Phytoplankton Diversity Pattern In Urban River Network

Urban river network ecosystem is an important carrier of urban material circulation,and its water quality directly affects the construction of urban ecological civilization.Phytoplankton,as excellent environmental indicators,can be used to evaluate and monitor the water quality of urban river network.The characteristics and species diversity of its community structure can be used to evaluate and monitor the water quality of urban river network.The structure of Harbin urban river network is composed of Songhua River as the main stream and Hejiagou,Majiagou and Ashi River as tributaries,which is located in Harbin City,Heilongjiang Province.The river network is in the shape of a trident,with distinct climate,abundant rainfall in wet season and long dry season.The water quality of Harbin urban river network is related to the appearance of Harbin city,sewage drainage,landscape construction and other important aspects,so it has very practical ecological significance for the study of phytoplankton community structure and diversity of Harbin urban river network.In this study,the phytoplankton samples were collected and nine physical and chemical indexes were determined,including water temperature(WT),dissolved oxygen(DO),pH(pH),conductivity(Sp Cond.),turbidity(Tur.),total nitrogen(TN),total phosphorus(TP),chemical oxygen demand(COD_Mn)and five-day biochemical oxygen demand(BOD₅),for 22 sampling sites from June to November 2019.The species composition,dominant species distribution,cell density of phytoplankton community,he temporal and spatial changes of phytoplankton community structure were further analyzed in Harbin urban river network.Based on?diversity index and?diversity index,the spatial and temporal similarities and differences of phytoplankton communities were analyzed comprehensively,and the spatial heterogeneity of the urban river network in Harbin was discussed.Through principal component analysis(PCA)and canonical correspondence analysis(CCA),the main environmental factors of Harbin urban river network and the correlation between phytoplankton community and environmental factors were discussed,which provided basic data for water ecological protection and diversity protection of urban river network in China.The main findings are as follows:1.The results of physical and chemical indexes of water environment in Harbin city show that each physical and chemical index has obvious difference in time and space.,Average water temperature is 17.63?;The mean pH is 7.65,indicating that the water body is alkaline;Average conductivity 373.76?S/cm;An average of 6.24 mg/L;of dissolved oxygen Average turbidity was 66.49 NTU;Average total nitrogen content is1.28 mg/L;Average total phosphorus content was 0.56 mg/L;An average of 7.67 mg/L;permanganate index Average of 5 days biochemical oxygen demand 1.52 mg/L.The results of trophic state index(TSI_M)evaluation showed that the urban river network in Harbin was in the range of medium to moderate eutrophication state,and the water quality of Songhua River sample points was excellent and the water of three tributaries.2.A total of 218 phytoplankton taxa,belonging to 8 phyla,12 classes,27 orders,45families and 97 genera,were identified in the urban river network of Harbin from June to November 2019.The highest species of green algae were 94 species,accounting for42%;diatoms were 72 species,accounting for 32%;then 28 species of cyanobacteria,accounting for 12%;other floating plants were less,a total of 26 species,accounting for11%of the total.The average phytoplankton abundance in the urban river network of Harbin is 200.32×10⁶ind./L,and the average phytoplankton abundance in the Songhua River sample is higher than that in the three tributaries.A total of 53 dominant species of phytoplankton were identified,which were mainly diatoms and Chlorophyta.The dominant species mainly included Cyclocystis meniniensis,Melosira granulata var.angustissima,Nitzschia palea,Ankistrodesmus angustus,Pseudorhythium lacustris and Cryptococcus ovalum.One-way analysis of variance(ANOSIM)showed that there were significant spatial and temporal differences in the distribution of dominant species.Simper analysis showed that the main species contributing to the differences between the Songhua River and its three tributaries were Pseudanabaena limnetica,Cyclotella meneghiniana,Melosira granulata var.angustissima,Nitzschia palea and the Aphanocapsa elachista.3.?diversity and?diversity index were used to evaluate phytoplankton diversity in Harbin urban river network.The variation range of Margalef diversity index(H)during the study period was:0.27-4.38;The variation range of Shannon-Weaver diversity index(H')is 0.32-4.16;The variation range of Pielou uniformity index(J)is 0.11-0.99;The variation range of Simpson's ecological dominance index(D)is:0.07-0.90;Diversity threshold Dv range of variation is:1.00-9.11.The result of Margalef diversity index evaluation of Harbin urban river network is?-pollution state;Shannon-Weaver diversity index evaluation results are clean to heavy pollution state;Evaluation result of Pielou evenness index is light pollution or medium pollution state;According to Simpson's ecological dominance index,the species were evenly dispersed and the community stability was high from June to August,while the species were relatively single and the community stability decreased from September to November;The result of diversity threshold evaluation is that the overall condition of water body is grade I,Phytoplankton species are very rich.The results of?-diversity index showed that the community structure was different among the four river reaches,and there was a great difference between the Songhua River and the three tributaries,and the cause of the difference was related to the spatial turnover of species.4.Based on the results of principal component analysis(PCA)and canonical correspondence analysis(CCA),the main environmental factors affecting the succession and spatial and temporal distribution of phytoplankton community in Harbin urban river network are as follows:WT(F=1.764,P=0.006),pH(F=2.300,P=0.004),TP(F=2.104,P=0.002),DO(F=1.818,P=0.002).These four environmental factors affect the phytoplankton community structure of Harbin urban river network,driving phytoplankton community succession and spatiotemporal distribution.