Study On Phytoplankton Community Structure Of Lakes In Cold Regin Based On Niche Method

Nanhai Lake is part of the Yellow River Wetland in Baotou city and is a typical lake in cold region.In recent years,due to the reduced recharge of the Yellow River and pollution from anthropogenic activities,the water quality of the Lake has deteriorated,transparency has decreased,and the problem of lake eutrophication has become serious.In order to understand the relationship between the change characteristics of phytoplankton community and the response of water environmental factors in eutrophic lakes in cold regions during frozen and unfrozen periods,in this study,from December 2017 to November 2020(except from March to June 2020),12 sampling points were set up in Nanhai Lake,and the distribution characteristics of water environment factors and phytoplankton community characteristics of each point were researched and analyzed.According to the dominance formula,the dominant species during the frozen and unfrozen periods was selected and determine the main dominant species,and then calculate their niche,analyze the relationship between dominant species and their state of development,and analyze relationship between the abundance of the main dominant species and water environment factors by grey relational analysis.This can provide theoretical support for the treatment and restoration of lake eutrophication and the protection of lakes ecological environment in cold regions.The main research results are as follows:(1)Nanhai Lake with an average annual temperature of 10.23℃,and the water temperature has little annual variation.The annual average p H value is 8.95,which shows the water is weakly alkaline.The content of total nitrogen,ammonia nitrogen,nitrate nitrogen and nitrite nitrogen during the frozen period is greater than that of the unfrozen period;the total phosphorus content of the unfrozen period is greater than that of the frozen period.From the spatial distribution point of view,the nutrients content is mainly distributed in the tourist area and the lake center area.Based on the single-factor evaluation method,the water quality of the Nanhai Lake is inferior to Class V in terms of the concentration of total nitrogen and total phosphorus,while the water quality of the lake is in Class Ⅳ in terms of the concentration of ammonia nitrogen,indicating that Nitrogen and phosphorus is the main pollution factor of Nanhai Lake.(2)A total of 7 phyla,77 genera,182 species of phytoplankton were identified at 12 sampling sites during the study period.The sort by number of species was: green algae>cyanobacteria>diatoms;the average annual abundance of phytoplankton was353.76×106cells/L,showing a "V" shape change in study period,in which cyanobacteria are the dominant group of phytoplankton,and the phytoplankton community ecological type is cyanobacteria-green algae-diatom type.The overall change of species abundance in time is:unfrozen period> frozen period.Using the phytoplankton diversity index to comprehensively evaluate the water quality of Nanhai Lake,the results show that Nanhai Lake is a moderately polluted lake.(3)After calculation of the dominance formula,a total of 4 phyla,39 species of phytoplankton dominant species were identified,including 20 species in the frozen period and 24 species in the unfrozen period.Then,the correlation analysis between the abundance of the dominant species and the total abundance of phytoplankton was obtained.There are four main dominant species of Scenedesmu squadricauda,Diatoma vulgare,Aphanizomenon flosaquae and Merismopedia tenuissima.The niche analysis of the main dominant species shows that the niche breadth values are all greater than 0.6,indicating that each dominant species has strong environmental adaptability.Compared with other dominant species,the niche overlap value of Merismopedia tenuissima is basically negative,indicating that it is a declining dominant species.(4)Grey relational analysis shows that TN is a key nutrient factor affecting the total abundance of phytoplankton,and p H is a key physical and chemical factor affecting the total abundance of phytoplankton.For the main dominant species,TN is the main nutrient factor that affects the abundance of each dominant species,which has a significant correlation with the annual abundance of Diatoma vulgare,Aphanizomenon flosaquae and the abundance of Merismopedia tenuissima during the frozen period.p H and DO are the main physical and chemical factors that affect the abundance of each dominant species.p H can affects the annual abundance of the Diatoma vulgare,the abundance of the Aphanizomenon flosaquae during frozen period,and the unfrozen of the Diatoma vulgare,and DO can affects the annual abundance of Scenedesmu squadricauda,the abundance of Merismopedia tenuissima during frozen period,and the abundance of Aphanizomenon flosaquae during unfrozen period.