The Geochemical Characteristics Of Surface Sediments Of Qionghai Lake Phase,Sichuan

Qionghai Lake,the second largest freshwater lake in Sichuan Province,is the main water source for life?industry and agriculture in Xi Chang city and its surrounding towns.In recent years,with the development of industrial and agricultural production and tourism,the water quality of Qionghai Lake has the trend of sharp deteriorating.This thesis is based on"Sichuan Anning River Agricultural Geological Survey Evaluation"project.This study was conducted in Qionghai Lake in Sichuan Province,to find out the characteristics of elements geochemistry of surface sediments in Qionghai Lake.On this basis,through the research of lake eutrophication and assessment of heavy metals potential ecological risk,this study was to investigate ecological environment quality of Qionghai Lake,explain the relationship between Qionghai Lake and its Valley,providing a scientific basis for the planning and treament of Qionghai Lake.The following results are achieved through research:(1)The macroelements contents of surface sediments in Qionghai Lake were higher than these in Yangtze River,the upper crust,East Lake and surface soil background values of Sichuan Province.Similarly,the microelements contents were higher than surface soil background value of Sichuan Province.The heavy metal elements contents were in the middle level of the domestic and foreign lakes.The contents of Cd and Cr were significantly higher than most lakes,but Cu,Pb and Ni contents were lower.(2)On the spatial distribution of elements,the results present different space distribution characteristics.P₂O₅,Si O₂and Mo distributed relatively concentrated in surface sediments of Qionghai Lake,while B and Co distributed evenly.High content areas of Ca O and Mo concentrated in the southeast of Qionghai Lake.High content areas of Mg O,Na₂O,S,TFe₂O₃concentrated in the north of Qionghai Lake.High content areas of P₂O₅,N,Cd,Zn,Cr,Ni,Pb,Cu,As,F,Cl,I,Tl and U concentrated in the southwest of Qionghai Lake.High content areas of Si O₂concentrated in the south of Qionghai Lake.(3)Different distribution characteristics of macroelements and microelements in the surface lake sediments are maily affected by such factors:element geochemical properties;sediment particle size;artificial fish culture zones;tourism resource development surrounding the city;weak strata in valley;higher farmland second ploughing index and the function of river back flow.(4)The quality of qionghai water is fine.The method of direct comparison and comprehensive trophic status index were used to estimate eutrophication level of Qionghai Lake,and it indicated that Qionghai Lake was at the poorly eutrophication.Under the monitoring and goverance of relevant units in recent years,the water quality of Qionghai Lake improved obviously,from the eutrophication down to the oligotrophication.(5)The index method of potential ecological harm was used to evaluate the ecological risk of heavy metal elements in surface sediments of Qionghai Lake,and it indicated that the enrichment capacity size order of heavy metal elements in surface sediments of Qionghai Lake is:Cd>Zn>Cr>Ni>Pb>Cu>As>Hg,the ecological risk size order is:Cd>Hg>As>Ni>Pb>Cu>Cr>Zn.Cd was in a slightly ecological damage level at estuary of Lantern river and Officer dam river,while Cd was in a bad–worse–the worst ecological damage level at the west of lake area and the east area.(6)The geochemical statistical methods of correlation analysis,factor analysis and cluster analysis was used to analysis the source of surface sediments of Qionghai Lake,and it indicated that the source were maily river rock weathering denudation,river flow backward,lantern river mud-rock flow and fish culture zones.(7)The relationship between Qionghai Lake and Valley:landform and vegetation of valley corresponded to space distribution and temporal dynamic property of lake structually;hydrological characteristics and material energy cycle of valley corresponded to lake sediment in the process;The structure and process of lake and valley affected mutually,and they determined the function of lake and valley.