Hydrochemical and stable isotope (δ2H and δ18O) characteristics and hydrogeochemical processes in the Baotu Spring Basin, Eastern China

The safety of groundwater quantity and quality is essential for economic development and the ecological environment in the Baotu Spring Basin (BTSB). Thus, it is important to correctly recognize groundwater recharge, the source of major ions, seasonal differences, and the mechanisms of groundwater hydrogeochemical processes. To investigate these issues, surface and groundwater samples were collected and analyzed for hydrochemical components in both the dry and wet seasons in the BTSB. Stable isotope samples of the surface water and groundwater were collected and analyzed in the dry season. The hydrochemical results show that Ca and HCO 3 are the dominant cations and anions, and HCO 3 ·SO 4 -Ca is the dominant groundwater type in the dry and wet seasons. The stable isotope results indicate that precipitation is the primary recharge source of groundwater and surface water in the study area, and precipitation may undergo secondary evaporation under clouds that are in the process of dropping. Moreover, surface water recharges groundwater in infiltration areas near rivers or lakes, where mixing action occurs. The dissolution of calcite, dolomite, and gypsum is the primary water-rock interaction in hydrochemical evolutionary processes. Furthermore, anthropogenic inputs, such as NO 3 and Cl, become more important factors affecting the chemical compositions of the surface water and groundwater. Moreover, three ion types (K, Na, and Cl/Ca; Mg and HCO 3 /NO 3 ; and SO 4 ) were classified in the study area according to the distribution of the ion ratios in the dry and wet seasons. This work provides hydrochemical evidence for water resource management and ecological restoration in the BTSB.