Hydrochemical Characteristics and Transformation Relationship of Surface Water and Groundwater in the Hua County, Guanzhong Plain (China)

ABSTRACT Understanding the hydrochemical characteristics and interactions between surface water and groundwater is crucial for the development and protection of water resources in the watershed. This research employs mathematical statistics, hydrogen and oxygen isotopes, IsoSource model, and hydrogeochemical simulation to analyze the interactions between surface water and groundwater in the Hua County, Guanzhong Plain, China. The findings revealed that the surface water and groundwater are weakly alkaline and low‐mineralization freshwater, and the primary hydrochemical types was HCO 3 SO 4 ·Ca type. The absolute dominance of HCO 3 − and Ca 2+ in both surface and groundwater can be largely attributed to the dissolution of carbonate and silicate rocks. Evaporation led to δ D and δ 18 O values enrichment in surface water samples from different tributaries, while groundwater samples, though less affected by evaporation, also displayed δ D and δ 18 O enrichment due to river water infiltration recharge. Overall, the transformation relationship between surface water and groundwater is dominated by surface water infiltration recharge to the groundwater, with recharge contribution rates ranging from 4.7% to 64.5%. Additionally, some surface water samples from the Shidi River were characterized with high fluoride, which may be ascribed to human activities and evaporation. Summary Surface water and groundwater are weakly alkaline, dominated by HCO 3 SO 4 ·Ca type. Hydrochemical components are primarily controlled by silicate rock dissolution. Surface–groundwater interaction mainly involves surface water infiltration. δ 18 O tracing reveals surface water infiltration recharge rates ranging from 4.7% to 64.5%.