Hydrogeochemical processes and water quality of the Aïn Taga Karst Spring, Tlemcen, Northwestern Algeria

This study presents the first long-term hydrogeochemical monitoring (2014-2024) of the Aïn Taga karst spring, located in the Ghar Boumaâza karst system (northwestern Algeria). The analysis is based on 71 samples, examined for major ions, salinity, hardness and saturation indices, interpreted using Piper and Chadha diagrams, multivariate statistical methods (PCA, CAH) and mineral balance calculations. The results reveal a clear dominance of the Ca-Mg-HCO₃ facies (94.4% of the samples), indicating that carbonate dissolution mainly controls mineralization, with waters supersaturated with calcite and dolomite and a limited influence of evaporitic formations. A cubic polynomial model HCO₃⁻-Q highlights a nonlinear relationship between bicarbonate concentration and flow, characterized by high concentrations at low flow rates (prolonged residence times and strong water-rock interaction) and progressive dilution during high-water episodes, with very good predictive performance (R² ≈ 0.95, MAE ≈ 15 mg/L, RMSE ≈ 19 mg/L). Principal component analysis clearly distinguishes natural mineralization from low anthropogenic inputs (NO₃⁻, Cl⁻, SO₄²⁻), while the marked negative correlation between flow and bicarbonate (ρ =  - 0.66) highlights the dilution processes during floods. In this strategic, highly vulnerable and historically understudied karst, this integrated approach provides an operational framework to link the hydrodynamic regime and hydrochemical signature, improve the interpretation of carbonate dissolution processes, identify localized contaminations and guide monitoring and protection strategies for water resources.