Sedimentary Characteristics Of Diatoms And Suitability Analysis Of Environmental Assessment Index In Dish Lakes From Nanjishan

The monitoring and evaluation of the water environment of rivers and lakes is the foundation of its ecological environment protection and an important support for the evaluation of the ecological health and safety of rivers and lakes.It plays an indispensable role in the construction of ecological civilization.In foreign countries,the diatom index developed by the European Union has been widely used.Used for freshwater ecosystem monitoring and evaluation.In China,most monitoring and evaluation based on diatom index have not been widely used.To this end,the thesis investigated the water quality parameters and the surface sedimentary diatom community structure of 20 sample points in 8 dish-shaped lakes in the Nanjishan Nature Reserve of Poyang Lake,and explored the European Diatom Index in the Nanjishan dish-shaped lake.The applicability provides basic data for constructing the diatom index of the Dish lake in Nanjishan wetland;at the same time,the paper studies the distribution characteristics of diatoms in the past historical sediments of the disc-shaped lake in Nanjishan and the environmental indication significance,combined with the Nanjishan wetland civil war preparation lake And the distribution characteristics of the physical and chemical indexes of the sedimentary columnar samples of the Shangbei Lake on the time scale,and through principal component analysis and redundancy analysis,the driving factors of the past historical environmental changes of the Nanjishan Wetland Dish Lake were discussed.The main conclusions of this study are:（1）A total of 77 species have been identified in the dish-shaped lake basin of the Nanjishan wetland,belonging to 5 orders,8 families and 11 genera.Melosira varians,Fragilaria capucina,Synedra ulna,Cyclotella meneghiniana,Cocconeis placentula,Navicula veneta are the dominant species in the basin;The changes in the sedimentary diatom community of the war prepared lake show that a total of 64 species of diatoms have been found in the sediments of the war prepared lake,belonging to 2 classes,5orders,9 families and 15 genera.The indicator species are Cyclotella meneghiniana,Synedra acus,Navicula capitata,Melosira varians,Cocconeis placentula;According to the changes in the sedimentary diatom community in Shangbei Lake,a total of 60species of diatoms have been found in the sedimentary diatoms of Shangbei Lake,belonging to 2 classes,5 orders,8 families and 13 genera.The indicator species are Cyclotella meneghiniana,Synedra acus,Melosira varians（2）After principal component（PCA）,correspondence analysis（DCA）,and redundant analysis（RDA）analysis of water environmental factors,it is found that the main driving factors in the dish-shaped lake basin of Nanjishan Wetland are total nitrogen（TN）and total nitrogen.Phosphorus（TP）and Chlorophyll（Chl-a）,the watershed is affected by eutrophication caused by human disturbance.PCA analysis and RDA analysis of the dominant species of diatoms and sedimentation indicators in the War Preparation Lake and the Shangbei lake show that the water bodies of the two lakes have experienced oligotrophic,mesotrophic,and eutrophic,and the main influencing factor or driving factor is total nitrogen（TN）,total phosphorus（TP）and total organic carbon（TOC）.（3）Using analysis methods such as principal component,hierarchical clustering,box diagram,etc.,the applicability of the diatom index in the dish lake was studied,and the analysis found that the Specific Pollution Sensitivity Index（IPS）,Biological Diatom Index（IBD）and the Louis Leclercq Diatom Index（IDSE）are the most suitable evaluation indexes for Nanjishan Wetland,and they are well applicable to the previous sedimentary environment of the ecological environment assessment.（4）According to the ²¹⁰Pb specific activity measurement results of the Zhan’bei Lake,the effective depth of the Zhan’bei Lake is 0-32 cm,and the corresponding period is:1952-2018,a total of 67 years,combined with the change characteristics of the sedimentary diatoms of the Zhan’bei Lake on the time scale,The diatom community structure of the Zhan’bei Lake can be divided into three combination zones,combination zone 1（period:1952-1975）,combination zone 2（period:1980-1999）,and combination zone 3（period:2001-2018）.According to the measurement results of the²¹⁰Pb specific activity of the Shangbei lake,the effective depth of the Shangbei lake is0-40cm,and the corresponding period is:1944-2018,a total of 75 years.Combining the change characteristics of the sedimentary diatoms in Shangbei lake on a time scale,the community structure of diatoms in Shangbei lake can be divided into two combination zones:combination zone 1（time period:1944-2001）and combination zone 2（The time period is:2003-2018）.