How do stabilized river meanders affect microbial communities and water quality in urban rivers?

Urban river meanders are frequently stabilized and hardened for flood control, thereby substantially altering their natural hydrodynamics and ecological functions. However, the influence of such engineered bends on sediment microbial communities, key players in nutrient cycling and thus water quality, remains poorly understood. Here, we integrate 16S rRNA amplicon sequencing, co-occurrence network analysis, and community assembly modeling to investigate seven stabilized meanders along Guangzhou's Yangmei River during a single summer sampling campaign. We found that bend-position-related habitat differences were associated with the spatial organization of microbial diversity and putative co-occurrence patterns. Mid-bend sections showed ecological patterns consistent with stronger local hydraulic disturbance, while post-bend sections were more consistent with relatively depositional habitat conditions. Mid-bend sediments, associated with relatively high hydraulic energy, exhibited the lowest α-diversity and distinct co-occurrence patterns, consistent with greater local hydraulic disturbance than at pre- and post-bend sites. Within the sampling campaign, spatial differences in water chemistry were more closely associated with external nitrogen and phosphorus inputs, whereas the spatial heterogeneity of benthic microbiota was more strongly linked to localized hydrodynamic conditions. Co-occurrence patterns also varied among bend positions along the meander transition. Neutral-community modeling suggested that stochastic processes played an important role in bacterial community assembly during the sampling period. Complementary βNTI-RCbray null-model analyses identified dispersal limitation as the predominant inferred process, whereas heterogeneous selection contributed relatively more in post-bend depositional sediments. Our findings highlight local heterogeneity in benthic habitats and water-sediment exchange conditions within stabilized meanders, which may influence local nutrient dynamics. These results suggest that bend-scale hydraulic conditions and microbial habitats warrant consideration in urban river restoration.