Spatial and Temporal Variations of Heavy Metal Pollution in Sediments of Daning River Under the Scheduling of Three Gorges Reservoir

In order to explore the influence of Three Gorges Reservoir (TGR) operation on heavy metal pollution of sediment in tributaries, taking Daning river as a case study area, the variation characteristics of heavy metal distributions (in sections of DC, BSH, CZB, Yangtze River) were investigated, and the potential ecological hazards were evaluated by potential ecological risk index. The results showed that the average contents of Cr, Cu, As, Cd and Pb were 116.782, 92.676, 19.877, 1.168, 46.194 mg/kg, respectively. The contents of the studied five kinds of heavy metals in sediment were ranked as follows: Cr > Cu > Pb > As > Cd, and exceeded the background value by 1.23, 3.31, 1.61, 6.79, 1.16 times, respectively. Spatial distributions of the five heavy metals had accumulated along the Daning river from upstream to downstream with the maximum contents in CZB. Temporal distributions of the five heavy metals showed that the higher content levels appeared after water release (drainage) from the TGR. Vertical distributions of the five heavy metals showed an increasing trend from the surface to the bottom at the period before and after drainage and high water level period, while showed a decreasing trend from the surface to the bottom at the impounding period. The potential ecological risk indexes of the five heavy metals ranked as follows: Cd > As > Cu > Pb > Cr. Cd (E-r(i) was 115 similar to 1133) was the major pollutant in 4 sites, which showed a high level of risk. Correlation analysis showed a highly significant correlation between Cu, As, Cd and Pb, which indicated that they may have the similar sources.