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

Abstract

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 SO₄^2-, showing the characteristics of HCO₃^->SO₄^2->NO₃^->Cl^-. The variation coefficients of Na⁺, SO₄^2-, 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; SO₄^2- 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.

Keywords: APCS-MLR model; Kuaize River; Upper Pearl River; hydrochemical characteristics; surface water.