Diagnosis Of The Succession Interaction And Decline Mechanism Of Algae From Water Source Reservoir

Since the fresh water resources that can be directly used in nature are extremely limited,humans manage and deploy them through reservoirs.However,with the continuous operation of reservoirs,the input of external pollutants and the accumulation of endogenous pollutants,a large number of reservoirs are being challenged by eutrophication.In the aquatic ecosystem of reservoirs,algae,as a vital part of the ecosystem,are extremely sensitive to variations in water quality.The large amount of dissolved organic matter released during the decline phase of algae will affect the metabolism of bacteria and the utilization of carbon sources.In order to explore the succession mechanism of algae populations in water source reservoirs,this article takes water source reservoirs as the experimental research object,combined with high-throughput DNA sequencing technology and symbiotic network analysis methods,and continuously monitors reservoir water quality indicators,changes in algae population structure,and inter-genus algae The interaction relationship and the response relationship between algae and water quality changes are analyzed.In addition,combined with the bacterial metabolism atlas,reveals the changing law of bacterial metabolic activity in the process of algae decline,aiming to provide a scientific basis for the improvement of water quality in water source reservoirs and the prevention and control of algal blooms.The main findings include:（1）Chlorophyta was the dominant algae of Jinpen Reservoir.The relative abundance of Bacillariophyta increases in late summer and autumn,and the relative abundance of Cyanophyta was higher in June.Chlorella sp.,Cyclotella sp.,Melosira sp.,Tetraselmis sp.,and Thalassiosira sp.were the dominant algae genus during the Jinpen Reservoir research period,while Protoperidinium sp.,Cryptomonas sp.,Mallomonas sp.and Dinobryon sp.only appeared at a specific time.All water quality nodes and algae nodes were mostly negatively correlated.Fe,ammonia nitrogen,electrical conductivity,turbidity,temperature,and DOC have strong responses with algae.There were strong specific interactions between certain algae.（2）Similar to Jinpan Reservoir,Chlorophyta was the dominant genus of algae in Lijiahe Reservoir.Cyanophyta was relatively abundant in June,while Chlorophyta,Chrysophyta and Cryptophyta were at a low level during the whole study period.Chlorella sp.,Cyclotella sp.and Melosira sp.were the dominant algae genus during the research period of Lijiahe Reservoir,while Protoperidinium sp.,Cryptomonas sp.and Kephyrion sp.were only appeared at a specific time.The monthly variation of relative abundance of Chlamydomonas sp.was opposite to that of Tetraselmis sp.,but the same as that of Melosira sp.Network analysis showed that the changes of electrical conductivity,p H,Fe,water temperature and total nitrogen were mainly negatively correlated with eukaryotic algae,in which the electrical conductivity and the interaction between p H and algae were more significant.There were many correlations between Desmodesmus sp.and other algae genera,and most of them were positive correlation.（3）During the water lift and aeration operation,the water quality tended to be the same vertically,and the chlorophyll a and algae density showed that in the middle and late stages of the operation,the vertical direction tended to be the same.In the 0-20m depth range of the surface layer,Bacillariophyta and Chlorophyta were the dominant algae.As the depth increases,the proportion of Bacillariophyta gradually decreased,while the Chlorophyta was the opposite.Dinophyta and Phaeophyta were only active in the first and mid-stage of water-lifting aeration operation,indicating that water-lifting aeration can effectively control these two types of algae.The relative abundance of Aphanocapsa sp.,Mallomonas sp.,and Ochromonas sp.was relatively high only in the early stage of operation.The network analysis results show that as the water depth increases,the response relationship between water quality parameters and algae gradually weakens,and the interaction relationship between algae genera also shows the same trend.（4）During the decline of Chlorella,p H,Chl-a,TN,NH₄⁺-N and TP gradually decreased,while NO₃^--N gradually increased.Among them,NH₄⁺-N and TP had the most significant decrease on the 5th day,decreasing by 84.95%（P<0.001）and 30.84%（P<0.001）,respectively.The total number of bacteria maintained a downward trend after rising on the 5th day.The fluorescent soluble organic matter is fulvic acid-like,which decreases continuously from 0 to10 days and then basically does not change.The metabolic activity of bacterial communities gradually weakened,and the types of carbon source utilization changed significantly.On the15th day,the metabolic activity of the bacterial community was mutated,and lipids were the main carbon source,and only high consumption of methyl pyruvate was shown.On the 10th day,it showed additional utilization of glucose-1-phosphate andβ-methyl D-glucoside.