天津北大港水库水质存在咸化问题，水质咸化可能会导致微生物群落组成和多样性发生显著变化。为探究 水质咸化条件下水库微生物群落组成的空间分布特征，于 2021 年 12 月在北大港水库采集表层、中层和底层的水 样，利用高通量测序技术，对北大港水库不同深度及上下游的微生物群落组成及多样性进行分析，并探究溶解性 总固体与微生物群落的关系。结果表明：北大港水库的溶解性总固体（total?dissolved?solids,TDS）质量浓度在表层、 中层和底层存在差异，下游高于上游。微生物的主要优势菌门为变形菌门、拟杆菌门和放线菌门，变形菌门的相 对丰度均超过 50%。优势菌属是 Clade_III 未定属（相对丰度 1.10％～72.72％）和黄杆菌属（Flavobacterium相对丰 度 0.32％～20.09％），Clade_III 未定属的相对丰度上游高于下游，黄杆菌属的相对丰度表层高于中层和底层。上 游水体表层的微生物群落组成与中层、底层的微生物群落组成存在显著差异，下游在不同深度微生物群落组成差 异不显著，中层和底层的微生物群落组成存在相似性。Chao1 和 Shannon 指数表现出表层<中层<底层，下游略高 于上游，微生物 Alpha 多样性指数随 TDS 质量浓度的增大而减小。在科水平上，Clade_Ⅲ能够耐受较高的盐度，但 当 TDS 质量浓度>3?000?mg/L 时其丰度降低。

Beidagang Reservoir has the function of water supply in the utilization of water resources. The reservoir can provide local residents with drinking water and irrigation water. There is a problem of salting in the water quality in the Beidagang Reservoir. The salting law and mechanism of Beidagang Reservoir were mainly studied, and the microbial community structure was less studied. Salinization of water quality may lead to significant changes in microbial community composition and diversity. The reservoir mainly focuses on the exploration of the diversity of microbial communities. There is a lack of comparative studies of reservoirs between different microorganisms at different water depths. The microbial communities of coastal reservoirs have been poorly studied. Microorganisms are sensitive indicators of salinity. The spatial distribution characteristics of microbial community composition under salinization of water quality in reservoirs are still unclear. It is of great significance to study the community distribution of microorganisms in salty reservoirs. It can not only understand the structural composition of microbial communities and the relationship between salinity, but also provide a theoretical basis for bioremediation of high salt water treatment. It provides basic data and scientific basis for Beidagang Reservoir to play the function of water supply and water resource utilization.In order to explore the salinization and the spatial distribution characteristics of microbial communities, Beidagang Reservoir was chosen as our research area. The water samples from the surface, middle and bottom layers of Beidagang Reservoir were collected in December 2021. The composition and diversity of microbial communities at different depths and upstream and downstream of Beidagang Reservoir were analyzed by high-throughput sequencing technology to understand the spatial distribution characteristics of the microbial community composition structure of Beidagang Reservoir. The relationship between dissolved total solids and microbial communities was explored. The influence of reservoir salty water on microbial community structure was explored. The results show that there are differences in the surface, middle and bottom layers of dissolved total solids (TDS) mass concentration in Beidagang Reservoir, and the downstream is higher than that in the upstream. The main dominant phylums of microorganisms are Proteobacteria,Bacteroidetes and Actinobacteria, and the abundance of Proteobacteria is more than 50%. The dominant genera are Clade_III undetermined genus (1.10%-72.72%) and Flavobacterium(0.32%-20.09%), the abundance of upstream Clade_III undetermined genera is higher than that of the downstream, and the abundance of surface Flavobacterium is higher than that of the middle and bottom layers. There were significant differences between the microbial community composition of the upper surface layer and the middle and bottom microbial community composition, while the downstream microbial community composition at different depths was not significant, and the composition of the middle and bottom microbial communities was similar. The Chao1 and Shannon indices showed that the surface < middle layer < the bottom layer, and the downstream was slightly higher than the upstream, and the microbial Alpha diversity index decreased with the increase of TDS mass concentration. At the class level, the abundance of Alphaproteobacteria and Verrucomicrobiae was positively correlated with TDS mass concentration. At the family level, Clade_III abundance was positively correlated with TDS mass concentration. Comamonadaceae abundance was negatively correlated with TDS mass concentration. The abundance of Clade_III and Comamonadaceae decreased at high mass concentrations of TDS (>3 000 mg/L), which may inhibit their growth.