Integration of Hydrochemistry and Stable Isotopes for Assessing Groundwater Recharge and Evaporation in Pre- and Post-Rainy Seasons in Hua County, China

Groundwater resource management is crucial for promoting sustainable development in areas with surface water scarcity, such as Hua County in China. This paper aims to estimate groundwater recharge and evaporation during the pre- and post-rainy seasons in Hua County. The non-equilibrium evaporation model was established to quantify the degree of evaporation. Ternary end-member mixing analysis (EMMA) was used to evaluate the contributions of recharge sources to groundwater recharge. The concentrations of major ions in surface water and groundwater showed some differences, which may be due to differences in their lithological classes and hydrogeochemical evolution. The ion concentrations of both surface water and groundwater were observed to be lower in the post-rainy season, because rainfall infiltration during the rainy season diluted ion concentrations. The Gibbs diagram, end-member diagram, and δ 2 H versus δ 18 O diagram all revealed that groundwater was affected by evaporation to some extent, especially in the pre-rainy season. The non-equilibrium evaporation model showed that the remaining proportions of evaporation calculated using 18 O and 2 H were 0.96 and 0.94%, respectively, during the pre-rainy season and 0.97% and 0.96%, respectively, during the post-rainy season. According to EMMA, the mean contributions of subsurface lateral flow, precipitation infiltration, and river percolation to groundwater were 47%, 28%, and 25%, respectively, during the pre-rainy season and 57%, 30%, and 13%, respectively, in the post-rainy season. The findings of the present study demonstrated that integration of hydrochemistry and isotopic signatures supports better understanding of groundwater recharge and evaporation processes.