Phytoplankton Functional Groups And Their Relationship With Water Environmental Factors In Hulun Lake

The largest lake in Inner Mongolia Autonomous Region is Hulun Lake which located in the hinterland of Hulunbuir prairie.It also enjoys a good reputation of "Pearl of Grassland".This area of water is rich in biological resources,plays a special role in the protection of regional ecological environment,and it is of great significance in maintaining the biodiversity of Hulunbuir prairie.However,with the phenomenon of eutrophication and cyanobacteria bloom becoming more and more serious,the water quality in the lake is deteriorating gradually.Therefore,to explore the relationship between phytoplankton functional groups and water environmental factors,summarize the law of cyanobacteria bloom,also evaluate the water quality of Hulun Lake,methods of physicochemical and biological monitoring were used simultaneously,phytoplankton and physicochemical factors were investigated month by month in ten sampling points in Hulun Lake from May to October in 2018.Main results for this study are as follows:During the investigation,86 species(including varieties)of 7 phyla of phytoplanktonwere identified in Hulun Lake,including 41 species of Chlorophyta,25 species of Bacillariophyta,12 species of Cyanophyta,3 species of Chrysophyta and 3 species of Euglenophyta,1 species of Cryptophyta and 1 species of Pyrrophyta respectively.Phytoplankton abundance fluctuated between 202×104ind./L and 6190×104ind./L,biomass fluctuated between 0.25mg/L and 5.96mg/L.According to the classification method of functional groups proposed by Reynolds andPadisak,21 functional groups of phytoplankton were identified in Hulun Lake,including 7 dominant functional groups which namely as J,X2,W1,F,H1,M and MP.With the passage of time,phytoplankton functional group showed the variation trend of J+X2(May)?H1+X2(June)? H1+J(July)?M+H1(August)?X2+J(September)?J+X2+MP(October).The phenomenon of cyanobacteria bloom in lake began in June,reached its peak in July and August,basically disappeared in September.The main phytoplankton functional groups causing cyanobacteria bloom in the lake were H1 and M.Moreover,cyanobacteria bloom in June and July was dominated by functional group H1,while in August,it was dominated by group M.The horizontal distribution difference of phytoplankton functional groups caused by cyanobacteria bloom were obvious.The correlation between phytoplankton functional groups and environmental factors was studied by using RDA and Pearson correlation analysis.It turned out that water temperature,dissolved oxygen,total phosphorus and total nitrogen were the most important environmental factors affecting the distribution of phytoplankton functional groups in Hulun Lake,water temperature is also the main environmental factor causing the cyanobacteria bloom in Hulun Lake.Meanwhile,the persistently high content of nitrogen and phosphorus in Hulun Lake provides rich nutrients for phytoplankton.Therefore,total nitrogen and total phosphorus are not the main limiting factors of cyanobacteria bloom in Hulun Lake.In order to evaluate the water quality of Hulun Lake,a variety of methods were selected.The comprehensive result of evaluating Hulun Lake by using Q index,phytoplankton biomass,phytoplankton functional group and hydrochemical index is that Hulun Lake is in the stage of mesotrophication to eutrophication and the water quality is in the moderate to severe polluted state.