| Stratified reservoir is different from general natural shallow water reservoir,most of which are deep water reservoirs constructed artificially and have unique hydraulic characteristics.Comprehensive diagnosis of the internal coupling mechanism of "hydraulic characteristics-water pollution characteristics-microbial population composition and metabolic activity" in the reservoir ecosystem is of great scientific significance and social value for further revealing the structure and water quality control function of the micro-ecosystem of the source reservoir.In this study,JINPEN reservoir,LIJIAHE reservoir and HONGZHUANG reservoir were taken as research objects to study the regulation of thermal stratification on the vertical water quality evolution of reservoirs,diagnose the vertical migration and maintenance mechanism of microbial population in reservoirs driven by thermal stratification,and explore the coupling mechanism between microbial community structure and water environmental factors in reservoirs,so as to provide scientific basis for improving the water quality and health of water sources.The main conclusions of this study include:(1)A stable vertical stratification structure of epilimnion,metalimnion and hypolimnion was formed during thermal stratification of LIJIAHE reservoir.DNA sequencing results showed that a total of 40 phylums and 593 genera of bacteria were identified during thermal stratification in the LIJIAHE reservoir.Proteobacteria,Actinobacteria,Bacteroidetes and Cyanobacteria are the dominant flora.Principal component analysis showed that temperature,dissolved oxygen,oxidation-reduction potential and pH regulated the vertical migration of bacteria in water.(2)In the stable stage of thermal stratification,a stable vertical stratification structure was formed in LIJIAHE reservoir.A total of 6 phylums and 701 genera of fungi were identified,and ascomycetes were the most dominant species in all stratified areas.In addition,basidiomycetes were the second dominant species in the reservoir.The species of fungi in different zones are abundant,and their dominant populations and diversity are significantly different.Redundancy analysis showed that Chytridiomycota is positively correlated with conductivity,but negatively correlated with Chl-a;Basidiomycota and Ascomycota are positively correlated with total nitrogen;Zoopagomycota and Blastocladiomycota are positively correlated with temperature.(3)It was found that the vertical water body of JINPEN reservoir formed a stable stratified structure of epilimnion,metalimnion and hypolimnion during thermal stratification.DNA sequencing results showed that during thermal stratification,the denitrifying bacteria species were relatively single in class level,and the dominant bacteria in each layer were consistent.Betaproteobacteria is the dominant species in each stratified region,while Actinobacteria,Alphaproteobacteria and Gammaproteobacteria account for a small proportion.The dominant genera of denitrifying bacteria in different water depths are similar,but the diversity of bacteria is different.Redundancy analysis showed that Paracoccus was positively correlated with Nitrate nitrogen,total nitrogen and total phosphorus,Pseudomonas and Copperacillus were positively correlated with total nitrogen during reservoir thermal stratification.Denitrifying bacteria community structure in Jinpen reservoir thermal stratification water was significantly affected by different water quality indicators.(4)Sequencing results of water quality and eukaryotic microbial population structure in JINPEN reservoir during thermal stratification and stabilization period showed that the similarity of eukaryotic microorganisms in epilimnion/metalimnion/hypolimnion was high.The proportion of protozoa was the largest in the whole reservoir area,accounting for 16.97-25.79%,followed by eukaryotic algae,accounting for 5.81-8.54%,metazoa,1.33-2.94% and fungi,accounting for 0.97-1.09%.Eukaryotic microorganisms mainly consist of 11 phylums.The dominant species are Cnidaria,Arthropoda,Rotifera,Chytridiomycota,Bacillariophyta and Chlorophyta.RDA showed that temperature/total phosphorus/total iron had significant effects on the structure of eukaryotic microbial community in the epilimnion/metalimnion/hypolimnion,respectively.(5)The concentration of total phosphorus and ammonia nitrogen in HONGZHUANG reservoir water is at a low level during the natural mixing period;the concentration of nitrate nitrogen is maintained at about 1.8-2.5 mg/L,which is consistent with the trend of total nitrogen change;dissolved oxygen begins to stratify in the middle of may,and gradually forms stratification at the end of june.At the stage of stratification,15 genera and 3 phyla of microalgae were identified,including 10 genera of Chlorophyta(62.56%),3 genera of Bacillariophyta(24.45%)and 2 genera of Cyanobacteria(12.99%).During the stratification period,the vertical niche of phytoplankton in HONGZHUANG reservoir did not change significantly. |
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