Correlation Between Dynamic Changes Of Phytoplankton Community Structure And Environmental Factors In Harbin Section Of The Songhua River

Rivers play an indispensable role in ecosystem and society.River ecosystem,an integral link of material cycle,is a special ecosystem with multifunction providing services,including shelter and food source,flood management,and other social purposes.As the primary producers,phytoplankton can respond rapidly to environmental changes.The species composition and community structure in rivers will make differences along the environmental gradients.Therefore,phytoplankton community was mainly used to monitor the water quality.The Harbin section of the Songhua River is located in the northeast of China,which flows through the main urban area of Harbin city.It brings significant water supplies for production and daily life.In this paper,phytoplankton samples were collected at nineteen sites in Harbin section of the Songhua River in spring,summer and autumn from 2018 to 2019.Meanwhile,the physical and chemical parameters were determined.The temporal and spatial variation of algae biodiversity and community structure were analysed,as well as the succession characters of dominant species.Redundant analysis?RDA?was used to explore the correlation between phytoplankton and various environmental factors within two years,with identifing the key factors of driving succession.Based on biological,physical and chemical indicators,the water quality in Harbin section of the Songhua River was comprehensively evaluated in order to provide basic data for the improvement and protection of the water environment.Main results for this study are as follows:1.A total of 175 taxa of phytoplankton were identified,belonging to 7 phyla,10classes,19 orders,33 families and 75 genera.Chlorophyta is the most species rich group,next is the Bacillariophyta.In 2018,the mean abundance of phytoplankton in Harbin section of the Songhua River was 21.88×10⁶ ind./L,while 20.89×10⁶ ind./L in 2019.The composition and abundance of phytoplankton community showed siginificant variation in time and space,predominated by Chlorophyta-Bacillariophyta.2.During the study,a total of 16 phytoplankton dominant species were observed.The common species in the two years included Cyclotella meneghiniana,Melosira granulata var.angustissima,Nitzschia palea,Synedra acus,Surirella linearis,Asterionella formosa,Chlorella vulgaris,Ankistrodesmus angustus,Scenedesmus quadricauda,Pseudanabaena limnetica,Chroococcus minutus,Chroomonas acuta and Cryptomonas ovata.SIMPER analysis and ANOSIM analysis showed the succession of the dominant species in different seasons had the similar pattern in two years:In spring,Bacillariophyta predominates numerically until Chlorophyta and Cyanophyta replace it as the dominant groups in summer.And the dominant species of Bacillariophyta and Chlorophyta are rich in autumn again.3.The diversity indices were performed to evaluate the water quality of Harbin section of the Songhua River.The results demonstrated that the range of Margalef index?H?varied from 1.07 to 6.18.The Shannon-Weaver index?H'?was from 1.31 to 5.28.The Simpson's ecological dominance?D?presented from 0.33 to 0.98.The Simpson reciprocal index?D'?showed from 1.48 to 16.35.The Pielou evenness index?J?ranged from 0.30 to0.96.The Lloyd-Gherlandi evenness index?E?indicated from 0.12 to 0.64.The range of diversity threshold value?Dv?was from 3.58 to 6.43.The results of the seven diversity indices showed that the phytoplankton biodiversity in Harbin section of the Songhua River were rich,and the individual distribution in summer was more even.However,the phytoplankton diversity didn't change significantly in spatial terms.4.Physical and chemical factors were monitored in Harbin section of the Songhua River showed that the range of the water temperature?WT?was from 6.3 to 28.5?.The dissolved oxygen?DO?varied from 3.3 to 10.9 mg/L.The pH presented from 6.8 to 9.2.The specific conductivity?SpCond.?was 136.6 to 975.1?S/cm.The turbidity?Tur.?showed from 12.8 to 161 NTU.The concentration of total nitrogen?TN?was 0.54 to 2.50mg/L,and total phosphorus?TP?was 0.10 to 2.05 mg/L.The chemical oxygen demand(COD_Mn)ranged from 3.06 to 12.86 mg/L.The five-day biochemical oxygen demand?BOD₅?indicated from 1.1 to 6.2 mg/L.One-way analysis of variance?ANOVA?showed significant differences of WT,DO,pH,SpCond.,Tur.,TN,and COD_Mn among three seasons.SpCond.,Tur.,TN,TP and COD_Mn were significantly different in spatial scale.5.Phytoplankton community patterns in Harbin section of the Songhua River was closely related to water environmental factors.RDA analysis and Pearson correlation analysis showed that Tur.?P=0.002?,WT?P=0.002?,SpCond.?P=0.002?and BOD₅?P=0.03?were the key factors driving algae succession in 2018,while DO?P=0.002?,TN?P=0.002?,pH?P=0.002?,Tur.?P=0.02?and COD_Mn?P=0.02?in 2019.6.In the study,water quality was evaluated with various methods.The results of the Environmental Quality Standards for Surface Water showed that the water quality was mild pollution during the two years and the major indicators were TP,TN and COD_Mn.Based on the Trophic State Index?TSI_M?,the water body was light to moderate eutrophication.The pollution indicator species showed the water was mesotrophic to eutrophic.According to the diversity index,the water quality of Harbin section of the Songhua River was mildly to moderately polluted.Functional groups with Q index indicated the water generally tolerable or medium.In conclusion,the water quality and trophic state of Harbin section of the Songhua River in 2018-2019 evaluated primarily was slight polluted and light to moderate eutrophication.