Heavy metal contamination in the water level fluctuation zone (WLFZ) has been a particularly important issue for water quality in China’s Three Gorges Reservoir (TGR) since the TGR has been operational for the past 10 years. In this study, surface soils were collected from 21 sites in the WLFZ of the TGR during the periods of 2008-2016 to investigate the spatial and temporal distributions of heavy metals (Hg, As, Cr, Cd, Pb, Cu, and Zn) and determine their controlling factors using regression analysis and redundancy analysis (RDA). Their possible sources were also identified and quantified using factore analysis (FA) and factor analysis-multiple linear regression (FA-MLR). Afterwards, multiple indices, including enrichment factors (EF), geoaccumulation index (Igeo), and potential eco-risk index were used to assess the potential risk of heavy metals. The study intended to provide new insights into the contamination state of heavy metals in the WLFZ and thereby the ecological remediation in the TGR region.
Results/Conclusions
Results showed that heavy metal concentrations remarkably decreased from upstream, revealing that dams have a considerable effect on the distribution and transfer of heavy metals in the riparian zone. Also, the decreased concentrations from upstream to downstream was also associated with the phosphorus (P) pollution, indicating that agricultural activity was an important controlling factor for this spatial pattern. Soil pollution state in the WLFZ was improved after the year of 2012, which could be contributed to the decreasing input of the organic matter (OM) contaminants related to the industrial, urban and traffic pollution. In addition, soil physiochemical properties (e.g., grain size, pH, and Mn oxides) also controlled the mobility and transfer of heavy metals in the WLFZ. Analyses indicated that the soils in the WLFZ were moderately contaminated by As and Pb. Our results indicate that priority should be prevention of As and Pb pollution and P contaminants in the TGR.