[Hydrochemical Composition Characteristics and Control Factors of Xiaohuangni River Basin in the Upper Pearl River]

In order to serve the water resources management of the Xiaohuangni River basin, this study explored the hydrochemical composition characteristics and ion sources of surface water in the basin. Samples of main stream and tributary river water and mine water were systematically collected. By means of a Piper diagram, Gibbs diagram, ion ratio coefficient, and mathematical statistical analysis, we analyzed the hydrochemical composition, spatial distribution characteristics, and main control factors of the Xiaohuangni River and evaluated the solute contribution rates of different sources. The results showed that the pH of the Xiaohuangni River basin ranged between 7.17 to 9.14, with an average of 8.00, which is generally considered weakly alkaline. Additionally, the total dissolved solids ranged between 154 mg·L^-1 to 460 mg·L^-1, with an average of 257.39 mg·L^-1, which was equivalent to that of the main stream of the Xijiang River. The dominant cation was Ca²⁺, accounting for 69% of the total cations; the dominant anions were HCO₃^- and SO₄^2-, accounting for 65% and 30% of the total anions, respectively. The main chemical type of the main stream was HCO₃-Ca. Affected by mining activities, the tributaries transitioned from HCO₃-Ca to HCO₃·SO₄-Ca and HCO₃·SO₄-Ca·Na type. River water solute was mainly controlled by the weathering of carbonate rock and silicate rock, with the participation of sulfuric and carbonic acid. The contribution rate of carbonate weathering to river water solute was 63%, and that of silicate weathering was 16.33%. Meanwhile, human activities contributed markedly to the dissolved solutes of the Xiaohuangni River basin, in which the contribution rate of mining activities was 13.4%, and the contribution rate of agricultural activities and domestic sewage was 4%.