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Understanding how karst springs integrate seasonal recharge, internal storage, and event-scale flow-path activation is essential for interpreting their hydrochemical behavior and vulnerability. This study investigated Shuifang Spring, a small karst spring influenced by seasonal rainfall and low-intensity tourism, using stable isotopes, major hydrochemical indicators, MixSIAR, Gaussian Mixture Model (GMM) clustering, and event-scale concentration-discharge (C–Q) relationships with hysteresis analysis. Results showed clear seasonal shifts in recharge composition. Near-surface sources dominated during rainy periods, whereas fracture-matrix groundwater becomes more important during dry periods, indicating alternating dominance of rapid recharge and delayed storage release. Continuous specific electrical conductivity (SpC) data identified multiple recurrent hydrochemical states rather than a simple wet–dry binary. Low-SpC states reflected rapid recharge, intermediate states represented mixed-flow conditions, and high-SpC states indicated stronger storage control and possible weak anthropogenic influence. Event-scale C–Q analysis further showed that antecedent wetness and event sequencing exert stronger control on spring response than rainfall amount alone. Wetter antecedent conditions favored stronger dilution and clearer clockwise hysteresis, whereas drier conditions produced more buffered responses dominated by stored groundwater. Weak sewage influence was detectable, but it acted mainly as a secondary signal linked to hydrological connectivity. Overall, Shuifang Spring behaved as a dynamic multi-state karst system in which seasonal source mixing, storage-release processes, and event-scale connectivity jointly shape hydrochemistry. This integrated approach improves understanding of karst spring functioning and the sensitivity of small karst catchments to natural variability and low-level human disturbance.
Minghong et al. (Tue,) studied this question.