Spatial-temporal Pattern And Environmental Analysis Of Phytoplankton In Poyang Lake

Phytoplankton is the main primary producer in Poyang Lake ecosystem,which plays an important role in the lake ecosystem.Therefore,the study of phytoplankton in Poyang Lake is of great theoretical and practical significance.Poyang Lake is the largest fresh water lake in China.It is the only large-scale river lake in the Yangtze River Basin.It is an important source of water for cities in the lower reaches of the Yangtze River.It is of great significance to study the temporal and spatial pattern of phytoplankton in Poyang Lake.This study investigated phytoplankton in five habitats of Poyang Lake(entrance,main lake area,saucer lake,Lake branch and exit)from 2015 to 2017,analyzed the changes of phytoplankton community structure and quantitative biomass of Poyang Lake,and used analysis software such as canoco,SAS and JMP to carry out redundancy analysis and correlation analysis,and discussed the temporal and spatial pattern of phytoplankton and its environmental factors in Poyang Lake.The correlation between them provides an important scientific basis for the ecological environment protection of Poyang Lake.The main results are as follows:1.Species composition and characteristics of phytoplankton in Poyang Lake:7 phyla,73 genera and 115 species of phytoplankton have been identified in Poyang Lake,including 39 genera and 66 species of Chlorophyta,18 genera and 25 species of Bacillariophyta,9 genera and 13 species of Cyanophyta,2 genera and 2 species of Pyrrophyta,3 genera and 7 species of Euglenophyta,1 genus and 1 species of Chrysophyta,and 1 species of Cryptophyta.Yptophyta)1 belongs to 1 species,indicating that the phytoplankton composition of Poyang Lake belongs to green diatom or green cyanobacteria water body.The distribution pattern of phytoplankton in Poyang Lake shows that there are more kinds of phytoplankton in the entrance and less in the exit.There are 6 phyla,69 genera and 111 species of phytoplankton in the Lake entrance,with 66 species of Chlorophyta at most,and the trend of seasonal variation is more in spring and summer,less in autumn and winter;there are 6 phyla,66 genera and 111 species of phytoplankton in the main lake area,with 66 species of Chlorophyta at most,more in spring and summer,less in autumn and winter;there are 6 phyla,57 genera and 78 species of phytoplankton in the dish lake,with 45 species of Chlorophyta at most,more in spring and summer,and more in autumn and winter.There are 37 species of phytoplankton in 45genera and 6 phyla in winter,among which the species of green algae are dominant,and the species in spring are 29 at most;there are 36 species of phytoplankton in 23 genera and 5 phyla in lake mouth,among which the species of diatom are dominant,more in spring and summer,less in autumn and winter.The comparative analysis of the survey data of Poyang Lake from 1987 to 2017 found that the number of phytoplankton species decreased significantly,from 319 to 115,a decrease of 63.9%.2.Phytoplankton dominant species and their distribution:the main dominant species of Poyang Lake include:Pedistrum,Scenedesmus,staurastrum,cosmorium,eudorina and closterium of Chlorophyta;mesosira,fragilaria and Stellaria of diatom.The dominant species of phytoplankton are different in five habitats.Among the five habitats,the dominant species of phytoplankton in the Lake entrance of Poyang Lake are mainly diatom and green algae,while the other phytoplankton,especially cyanobacteria,are less;the dominant species of phytoplankton in the Lake branch and dish lake are mainly cyanobacteria and green algae;The dominant species in the Lake entrance and main lake area are mainly green algae and diatom.The hydrological characteristics of "high water is lake,low water is river" in Poyang Lake lead to the composition of dominant species of phytoplankton in dished lake and main lake area is similar to that in river.The dominant species of phytoplankton at the entrance of Poyang Lake is diatom,which leads to the dominant species of diatom in main lake area of Poyang Lake.3.Phytoplankton biomass and its change rule:the size of phytoplankton biomass has significant difference in five habitats.The biomass of phytoplankton in the five habitats varied greatly,ranging from 1×104-21×104ind/L on average.The biomass of phytoplankton in most sampling sites exceeded 1×104ind/L.The biomass of phytoplankton in the lake inlet is 1.49×104ind/L,the biomass of phytoplankton in the main lake area is 5.58×104ind/L,the biomass of phytoplankton in the dish lake is 3.76×104ind/L,the biomass of phytoplankton in the lake inlet is 21.00×104ind/L,the biomass of phytoplankton in the lake inlet is 1.26×104ind/L,and the biomass of phytoplankton in the lake outlet is usually less than 1×104ind/L.?The biomass of phytoplankton in Poyang Lake is generally high.In terms of the proportion of various types of phytoplankton,the biomass of phytoplankton in five habitats is dominated by green algae,cyanobacteria and diatoms,accounting for more than 80%of the total biomass,and cyanobacteria has not become the main biomass contributor.The proportion of the total biomass of the other 4 phylum phytoplankton(Dinophyta,Euglenophyta,Chrysophyta,cryptoalgae)in the whole investigation is very low,even some habitats can not be detected.4.The impact of environmental factors on phytoplankton in Poyang Lake:through the analysis of phytoplankton community structure and environmental factors in five habitats(entrance,main lake area,shalow lake,Lake branch and out)of Poyang Lake,the spatial-temporal pattern of phytoplankton in Poyang Lake is mainly affected by the change of water level in Poyang Lake,and floating plants in four habitats(entrance,main lake area,shallow lake and out)of Poyang Lake.The change of water level in Poyang Lake is the main influencing factor of phytoplankton community structure.Among them,the total nitrogen,total phosphorus and transparency of Poyang Lake environmental factors also have an impact on the changes of phytoplankton community structure.