Hydrochemical characteristics and ion sources of river water in the upstream of the Shiyang River, China

As the largest tributary of the Shiyang River, with the average annual inflow of total runoff accounting for 23%, the Xiying River has representative of mountain runoff of inland rivers in the Northwest of China. Using samples collected in this basin from September 2016 to October 2017, the water chemical composition and ion source characteristics of river were studied. The results show that the river is weakly alkaline, the average pH is 8.0 and the TDS is 179.29 mg·L−1. With the elevation decreasing along the river, the TDS of main stream tend to increase first and then decrease, but those of TDS of each tributary decrease, and the latter is lower than the former. Affected significantly by the flow, the lowest value of ion concentration in river occurs in summer, and the highest occurs in autumn and winter. The hydrochemical type of river is CaMg–HCO3. In the river, the order of cation mass concentration is NH4+ < K+ < Na+ < Mg2+ < Ca2+, and that of anion is F− < NO3− < Cl− < SO42− < HCO3−. The sources of ions in river are mainly from the weathering of silicates and carbonates. With the elevation decreasing along the river, the influence of silicates on the inflowing tributaries is gradually strengthened.