Characteristics of Bacterial Community in the Surface Sediment of Three Gorges Reservoir

Abstract: Bacteria are ubiquitous in aqueous environment and crucial for the biogeochemical processes. The characteristics and distribution of bacterial community will be an important reflection of human activities. In this study, surface sediment samples were collected from the Three Gorges Reservoir (TGR) in June, 2015 to characterize the bacterial communities using 16S rRNA gene sequencing, including sediment samples from the dam area, mainstream, urban area, and tributaries. The responses of bacterial communities to environmental variables are then statistically analyzed using the Redundancy analysis (RDA) and heatmap. Results show that Proteobacteria, Acidobacteria, Chloroflexi, Bacteroidetes, Firmicutes, Nitrospirae are the dominant phyla of the bacterial communities, accounting for over 80% of the total abundance. There is a greater abundance of Proteobacteria and Nitrospirae in the mainstream sites, while more Acidobacteria, Chloroflexi, and Bacteroidetes in the urban area sites, and more Firmicutes in the tributary sites. The bacterial communities are affected by environmental variables such as the sediment size D₅₀, water depth, dissolved oxygen DO, and potential ecological risk index R_I. For example, Firmicutes is negatively correlated with the DO concentration, i.e. preferring an anaerobic condition. Cyanobacteria is positively correlated with the water depth, probably due to the eutrophication of the reservoir. Aminicenantes, Armatimonadetes, Actinobacteria, and Caldiserica are all positively correlated with the R_I index, implying a potential effect of heavy metal distribution on the bacterial communities. The reservoir operation results in sediment sorting and increasing water depth along the mainstream, as well as heavy metal accumulation in the surface sediment, thus exerting effects on the characteristics of bacterial community and accordingly affecting the biogeochemical processes. Overall, there is no significant difference of the community richness and diversity among these sediment samples. This study will provide a better understand of the effects of impoundment on bacterial community and the resultant ecological implications.

Keywords: bacterial community; sediment; environmental variables; Three Gorges Reservoir