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Under the fragile ecological conditions characteristic of karst terrains, the synergistic effects of soil erosion and anthropogenic activities have significantly intensified sulfate (SO 4 2- ) mobilization and dispersion, profoundly influencing aquatic ecosystem stability and regional carbon cycling dynamics. To systematically investigate SO 4 2- geochemical behavior mechanisms in such environments, this study focused on the Chiwu Creek Basin, a representative karst agricultural basin. By integrated water chemistry analysis with multi-isotope tracing techniques (δ³⁴S SO4 , δ 18 O SO4 , δD and δ18O H2O ) and Bayesian mixing modeling (Simmr) to characterize hydrochemical features and quantitatively apportion SO 4 2- sources and transformation processes. Key findings reveal: Distinct karst hydrochemical signatures (HCO 3 -Ca·Mg type) with rainfall dilution driving pronounced seasonal SO 4 2- concentration variations; Dominant sulfate contributions from gypsum dissolution (surface water 49.7% > groundwater 28.7%) and soil sulfates (groundwater 33.3% > surface water 28.7%), exhibiting marked wet-season increases that underscore rainfall-erosion coupling in sulfur cycling; Substantial uncertainty (UI 90 ) in natural source contributions (31.3–34.4%) versus more stable anthropogenic inputs (< 12% combined), highlighting natural process amplification in sulfate geochemistry. While anthropogenic sources (sewage/fertilizers/detergents) constitute minor proportions, their environmental significance remains non-negligible. These insights advance fundamental understanding of karst sulfur biogeochemistry while providing critical scientific support for water resource management and carbon sink quantification in Southwest China’s ecologically sensitive karst regions.
Wang et al. (Thu,) studied this question.