Influence of Tributary Inflows on Sediment Bacterial Community Composition of the River Mainstem.

River sediment microbial communities are an integral part of fluvial ecosystems, where they play a central role in nutrient cycling. Although these communities share a core group of microorganisms, their overall composition can be influenced by natural environmental conditions and anthropogenic factors. While anthropogenic influences on river microbial communities have been extensively studied, natural drivers have received comparatively less attention. In this study, we evaluated the impact of tributary inflow on the microbial assemblages of a main river stem. Sediment samples were collected from both the main channel and some of its tributaries, and bacterial community composition was characterized using 16S rRNA gene amplicon sequencing. Taxonomic profiling revealed a largely shared core community typical of riverine sediments across all sites. While alpha diversity did not differ significantly between main river and tributary samples, beta diversity analyses demonstrated clear segregation between the two environments, indicating distinct community structures. Correlation analyses further showed that microbial assemblages in the main river downstream of tributary confluences were significantly associated with tributary community composition, highlighting the influence of tributary inflow on bacterial communities in the main river.