The Community Structure Characteristics Of Phytoplankton And Their Relationship With Environmental Factors In River Courses In The Urban Area Of Suzhou City

As an important central city in the Yangtze River Delta,there are numerous river courses in Suzhou City,with river network crisscross and complex water situation.In recent years,with the development of economy and the increasing of population,the river courses in Suzhou City has caused a lot of pollution,which seriously endangered the water security of human beings.In the early stage of river courses ecological monitoring and treatment,more attention was paid to the improvement of water quality indexes,and the influence of biological factors was ignored,so that the treatment results were capricious.Phytoplankton is the producer of water ecosystem that monitoring the change of algae has become a key means of ecological environment management.This study was aimed at the current needs of Suzhou City to build a healthy water ecology,combined with the national water special overall deployment and research and development focus,23 monitoring sites in 8 urban areas of Suzhou were sampled and a bimonthly survey and its analysis were conducted in 2018.Investigated the spatial and temporal differences and standing crop of phytoplankton community structure in river courses during the inquiry period in detail,the functional groups of phytoplankton were classified,the environmental factors of collected water samples were determined to understand the relationship between phytoplankton community structure change and environmental factors.Finally,based on the ecological indexes of phytoplankton and physicochemical factor indexes,the water quality of the river courses in Suzhou City was preliminarily evaluated and the evaluation method suitable for river courses was discussed.It's expected to further select the evaluation parameters of the ecological health of urban rivers,form the evaluation method of the ecological health of urban rivers,and provide basic data for the demonstration and verification of key technologies in the comprehensive demonstration area of Suzhou City,so as to play a positive demonstration and leading role in the water environment management of similar cities in China.1.A total of 209 phytoplankton species were identified from 85 genera and 7phyla in the urban river courses of Suzhou City in 2018,among 76 species(36.36%)in33 genera of Chlorophyta,63 species(30.14%)in 23 genera of Bacillariophyta,and 33species(15.79%)in 18 genera of Cyanophyta,accounting for 82.29%of the total species.2.A total of 30 phytoplankton annual dominant species were identified from 19genera and 3 phyla throughout the year in the urban river courses of Suzhou City in2018,among which 16 species were Cyanophyta,7 species were Bacillariophyta and 7species were Chlorophyta.The dominant species included Microcysitis sp.,Anabaena sp.,Chroococcus sp.,Pseudanabaena sp.,Aulacoseira granulate var.Angustissima,Cyclotella sp.and Chlorella vulgaris.3.The annual mean density and biomass of phytoplankton were(20462.92±19092.87)×10~4cells/L and(34.15±38.84)mg/L in the urban river courses of Suzhou City in 2018.The cell density and biomass of Shantang area and Chengxi area were relatively large.However,all of them showed the highest proportion of Cyanobacteria,followed by Bacillariophyta and Chlorophyta.4.The annual values of phytoplankton biodiversity indexes H'?J and D in the urban river courses of Suzhou City in 2018 were(1.45±0.56),(0.46±0.11)and(1.43±0.64),respectively.The values in spring and summer were higher than in autumn and winter.H'?J and D were highest in July and lowest in November.5.According to the classification method of phytoplankton functional groups,29phytoplankton functional groups were identified,among which 19(B,C,D,G,H1,J,Lo,M,MP,P,S1,S2,T,TC,W1,X1,X2,Y and Z)were the dominant functional groups in the urban river courses of Suzhou City in 2018.The annual succession of phytoplankton functional groups was characterized as follows:B+C+D+H1?W1+H1?P+G+H1?M+S1+H1.H1 was found to be dominant throughout the year.6.RDA revealed that most functional groups were related to phytoplankton water temperature(WT),total nitrogen(TN),total phosphorus(TP)and electrical conductivity(Ec)were positively correlated in the urban river courses of Suzhou City in 2018.Pearson correlation analysis showed that phytoplankton diversity indexes H',J and D were significantly positively correlated with water temperature(WT)and electrical conductivity(Ec).7.Water quality evaluation in the urban river courses of Suzhou City in 2018 was conducted by physical and chemical factors(single factor evaluation method,comprehensive pollution index method)and phytoplankton(cell density,biomass,biodiversity indexes,functional group classification method,Q index),according to the comprehensive application of various evaluation methods in river courses,the comprehensive pollution index method,phytoplankton diversity indexes method and the evaluation effect combining with the habitat characteristics of phytoplankton dominant functional groups can better reflect the nutritional status of the river courses,and determine that the water quality of the river courses in Suzhou urban area is in a medium-heavy nutritional state in 2018.