Study On Microbial Community Diversity In The Reclaimed Water Reclaimed Water Section Of Licun River In Qingdao

Microorganisms are the most widely distributed and diverse species in river ecosystems,and play an important role in the flow of energy and the cycling of materials on Earth.The community structure and diversity of microorganisms are closely related to the function and health of ecosystems.Understanding the microbial community structure of rivers is important for maintaining the ecology of rivers and improving the urban environment.The recharge of reclaimed water to natural water bodies is an efficient way to realise the recycling of regional water resources.This is in line with the national water resources use development plan.The quality of reclaimed water differs from that of natural water bodies,especially when there are traces of emerging pollutants and other potentially harmful substances remaining in the reclaimed water.This difference in water quality may have an impact on the original microorganisms in the natural water body and even destroy the structure of the indigenous community.In this study,the seasonal variation characteristics of water quality indexes were investigated and analyzed by taking the reclaimed water replenishment channel of Licun River in Qingdao as the research object.Based on 16 S r RNA high-throughput sequencing technology,the bacterial community structure of planktonic bacteria and sediment was analyzed,and the dominant bacteria in each season were compared.The main influencing factors of microbial community structure were explored,and the function of microbial community was annotated by using FAPROTAX function prediction.The main results are as follows:(1)The results of water quality monitoring showed that the water quality was improved obviously,and the river section was in line with the surface water environmental quality IV water standard after water replenishment.There were obvious seasonal differences in water quality.The concentrations of ammonia nitrogen and total phosphorus in summer were higher than those in other seasons.The concentration of nitrate nitrogen was the highest in autumn,and the concentration of sulfate was the highest in spring and winter.The concentration of nitrate nitrogen and chloride increased along the river.The concentration of total phosphorus in spring,the concentration of ammonia nitrogen in summer and the concentration of COD in winter decreased along the river.At the same time,the replenishment of reclaimed water can effectively reduce the number of fecal Escherichia coli in the river and reduce the safety risk of pathogenic microorganisms to human health.The main environmental factors affecting the quality of water environment were fecal Escherichia coli,ammonia nitrogen and total phosphorus.It is necessary to be alert to the risk that total nitrogen and TP may cause eutrophication of river water.(2)All samples were classified into 59 phyla and 1696 genera.The dominant bacteria of planktonic bacteria were Proteobacteria,Actinobacteriota,Firmicutes,Bacteroidota and Chloroflexi.The dominant bacteria of sediment bacteria were Firmicutes,Chloroflexi,Actinobacteria,Myxococcota,Acidobacteria and Deinococcota.The dominant genera of planktonic bacteria were Rhodococcus,Glutamicibacter,Brevundimonas,Bacillus,Flavobacterium,etc.The dominant genera of sediment bacteria were Romboutsia,Clostridium＿sensu＿stricto＿13,Clostridium＿sensu＿stricto＿1,Sporacetigenium and Fonticella.(3)The planktonic bacteria were greatly affected by the season,and the sediment bacterial community structure was less affected by the season.The results of difference analysis showed that there were significant seasonal differences in the main dominant bacteria at the level of bacterioplankton,and only non-dominant bacteria such as Desulfobacterota and Planctomycetota were significantly different in sediment bacteria.The replenishment of reclaimed water would affect the community structure of planktonic bacteria near the replenishment point,resulting in an increase in the abundance of chlorine-resistant bacteria such as Methylobacteria in the planktonic bacterial community,but the change in the bacterial community structure of the sediment was not obvious.At the same time,with the flow of the river,the structure of planktonic microorganisms would gradually recover.Cluster analysis showed that reclaimed water had a greater impact on planktonic bacteria in the non-rainy season and a smaller impact on planktonic bacterial communities in the rainy season.(4)Correlation analysis showed that the bacterial community structure was mainly affected by water temperature,COD,and total phosphorus.The influence of river water quality on sediment bacterial community structure was less than that of planktonic bacteria.Chemical indicators such as COD,nitrite nitrogen and chloride had a great influence on sediment bacterial community,while physical factors such as p H,DO and water temperature had little influence on sediment bacterial community.The main driving factors of microbial community structure change were different from the environmental factors caused by reclaimed water replenishment,indicating that the water quality change caused by reclaimed water replenishment was not the main cause of microbial community structure change.(5)There were differences in the functions of sediments and planktonic bacteria in the ecosystem.The chemotrophic nutrition of planktonic bacteria was mainly aerobic chemoheterotrophy,while sediment bacteria were mainly anaerobic fermentation.The abundance of sulfate respiration,iron respiration,sulfite respiration,sulfur respiration and other functional annotations in sediment bacteria were significantly higher than those in planktonic bacteria,and anaerobic ammonia oxidation functional annotations that were not found in planktonic bacteria were found in sediments,indicating that sediment bacteria participated in the material and energy cycle in the aquatic ecosystem.There were differences between the way and planktonic bacteria.