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Pyrite oxidation and sedimentary sulfate dissolution are the primary components of riverine sulfate (SO 4 2−) and are predominant in global SO 4 2− flux into the ocean. However, the proportions of anthropogenic SO 4 2− inputs have been unclear, and their tempo-spatial variations due to human activities have been unknown. Thus, field work was conducted in a spatially heterogeneous human-affected area of the Yihe River Basin (YRB) during a wet year (2010) and drought years (2017/2018). Dual sulfate isotopes (δ34S–SO 4 2- and δ18O–SO 4 2-) and Bayesian isotope mixing models were used to calculate the variable anthropogenic SO 4 2− inputs and elucidate their temporal impacts on riverine SO 4 2− flux. The results of the mixing models indicated acid mine drainage (AMD) contributions increased from 56.1% to 83.1% of upstream sulfate and slightly decreased from 46.3% to 44.0% of midstream sulfate in 2010 and 2017/2018, respectively, in the Yihe River Basin. The higher upstream contribution was due to extensive metal-sulfide-bearing mine drainage. Sewage-derived SO 4 2− and fertilizer-derived SO 4 2− inputs in the lower reaches had dramatically altered SO 4 2− concentrations and δ34S–SO 4 2- and δ18O–SO 4 2- values. Due to climate change, the water flow discharge decreased by about 70% between 2010 and 2017/2018, but the riverine sulfate flux was reduced by only about 58%. The non-proportional increases in anthropogenic sulfate inputs led to decreases in the flow-weighted average values of δ34S–SO 4 2- and δ18O–SO 4 2- from 10.3‰ to 9.9‰ and from 6.1‰ to 4.4‰, respectively. These outcomes confirm that anthropogenic SO 4 2− inputs from acid mine drainage (AMD) have increased, but sewage effluents SO 4 2− inputs have decreased. [Display omitted] • Bayesian Isotope Mixing Model quantified sulfate contributions from anthropogenic sources. • AMD contributions had increased from 56% to 83% upstream over the last decade. • Downstream sewage sulfate input had dramatically altered δ 34S–SO 4 2- and δ 18O–SO 4 2−values. • Flow-weighted average δ 34S–SO 4 2- and δ 18O–SO 4 2−values had decreased to 9.9‰ and 4.4‰, respectively. [ABSTRACT FROM AUTHOR]

Dissolved heavy metals (DHMs) contamination has raised global concern for ecological and human health development. Weathering of sulfide-bearing ore metals can produce acidic, sulfate-rich solutions in the presence of water and oxygen (O 2), and DHMs are released to deprave the river water quality. Sulfur and oxygen isotope signatures (δ 34S SO4 and δ 18O SO4) could identify this pyrite-derived sulfate; however, it is yet not well known whether the δ 34S SO4 and δ 18O SO4 values could limit the DHMs sources and illustrate anthropogenic impacts on DHMs along the river corridor. We tried to solve this problem through field works in the Luohe River and Yihe River, two tributaries of the Yellow River, China, where metal sulfide mine activities mostly occurred upstream, but agricultural and domestic behaviors concentrated in the lower plain reaches. In the Luohe River upper areas, δ 34S SO4 values had negative correlations with concentrations of cadmium (Cd) (p < 0.01), nickel (Ni) (p < 0.05), molybdenum (Mo) (p < 0.01), uranium (U) (p < 0.01), and SO 4 2− (p < 0.01). However, as the δ 34S SO4 values increased downstream in the Luohe River, concentrations of copper (Cu) (p < 0.05), mercury (Hg) (p < 0.05), Ni (p < 0.05), and SO 4 2− (p < 0.01) simultaneously elevated. The Bayesian Isotope Mixing Model (BIMM) results via δ 34S SO4 values demonstrated 64.3%–65.3% of SO 4 2− from acid mine drainage (AMD) in the Luohe River's upper reaches and 63.5%–67.7% in the Yihe River's upper reaches, and about 33% from sewage and industrial effluents in the Luohe River's lower reaches and 27% in Yihe River's lower reaches. Our results confirmed the different anthropogenic impacts on the DHMs concentrations in Luohe River and Yihe River and provided a robust method for DHMs sources appointment and pollution management in river systems. [Display omitted] • Mo and SO 4 2− concentrations had negative relations with δ 34S SO4 values in the upstream. • Sulfide mine drainage contributed 64% to 68% of upstream riverine SO 4 2−. • Sewage and industrial effluents exported 27%–33% of downstream riverine SO 4 2−. • δ 34S SO4 and δ18O SO4 values could be used to distinguish different anthropogenic metal inputs. [ABSTRACT FROM AUTHOR]