Assessing soil heavy metal pollution in the water-level-fluctuation zone of the Three Gorges Reservoir, China

Background/Question/Methods

With the completion of the Three Gorges Dam of China, the water level of the Three Gorges Reservoir fluctuates from 145 m above sea level in summer (May to September) to May to 175 m in winter (October to April), resulting in formation of the water-level-fluctuation zone (WLFZ) with a total area of 350 km2 in the reservoir. There is great concern that heavy metals from industrial activities and domestic consumptions may be carried on to and accumulated in the WLFZ. We hypothesize that the heavy metal concentrations, source profiles, and source distributions have altered after submergence. In September 2008 (before submergence) and June 2009 (after submergence), soil samples were collected in 12 sampling sties in the WLFZ and heavy metals (Hg, As, Cr, Cd, Pb, Cu, Zn, Fe, and Mn) were detected using total sediment digestion. Enrichment factor (EF), factor analysis (FA), and factor analysis-multiple linear regression (FA-MLR) were employed for heavy metal pollution assessment, source identification, and source apportionment before and after submergence. The objective was to help develop soil and water conservation strategies for the reservoir.

Results/Conclusions

The heavy metals show significantly spatial variability both before and after submergence in the soil of WLFZ of the reservoir. Heavy metals including As, Cd, Pb, Cu, and Zn are higher in the upper and low reaches. FA and FA-MLR reveal that As and Cd are the primary pollutants before submergence and they primarily originate from domestic sewage and industrial wastes, accounting 45.20% and 58.97% for As and Cd, respectively. After submergence, the primary contaminations are Hg, Cd, and Pb, and traffic exhaust contributed 80.63% to Hg, and industrial effluents account 35.52% for Cd and 72.85% for Pb. Moreover, submergence increases the concentrations of Hg, Cd, Pb, Cu, and Zn by providing additional non-point source of pollutants in the WLFZ, while decrease in As and Fe due to facilitation of material exchange by flooding. Our results suggest that during the submergence period increased shipping and industrial wastes may have deposited large amount of heavy metals in the WLFZ in the Three Gorges Reservoir, China.