Spatial And Temporal Succession Characteristics Of Phytoplankton Functional Groups And Their Relationship With Environmental Factors In Erwangzhaung Reservoir

Phytoplankton is the primary producer of aquatic ecosystem and the basic link of food chain.The community structure,abundance,dominant species,biomass of phytoplankton as the same as the scope and intensity of water bloom are important indicators to analyze the change of water environment.The future impact of the South-to-North Water Diversion Project on the ecological environment of Erwangzhuang Reservoir is unknown.It is necessary to carry out prospective research and prediction on the possible impact of species in the South after entering the reservoir with water.Therefore,in the initial stage of water diversion from South-to-North into Erwangzhuang Reservoir,the current situation of water quality and biological life in Qingshui reservoir was explored.From March to December in 2018,through the monitoring of phytoplankton and physical and chemical indicators of Erwangzhuang Reservoir,this paper studied the temporal and spatial succession characteristics of phytoplankton functional groups with rational D analysis（RDA）,and Pearson linear correlation analysis method were used to study the influencing factors of phytoplankton functional groups.In addition,Q-index method was used to evaluate the water quality,so as to provide a certain data basis for the comprehensive coordination and safety guarantee of Tianjin drinking water supply in the future.The results are as follows:（1）From March to December in 2018,77 species of phytoplankton were identified in Erwangzhuang Reservoir,belonging to 61 genera of 7 phyla.They included 25 genera and 32species of Chlorophyta（41.56%）,13 genera and 16 species of Diatom（20.78%）,9 genera and13 species of Cyanophyta（16.88%）,4 genera and 4 species of Cryptophylum（5.19%）,4genera and 5 species of Chrysophyta（6.49%）,3 genera and 4 species of Gymnophylum（5.19%）,3 genera and 3 species of Dinoflagellate（3.90%）.From the perspective of time succession,there are significant differences in the composition of phytoplankton species and genera in each month.The species and genera of phytoplankton gradually change from the initial dominance of Diatom and Chlorophyta to the dominance of Diatom,Chlorophyta and Cyanophyta,and the species and genera of Cyanophyta gradually increase with time.（2）The seasonal variation of relative cell abundance of phytoplankton in Erwangzhuang Reservoir is as follows:wintersummer>spring>winter,in which the proportion of the relative biomass in autumn is 41.32%,in summer14.73%,in spring 20.16%,in winter 9.44%.The spatial change rule of phytoplankton relative biomass in Erwangzhuang Reservoir is S3>S5>S1>S4>S2.The annual average relative biomass of S3 station is higher than that of other stations,which is 13.85×10~4mg/L.The results of the traditional Shannon Wiener index method show that Erwangzhuang Reservoir is in the middle pollution state.（3）From 2013 to 2018,the phytoplankton cell abundance of Erwangzhuang Reservoir ranged from 260.83 to 13184.4×10~4cells/L,with an average of 2562.57×10~4cells/L.The phytoplankton cell abundance of Erwangzhuang Reservoir in 2018 was higher than that in previous years.From the maximum value,the cell abundance in 2018 was lower than that in2017.The results of time change of physical and chemical indexes of Erwangzhuang Reservoir from 2013 to 2018 showed that p H and total phosphorus have a small change range,total nitrogen in 2018 decreased by 84.86%compared with 2013,chlorophyll in 2018decreased by 51.99%compared with 2017,and ammonia nitrogen in 2018 increased by34.62%compared with 2013.（4）Erwangzhuang Reservoir is divided into 21 functional groups,including C,D,E,F,G,H1,J,LM,Lo,M,MP,P,S1,SN,T,W1,W2,WS,X1,X2,Y.15 groups are important functional groups,including C,D,E,F,G,J,LM,Lo,MP,P,S1,W1,WS,X2,Y,which are dominated by D functional groups,and their representative species is Synedra sp.The species of Cyanophyta,Chlorophyta and Diatom all appear in the whole year.The annual proportion of Cyanophyta is the highest（51%）,followed by Chlorophyta（24%）and Diatom（19%）.The biomass of functional groups in summer and autumn were significantly higher than that in spring and winter.The succession process was spring（C,D,E）-Summer（D,S1,WS）-Autumn（D）-winter（D）.The characteristics of the relative biomass of phytoplankton functional groups with spatial change:S3>S1>S5>S4>S2.The changes of the important functional groups at various points are S1（C+D+P+S1+WS）-S2（C+D+j+S1）-S3（C+D+S1）-S4（D+LM+S1+WS）-S5（D+G+S1）.The result of Q index evaluation shows that the water quality of Erwangzhuang Reservoir is in the middle nutrition level.（5）RDA analysis showed that the main environmental factors affecting the community structure of phytoplankton in Erwangzhuang Reservoir were DO,Chla and NH₄⁺-N.The temporal and spatial changes of phytoplankton functional groups were affected by environmental factors,among which MP and C were positively correlated with DO;LM and S1 were positively correlated with TN,TP and WT;P,LM,Lo and Y were positively correlated with TN,TP,PO₄^3--P,NH₄⁺-N and NO₂^--N,and negatively correlated with p H.NH₄⁺-N,WT,DO and TN are the main environmental factors affecting the dynamic changes of phytoplankton functional groups in Erwangzhuang Reservoir.（6）Pearson correlation analysis showed that Shannon Wiener index was negatively correlated with PO₄^3--P and NO₂^--N,and positively correlated with Chla.Q index was negatively correlated with Chla and positively correlated with NO₂^--N.Therefore,NO₂^--N is the main physical and chemical factor affecting phytoplankton community in Erwangzhuang Reservoir.The evaluation results of Q index and Shannon Wiener index showed that the water body of Erwangzhuang Reservoir was in the middle eutrophication level,and the stable water quality was better.