As flood events are expected to become more frequent due to climate change, investigating how overland flow exports terrestrial nutrients, carbon and living organisms into aquatic systems is essential for understanding both soil and stream ecosystem status. Here we assessed how dissolved organic carbon (DOC), total suspended sediments (TSS), and stream bacterial diversity responded to stream discharge and overland flow during stormflow in a tropical catchment. A higher humification index and a decreasing ratio of allochthonous to autochthonous DOC indicated that DOC from soils was exported to stream during the flood. The δ¹³C and δ¹⁵N of particulate matter was indicative of a source in the cultivated areas of the upper catchment and of subsurface soils (stream banks and gullies) in the downstream section. Bacterial richness of particle-attached (PA) and the free-living (FL) fractions increased with the flood progression in the upstream section. Moreover, the community structure of the PA fraction in the stream was more similar to that of overland flow than was the FL fraction. This suggests that the soil PA bacterial community was washed-out with overland flow during the flood recession. The relative contribution of sources and the composition of TSS, rather than hydrological regime, significantly drove the composition of bacterial community. In conclusion, our results emphasize that overland flow during a flood event strongly influences the structure of stream bacterial communities further underlining the biological connectivity between terrestrial runoff and stream flow.

由于气候变化，洪水事件预计将变得更加频繁，因此调查地表水流如何将陆地养分、碳和活生物体输出到水生系统中对于了解土壤和河流生态系统状态至关重要。在这里，我们评估了热带集水区风暴流期间溶解有机碳 (DOC)、总悬浮沉积物 (TSS) 和河流细菌多样性如何响应河流排放和地表流量。较高的腐殖化指数和外来与本地 DOC 的比率下降表明，在洪水期间，土壤中的 DOC 被输出到河流中。δ ¹³ C 和δ ¹⁵颗粒物的 N 表示上游集水区的耕作区和下游部分的地下土壤（河岸和沟壑）的来源。随着上游部分的洪水进展，颗粒附着 (PA) 和自由生活 (FL) 部分的细菌丰富度增加。此外，河流中 PA 部分的群落结构比 FL 部分更类似于地表流的群落结构。这表明土壤 PA 细菌群落在洪水衰退期间被地表水冲刷。来源的相对贡献和 TSS 的组成，而不是水文状况，显着推动了细菌群落的组成。综上所述，