Effects Of Water Environmental Factors And Zooplankton On Phytoplankton Functional Groups In Chagan Lake

Chagan Lake,located in the northwest of Jilin Province,is the largest inland lake in Jilin Province.As the main primary producer in the lake,phytoplankton is the natural food for many aquatic organisms,and it is very important to the ecological status of Chagan Lake,which is famous for fishing.Aiming at Chagan Lake,which is dominated by alkaline eutrophication filter feeders in the northern cold region,this paper collected and identified phytoplankton and zooplankton at 14 sites in August,September 2020 and May 2021 by combining chemical detection and biological detection,and analyzed the characteristics of phytoplankton community structure and phytoplankton functional groups.Combined with the physical and chemical data of zooplankton functional groups and water environment,the effects of water environmental factors and zooplankton on phytoplankton functional groups in Chagan Lake were studied.The research results are as follows:During the investigation,94 species of phytoplankton were identified in 7 phyla,including 46 Chlorophyta,25 Bacillariophyta,14 Cyanobacteria,4 Euglenophyta,3Chrysoderma,and 1 Cryptophyta and 1 Pyrrophyta.The abundance of phytoplankton fluctuated between 1070.40×10⁴ind./L and 14998.80×10⁴ind./L,and the biomass of phytoplankton fluctuated between 1.98mg/L and 11.65mg/L.According to Reynolds and Padisak’s method,94 species of phytoplankton in Chagan Lake were divided into 20 functional groups.There are three dominant functional groups,namely X2,J and C.The seasonal variation of X2+J+C（spring）→X2+J（summer）→X2+J（autumn）was observed.A total of 57 species of zooplankton were identified in Chagan Lake,including 20 species of rotifers,14 species of protozoa,12 species of cladocerans and 11 species of copepods.Zooplankton biomass fluctuated between 0.26mg/L and 5.82mg/L 57 species of zooplankton in Chagan Lake were divided into 9 functional groups.According to the analysis of water environment factors,the water quality of Xinmiaopao is better than other points in Chagan Lake.RDA and Pearson correlation analysis were used to study the effects of ascending and descending effects on phytoplankton functional groups in Chagan Lake.It was found that total nitrogen（TN）,total phosphorus（TP）in nutrients,filter feeding protozoa（PF）and filter feeding rotifer（RF）in small filter feeding zooplankton were the most important factors affecting phytoplankton functional groups in Chagan Lake.The dominant phytoplankton functional group X2 accounted for 43.68%of the total biomass,and was negatively correlated with total nitrogen（TN）,significantly negatively correlated with total phosphorus（TP）,and positively correlated with all zooplankton functional groups.The functional group J of phytoplankton was positively correlated with total nitrogen（TN）and total phosphorus（TP）,negatively correlated with transparency（SD）,negatively correlated with protozoa PF,PC and carnivorous rotifer RC,and positively correlated with other zooplankton functional groups.The phytoplankton functional group C was negatively correlated with total nitrogen（TN）,total phosphorus（TP）and permanganate index(COD_Mn),and positively correlated with all zooplankton functional groups.In this study,it is found that most zooplankton functional groups are positively correlated with phytoplankton functional groups,which may prove that the top-down effect of zooplankton on phytoplankton functional groups has not produced excessive inhibition to produce negative effects.On the whole,phytoplankton in Chagan Lake are regulated by water chemical factors and zooplankton.Total nitrogen（TN）and total phosphorus（TP）as well as filter feeding zooplankton functional groups PF and RF have more significant effects on phytoplankton growth.