Geochemical Study On Heavy-metal Contamination In Sediments From Inlet Of Lishui River To The Dongting Lake,China

The riverbed sediment samples for this study were collected from three sediment cores obtained in inlet area of the Lishui River to Dongting Lake,China.Analysis of major elements and trace elements in sediment samples from whole rock samples by analytical techniques such as plasma mass spectrometry?ICP-MS?and X-ray fluorescence spectrometry?XRF?.And the sedimentation rate of sediments was determined by ²¹⁰Pb isotope method.Based on this,this paper systematically analyzes the main and trace elements in the sediments of the inlet area of the Lishui River to Dongting Lake by means of elemental geochemical analysis.On the basis of evaluating the degree of heavy metal contamination,discussing the geochemical indicators of heavy metal contamination,analyzing the occurrence characteristics and sources of heavy metals,the formation mechanism and evolution history of heavy metal contamination were explored.The findings are as follows.?1?The main elements such as TiO₂,MgO,and P₂O₅ are relatively rich in a inlet area of the Lishui River to Dongting Lake and the Na₂O lost.In the inlet to Dongting lake from upstream to downstream?Sediment cores LJ?LW?LH?,Sediment has the characteristics of finer grain size,lower maturity and higher stability.It shows that the chemical composition of sediments in inlet area of the Lishui River to Dongting Lake is relatively uneven.In addition,the average value of the chemical alteration index?CIA?of the sediment in the Lishui River is 69.97,which is at a moderate chemical weathering level;And in the A-CN-K diagram,its weathering trend is parallel to the A-CN axis.Reflecting the formation of sediments,minerals containing K?such as potassium feldspar?are relatively stable,while minerals containing Ca and Na?such as calcite,plagioclase?are weathered and decomposed.?2?The enrichment factor?EF value?of heavy metal in sediment shows sediment in the inlet area of the Lishui River to Dongting Lake is relatively rich in heavy metals such as Bi,Cd,Pb,Zn,Cu,Co,Ni,Mn and Cr;while Sc,V,U,Th,Tl,Ba,Mo and other elements are not obviously rich.The ground accumulation index?Igeo?and the comprehensive pollution index method?EI?show that heavy metal contamination from sediments in the lake from upstream to downstream?LJ?LW?LH?transformed from simple elements-Mn-Ni-Cd to the complex pollution of multi-element such as Cr-Mn-Co-Ni-Cu-Zn-Pb-Cd-Bi,and the intensity of heavy metal contamination gradually strengthened.?3?Except for the moderate enrichment of Ge and Ta,the other high field strength elements and rare earth elements are not significantly enriched in the sediments of the lake.Rare earth elements show the relative enrichment of light rare earths and the relative loss of heavy rare earths.In addition,the high field strength and rare earth element normalized partition pattern diagrams are consistent with the trend of clastic rock normalization curve.?4?Principal component analysis of trace elements shows the heavy metal elements such as Bi,Cd,Pb,Zn,Cu,Co,Ni,Mn and Cr in the sediment of the inlet area of the Lishui River to Dongting Lake were mostly contributed from natural processes and anthropogenic activities.And the average of anthropogenic ratio are47.66%,88.87%,44.83%,35.85%,48.27%,46.51%,42.61%,38.53%,36.52%;and Sc,V,Sr,U,Th,Tl,Zr,Hf,Y,Nb,Ta,Ga,Ge,Ba and REE which have no obvious enrichment characteristics are natural sources.?5?The comparative analysis of sedimentary ²¹⁰Pb isotopic dating results shows that the evolution process of heavy metal contamination in the Lishui River Basin can be roughly divided into two stages:the first stage is from the early stage of the founding of the People's Republic of China to the exploration and opening up period?1942-1993?.Chinese national economy is developing rapidly,and the proportion of anthropogenic heavy metals in sediments tends to rise.The second stage is the period from the construction of the reform and development period to the period of institutional improvement?1993-?.The proportion of anthropogenic heavy metals in the basin tends to decrease overall.It shows that in recent years,due to people's attention to the prevention and control of environmental pollution,heavy metal pollution in the basin has been improved,and may have a good impact on the pollution control of Dongting Lake.?6?According to the heavy metal accumulation index?Igeo?evaluation results and Pearson correlation of each element parameter,it was found that chemical indexes such as AF,SI,Al₂O₃/SiO₂,Fe₂O₃/SiO₂,Rb/Zr,?REE,?La/Sm?n have certain indications for heavy metal pollution in sediments.Studies have shown that the higher the values of AF,Al₂O₃/SiO₂,Fe₂O₃/SiO₂ in sediments and the lower the SI value lead to the higher the degree of heavy metal pollution.