Microorganisms play an important role in the urban river nitrogen cycle. Due to the three-dimensional fluidity of river water, it is necessary to clarify the vertical distribution of community composition and nitrogen metabolism functions of microorganisms and discover how hydrodynamic factors influence microorganism sources and community composition. Based on 16S rRNA high-throughput sequencing technology, the bacteria community composition and nitrogen metabolism function of water and sediment in the North Canal at Tongzhou District Beijing City were analyzed. The effect of environmental and hydrodynamic factors on community composition and sources were studied. The results showed that the α diversity of sediment was significantly higher than that of water. Proteobacteria was the most abundant phylum, which accounted for 54.72% and 32.36% in water and sediment, respectively. Functional prediction conducted using PICRUSt2 showed that the studied North Canal had an abundance of nitrogen metabolism ability, and 47 genes related to the nitrogen cycle were obtained. Water and sediment microorganisms had a similar distribution of nitrogen metabolism functions. The copy number of genes involved with denitrification, nitrogen assimilation, and dissimilation-reduction were high, whereas the abundance of genes related to biological nitrogen fixation and nitrification were relatively low. Source tracking analysis showed that bacteria in the water that originated from upstream, neighboring sides, and sediment were 60.05%, 37.93%, and 1.05%, respectively. The amounts of bacteria in sediment that migrated from upstream, neighboring sides, and water were 50.16%, 45.55%, and 1.55%, respectively. Environmental factors, hydrodynamic conditions, and their interactions explained water bacteria community composition for 44.22%, 3.21%, and 15.60%, respectively. For sediment bacteria, the degree of explanation was 13.05%, 1.56%, and 8.51%, respectively. This indicated that environmental factors and hydrodynamic factors controlled the community composition and nitrogen cycle functions together.
Keywords: bacteria; hydrodynamics; nitrogen metabolism; sediment; source tracking; water.