Significant influence of water diversion and anthropogenic input on riverine sulfate based on sulfur and oxygen isotopes

The transportation of dissolved sulfate (SO42-) to the ocean via river systems plays a critical role in the global sulfur cycle. However, the increasing anthropogenic input has made it challenging to quantify the various pristine contributions accurately. The riverine sulfur and oxygen isotopes of sulfates (delta(SSO4)-S-34 and delta(OSO4)-O-18) and the advantages of the Markov-Chain Monte Carlo model were used to distinguish the anthropogenic input in Fenhe River, a tributary of the Yellow River. The SO(4)(2-)concentrations and delta(SSO4)-S-34 and delta(OSO4)-O-18 values of the mainstream river were normally distributed with minor seasonal variations (P > 0.05). However, the upstream riverine SO(4)(2-)concentrations were significantly altered by the water diversion from the Yellow River. The midstream and downstream sections exhibited a continuous increase in the riverine SO(4)(2-)concentration and delta(SSO4)-S-34 and delta(OSO4)-O-18 values during both seasons. The coal mining drainage significantly impacted the tributaries near coal mining activities, and chemical fertilizers and sewage contributed more sulfate in the midstream and downstream sections. The yearly sulfate flux of the Fenhe River accounted for 4.2% of that of Yellow River, among which over 60% was from anthropogenic sources. The average delta(34)SSO(4 )and delta(OSO4)-O-18 values had elevated to 11.0%o and 6.0%o, respectively, due to the extensive input of anthropogenic sulfate. Our findings confirm the utility of delta(SSO4)-S-34 and delta(OSO4)-O-18 for tracing anthropogenic input and underscore its impacts on river systems and the global sulfur cycle.