Dynamic Changes Of Phytoplankton Community Structure And Niche Characteristics In Maotiao River Basin

The Maotiao River is a plateau river with typical karst landforms.Hongfeng Reservoir and Baihua Reservoir are the important drinking water sources for more than 5 million people in Guiyang,the quality of water directly affects the safety of drinking water.Phytoplankton is an excellent and efficient environmental indicator species,and its community structure characteristics and species diversity can be used as an important indicator for quality of reservoir water assessment and monitoring.In order to investigate the phytoplankton community characteristics,succession rules of functional groups,ecological niche and interspecific association in Maotiao River basin,this study was conducted in November 2020(dry period),March 2021(normal period)and July 2021(wet period),based on the analysis of phytoplankton community dynamics at 14 sampling sections in Maotiao River basin and the interaction between phytoplankton community and habitat,the aquatic ecological characteristics,niche and interspecies association of dominant species in Maotiao River basin were discussed,in order to provide reference for river basin water resources management,ecological environment protection and aquatic ecosystem restoration in plateau karst area.The main results are as follows:(1)Phytoplankton species composition:A total of 62 species(genus)of 7 phyla of phytoplankton were detected in the three hydrological periods,of which chlorophyta and diatom were the main species,and the phytoplankton showed obvious seasonal differences.A total of 51 species(genus)of 7 phyla were detected in dry periods,40 species(genus)of 7 phyla in normal period,and 52 species(genus)of7 phyla in wet period.Through comparative analysis,it was found that the changes of phytoplankton community structure had obvious spatial and temporal differences.Cyanophyta was the dominant species in the wet period,and Pseudanabaena limnetica was the dominant species.The dominant algal species in the three hydrological periods of the basin were Pseudanabaena limnetica,Trichocephalus,Cyclotellasp.,Synedra sp.,Achnanthes sp.,Navyweed and Cryptophyta,among which the dominant species was Pseudanabaena limnetica.The cell abundance was 4.16×10~6 cells·L^-1 and the dominance value was 0.46.(2)The functional groups D,J,and MP were the most regularly occurring at each sampling section in the three hydrological periods.The functional groups comprised Synedra sp.,Scenedesmus sp.,Achnanthes sp.respectively.Among them,the frequency of functional groups B,Y,S1,P and Lo was more than 50%in the scientific research survey of Maotiao River basin,and the representative algal species of functional groups were Cyclotella sp.,Cryptoalgae,Pseudanabaena limnetica,Melosira granulata,and Peridinean.The community structure and succession law of phytoplankton functional groups at each sampling section of the Maotiao River basin in three hydrological periods were clearly distinct in time and space.(3)The biomass of phytoplankton functional groups in each sampling section was compared,it can be found that the eutrophication degree of water body with greater biomass is also higher,it may be due to the large area of the reservoir area,and the nutrients are imported through surface runoff and other ways.In addition,the discharge of reservoir water did not increase,resulting in an increase in nutrient salt content,resulting in eutrophication of reservoir water.According to the biological diversity index analysis,the water body of the Maotiao River is in a medium trophic state.(4)The results of redundancy analysis showed that the main environmental factors restricting the growth and reproduction of phytoplankton dominant functional groups in the Maotiao River Basin were p H,water temperature(WT),potassium permanganate index(COD_Mn),N-NO₃,Electrical conductivity(EC).(5)The results of phytoplankton analysis based on niche theory show that:in the three hydrological periods,the niche width of Pseudanabaena limnetica is relatively large,and each sampling section occupies a relatively wide range of habitat resources,which overlaps with the range of habitat resource requirements of other dominant populations.larger value;most dominant species only became dominant species in a certain hydrological period,and their niche was narrow.The dominant species in dry and wet periods were recessionary.The dominant species in normal period was developmental.The density of dominant species was significantly correlated with dominance.In the dry period,the overlap value of dominant species Pseudanabaena limnetica(Bi=0.41)and Navicular(Bi=0.49)was the lowest,which was only0.22,the results indicated that the utilization of resources of Pseudanabaena limnetica and Navicular algae was less interlacing in the dry period,and there was a great difference in the adaptation habitat,so the competition between the two species was weak.