Major ion compositions, sources and risk assessment of karst stream under the influence of anthropogenic activities, Guizhou Province, Southwest China

Abstract

To explore the influence of different types of anthropogenic activity on the rivers, we investigate the major ion composition, sources and risk assessment of the karst stream (Youyu stream and Jinzhong stream), which are heavily influenced by mining activities and urban sewage, respectively. The chemical compositions of the Youyu stream water, which is heavily influenced by mining activities, are dominated by Ca2+ and SO42–. However, the chemical compositions of the Jinzhong stream water, which is heavily influenced by urban sewage, are dominated by Ca2+ and HCO3–. The Ca2+, Mg2+ and HCO3– in Jinzhong stream are mainly derived from rock weathering, while the Youyu stream is affected by acid mine drainage, and sulfuric acid is involved in the weathering process. Ion sources analysis indicates that the Na+, K+, NO3–, and Cl– in the Jinzhong stream mainly derive from urban sewage discharge; but NO3– and Cl– of the Youyu stream mainly derive from agricultural activities, and Na+, K+ are mainly from natural sources. The element ratios analysis indicates the ratio of SO42–/Mg2+ in Youyu stream (4.61) polluted by coal mine is much higher than that in Jinzhong stream (1.29), and the ratio of (Na++K++Cl–)/Mg2+ in Jinzhong stream (1.81) polluted by urban sewage is higher than Youyu stream (0.64). Moreover, the ratios of NO3−/Na+, NO3−/K+, and NO3−/Cl− in the agriculturally polluted Youyu stream were higher than those in the Jinzhong stream. We can identify the impact of human activities on streams by ion ratios (SO42–/Mg2+, (Na++K++Cl–)/Mg2+, NO3−/Na+, NO3−/K+, and NO3−/Cl−). The health risk assessment shows the HQT and HQN for children and adults are higher in Jinzhong stream than in Youyu stream and the total HQ value (HQT) of children was higher than one at J1 in the Jinzhong stream, which shows that children in Jinzhong stream basin are threatened by non-carcinogenic pollutants. Each HQ value of F− and NO3− for children was higher than 0.1 in the tributaries into Aha Lake, indicating that the children may also be potentially endangered.