃ ·Cl-Ca·Na·Mg. There were great differences in hydrochemical components of tributaries and karst water in the basin. There were also great differences in hydrochemical components of tributaries in the basin. The hydrochemical types of surface water of karst water were mainly SO ₄ ·HCO ₃ -Ca·Mg. The hydrochemical composition of surface water in Fenhe River basin was mainly affected by rock weathering and evaporation crystallization, whereas rainfall had little effect. Na ⁺ and K ⁺ mainly came from the dissolution of evaporated salt rocks with Na in the surrounding loess. Ca ²⁺ , Mg ²⁺ , and HCO ₃ ^- mainly came from the dissolution of carbonate rocks. SO ₄ ^2- may have also come from the dissolution of sulfide minerals in the loess layer around Fenhe River in addition to the dissolution of gypsum. The values of δ D and δ ¹⁸ O of Fenhe River surface water were gradually enriched from upstream to downstream. The characteristics of hydrogen and oxygen isotopes further showed that the surface water was mainly affected by evaporation. The results of this study can provide evidence for ecological restoration and protection and ecological civilization construction in the Fenhe River basin.