[Water Quality Characteristics and Distribution of Bacterial Communities During Thermal Stratification in the Miyun Reservoir]

As an important urban drinking water source, reservoirs are a special type of water body formed by artificial dams. Water quality of reservoirs directly affects the residents' drinking water safety. In order to reveal the characteristics of stratification and vertical changes of bacterial communities in the Miyun Reservoir, a drinking water source of Beijing, vertical stratified samples were collected during the stable stratified period of the reservoir (autumn). The vertical distribution characteristics of bacterial communities in the Miyun Reservoir were studied by using 16S rDNA terminal restriction fragment length polymorphism (T-RFLP) and quantitative PCR. Cluster analysis and multivariate statistical analysis were used to reveal the response relationships between bacterial communities and environmental factors. The results were as follows. ①The thermocline of the Miyun Reservoir was located at a water depth of 20-30 m, and the water temperature range was 15-19℃. The cluster analysis data of the seven sampled water layers were divided into an aerobic area (upper layer) and anoxic area (lower layer). The temperature, dissolved oxygen, and pH gradually decreased below 15 m. The electrical conductivity, ammonia nitrogen, nitrate nitrogen, nitrite nitrogen, and total nitrogen changed significantly after 15 m. The water quality showed obvious features in the vertical direction. ② The redundancy analysis (RDA) results showed that there were obvious vertical changes in the dissolved oxygen, pH, electrical conductivity, ammonia nitrogen, nitrate nitrogen, and nitrite nitrogen between the aerobic and anoxic water layer. Those factors were the main environmental factors affecting the vertical distribution of the bacterial communities in the Miyun Reservoir. ③ The total bacterial number fluctuated with changes in the water depth. The Shannon-Wiener index and the number of T-RFs of bacteria in the aerobic zone were significantly higher than those in the anoxic zone, which indicates that there was significant stratification in the distribution of bacterial communities in the water of the Miyun Reservoir in autumn. This study explored the effects of water stratification on reservoir water quality and bacterial communities, and the findings provide a scientific basis for predicting water quality changes and reservoir management.