Spatial and Temporal Distribution and Pollution Evaluation of Soluble Heavy Metals in Liujiang River Basin

Abstract

In the Liujiang River, soluble heavy metals Zn, Al, Co, As, Ni, Cr, Cu, Mn, Pb, Hg, and Cd were monitored day and night to determine their temporal and spatial distribution as well as the sources of this pollution. The Nemerow comprehensive pollution index method was then used to evaluate the environmental quality of the Liujiang River water body. The results showed that: ① For each river section (Lutang and Luowei), the amounts of soluble Al, Co, As, Ni, Cr, Mn, Pb, and Cd all met the Class Ⅲ water quality standard limit, as defined in the National Surface Water Quality Class Ⅲ Standard. The concentration of Zn and Cu was far below the standard limit, while the Hg content slightly exceeded the standard; the concentration of heavy metals in Liujiang River basin was highest in the normal season and lowest in the wet season. In terms of spatial distribution, the Luowei section had a higher heavy metal concentration. ② The single factor pollution indexes for elemental Hg, Cd, and As were higher in the Liujiang River basin. The Nemerow comprehensive pollution index evaluation shows that the risk of heavy metal pollution in the water body exhibits certain seasonal variations (March > November > June), indicating that rainfall in different seasons may result in reduced drinking water safety in the study area. The water of the Lutang and Luowei sections generally exhibited a moderate level of heavy metal pollution. The comprehensive pollution index of the Luowei section was higher than that of the Lutang section, and the pollution level was relatively severe. Therefore, the Luowei section should be listed as a priority control section of the Liujiang River basin by the water environment management department; ③ After assessing the difference in heavy metal pollution between annual and monthly rainfall periods, it was found that the selection of rainy season or conventional season has no significant impact on the assessment of heavy metal pollution in rivers, when the mass concentration of Cu in the river is used. However, the presence of As, Mn, Pb, Al, Cr, and Ni elements in the river will cause significant differences in the evaluation of heavy metal pollution on an interannual scale; ④ Multivariate statistical analysis results show that Cd, Cr, Ni, Co, and Pb in the Liujiang River are mainly derived from industrial production activities; As and Zn are mainly derived from rainwater leaching of domestic pollution waste; Mn, Al, and Cu are mainly derived from the application of pesticides and fertilizers.