EGU22-5708
https://doi.org/10.5194/egusphere-egu22-5708
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Natural Flood Management features mitigate sediment and nutrient loading in a lowland agricultural catchment in England

John Robotham1,2, Gareth Old1, Ponnambalam Rameshwaran1, David Sear2, Emily Trill1, James Bishop1,3, David Gasca-Tucker4, Joanne Old5, and David McKnight5
John Robotham et al.
  • 1UK Centre for Ecology & Hydrology, Hydro-Climate Risks, Wallingford, United Kingdom of Great Britain – England, Scotland, Wales (johrob@ceh.ac.uk)
  • 2School of Geography and Environmental Sciences, University of Southampton, Southampton, United Kingdom
  • 3School of Archaeology, Geography and Environmental Science, University of Reading, Reading, United Kingdom
  • 4Atkins, Oxford, United Kingdom
  • 5Environment Agency, Wallingford, United Kingdom

Natural Flood Management (NFM) is a nature-based solution for reducing flood risk whilst delivering multiple benefits such as water quality improvements through the mitigation of diffuse pollution (e.g. from soil erosion). This study aimed to assess the ability of NFM storage features to trap potential pollutants in run-off from two small (3.4 km2) agricultural catchments. The masses of sediment, total phosphorus and organic carbon trapped by 14 NFM features (since construction 2 to 3 years previously) were quantified through sediment surveying and sampling. Streamflow and suspended sediment monitoring downstream of the features enabled catchment fluxes to be calculated. The features trapped a total of 83 tonnes sediment, 122 kg phosphorus, and 4.3 tonnes organic carbon over 2 to 3 years of functioning. Although the footprint of the features was <1% of the catchment area, they drained 44% of the total land area and were able to capture the equivalent of 25% of the total suspended sediment flux (22% of the fine (silt and clay) sediment flux), 14% of the total phosphorus flux, and 13% of the particulate organic carbon flux during the monitored period. Results show how accumulation rates were influenced by hydrological connectivity, with greater accumulation in features constructed directly on streams (online features), and offline features which filled from streamflow diverted by instream woody dams. Compared with the topsoil in each contributing area, trapped sediment was enriched in phosphorus and carbon in the majority of features, having on average 50% higher phosphorus and 17% higher organic carbon concentrations than surrounding arable soils, highlighting its potential value for redistribution on farmland. The results of this monitoring demonstrate the potential of NFM interventions to provide additional value by mitigating diffuse pollution in lowland catchments.

How to cite: Robotham, J., Old, G., Rameshwaran, P., Sear, D., Trill, E., Bishop, J., Gasca-Tucker, D., Old, J., and McKnight, D.: Natural Flood Management features mitigate sediment and nutrient loading in a lowland agricultural catchment in England, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5708, https://doi.org/10.5194/egusphere-egu22-5708, 2022.

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