Hydrochemical and stable isotopic analysis of surface water and groundwater in the Guanzhong Basin, China: Implication to understanding their interactions

Managing water resources sustainably requires a thorough grasp of surface-groundwater interactions to maintain healthy ecosystems. This study investigated surface water-groundwater interactions in the Guanzhong Basin, a typical semi-humid continental monsoon region in Northwest China, by examining hydrochemistry and stable isotopes (δD and δ¹⁸O) of surface water and groundwater. A total of 27 monitoring sites across the target cities (Weinan, Xi'an, and Baoji) were sampled in 2022. The surface and groundwater hydrochemical properties show distinct spatial patterns across the region. The HCO₃–Ca·Mg hydrochemical type was the most prevalent in surface water and groundwater. The distribution of hydraulic connectivity varies significantly across the four sites in Baoji, Xi'an, and Weinan, with Weinan showing dominant high connectivity at Sites 1 and 2, Xi'an at Site 3, and Baoji at Site 4. This spatial pattern highlights distinct hydrogeological characteristics governed by site-specific hydraulic properties, reflecting localized differences in subsurface properties. Groundwater in Baoji, Xi'an, and Weinan was primarily recharged by precipitation (17 %, 68 %, and 15 %), surface water (50 %, 41 %, and 9 %), and inflow from upstream areas (52 %, 40 %, and 8 %), respectively. The combined hydrochemical and isotopic results indicated spatial variability in surface water and groundwater interactions. These findings provide a robust scientific foundation for the region's integrated groundwater and surface water interaction management.