Hydrochemical fingerprints of water resources in a karst watershed affected by mining activity in southwestern China

Investigating the hydrogeochemical processes is a significant basis for achieving sustainable water resource management in karst watersheds. A total of 42 water samples were collected from the Wudu River karst watershed in southwestern China during May 2022, comprising surface water (SFW) (N = 42), groundwater (GDW) (N = 5), and mine water (MEW) (N = 3). Field sampling and hydrogeochemical analysis were conducted to identify water quality features, recharge sources, and dominant geochemical mechanisms. The results show that water samples are generally weakly alkaline (mean pH = 7.45), with total hardness indicating moderately hard water. The hydrochemical facies are primarily of the HCO₃–Ca type (88.10 %). Hydrochemical types transition from GDW (HCO₃–Ca) to SFW (HCO₃–Ca and mixed) and further to MEW (HCO₃–Na). Stable δ¹⁸O and δD isotopic characteristics indicate that both surface and groundwater receive recharge primarily through atmospheric precipitation and are influenced by evapotranspiration. Atmospheric precipitation is the primary recharge source of mine water, accounting for 95.50 %. Carbonate dissolution and silicate weathering dominate ion chemistry, supplemented by cation exchange and CO₂ dissolution. Anthropogenic influences are evident, as agricultural activities elevate nitrate (NO₃⁻) concentrations in GDW and SFW, while acid mine drainage (AMD) increases sulfate (SO₄²⁻) and chloride (Cl⁻) in MEW. Despite limited temporal resolution, the study results provide new insights into water-rock interactions and recharge mechanisms of water resources in karst regions.