Spatial And Temporal Characteristics Of Phytoplankton Functional Groups And Relationship With Water Environment Factors In The Main Rivers Of Hulun Lake

Hulun Lake is the largest lake in the north of China,and the excellent degree of its water ecological environment is related to the water ecological security of Hulunbeier and the whole northeast region.As the main rivers of Hulun Lake,Hailar River,Kulun River and Wulson River have certain influence on Hulun Lake in terms of phytoplankton composition and evolution of water chemistry index,so the study of the main rivers of Hulun Lake has also risen to an important position.Therefore,the study of the main rivers of Hulun Lake can be more relevant to the ecological protection management of Hulun Lake.In this study,to investigate the relationship between phytoplankton composition and changes,phytoplankton functional groups composition and changes,and water environmental factors in three major rivers of Hulun Lake,16 sampling sites in the Hailar River basin,11 sampling sites in the Wursun River basin,and 7 sampling sites in the Kulun River basin were investigated and analyzed for phytoplankton and water environmental factors in spring,summer,and autumn of2021.The results of the study are as follows:During the survey,a total of 92 phytoplankton species from 7 phyla were identified in the watersheds of the three rivers,with the number of species showing the characteristics of Ulsun River>Hailar River>Kruren River,in which 85 phytoplankton species from 7 phyla were identified in Ulsun River,79 phytoplankton species from 6 phyla were identified in Hailar River,and 63 phytoplankton species from 6 phyla were identified in Kruren River,with the highest proportion of green algae and diatoms.The variation in abundance and biomass of the three rivers showed the characteristics of Hailar River>Ulsen River>Kruren River,and the overall variation in abundance in time scale was large,while the variation in spatial scale was consistent,showing that the downstream was larger than the midstream and upstream;the variation in biomass in time scale was consistent,showing that the summer and autumn seasons were larger than the spring season,and the distribution in spatial scale was also consistent,showing that the downstream was larger than the midstream and upstream.The abundance of Hailar River ranged from 33.6×10~4ind./L to 888×10~4ind./L,and the biomass ranged from 0.02 mg/L to 4.19 mg/L;the abundance of Ulson River ranged from 45.6×10~4ind./L to 439.2×10~4ind./L,and the biomass ranged from 0.09 mg/L to 1.73 mg/L;the abundance of Kruren River ranged from 0.09 mg/L to 1.73 mg/L.L;the Krulen River abundance ranged from 18.0×10~4ind./L to 274.8×10~4ind./L,and biomass ranged from0.06mg/L to 1.08mg/L.The abundance of the Krulen River ranged from 18.0×104ind./L to274.8×104ind./L and biomass ranged from 0.06mg/L to 1.08mg/L.The phytoplankton identified in the three rivers were classified according to the functional group classification method,and a total of 22 phytoplankton functional groups were identified,among which there were seven dominant functional groups,namely C,D,MP,J,TB,X1,X2,and Y.Among them,functional groups C,D,MP,and X2 appeared as the dominant functional groups in the three rivers,and functional group X1 appeared as the dominant functional group in the Ulson River and the Kruren River.The temporal and spatial variation of phytoplankton dominant functional groups in the three rivers varied greatly,and the temporal scale variation showed that C+X2+D(spring)→X2+MP+D+C(summer)→D+C+MP(autumn)in the Hailar River,J+C+MP+D(spring)→X2+C+J(summer)→D+X1(autumn),Krulen River C+D+MP+X1(spring)→X2+C+Y(summer)→X2+D+C+TB(autumn).the spatial scale of phytoplankton dominant functional groups in the three rivers showed that Hailar River D+X2+MP(upstream)→X2+D+MP+C(midstream)→C+X2+D(downstream),Ulsen River C+MP+J+X2(upstream)→J+C+X2(midstream)→D+X1+X2+C(downstream),and the Krulen River X2+C(upstream)→X2+C+D(midstream)→C+D+X2(downstream).Pearson linear correlation analysis and redundancy analysis were performed to correlate the phytoplankton dominant functional groups with the water environmental factors in the three rivers,and the results showed that total phosphorus(TP),p H and dissolved oxygen(DO)were the main environmental factors affecting the composition and distribution of phytoplankton dominant functional groups in the three rivers.