[Hydrochemical Characteristics and Control Factors of Surface Water in Kuaize River Basin at the Upper Pearl River].

The Kuaize River is a small typical karst watershed in the source area of the Pearl River as well as an important coal mining area in Eastern Yunnan with a fragile ecological environment. Strengthening the research on the water environment in the region plays an important role in supporting the comprehensive management of the ecological environment and water resources in the source region of the Pearl River. Through the systematic collection of surface water, karst groundwater, and mine water samples, mathematical statistics analysis, correlation analysis, ion ratio analysis, absolute principal component scores multiple linear regression(APCS-MLR), and other methods were used to study the characteristics of hydrochemical evolution and control factors in Kuaize River Basin. The results showed that the average pH value of surface water in Kuaize River Basin was 7.8, which was weakly alkaline. The main cations were Ca2+ and Na+, showing the characteristics of Ca2+>Na+>Mg2+>K+. The main anions were HCO3- and SO42-, showing the characteristics of HCO3->SO42->NO3->Cl-. The variation coefficients of Na+, SO42-, and NO3- in surface water were high, showing strong spatial variability. The water chemical type of the trunk stream was mainly HCO3-Ca, whereas the water chemical type of the tributary was relatively complex, mainly HCO3-Ca, HCO3-Ca·Na, and HCO3·SO4-Ca·Na. The chemical composition of surface water was mainly affected by rock weathering, cation exchange, and human activities. Ca2+, Mg2+, Na+, and HCO3- in surface water mainly came from the weathering of carbonate rock and silicate rock; SO42- mainly came from the oxidation of sulfide, such as pyrite in coal seams; K+, Cl-, and NO3- mainly came from domestic sewage and agricultural activities. The APCS-MLR receptor model analysis results showed that the surface water in the Kuaize River Basin was mainly affected by sulfide oxidation, carbonate weathering, weathering of silicate rock in mine water, domestic sewage, agricultural activities, and unknown sources. In general, the contribution rate of human activities such as mining, domestic sewage, and agricultural activities to the surface water reached 47.17%, indicating that human activities were the key driving factor of surface water chemistry in the Kuaize River Basin.

[Hydrochemical Characteristics and Controlling Factors in Wudu River Basin of Guizhou Province].

TheWudu River is a typical mining-type watershed in the karst mountainous area of western Guizhou Province. Based on the collection of the main stream, tributaries, spring water, and mine water samples in Wudu River Basin, the hydrochemical characteristics and control factors of Wudu River Basin were studied using Gibbs diagram, Piper diagram, and mathematical statistics analysis, and the solute contribution rate of different sources was calculated. The results revealed that the pH value of the water in the Wudu River Basin ranged from 7.87 to 8.52, with an average of 8.14. The TDS values ranged from 135 to 243 mg·L-1, with an average of 191.7 mg·L-1. The major cations in natural river and spring water were Ca2+ and Mg2+, the major anion was HCO3-, and the hydrochemical type was HCO3-Ca. However, owing to the influence of mining activities, the major cations in some tributaries were Ca2+ and Na+, and the hydrochemical types transitioned to HCO3·SO4-Ca and HCO3·SO4-Ca·Na. The ion components of river water in Wudu River Basin were affected by mine water discharge and cation exchange, carbonate rock weathering, silicate rock weathering, and agricultural fertilization. The high concentration of SO42- and Na+in mine water was the primary source of SO42- and Na+in the tributaries of the Wudu River. The method for calculating chemical material balance showed that the contribution rate of carbonate rock weathering ranged from 44.12% to 86.92%, with an average of 74.32%. The contribution rate of mining activities ranged from 3.28% to 37.07%, with an average of 11.61%. Carbonate rock weathering was the main controlling factor of hydrochemical components in the Wudu River Basin; meanwhile, mining activities also had a certain impact on river water chemistry but they showed spatial heterogeneity. The average contribution rates of atmospheric precipitation, silicate rock weathering, agricultural activities, and domestic sewage were 3.75%, 4.67%, 2.85%, and 2.81%, respectively, which had a limited impact on the hydrochemical components of the basin.

[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 SO42-, 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%.