[Characteristics and Driving Factors of Hydrochemical Evolution in Tuochangjiang River Basin, Western Guizhou Province].

Tuochangjiang River is a typical mining-type watershed in the karst mountainous area of western Guizhou province. The study of its hydrochemical evolution characteristics and driving factors is of great significance to the local economic development and the scientific management of water resources. The samples of river water, spring water, and mine water in the Tuochangjiang River Basin were collected, and the sources of solutes and their contribution to the chemical components of river water were discussed by means of hydrochemical diagrams, mathematical statistics, and the absolute principal component scores-multivariate linear regression model (APCS-MLR). The results showed that the pH of the river water ranged between 7.30 to 8.31, and the TDS value ranged between 40 to 520 mg·L, which was mainly contributed by Ca, Na, HCO, and SO. The dominant cations in river water were Ca and Na, the dominant anions were HCO and SO, and the main water chemistry transitioned from HCO-Ca to HCO-Ca·Na and HCO·SO-Ca·Na type, whereas that of the mine water was mainly the HCO-Na and HCO·SO-Na types. The chemical composition of river water was affected by rock weathering, exchange adsorption of anions, mineral dissolution and precipitation, and human activities, in which Ca, Mg, and HCO were mainly derived from the weathering and dissolution of carbonate and silicate rocks, Naand SO were mainly from the discharge of mining wastewater, and Cl and NO were affected by domestic sewage and agricultural activities, respectively. APCS-MLR analysis further showed that the river water solutes mainly included five sources:discharge of mining wastewater, dissolution of soil minerals, geological background, agricultural activities, and unknown sources, and their contribution rates to river water were 23.49%, 35.04%, 13.87%, 7.96%, and 20.63%, respectively. Mining factors and soil factors were the most important sources of solutes in the river water, and they were the main driving factors for the hydrochemical evolution of the Tuochangjiang River Basin.