Study On The Regulating Effect Of Water-lifting Aeration System On Planktonic Bacteria Community In Stratified Reservoirs

The seasonal thermal stratification has serious impacts on deep-water source water reservoirs,and it would cause the deterioration of water quality and eutrophication.As a new type of in-situ water quality improvement technology,the water-lifting aeration system?WLAs?can break the thermal stratification by its mixing and oxygenation functions.It has been used in many domestic source water reservoirs for water quality restoration.In order to study the regulation effect and its mechanism of the WLAs on the planktonic bacteria in the typical stratified reservoir,two reservoirs?Lijiahe Reservoir and Jinpen Reservoir?with different nutritional conditions were selected as the objects.Based on the water quality analysis,the changes in the number,metabolic activity and species distribution of planktonic bacteria in the two reservoirs were examined before and after the operation of the WLAs,using Flow Cytomertry technology,Biolog Microplate technology and 16s rRNA High-Throughput Sequencing technology.The possible reasons for these changes were discussed,and the regulating mechanism of WLAs on planktonic bacteria were explained.The main conclusions are as follows:?1?The mixing and oxygenation functions of the WLAs can effectively break the thermal stratification structure of the source water reservoirs.The vertical temperature difference was decreased to below 1?,and the low-oxygen zone caused by thermocline migrates downward till disappeares.After the WLAs was operated,the peaks of COD_Mn in the two reservoirs were reduced by 45.40%and 20.63%,respectively.After the nitrogen pollution caused by external source,the continuous operation of WLAs reduced the averaged nitrogen concentration of two reservoirs by 26.28%and 25.00%,respectively.Changes of the water quality indicators could influence the species and activity of indigenous planktonic bacteria,and the reduction of the water pollutants may be related to the enhanced metabolic capacity of planktonic bacteria.?2?In terms of the number of planktonic bacteria,after the operation of the WLAs,the stratification difference in the vertical total bacterial counts was significantly reduced,and the culturable number of bacteria increased nearly 10 times higher than that before.Meanwhile,the WLAs can also effectively increase the high nucleic acid bacteria?HNA?ratio,which reflects the promotion of planktonic bacteria activities under the system operation to some extent.?3?In terms of the activity and metabolic capacity of planktonic bacteria,the WLAs can break the distribution pattern of“lower at top and bottom,higher at middle”formed during the thermal stratification period,and replaced by a balanced shape in the vertical distribution;During the operation period,the total metabolic activity of planktonic bacteria increased by 174.15%compared with that before operation,and the McIntosh diversity index increased by 92.10%in average.Moreover,this rising tendency was sustained after the end of the operation.Besides,the system increased the metabolic capacity of planktonic bacteria to sugars and alcohols by more than 200%,and the utilization of four carbon sources?a-D-lactose,L-phenylalanine,I-erythritol and 2-hydroxybenzoic acid?reached 8 times or more after operation.This result indicates that the WLAs can enhance the biodegradation function and efficiency on water pollutants,thereby effectively control the endogenous pollution.?4?The community structure of planktonic bacteria is multiply subject to water quality,rainfall runoff and the WLAs operation.The WLAs operation is able to improve and balance the richness,diversity and uniformity of planktonic bacteria species,and can also reduce the cyanobacteria in Lijiahe Reservoir by 94.08%,proving its significant algae control function.As for the impacts and fluctuations caused by rainfall runoff,the WLAs can rapidly restore the steady the aquatic ecosystem status by its vertically homogenization function on planktonic bacteria.?5?The WLAs also has regulating effects on the participation of planktonic bacteria in the earth biochemical cycle:the photosynthesis flora was significantly inhibited,while the flora involved in nitrogen,sulfur,hydrogen,iron and manganese cycle was enhanced.Additionally,the aerobic denitrification potential flora,which is able to remove nitrogen in aerobic conditions,was effectively enhanced as well.By changing the water environment,the WLAs strengthened the growth and reproduction of functional flora,activated the transformation of environmental substance and the energy cycle in the reservoirs,thereby promoted the biodegradation of endogenous and exogenous pollution,and ultimately achieved the purpose of improving the water quality of the reservoir.?6?Because of the response relationship between the planktonic bacteria and the water quality,the number,metabolic activity and species distribution of planktonic bacteria have several differences in two reservoirs with different nutritional status,while the water quality improvement and biological regulation mechanism of the WLAs are similar.