Spatiotemporal variations in the hydrochemical characteristics and controlling factors of streamflow and groundwater in the Wei River of China

Analysis of hydrochemical characteristics and controlling factors of streamflow and groundwater in arid regions is important for water security. In this study, we collected samples of streamflow and groundwater from the Wei River in China, analyzed their hydrochemical characteristics, and identified the major solute sources using ion concentrations, δ15N–NO3− and δ18O–NO3−. The major downstream ion contents were greater than the corresponding upstream values and the ion content in streamflow during the wet season is much higher than that during the dry season. The water quality during the wet season was unsatisfactory as approximately one third of the water samples were categorized as the worst water quality based on excessive nitrates and carbonate weathering. Rock weathering contributed the greatest proportion of solutes to both streamflow and groundwater. Evaporite dissolution and carbonate weathering dominated solutes in the wet and dry seasons, respectively. Human activities cannot be ignored in certain areas. Fertilizer application accounts for 43% of the total anthropogenic solute inputs. These results point to the increasing impact of agriculture on water quality.