Groundwater quality changes induced by overexploitation in the Qiantao Basin near the Yellow River

Groundwater pumping near large rivers is commonly used to prevent agricultural water shortages, yet the impacts of high extraction rates on groundwater systems require clarification. In Dalat County along the Yellow River, intensive extraction has reshaped groundwater flow patterns, forming a cone of depression that reversed groundwater discharge to recharge from the river. The values of groundwater δ18O, EC and Cl within the cone are lower than in the Yellow River irrigation zones. Paradoxically, groundwater in the cone exhibits an older groundwater age, confirming the shift of groundwater flow patterns. This stems from shallow, salinized aquifers in river-irrigated areas, where increased leaching after river recharge elevated EC/Cl despite younger groundwater ages. The cone's depleted δ18O signals suggest mountain-sourced recharge from southern highlands. These findings elucidate recharge dynamics critical for sustainable water management in changing environments.