Quantitative Source Apportionment and Origin Analysis of Sulfide in the Middle and Lower Reaches Groundwater of Chaobai-Wenyu Alluvial-proluvial Fan, Beijing
Groundwater is a vital component of Beijing's water supply, yet elevated sulfide concentrations restrict its utilization. This study employed principal component analysis (PCA) and absolute principal component-multiple linear regression (APCS-MLR) to apportion sulfide sources and quantify their contributions in the middle and lower reaches of the Chaobai-Wenyu alluvial-proluvial fan. Sulfur and oxygen isotopes (δ34S and δ18O) were used to identify sulfate sources and discern anthropogenic versus natural influences. Results showed that high-sulfide groundwater predominantly occurred in Na-type water, with sulfide accumulation from desulphidation widespread, particularly in Shunyi and within the first, second, and third aquifers, independent of wet/dry seasons. Isotopic analysis indicated sulfate mainly originated from evaporite dissolution, and sulfides from desulphidation were of geological background origin. PCA extracted four principal components: leaching-enrichment (F1), natural dissolution of iron-manganese oxides (F2), water desulphidation (F3), and CaF2 dissolution equilibrium (F4). F3 exhibited the highest factor loading for sulfide (0.418), while other components had small negative loadings. APCS-MLR revealed F3 contributed 21.32% of sulfide, while indigenous sources (e.g., acid-volatile sulfide dissolution, elemental sulfur disproportionation, geothermal activity, well casing materials) contributed 63.66%. Overall, sulfide in the study area is a geological background factor, with limited anthropogenic influence.