Distribution Characteristics Of Diatoms In Urban Landscape Water Bodies And Water Quality Evaluation Study

Urban development and population expansion make the carrying capacity of urban environment decrease,the ecological and environmental self-healing capacity gradually imbalance,the ecological and environmental problems of urban water system become more and more serious,and improving the environmental carrying capacity of urban water system is the key step to solve the problem.The evaluation of urban landscape water bodies is the basic theory to improve the carrying capacity of water environment.At present,the comprehensive evaluation of most urban landscape water bodies is still limited to the traditional evaluation of physical and chemical factors,and there is little research on the biological evaluation of urban landscape water bodies.This paper draws on the evaluation methods of domestic and foreign scholars for large lakes and watersheds,combines the improved physical and chemical factor evaluation with diatom biological evaluation,and makes an effective assessment of the water quality level and actual condition of urban landscape water bodies,providing a certain theoretical basis for the subsequent work of ecological restoration and water quality improvement of urban landscape water bodies.The main research findings are as follows:（1）The physicochemical factors of urban landscape water bodies change with the change of seasons,and their overall trend is rising first and then falling.Among them,Temp shows negative correlation with p H,DO,NO₃^--N,TP,positive correlation with TN,Chl a,NH₄⁺-N,COD,Temp has the highest negative correlation with DO,and the highest positive correlation with Chl a.DO,TN,Temp,COD,TP are the main water quality parameters in the main sub-lake area.The AEI model shows that the water quality category of the main lake is IV（Weak）from June to August,and the water quality category of the sub-lake is IV（Weak）from June to October,especially in July and August,the water quality category of the sub-lake is close to V（Bad）.（2）In this experiment,a total of 42 species of diatoms belonging to 23 genera of 10families in 1 phylum,2 orders and 7 families were identified in summer,and the dominant species were Cyclostephanos dubius,Cyclostephanos tholiformis and Discostella nipponica;in autumn,a total of 33 species of diatoms belonging to 19genera of 12 families in 1 phylum,2 orders and 9 families were identified,and the dominant species was Nitzschia palea,Stephanocyclus meneghinianus and Nitzschia acicularis.In summer,the dominant species showed positive correlation with TN,Chl a and COD,and negative correlation with p H and NO₃^--N;in autumn,most of the dominant species showed negative correlation with environmental factors.In autumn,most dominant species showed negative correlations with environmental factors.In summer,COD and TN were the stressors driving the change of planktonic diatom community structure in the main lake,and TP was the sub-lake stressor;in autumn,DO was the stressor driving the change of planktonic diatom community structure in the main lake,and TN and Temp were the sub-lake stressors.In summer,the interactions between the genera Nitzschia,Discostella,Cyclostephanos and Melosira were much higher in number and correlation than the other species（OTU）;in autumn,the interactions between the genera Nitzschia,Melosira and Cymbella were much higher in number and The interactions between Nitzschia,Melosira and Cymbella were much higher in number and degree of correlation than other species（OTU）.（3）The improved physicochemical factor evaluation method and diatom biological evaluation method were used to comprehensively evaluate the water quality of urban landscape water bodies,and the TDI score was found to be more stringent in describing the trophic state of the water bodies.The distribution characteristics of diatom populations can accurately indicate the trophic state level,the degree of organic pollution or nitrogen and phosphorus pollution,and the decay value of water bodies,and AEI evaluation can accurately provide the deviation values of water quality parameters,and can propose effective countermeasures for some of the excess deviation values,confirming that The two can complement each other water quality information.