Spatiotemporal propagation of recharge-derived isotopic signals in an alluvial fan aquifer using probabilistic endmember mixing analysis

This is the authors' abstract. We don't add key points for this paper.

Study region Artificial recharge facilities near the apex of the Choushui River alluvial fan, central Taiwan, were examined. Local groundwater was represented by monitoring wells within or adjacent to the recharge area, whereas regional groundwater was represented by irrigation wells distributed across the surrounding fan. Study focus This study investigates how recharge-derived isotopic signals differ between near-field monitoring wells and regional irrigation wells. We integrated multiyear δ 18 O and δ 2 H records with probabilistic endmember mixing analysis to estimate contributions from precipitation, surface water, hyporheic flow, and groundwater endmembers. Reciprocal configurations compared the two groundwater observation scales, and we evaluated posterior contributions by distance, recharge-operation period, and lagged correlation with monthly recharge volume. New hydrological insights for the region Local groundwater showed a larger estimated surface-water contribution and greater spatial and temporal variability than regional groundwater. Regional groundwater showed more evenly distributed source contributions and greater overlap among posterior distributions, indicating less isotope-based source discrimination at the broader observation scale. Descriptive differences between operational periods were larger in local groundwater than in regional groundwater. Small phase contrasts and some source rankings were sensitive to the prior specification. Maximum positive correlations occurred at different lags, but their modest magnitudes indicate descriptive temporal correspondence rather than groundwater travel time. Near-field and regional wells therefore provide complementary information on the expression of recharge-derived isotopic signals.