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

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 Ca(2+) and SO(4)(2)(–). However, the chemical compositions of the Jinzhong stream water, which is heavily influenced by urban sewage, are dominated by Ca(2+) and HCO(3)(–). The Ca(2+), Mg(2+) and HCO(3)(–) 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(+), NO(3)(–), and Cl(–) in the Jinzhong stream mainly derive from urban sewage discharge; but NO(3)(–) 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 SO(4)(2)(–)/Mg(2+) 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(–))/Mg(2+) in Jinzhong stream (1.81) polluted by urban sewage is higher than Youyu stream (0.64). Moreover, the ratios of NO(3)(−)/Na(+), NO(3)(−)/K(+), and NO(3)(−)/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 (SO(4)(2)(–)/Mg(2+), (Na(+)+K(+)+Cl(–))/Mg(2+), NO(3)(−)/Na(+), NO(3)(−)/K(+), and NO(3)(−)/Cl(−)). The health risk assessment shows the HQ(T) and HQ(N) for children and adults are higher in Jinzhong stream than in Youyu stream and the total HQ value (HQ(T)) 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 NO(3)(−) for children was higher than 0.1 in the tributaries into Aha Lake, indicating that the children may also be potentially endangered.