Hydrochemical evolution and formation mechanisms of groundwater in the Daihai Lake Basin plain under ongoing ecological water replenishment

, requiring additional cations for charge balance. (2) Groundwater evolution is jointly controlled by water-rock interaction and evaporative concentration, with limited influence from atmospheric precipitation. (3) Three high-fluoride enrichment mechanisms are identified: mineral dissolution under weakly alkaline conditions, evaporative concentration-driven F⁻ enrichment, and accelerated dissolution of fluorine-bearing minerals induced by acidic mining wastewater. (4) 89% of Cluster-3 groundwater meets drinking standards (EWQI < 50), while 70% of groundwater samples from Cluster 1 and Cluster 2 are of poor quality, mainly distributed in the southwestern lakeshore. This study systematically elucidates the hydrochemical characteristics and formation mechanisms of groundwater in the Daihai Lake Basin under continuous ecological water replenishment, identifies key risk zones for groundwater quality, and provides a solid scientific basis for the protection and sustainable utilization of regional groundwater resources, as well as the optimization of ecological water replenishment strategies in similar arid and semi-arid inland lake basins.