Data for "Dynamics of underground soil loss and its response to rainfall based on karst spring monitoring"

This dataset underpins the study “Dynamics of underground soil loss and its response to rainfall based on karst spring monitoring”, including real-time monitoring and sampling analysis data collected in the Shamuhe Catchment, Shibing County, Guizhou Province, a typical subtropical humid karst area with well-developed fissures and dual surface–subsurface hydrological structure. Observation lasted 373 consecutive days from April 26, 2021 to May 4, 2022, covering a full hydrological year. Two springs with contrasting discharge and land use were monitored: SP1, a large-discharge spring (181 L·s⁻¹) under forest cover; SP2, a small-discharge spring (2 L·s⁻¹) under cropland and shrubland. SP1 was equipped with a French AQUALABO turbidity system recording at 15‑minute intervals. SP2 was sampled monthly with intensified frequency when 12‑hour rainfall exceeded 15 mm. HOBO water level loggers recorded at both springs at 15‑minute intervals. Rainfall was measured at 30‑minute intervals using a standard rain gauge. Water and rainfall samples were collected monthly and intensified during heavy rain. TOC and TN were analyzed with a Shimadzu TOC‑V CPN analyzer; δD and δ¹⁸O with a Los Gatos Research DLT‑100 isotope analyzer; Cl⁻, NO₃⁻, SO₄²⁻ with a Thermo Fisher Dionex ICS‑1100 ion chromatograph. Sediment concentration was determined by gravimetry (SP2) and turbidity calibration (SP1). Key findings: Among 198 rainfall events, only 48 exceeding 6.2 mm or 0.54 mm·h⁻¹ triggered significant spring responses, showing a clear threshold effect. Above the threshold, sediment concentration and water level rose and fell sharply, with SP1 peaking at 650.35 mg·L⁻¹. Stable isotopes remained stable, indicating spring water was dominated by old groundwater; increased sediment reflected flushing of legacy sediment by rainfall‑driven pressure waves, supporting an “accumulation‑trigger” mechanism. Annual mean sediment concentration was 23.52 mg·L⁻¹ for SP1 and 14.30 mg·L⁻¹ for SP2; annual soil loss was 134.25 t·yr⁻¹ and 1.27 t·yr⁻¹, respectively. Catchment‑scale underground soil loss was 0.75 t·km⁻²·yr⁻¹, accounting for 0.69% of total regional erosion. Major influencing factors include rainfall threshold, karst conduit development, and spring discharge, which jointly control sediment transport capacity and underground soil loss magnitude.