537 / 2024-07-04 15:33:37

Urban channel confluence shifts microbial community assembly and stimulates nitrogen removal

urban channel confluences,bacterial community,ecological assembly processes,transport and transformation of nitrogen,hydrodynamic

Subtheme 3: Eco-hydraulics and Environment > Topic 2: Water Eco-environment Monitoring and Simulation

Urban channel confluences are the interconnections of different river systems. Understanding microbial community assembly and the characteristics of biogeochemical processes at this area is essential for the evaluation and improvement of water environmental capacity. However, a substantial knowledge gap persists as few studies have investigated confluence microbial composition and the features of biogeochemical reactions rates. To address this gap, the present study proposed a novel mathematical modelling system, based on microbial community assembly theory and fluid kinetics, to decouple nitrogen dynamics into flow-induced transport and microorganism-induced transformation processes, and quantified their contributions to nitrogen concentrations. Results revealed that complex hydrodynamic conditions contributed to significant variance in confluence microbial communities. Analysis of ecological assembly processes supported this conclusion. It indicated that difference in microbial communities was dominated by variable selection (including hydrodynamic conditions), which fell under deterministic processes and accounted for 22.99% of ecological assembly processes. Microbial diversity in areas dominant by straight flow (average Shannon index, 7.48) was greater than that in areas governed by recirculating flow (average Shannon index, 7.25; p<0.01). Variation in microbial communities further shifted transformation processes. Rhodobacterales and Sphingomonadales, which were reported to be vital participants in denitrification process, were enriched in flow separation region (characterized by recirculating flow), and promoted it as a hotspot of nitrogen removal. In flow separation region, microbial-induced biogeochemical reactions accounted for 56% of total nitrogen removal, which was significantly higher than that in other regions (12% on average; p<0.01). Results and findings could provide useful information for the improvement of water environmental capacity.