Seasonal Succession Characteristics Of Phytoplankton Functional Groups And Analysis Of Its Influencing Factors Of The Nanhai Lake

As a typical urban lake,Nanhai Lake,a part of the Nanhai Wetland in Baotou,is bothering by severe environmental problems in recent years,and its concrete manifestations are as follows:water quality of the lake has deteriorated,transparency has decreased,and environmental problems have become increasingly serious.In order to understanding the relationship between phytoplankton functional group and water environmental factors and the changes of phytoplankton functional groups of which caused by deterioration of water quality,also for a supplement to eutrophication prevention,ecological function restoration and ecological protection for Nanhai Lake.12 sampling points were set up according to the water area and surrounding environment characteristics of Nanhai Lake and the area of it was divided into four areas in this study.Samples were collected every month from May 2017 to February 2019,the phytoplankton was identified and the physical and chemical indicators of water quality at each sampling point were detected during the sampling period.Dominant functional groups of phytoplankton in the lake were determined,and the distribution characteristics of phytoplankton functional groups in different seasons were discussed by analyzing the species composition of phytoplankton.Principal component analysis?PCA?was used to explore the main influencing factors changes of the lake,and redundancy analysis?RDA?analysis was employed for a discussion of main reasons affecting the distribution of phytoplankton functional groups.The main conclusions are as follows:Water quality factor of Nanhai Lake has significant differences at time span,nevertheless the spatial difference of it is not obvious.Both the Carlson Nutritional Status Index and the Comprehensive Nutritional Status Index indicated that the water body of Nanhai Lake was at a state of eutrophication.Outcome of PCA showed that total nitrogen,total phosphorus and pH were the main factors which affected the change of water quality in the Lake.There were 209 species of phyla of 7 species,84 genera and phytoplankton have been identified during the study period,and the quantity of green algae gates was maximum.Quantity of algae species in summer climbed to the summit,whereas it showed a descending trend in winter from the perspective of season.In terms of space,the lake area has the most phytoplankton species,but the tourist area has the fewest types.The variation of phytoplankton density ranged from 7.17×10⁶ to 88.40×10⁶ cells/L,and the overall density of phytoplankton in2017²018 had a display of similarity.Green algae gate and the diatom gate seated in the leading position in the spring,and the cyanobacteria gates dominated in summer and autumn,while the green algae gates had the largest number in winter.In terms of space,the overall density of algal in the middle of a lake is relatively high,while the density of it in the tourist area and the reed area is relatively low.There were 19 species of phytoplankton dominant species in the Nanhai Lake have been identified,based on the analysis of dominance.28 functional groups of phytoplankton and 9 dominant functional groups have been identified during the study period.The outcome of comprehensive analysis shows that the seasonal changes of density of each functional group in 2017 are as follows:In the spring,X3and D functional groups are dominant.The main functional groups in summer are Lo,H1 and X3.In autumn,D,X3 and H1 are dominant,and in winter,they are mainly D and X3 functional groups.The seasonal variation of functional group density in 2018 is dominated by H1,F and X3 functional groups in spring,H1 functional groups in summer,functional groups F and X3 in autumn,and D,X3 and W1 functional groups in winter.There is slight difference between the functional group compositions of each functional area in space.Results of RDA ranking indicated that the main water quality factors influenced the distribution of phytoplankton functional groups were water temperature,TN,TP and pH.Functional groups J,NA,X3 and K had a positive correlation with TN;functional groups H1,Lo,W1 and M were correlated significantly with TP;functional groups H1 and Lo also had a relationship of positive correlation with water temperature;functional group D and pH correlation showed a correlation markedly;and functional groups Y and G were more correlated with NH₃-N.