Functional Group Composition And Spatial-temporal Distribution Characteristics Of The Phytoplanktons In The Typical Lake And Reservoir Connected Area

Phytoplankton are the primary producers of the aquatic ecosystem.As an important part of the lake and reservoir,phytoplankton form the basis of aquatic food chain and play an important role in the material circulation and energy flow of the entire ecosystem.To understand the applicability and differences of the three phytoplankton functional group classification methods of RFG(Reynolds Functional Group),MFG(Morpho-Functional Group)and MBFG(Morphology-Based Functional Group)in indicating changes in lake and reservoir,we combined domestic research with foreign researches,we selected the typical lake and reservoir connected area such as the east Taihu lake,Taipuriver and Jinze reservoir as the research areas and seted up the wild fixed sampling sites,then we conducted an investigation on the chlorophyll a,phytoplankton and environmental factors during January 2018 to December 2019 on a monthly basis.In addition,based on the theoretical basis and division method of the RFG,MFG and MBFG,we selected the survey data of the representative months(every year in January,April,July and October)during January2018 to December 2019,divided the phytoplankton communities,and the species number,biomass composition,distribution characteristics of different functional groups,the corresponding physical and chemical indexes of water environment and their distribution characteristics were analyzed.On this basis,the relationship between phytoplankton functional groups and environmental factors was studied.The main research results can be summarized as follows:1.Composition and distribution characteristics of phytoplankton functional groups(1)During the investigations,148 species of phytoplankton were recorded,belonging to 8 phylums.There were 63 species of Chlorophyta,34 species of Cyanophyta,and 32 species of Diatom.The species of Cryptophyta,Chrysophyta,Gymnophyta,Euglenophyta,and Xanthophyta account for relatively few,less than5%.The absolute dominant species in the study area was Microcystis aeruginaosa throughout the investigation.Among them,the dominant species were Microcystis aeruginaosa and Melosira granulatain in 2018,was Microcystis aeruginaosa in 2019.The overall density,biomass and chlorophyll a concentration of phytoplankton in different years were significantly different between months(P<0.05),and even presented extremely significant differences(P<0.01).Compared with 2018,the density and biomass of phytoplankton had decreased in 2019.There were significant differences between some months in the same year(P<0.05),and varied in different months.During the survey period,the phytoplankton density,chlorophyll a concentration and biomass were the lowest in November,but the highest values occurred in different months in summer.In addition,cluster analysis also showed that the similarity relationship between the months was credible.The overall phytoplankton density,biomass and chlorophyll a concentrations varied significantly between sites in different years,such as the overall density and chlorophyll a in 2018 were significantly different between sites(P<0.05),but there were no significant differences in 2019(P>0.05),and the overall biomass in different years were not significantly different between sites(P>0.05).In the same year,the density,biomass and chlorophyll a of phytoplankton at different sites along the lake-reservoir connected area were significantly different among some sites(P<0.05),and varied in different years.During different years,phytoplankton density and biomass decreased significantly from the East Taihu Lake through the diversion channel to the Jinze Reservoir(P<0.05);In 2018,the concentration of chlorophyll a decreased significantly in the entire lake and reservoir connected area(P<0.05),and fluctuated in the middle section in 2019.The general trend was a decline,but there was no significant difference(P>0.05).In addition,cluster analysis had a certain reference value for the similarity between sites in different years.(2)Phytoplankton communities were divided according to RFG、MFG、MBFG functional groups.The 135 species of phytoplankton recorded in 8 months can be divided into 26 RFG,and the dominant functional groups were M、P and S1.Among them,the dominant functional groups were M and P in different years.The phytoplankton recorded in the eight months of the MFG can be divided into 23 functional groups,and the dominant functional groups were 5a,5b and 6a.Among them,the dominant functional groups were both contain 5b and 6a.The number of11 a functional group species is the highest,6b the second.MBFG functional groups can be divided into 7 functional groups(Group I-Group VII).Among them,the dominant functional groups in different years were both Group III and VII.(3)The division of different functional groups in the lake reservoir connected area had a significant impact on the research results of the distribution characteristics of phytoplankton community.There were differences in the overall spatial-temporal distribution characteristics of phytoplankton functional groups in different divisions from the perspective of species number and biomass.From the perspective of species number,the total number of species in the three functional groups in different years had a very significant difference between seasons(P<0.01),and there were no significant different between the sites(P>0.05);For biomass,the three functional groups were different between different seasons in different years.There were extremely significant differences in 2018(P<0.01),but in 2019,there were no significant difference(P>0.05);the total biomass of the three functional groups in different years were not significantly different between different sites(P>0.05).(4)Even under the same division method,the spatial-temporal distribution characteristics of individual functional groups were also different.Among the three functional groups,there were no significant differences in the number of species and biomass of the dominant functional groups in different years(P>0.05),that was,the longitudinal change along the lake-reservoir connecting area was not significant(P>0.05);The difference was obvious between different seasons.Most of the dominant functional groups had significant differences in species number and biomass(P<0.05),and even extremely significant different(P<0.01).Among them,the number of species or biomass of individual dominant functional groups had no significant different between different seasons in 2019(P>0.05).2.Relationship between phytoplankton functional groups and environmental factors(1)The main influencing factors of functional group distribution are closely related to its aquatic ecological environment.The main environment factors that affect the overall species number and biomass distribution of the three functional groups are also different and have inter-annual differences.In terms of the number of whole species and biomass of functional groups,there was some overlap between RFG and MFG in the whole lake-reservoir connected areas under different divisions,and being the same with inter annual variation and the main influencing factors,that was,except for 2019,the whole biomass was significantly correlated with pH、water temperature and water intensity in RFG and MFG(P<0.05),and there were no correlation between the total number of species and the biomass in 2018(P>0.05);Moreover,only the total number of species in 2019 was extremely significant correlated with COD(P<0.01),and there were no correlation between the total biomass and the total number of species with environmental factors among different years in 2018(P>0.05).(2)Even under the same division method,the correspondence among different years and different dominant functional groups with environmental factors were also different.The spatial-temporal changes of different dominant functional groups were the result of the interaction of environmental factors.The greatest influential environmental factors on the dominant functional group in different years were pH,water temperature,transparency and total nitrogen;The environmental factors that had the greatest influence on the MFG dominant functional group were pH,totalphosphorus,conductivity,water temperature and light intensity;Environmental factors that had a greater impact on the MBFG dominant functional group were water temperature,pH,underwater light intensity and ammonia nitrogen.At the same time,except for the environmental factors that explained the biomass of the MBFG dominant functional group slightly lower than that of the species in 2019,the other environmental factors explained the biomass of the three functional groups of phytoplankton biomass better than that of the species number,which also explained the advantages of phytoplankton biomass research to a certain extent.In addition,the RFG and MFG dominant functional group biomass explained higher environmental factors in different years,and the interpretation of MBFG dominant functional group was relatively poor.In general,different division methods of functional groups have significant influence on the results of phytoplankton community distribution.Therefore,in the process of using functional group method to study phytoplankton community,it is necessary to select effective functional group division methods according to the research objectives,the information reflected by the specific functional groups.If necessary,the combination of different functional group division methods can be considered to obtain the multi-level aquatic ecosystem information.This paper mainly aims at the study of different phytoplankton functional groups in the linear water environment,passing through the diversion channel in the middle.The research results have certain reference significance for the response between the phytoplankton functional group in the lake and reservoir connected area and the environment.