Water Quality And Plankton Community Characteristics Of The Typical Trans-provincial Sections In The Songhua River Basin During The Freezing Seasons(

The Songhua River Basin has the longest frozen period,and there are many rivers that cross the provincial boundary.However,studies on water quality characteristics and plankton community composition during the freezing seasons in the transprovincial sections of the Songhua River Basin are still rare.This study took the provincial boundary buffer zone of the Songhua River Basin involving Heilongjiang Province as the research object,not only analyzed the physicochemical characteristics of water quality,but also explored the community structure of planktonduring the freezing seasons,and explored the indicative effect of dominant species of plankton on water quality,made up for the deficiency of the study on the water environment characteristics in the buffer zone of the Songhua river basin.This study collected the monitoring values of 24 physicochemical indexes in 41 provincial boundary monitoring sections of the Heimeng(HM)and Heiji(HJ)provincial boundary buffer zones in the Songhua River Basin during the freezing period(January-March)of 2017 ? 2019.Firstly,the single-factor index method was used to evaluate the water quality,and the water quality types of the various sections at different periods were obtained.It was found that the water quality in the freezing seasons of 2017 was the best,and the water quality of the HM provincial boundary buffer zone was better than that of the HJ provincial boundary buffer zone.Secondly,the main physicochemical indexes affecting the water quality in the research area during the freezing period were selected by principal component analysis,which were NH3-N,TP,BOD5,CODMn and COD.Based on the monitoring data,the possible causes of water pollution in the study area were found: the watershed where the section is located was polluted,the production of industry and agriculture has caused long-term water quality pollution in some waters,sudden organic pollution caused water quality pollution in small watershed in a short time,water pollution caused by changing seasons and melting rivers.Finally,7 typical monitoring sections were selected for single index analysis,and the sections were classified according to different pollution types.In December 2019,high-throughput sequencing was performed on bacteria,phytoplankton and zooplankton samples collected from seven typical sections.The results showed that the species abundance and diversity of plankton in the HM provincial boundary buffer zone were significantly higher than those in the HJ provincial boundary buffer zone during the freezing seasons.The species of plankton in the two provincial boundaries were quite different,the abundance of Pseudomonas and phytoplankton in the HJ provincial boundary buffer zone was significantly higher than that in the HM provincial boundary buffer zone.A variety of statistical methods were used to analyze the differences in plankton community structure between the sections,and the results were almost the same as the clustering results based on the physicochemical characteristics of water quality,indicating that the sections with similar phytoplankton community structure had similar physicochemical characteristics of water quality.In order to explore the relationship between plankton community and water environment factors,this study used five water quality indexes to conduct redundant analysis with the dominant species of bacteria,phytoplankton and zooplankton,respectively.The results showed that TP,BOD5 and p H had a great influence on the plankton community during the freezing seasons;Pseudomonas,Acinetobacter,Candidatus Pelagibacter,Geothrix,Hydrurus,Chrysophyceae,Cryptophyta,Katablepharidaceae,Stephanodiscus,Hemiophrys and Vampyrellida can indicate the water quality of the study area.