湘江下游河床沉积物重金属污染模糊评价及污染源地球化学示踪

发布时间：2018-11-09 12:40

【摘要】：本研究对湘江下游株洲、湘潭和长沙段河床沉积物进行沉积柱取样,利用同位素质谱仪(ICP-MS)和多接收器电感耦合等离子体质谱(MC-ICP-MS)等分析技术手段进行微量元素和铅同位素分析。研究表明,湘江下游沉积柱中重金属元素含量在垂直方向不具有明显的变化特征,但重金属元素平均含量随流向呈降低趋势。研究区域中,株洲河段各重金属元素含量最高,变异程度最大,长沙段次之,湘潭段最小。由于湘江下游沉积物中重金属分布不均匀,采样或监测地点有局限性等原因,该区域重金属污染评价结果常存在随机性和模糊性。因此,本研究将随机模糊理论引进重金属污染评价体系,建立随机模拟与三角模糊数耦合模型,通过修正地累积指数评价中修正系数K值,利用改进的地累积指数法评价研究区域沉积物重金属污染程度。研究表明,湘江下游长株潭河床中Sc主要为轻度污染,并有向偏中度污染发展趋势；Cr、Ni在整个研究区域都为偏中度污染；V、Co仅在ZX2沉积柱中达到中度污染；Mn、Cu、Zn和Pb在研究区域均超过中等污染程度,是研究区域的主要污染元素。重金属综合污染程度评价显示株洲河段污染最严重,湘潭次之,长沙最轻。湘江下游河段沉积物中稀土元素配分曲线表现为总体右倾型,呈明显的Eu负异常和轻度的Ce负异常,体现了典型的陆壳稀土元素特征。根据La/Yb-REE投影推断沉积物的主要物源来自上游的花岗岩风化、搬运和沉积；La-Th-Sc投影显示沉积物的物源来源有多个端元,即来自花岗岩端元和粘土、淤泥、颗粒等混合来源端元。归一化法发现：株洲段重金属元素Co、Mn主要来源于自然分化沉积,Zn主要来源于人为污染,Sc、V、Cr、Cu和Pb为自然源与人为源混合污染；湘潭段重金属元素Mn为自然源与人为源双重污染,而Sc、V、Cr、Co、Cu、Zn和Pb主要为人为污染；长沙段重金属元素V、Mn和Pb主要来自然活动,Sc、Cr、Co、Cu和Zn除了自然来源之外,还存在着明显的人为污染。铅同位素分析表明,河床沉积物中铅来源于人为源和自然源,其中自然来源的铅主要结合在沉积物晶格中,较为稳定；人为活动来源的铅主要富集在可溶相中,易释放到水体中。铅同位素显示流域上游花岗岩等矿石风化是沉积物自然来源铅的主要贡献者；可溶相中铅的主要来源为流域上游Pb-Zn矿床矿石冶炼、流域周围煤和柴油的燃烧,且大气沉降也逐渐成为其重要的潜在来源。
[Abstract]:Sediment column sampling was carried out in Zhuzhou, Xiangtan and Changsha reach of Xiangjiang River. Trace elements and lead isotopes were analyzed by means of isotope mass spectrometer (ICP-MS) and multi-receiver inductively coupled plasma mass spectrometry (MC-ICP-MS). The results show that the content of heavy metal elements in the sediment column of the lower Xiangjiang River has no obvious change in the vertical direction, but the average content of heavy metal elements decreases with the flow direction. In the study area, the content of heavy metals in Zhuzhou reach was the highest and the degree of variation was the highest, followed by Changsha section and Xiangtan section. Due to the uneven distribution of heavy metals in the sediments of the lower reaches of Xiangjiang River and the limitation of sampling or monitoring sites, the assessment results of heavy metal pollution in this area are often random and fuzzy. Therefore, the random fuzzy theory is introduced into the heavy metal pollution assessment system, and the coupling model of random simulation and triangular fuzzy number is established. The pollution degree of heavy metals in the sediments of the study area was evaluated by using the improved ground accumulation index method. The results show that Sc in the bed of Changzhutan River in the lower reaches of Xiangjiang River is mainly mildly polluted and tends to be moderately polluted, Cr,Ni is moderately polluted in the whole study area, and Cr,Ni is only moderately polluted in the ZX2 sediment column. Mn,Cu,Zn and Pb are the main pollution elements in the study area. The comprehensive assessment of heavy metal pollution showed that Zhuzhou reach was the most polluted, Xiangtan was the second, Changsha was the lightest. The distribution curve of rare earth elements in the sediments of the lower reaches of Xiangjiang River shows a general right-dip pattern with obvious Eu negative anomalies and mild Ce negative anomalies which reflect the typical characteristics of continental crust rare earth elements. According to the La/Yb-REE projection, the main provenance of the sediments is derived from the weathering, transport and deposition of the granites in the upper reaches. The La-Th-Sc projection shows that the source of the sediment is composed of several endelements, I. E. from granite and clay, silt, particles and so on. The normalized method found that the heavy metal elements Co,Mn mainly came from natural differentiation deposition, Zn mainly came from man-made pollution, and Sc,V,Cr,Cu and Pb were mixed pollution of natural and man-made sources. The heavy metal element Mn in Xiangtan section was polluted by both natural and man-made sources, while Sc,V,Cr,Co,Cu,Zn and Pb were mainly human pollution. The heavy metal elements VN mn and Pb mainly come from natural activities in Changsha segment. In addition to natural sources Sc,Cr,Co,Cu and Zn also have obvious anthropogenic pollution. Lead isotopic analysis shows that lead in riverbed sediments comes from both man-made and natural sources, in which lead from natural sources is mainly bound to the lattice of sediments and is relatively stable. Lead from anthropogenic sources is mainly enriched in soluble phase and easily released into water. Lead isotopes show that the weathering of granites in the upper reaches of the basin is the main contributor to lead from the sediments. The main source of lead in the soluble phase is ore smelting of Pb-Zn deposits in the upper reaches of the basin, the combustion of coal and diesel oil around the basin, and the atmospheric deposition has gradually become an important potential source.
【学位授予单位】：湖南师范大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：X824;X52

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