Seasonal Variation And Influencing Factors Of Bacterial Community In Jihongtan Reservoir,Qingdao

As an important part of water ecosystem,microorganisms play an important role in energy flow and material circulation.Environmental factors can affect the composition of microbial community structure and change the ecological function of microbial communities.Due to the differences in physical and chemical properties of water bodies,the composition of microbial community structure varies greatly in different time and space.Therefore,understanding the composition and dynamics of reservoir microbial community structure is crucial for maintaining freshwater ecosystem functions and exploring their biogeochemical cycles.The Yellow River Diversion project is a large-scale cross-basin and long-distance water diversion project to divert water from the Yellow River to Qingdao,which solves the problem of insufficient water supply in Qingdao and other cities along the route.As the only regulating and storage reservoir of the Yellow River diversion project,Qingdao Jihongtan Reservoir is the largest plain dam type reservoir in Asia.As the largest source of drinking water in Qingdao,Jihongtan Reservoir takes over 90% of the water used by Qingdao residents,and its water environment quality is closely related to people’s production and life.This paper takes Qingdao Jihongtan Reservoir as the research object.Based on the analysis of physical and chemical indicators of water quality,high-throughput technology is used to characterize the structure of bacterial and eukaryotic microbial communities,and to analyze the seasonal differences in relative abundance of representative species.The association network was used to explore the interaction relationship between species communities in different seasons.Redundancy analysis and correlation heatmap were used to explore the main factors affecting the composition of bacterial and eukaryotic microbial communities,and FAPROTAX functional prediction of bacterial communities was predicted.The main conclusions are as follows:(1)There were significant seasonal differences in temperature,DO,nitrate nitrogen and sulfate,but no significant seasonal differences in p H,turbidity,COD,nitrite nitrogen,ammonia nitrogen,TN and TP,and TP was the key factor for eutrophication in the reservoir.Temperature was significantly positively correlated with nitrous nitrogen,and significantly negatively correlated with DO,nitrate nitrogen and TN;turbidity was significantly positively correlated with TP;p H was significantly negatively correlated with ammonia nitrogen,nitrite nitrogen and COD;ammonia nitrogen was significantly positively correlated with nitrite nitrogen;nitrate nitrogen was significantly positively correlated with total nitrogen and sulfate;total nitrogen was significantly positively correlated with total phosphorus;and COD was significantly negatively correlated with sulfate.The water body of Jihongtan Reservoir meets the GB 3838-2002 Class III standard,and COD,nitrate nitrogen,TN and TP are the main environmental factors affecting water quality.(2)The richness and diversity of bacterial community in Jihongtan Reservoir in Qingdao were highest in summer and lowest in winter,and the inlet was higher than the outlet.The bacterial community structure composition was similar in spring and winter,and similar in summer and autumn.They belong to 39 phyla and 909 genera.Actinobacteriota,Proteobacteria,Bacteroidota and Cyanobacteria were the dominant phyla.hgc I＿clade,CL500＿29＿marine＿group,Limnohabitans,norank＿f＿Sporichthyaceae,uncalssified＿f＿Chloroplast and Flavobacterium were the dominant species.In addition,two genera Acinetobacter and Mycobacterium were found in the water inlet in June,and the relative abundance of opportunistic pathogens was 2.36% and 6.26%,respectively.Spring and autumn are more complicated than summer and winter.In spring and autumn,competition and antagonism were the main factors,while mutualism was the main factor in winter.There were significant differences in the key species of bacterial interaction in each season.Compared with the water inlet,it is more complex,and both are mainly based on mutualism.There are significant differences in the key species of bacterial interaction between the water inlet and the water outlet.(3)The diversity and richness of eukaryotic microbial community in Jihongtan Reservoir in Qingdao were highest in summer and lowest in winter;the inlet is higher than the outlet.The community structure in summer,autumn and winter had obvious seasonal alternation.Eukaryotic microorganisms belong to 46 phyla and 509 genera.At the phylum level,the unclassifed＿k＿Eukaryota and Arthropoda were the dominant species in zooplankton;the Chlorophyta and Bacillariophyta were the dominant species in phytoplankton;the Cryptomycota and Chytridiomycota were the dominant species in fungus.At the class level,the unclassified＿k＿Eukaryota and Hexanauplia were the dominant species in zooplankton;the Chlorophyceae and Cryptophyceae were the dominant species in phytoplankton;the unclassified＿p＿Cryptomycota and unclassified＿k＿Fungi were the dominant species in fungus.At the genus level,unclassified＿d＿Eukaryota,Paracyclopina and Sinocalanus were the dominant species in zooplankton;the unclassified＿o＿Chlamydomonadales and unclassified＿p＿Chlorophyta were the dominant species in phytoplankton;the unclassified＿p＿Cryptomycota and unclassified＿k＿Fungi were the dominant species in fungus.The interaction between spring and winter is more complex than that between summer and autumn.The relationship of mutualism is dominant in summer,while in winter,competition and antagonism are strong.There were significant differences among the key species interacting with each season.The interactions of the outlet were more complex than those of the inlet,and there were significant differences in key species.(4)Redundancy analysis and Heatmap analysis showed that the phylum level of bacterial community structure was mainly affected by temperature,DO and water storage,while the class level and genus level were mainly affected by temperature,DO,water storage and nitrite nitrogen.Nutritional methods are mainly chemotrophic.There were 11 functional notes related to the nitrogen cycle,including nitrate reduction,nitrate respiration,nitrite respiration,nitrate denitrification,nitrite denitrification and ureolysis.There were five functional notes related to the sulfur cycle,including sulfide respiration and sulfate respiration,etc.There are five functional annotations related to the carbon cycle,including methylotrophy and methanol oxidation,etc.The composition of phylum,class and genus of eukaryotic microbial community were mainly affected by temperature,DO,water storage and nitrate nitrogen.