Study On The Correlation Between Phytoplankton Community Structure And Water Environmental Factors In The Harbin Section Of Songhua Rive

Based on the most typical urban river ecosystem in Harbin section of Songhua River,this paper reflects the characteristics of water quality in Harbin section by studying the changes in the characteristics of phytoplankton community structure,and makes a comprehensive evaluation,which provides scientific research data for the protection and improvement of water environment in Harbin section of Songhua River.In this study,nine monitoring sections were set up in Harbin section of Songhua River.Eight phytoplankton samples and water environment factors were sampled in September,October and November of autumn 2021,April and May of spring 2022,and July,August and September of summer 2022.Qualitative and quantitative analysis was conducted according to the sampling results to discuss the change characteristics of phytoplankton community structure,abundance and diversity in Harbin section,RDA redundancy analysis was used to explore the relationship between dominant species and physical and chemical factors of water body in three seasons,determine the physical and chemical factors driving species community change,and evaluate the water quality of Harbin section of Songhua River based on biological and abiotic factors.The research results are as follows:（1）During three seasons from 2021 to 2022,228 taxa of phytoplankton were identified,with diatoms being the most abundant（83 species,37 genera）,followed by green algae（82 species,33 genera）,accounting for 35.32%and 34.89%,respectively.The average species abundance was highest in the spring of 2022,followed by summer 2022and autumn 2021.The community structure presented a diatom-green algae pattern in both autumn 2021 and spring 2022,but shifted to a green algae-diatom-cyanobacteria pattern in summer 2022.（2）In this study,22 dominant species were identified,including 9 at most in Diatoma,5 in Chlorophyta and Cyanophyta,and 3 in Cryptophyta at least.There were significant differences in the time change of dominant species.Cylotella meneghiniana,Nitzschia palea,Pseudoanaena limnetica and Ankistrodesmus angustus are dominant species in each month.（3）Three diversity indices were used to investigate species diversity in the Harbin section of the Songhua River,including Shannon-Wiener,Pielou evenness,and Maraglef indices,with the ranges of 1.78-4.62,0.38-0.79,and 1.78-4.48,respectively.The results showed that there was no significant variation in species diversity of phytoplankton in the Harbin section of the Songhua River,and the community structure was relatively stable.（4）During the investigation,the variation range of water environment factors is as follows:water temperature（WT）:11.1～25.4℃,pH value:7.1～8.68,dissolved oxygen（DO）:0.22～10.12 mg/L,high fierce acid index(COD_Mn):3.83～12.28 mg/L,five-day biochemical oxygen demand（BOD₅）:1.82～20.68 mg/L,NH₃^-N:0.09～4.73 mg/L,total nitrogen（TN）:1.36～16.22 mg/L,total phosphorus（TP）:0.116～1.278 mg/L.The results showed that there were significant differences in the spatial distribution of nitrogen and phosphorus contents,and nutrients were the main factors affecting the changes of phytoplankton community in Harbin section.（5）Pearson and RDA analysis showed that TP,TN,DO and other organic matters and water temperature were the main factors affecting the changes of phytoplankton community structure in Harbin in the autumn of 2021;TP,TN,WT and BOD₅ are the main factors affecting the changes of phytoplankton community structure in Harbin in the spring of 2022;WT,pH and DO are the main factors affecting the changes of phytoplankton community structure in Harbin section in the summer of 2022.（6）According to the surface water evaluation standard,the water quality of Harbin section of Songhua River in 2021-2022 was moderately polluted by total nitrogen evaluation,while the other indexes were mildly polluted,so the water quality was preliminatively determined to be mildly pollute;The evaluation results of Shannon-Wiener diversity index and Pierou evenness index are the same.The evaluation results of spring and summer in 2022 are light pollution,and the evaluation results of autumn in2021 areβ-Medium pollution state;The evaluation result of Margalef diversity index is that the three quarters from 2021-2022 are all slightly polluted.