Evaluation of Heavy Metal Pollution in Surface Sediments of Southwest Liujiaxia Reservoir, Gansu

Liujiaxia reservoir is located in the upper reaches of the Yellow River in southwest Gansu province. As a large-scale hydropower project, Liujiaxia reservoir has played a great role in economic and social developments of Gansu and Qinghai provinces since it was built in 1974. In order to study the heavy metal pollution in surface sediments of southwest Liujiaxia reservoir, the contents of six metal elements such as Cr, Cd, Ni, Cu, Zn and Pb were measured by inductively coupled plasma mass spectrometer (ICP-MS) for 55 surface sediment samples from Liujiaxia reservoir. The results show the average concentrations of Cr, Cd, Ni, Cu, Zn and Pb were 77.03μg/g, 0.16μg/g, 33.53μg/g, 32.09μg/g, 291.77μg/g and 22.44μg/g, respectively. Based on comprehensive analyses of the spatial distribution of heavy metal content in surface sediments, the single factor pollution index, Nemero comprehensive index, geoaccumulation index and potential ecological risk index, the pollution degrees of the studied area and its potential ecological risk were evaluated. The pollution levels of the geoaccumulation index were in the order of Zn > Cu > Cd > Ni > Pb > Cr, the potential ecological risk were in the order of Cd > Cu > Pb > Zn > Ni > Cr. The pollution levels of heavy metal were in the order of the main channel of Yellow River > the estuary of Daxia River > the cross section of Yellow River. Zn, Cu and Cd were the most important pollutional factors in surface sediments in southwest Liujiaxia reservoir. Comprehensive correlation analysis and principal component analysis showed that Zn and Cu mainly come from domestic or industrial pollution while Cd mainly comes from pollution caused by industrial and agricultural activities.