Dual stable isotopes to rethink the watershed-scale spatiotemporal interaction between surface water and groundwater.

The interaction between groundwater and surface water, including their recharge relationship and ratio, is crucial for water cycling, management, and pollution control. However, accurately estimating their spatiotemporal interaction at the watershed scale remains challenging. In this study, we used dual stable isotopes (δ18O, δ2H, d-excess , and lc-excess) and hydrochemistry methods to rethink spatiotemporal interaction at the Yiluo River watershed in central China. We collected 20 groundwater and 40 surface water samples over four periods in two seasons (dry and wet). Our results showed that in the downstream region, groundwater recharged surface water in the dry season while surface water recharged groundwater in the wet season, with average recharge ratios of 89.82% and 90.02%, respectively. In the midstream region, surface water recharged groundwater in both seasons with average ratios of 93.79% and 91.35%. In contrast, in the upstream region, groundwater recharged surface water in both seasons with ratios of 67.35% and 76.89%. Seasonal changes in the recharge relationship between surface water and groundwater in the downstream region also been found. Our findings provide valuable insights for watershed-scale water resource and pollution management. Title Comprehensive dual isotopes and hydrogeochemistry method to rethink the interaction between groundwater and surface water at watershed scale. [Display omitted] • Study on spatiotemporal interaction at surface water-groundwater system at watershed-scale. • Using dual isotopes and hydro-geochemistry to analysis Groundwater-surface water interaction. • Recharge style changing in different seasons in Yiluo River watershed. • Groundwater and surface water interaction displayed significant seasonal variations. [ABSTRACT FROM AUTHOR]