The Effect Of Bacterial Community Activity And Water Quality By Water-lifting Aerators In The Reservoir

The stratification of reservoir water is an important cause of anaerobic bottom water and endogenous pollution.Artificial destratification can induce the water of deep reservoir to enter the mixing stage in advance.When the air temperature is lower than the mixed water temperature in autumn and winter,the water can still be mixed spontaneously after the system is stopped.In this way,the aerobic cycle of bottom water and sediment is greatly prolonged.In this study,the in-situ monitoring of the Jinpen reservoir was carried out from 2020 to 2021.The high-throughput DNA sequencing technology,Biolog technology,three-dimensional fluorescence spectroscopy-parallel factor（EEMs-PARAFAC）and ultraviolet-visible absorption spectroscopy（UV-Vis spectral）was used to analyze the damage of WLAs on the thermal stratification structure.The reduction of organic pollution and the influence of community composition and metabolic activity caused by the operation of WLAs will provide a theoretical basis for the improvement of the water environment quality of reservoir.The main research contents include:1)The effect of the operation of WLAs on the prolongation of the mixing time of the water and the improvement of the water quality;2)The operation of WLAs on the reduction of the organic matter in the water;3)Effects of mixed oxygenation and warming on bacterial community structure and metabolic activity.The main conclusions of this paper are as follows:（1）The operation of WLAs can weaken the thermal stratification of the water,extending mixing period from the usual 3 months to more than 5 months,and maintaining the vertical dissolved oxygen level during the continuous natural mixing period at 7-9 mg/L.Temperature and WLAs are the main factors affecting the stratification and mixing of reservoirs.The prerequisite for artificially inducing continuous natural mixing of the water is that the WLAs operates until the daily average temperature of the basin is lower than the mixed water temperature.Under these conditions,after the WLAs ceased operation,the water continued to mix until stratification occurred again.（2）The input of rainstorm runoff during the flood season is the main source of organic matter pollution in Jinpen Reservoir.The input of runoff significantly increases the organic matter content of Jinpen Reservoir in a short period of time,causing serious damage to water quality.WLAs can effectively controls the organic matter pollution of the reservoir and improves water environment.In the continuous natural mixing period under artificially induced mixing,higher dissolved oxygen and initial temperature are beneficial to increase the metabolic activity of bacteria,and have a continuous degradation effect on organic matter in the water.COD_Mnand DOC reduction rate reached 26.13%and 50.03%,respectively.（3）Three-dimensional fluorescence spectrum analysis results show that Jinpen Reservoir contains terrestrial humus（C1,C2,and C3）and tryptophan-like（C4）four DOM components.During the forced mixing period,the total fluorescence intensity of DOM decreased from 1.09R.U.and 0.85R.U.to 0.90R.U.and 0.61R.U.,respectively.The characteristic parameters of UV-vis absorption spectrum also show that DOM is degraded continuously during the system operation.The surface reduction rate is the highest and the small molecule DOM was preferentially degraded.（4）The dominant groups of water in the artificially induced continuous natural mixing process are Actinobacteria and Proteobacteria,the sum of their relative abundances is between 60.8%and 83.5%.At the genus level,the highest relative abundances are CL500-29＿marine＿group and hgcl＿clade.The operation of WLAs can change the dominant bacteria in Proteobacteria from anaerobic bacteria to aerobic bacteria,mainly Methylobacter and Methylocystis.From redundant analysis,during the stratification period,turbidity,conductivity,T and pH all have a greater impact on the bacterial community,and hydrometeorological conditions such as flow are also factors affecting the composition of the bacterial community;during the mixing period,DO,T and pH are closely related to bacterial community succession.（5）The operation of WLAs makes the bacterial community have a high abundance index and diversity index at the early stage of the mixing period.After connecting with the natural mixing period,with the decrease of water temperature,the ACE index decreased from 1110 to 928,the Chao 1 index decreased from 1121 to 720,the Shannon index decreased from 4.7 to 4.01,and the AWCD value decreased from 1.43 to 0.94.However,in the whole process,water bacteria have the same preference for carbon sources,and they use amino acids,esters and acids to a higher degree.