Revelation Of Modern Water Environment Evolution And Ecological Restoration Of Liuhua Lake In Guangzhou

Understand the past environmental evolution history and present water quality status of lakes is the basis of lake management and protection.In this paper,the evolution process of lake sedimentary environment is comprehensively analyzed and reconstructed by means of various sedimentary indexes.Through the establishment of Diatom-TP conversion function,quantitative reconstruction of the evolution sequence of nutrient level in Liuhua lake in the past,combined with the evolution process of heavy metal ecological risk in lake sediments,the pollution mechanisms such as eutrophication and heavy metals in Liuhua lake are discussed.On the basis of field monitoring of long-term water quality and biological multi-index,the historical process and current environmental state of Liuhua lake were clarified.To provide scientific basis for the protection and management of similar urban lakes.Based on the multivariate statistical analysis of multiple indicators?CA,PCA,RDA,R-cluster analysis,etc.?,this paper draws the following main conclusions:?1?There are 7 dominant speciesof diatom in Liuhua lake,among which Cyclotella meneghiniana is the absolute dominant species?42.04%?.On the whole,the frequency of"moderate to severe eutrophic"diatom species in Liuhua lake is relatively high,such as Cyclotella meneghiniana?Nitzschia plea?Aulacoseira granulata?Achnanthes minutissima?Cyclotella distinguenda?Navicula sp etc.The dominant species of diatom community in Liuhua lake are plankton,with a small number of benthos.According to the results of DI-TP reconstruction,the TP content of Liuhua lake has increased in recent decades,and the basic TP in LHH₂ is more than 80?g/L.In order to explore the main direction and environmental gradient of diatom community structure change in Liuhua lake.PCA analysis showed that the change of diatom community was significantly related to axis 1,axis 2 and axis 3,and the cumulative characteristic value of the three axes was 78.22%,which explained the change characteristics of most diatom community structure in Liuhua lake.RDA analysis of diatom community and environmental factors showed that the first two axes explain 58.39%of the diatom sample combination characteristics,and are mainly affected by the industry GDP and Cd.The positive half axis of the first axis is mainly the sample points with low eutrophication level below 43 cm of sediment core,and the main diatoms include Thalassiosira,Navicula sp.,etc.The negative half axis of the first axis is significantly related to the industrial output value,which is mainly the sedimentary column with more serious eutrophication over 43 cm.The corresponding diatom species include Cyclotella meneghiniana,Aulacoseira alpigena.In the second axis,the negative half axis is mainly composed of 43-23 cm heavy metal pollution in the middle of the sediment core,and diatoms mainly include Achnanthes minutissima.?2?The content of heavy metals in lake sediments?except Mn,V?was significantly higher than the background value of regional soil.The enrichment coefficient showed that only V,Co and Mn were affected by the input of natural sources?EF<1.5?.Cd,Zn,Sb,Cu,Pb and As,are seriously polluted in the evaluation results of Igeo,among which Cd is in the state of heavy pollution(I_geo=3.89).Eological risk of heavy metals above 55 cm of sedimenta core was more serious?average RI=1041.2?,and RI was only influenced by a few elements,such as Cd contributed 78.57%,followed by Sb and Cu contributed 7.94%and 3.14%respectively.The results of statistical analysis show that V,Tl and Co are mainly from natural sources,while the main metal elements Cd,Sb,Cu,Zn,Ni and Pb are mainly from human sources,showing obvious urban enrichment characteristics.?3?The average values of TN,TP and Chl-a in Liuhua lake are 6.76 mg/L,358.83?g/L and 116.93 mg/L respectively,indicating that the current eutrophication situation of Liuhua lake is relatively serious.The phytoplankton in Liuhua lake is a typical eutrophication community structure of"Cyanobacteria-Chlorophyta-Bacillariophyta".It includes a large number of dominant genera and species with rich preference for organic matter,for instance Chlamydomonas globosa,Merismopedia sp.,Cyclotella sp.,Trachelomonas sp.,indicat that Liuhua lake is rich in organic matters and nutrients.The main zooplankton groups in Liuhua lake are rotifers,protozoa and copepods.The dominant populations are eutrophication and pollution tolerance,for instance Polyarthra vulgaris,Trichocerca,Coleps hirtus,Ciliophora sp..The H index of zooplankton and phytoplankton in Liuhua lake is 2.26 and 1.31,respectively,indicating that the pollution state of Liuhua lake is moderate to severe.