Major ions and δ34SSO4 in Jiulongjiang River water: Investigating the relationships between natural chemical weathering and human perturbations.

The chemical weathering processes become a rising concern in carbon cycling research, because it can increase carbon budgets of lateral transport by rivers and effectively sequestrate atmospheric CO2. Recent studies suggest that the human perturbations can accelerate the chemical weathering, however, the processes of accelerated weathering and its potential environmental effects still remain questions. To examine the mechanism of the human-related accelerated weathering and its influences, the spatial-temporal distributions of the major ions and stable isotope compositions (δ34SSO4) in Jiulongjiang River are measured. The seasonal variations of the riverine solutes results from the hydrologic condition and different mineral dissolution rates of carbonate and silicate minerals. The H2SO4 and HNO3 indeed participate in the mineral dissolution, and increase the riverine C flux. S isotope compositions suggest the riverine H2SO4 is mainly derived from the anthropogenic sewage inputs and oxidation of sulfide, while the statistics and stoichiometry analysis indicating HNO3 are close related to the agricultural activities. On the watershed scale, the areas with high agricultural/urban land use areas (%) have significantly high TDS and DIC values in comparison with that in the areas with high forest covering, indicating the accelerated weathering processes have already been activated by the human perturbations. The assessments of the irrigation water quality suggest that the Jiulongjiang river water is facing the salinity hazard under the accelerated weathering conditions. More attention should be paid to the effect of human perturbations on chemical weathering.