Geochemistry of major and trace elements in sediments from inlets of the Xiangjiang and Yuanjiang River to Dongting Lake, China

Concentrations of major and trace elements in sediments from the Xiangjiang and Yuanjiang River inlets to Dongting Lake (China) were analyzed using XRF and ICP-MS methods, respectively. The results show that sediments from both rivers show comparable major element compositions and a similar distribution of high strength field elements (Zr, Hf, Nb, Ta, Th and U), large ion lithophile elements (Ba, Sc, Ga, Ge, Rb, Y, Cs), and rare earth elements (REE). However, the distribution of heavy metals V, Cr, Co, Ni, Cu, Zn, Pb, Cd, Tl and Bi varies significantly in sediments between the two rivers. The Xiangjiang River sediments are characterized by having a distinctly higher enrichment of the heavy metals Cr, Mn, Ni, Cu, Zn, Pb, Tl, Bi and Cd, and they are mostly contaminated by these heavy metals. That leads to the formation of heavy-metal contaminated (HMC) sediments. Sediments from these two rivers can be coincidentally divided into three groups by their REE patterns and factor load plots of principle component analyzing on major elements of 173 samples. The HMC sediments can further be separated from those of less contaminated sediments by plots of (Eu/Eu) NS* against the synthetic enrichment index values, and the HMC sediments are found to be significantly higher enriched in the major elements Al₂O₃, Fe₂O₃, MnO, P₂O₅ and LOI, and depleted in SiO₂ and Na₂O. Therefore, the distribution of the major elements Al₂O₃, Fe₂O₃, MnO, CaO, P₂O₅, LOI, SiO₂ and Na₂O in the river sediments can be used as indicators for identifying the HMC sediments. Thus, the ‘aluminium–iron index’ (AF), the ‘silicate index’ (SI), the ‘grain size index,’ and the Al₂O₃/SiO₂, Fe₂O₃/SiO₂ and Al₂O₃/Na₂O ratios are then established as chemical indices for the use of identifying the HMC sediments. River sediments that have values of AF > 25.6, SI < 67.5, Al₂O₃/SiO₂ > 0.29, Fe₂O₃/SiO₂ > 0.12 and Al₂O₃/Na₂O > 43.0 are then identified to be the HMC sediments in the study area.