| Sediment core samples were collected at Zhuzhou, Xiangtan, and Changsha sections of the lowermost Xiangjiang River, and the trace elements and Pb isotope in the sediments were analyzed using ICP-MS and MC-ICP-MS techniques respectively, in this study. The results show that there is no obvious variation in a vertical aspect for the concentrations of heavy metals in the sediments of the lowermost Xiangjiang River. But the average concentrations of heavy metals present a gradually decreased tendency from upstream to downstream. In the research sections, the concentrations of all heavy metals in sediments and the Coefficient of Variation at Zhuzhou section were the most remarkable, followed by Changsha and Xiangtan.The heavy metals in the sediments of the lowermost Xiangjiang River are distributed unevenly and the monitor points are limited, which lead to randomness and fuzziness when heavy metal contamination of the sediments was evaluated. So, the random-fuzzy method will be introduced to the heavy metal contamination of the sediments’system. Then heavy metal contamination of the sediments was evaluated using the Geo-accumulation index after it’s coefficient K value was corrected using a theoretical coupling model that is established on the base of stochastic simulation and triangular fuzzy number. The results show that sediments distributed at Changsha, Xiangtan, and Zhuzhou sections of the lowermost Xiangjiang River were slightly contaminated by metals Sc,which tends to be moderately contaminated. Sediments of all the research sections were moderately contaminated by metal Cr、Ni. The ZX2 sediments were moderately contaminated only by V、Co. Sediments of all the research sections were more moderately contaminated by Mn、 Cu> Zn and Pb which is the major contamination factors in the research river sections. The results show that the integrated heavy-metal contamination at Zhuzhou section were the most serious, followed by Changsha and Xiangtan was the least.The rare earth elements(REE) distribution patterns in sediments show the light rare earth elements are relatively enriched,and the heavy rare earth elements are deficient,presenting a distinct negative Eu anomaly and a slight negative Ce anomaly for the REE distribution patterns. According to the Plots of La/Yb to REE, it is concluded that the sediments mainly comes from weathering, moving and deposit of granite in upstream. The Plots of La-Th-Sc shows that sediments sources include multiple end members, namely the granite end members and the multiple end members by clay, sludge and particles etc.By using the Normalization Method, we found that in Zhuzhou section, heavy metal Co and Mn are mainly from natural deposits. Heavy metal Zn is mainly due to artificial contaminant. Heavy metal Sc、V、Cr、 Cu and Pb are attributed to mixed contamination of natural sources and artificial sources. In Xiangtan section, heavy metal Mn is attributed to both natural sources and artificial contaminant. Heavy metal Sc、V、Cr、 Co、Cu、Zn and Pb are mainly due to artificial contaminant. In Changsha section, heavy metals V, Mn and Pb are mainly attributed to natural activities. Heavy metal Sc、Cr、Co、Cu and Zn are due to natural sources and obvious artificial contaminant.Pb isotopic analysis suggest that Pb of the sediments is from natural sources and artificial sources. Among them, the natural source Pb mainly combined in lattice of sediments is relatively stable. The artificial sources Pb enriched in the sediments which are easily dissolved is easily to release into water. Pb isotope shows that the natural source Pb in the sediment is mainly due to the weathering of granite and other minerals in upstream. The man-made source Pb enriched in the sediments which are easily dissolved mainly attributed to the ore smelting of metal Pb-Zn in upstream, the burning of coal and diesel around the river. What’s more, atmospheric deposition gradually become its main potential source. |
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