Study Of Water Quality Improvement And Microbial Community Structure Regulation Of A Stratified Reservoir By Mixing And Oxygenation

Regarding the internal variations and external pollution input of the reservoir,based on the field monitoring,in-situ test and laboratory research,a study was carried out on Heihe Jinpen Reservoir,a stratified source water reservoir.The main research contents were included: a)Evolution of reservoir stratification structure and water quality response characteristics,dissolved oxygen consumption rate and pollutants release in sediments during stratification;b)Evolution mechanism of different intensity runoffs and their influence on water quality,pollution characteristics and sedimentation law of suspended solids;c)The effective combination of artificial forced mixing and natural mixing,enhancement of microbial activity in water and sediment by mixing and oxygenation;d)Effects of mixing and oxygenation on microbial community structure and regulation of carbon,nitrogen,hydrogen,sulfur,iron and manganese cycle related bacteria.The main results and conclusions were as following:(1)The annual May~August were the stable stratification period of the water in Heihe Jinpen Reservoir,and the dissolved oxygen at the bottom of the water body was exhausted,which led to the reduction of the chemical oxidation efficiency.The existence of metalimnion hindered the vertical water exchange,and the anaerobic layer thickness was as high as 22 m.The concentrations of total nitrogen,total phosphorus,iron and manganese increased to 2.30,0.125,0.97 and 0.32 mg/L in the metalimnion,respectively.During the period of stratification water and sediment oxygen consumption rate reached 4.13 ?mol O2 L-1?d-1 and 14.34 mmol O2 m-2?d-1.In September,under the condition of natural process and human intervention,the stability of water stratification structure weakened rapidly,and the stratification structure gradually disappeared.(2)Moderate and low intensity inflow runoffs would not cause adverse effects on the water quality of the main reservoir,and it gradually disappeared in the process of moving towards the main reservoir area.The high flow runoff(inflow 579 m3/s)not only destroyed the water stratification structure but also caused the main reservoir water turbidity increased to 266 NTU.The total phosphorus,total organic carbon and ammonia nitrogen increased to 0.107,3.9 and 0.48 mg/L in the main reservoir area,and the algal density decreased by up to 51.3%.The correlation analysis showed that the particle size,water content,and loss of the particles were the main factors affecting the pollution load.The sedimentation rate of Heihe Jinpen Reservoir was about 0.111 g·cm-2·a-1,at a relatively low level.(3)The artificial forced mixing destroyed the stable stratification structure of the water,which made the water entering the mixing state 2 months ahead,and the mixing water temperature increased by 6~8 °C compared with natural mixing.The water quality had been improved obviously,and the reduction rate of total nitrogen,total phosphorus,total organic carbon,ammonia nitrogen,iron and manganese were 47.8%,66.7%,22.9%,62.5%,76.2%,respectively.When the water temperature difference was still 3~4 °C,the forced mixing process stopped,and it was found that the effective convergence of the artificial forced mixing and the natural mixing made the algae density,total organic carbon,total nitrogen and total phosphorus still have 50%,23.5%,7.7% and 16% reduction.The effective combination of artificial forced mixing and natural mixing and the synergistic action of the two could effectively improve the water quality and keep the good condition of water quality to the next year's stratification.(4)The influence of mixing and oxygenation on the microbial community structure was changed by destroying the stratification structure and dissolved oxygen state.Redundancy analysis showed that physical environmental factors(temperature,dissolved oxygen),chemical environmental factors(Chlorophyll a,total organic carbon,total nitrogen)were the key factors affecting the change of microbial community in reservoir water.The structure of carbon,nitrogen,hydrogen,sulfur,iron and manganese cycle related bacterium were changed by mixing and oxygenation.For example,Lactobacillus?Pseudomonas and Rhodobacter,the main denitrifying bacterium were significantly increased,and the removal of carbon,nitrogen and other elements were strengthened.