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Overland flow during a storm event strongly affects stream water chemistry and bacterial community structure

Abstract

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.

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Data availability

The data are published on the DataSuds site of the IRD as Le et al. (2021) at http://doi.org/10.23708/K95OKX.

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Acknowledgements

The authors are grateful to the Lao PDR Department of Agricultural Land Management (DALaM). We also thank the M-TROPICS Critical Zone Observatory (https://mtropics.obs-mip.fr/), which belongs to the French Research Infrastructure OZCAR (http://www.ozcar-ri.org/), for the logistic support. Julie Legoupi is thanked for her help with the figures. This work forms part of the Ph.D. thesis requirements of HL who was financed by a Ph.D. grant from the USTH, Vietnam and the IRD (ARTS).

Funding

This study was funded by the Institute of Research for sustainable Development (IRD, main funding), the French National Research Agency (TecItEasy project, ANR-13-AGRO-0007).

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Correspondence to Emma Rochelle-Newall.

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Le, H.T., Pommier, T., Ribolzi, O. et al. Overland flow during a storm event strongly affects stream water chemistry and bacterial community structure. Aquat Sci 84, 7 (2022). https://doi.org/10.1007/s00027-021-00839-y

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Keywords

  • DOC
  • CDOM
  • Lao PDR (Laos)
  • Southeast Asia
  • Land degradation
  • Sustainability