Influence of Pleistocene glacial deposits on the transport of agricultural nitrate in the river Wensum catchment, UK

Hiscock, Kevin M. ORCID:, Cooper, Richard J. ORCID:, Lewis, Melinda A., Gooddy, Daren C., Howson, Thomas J. and Wexler, Sarah K. (2024) Influence of Pleistocene glacial deposits on the transport of agricultural nitrate in the river Wensum catchment, UK. Journal of Hydrology, 633. ISSN 0022-1694

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Mitigating NO3− pollution requires an understanding of the hydrological processes controlling contaminant mobilisation and transport, particularly in agricultural catchments underlain by Pleistocene glacial deposits. Focusing on the Wensum catchment in East Anglia, UK, precipitation (n = 20), stream water (n = 50), field drainage (n = 22) and groundwater (n = 84) samples collected between February–March 2011 and April–September 2012 were variously analysed for water stable isotopes (δ2HH2O and δ18OH2O), the dual-isotopes of NO3− (δ15NNO3 and δ18ONO3), groundwater residence time indicators (CFCs and SF6) and hydrochemical parameters. The residence time indicators suggested a component of modern (post-1960) groundwater throughout the sequence of glacial deposits that corresponds with the penetration of agricultural NO3−. Denitrification and lower NO3− concentrations (<8 mg L−1) are observed in the glacial tills, compared with higher NO3− concentrations (<90 mg L−1) observed under more oxidising conditions in the glacial sands and gravels. Storm hydrograph separation for two storms in April and September 2012 using two- and three-component mixing models showed a faster response with field drainage (36–38 %) and baseflow (5–37 %) contributing to the total stream discharge in areas of clay loam soils over glacial tills. In these areas, the dual stable isotopes of NO3− (δ15NNO3 = +11.8 ‰ and δ18ONO3 = +7.1 ‰) indicated a denitrified source of nitrogen from field drainage and groundwater. In comparison, a dampened response and a higher percentage of baseflow (29–80 %) was observed in areas of sandy clay loam soils over glacial sands and gravels. In these areas, mean NO3− isotopic signatures (δ15NNO3 = +7.8 ‰ and δ18ONO3 = +5.0 ‰) indicated a source of nitrified NH4+. In conclusion, understanding hydrological processes in catchments underlain by variable glacial deposits can inform nutrient management plans and cultivation practices to reduce the risk of agricultural NO3− contamination.

Item Type: Article
Additional Information: Funding Information: This research was supported by the River Wensum Demonstration Test Catchment project funded by the Department for Environment, Food and Rural Affairs (Defra) (awards WQ0212 and LM0304). Additional funding for the pore water sampling and analysis was provided by BGS through its Groundwater Science Programme. Author acknowledgements: We are grateful to Salle Farms Co. for hosting monitoring equipment and granting access. Anglian Water kindly provided sampling access to Salle Pumping Station. We thank Simon Ellis, Jenny Stevenson and John Brindle for fieldwork support and Alina Marca, Liz Rix, Alina Mihailova, Kim Goodey, Tony Hinchliffe, Graham Chilvers and Andy Hind for laboratory support. The following BGS staff are thanked for their contributions to the project: Michael Bird, Ian Woods, James Sorensen, Peter Williams, Dave Entwisle and David Morgan for assistance with borehole drilling supervision, geological logging and core material processing. Steve Booth and Jonathan Lee assisted with the geological interpretation. Daren Gooddy and Melinda Lewis publish with the permission of the Executive Director, British Geological Survey (UKRI).
Uncontrolled Keywords: agriculture,groundwater nitrate,groundwater residence time indicators,pleistocene glacial deposits,stable isotopes,storm hydrograph separation,water science and technology ,/dk/atira/pure/subjectarea/asjc/2300/2312
Faculty \ School: University of East Anglia Research Groups/Centres > Theme - ClimateUEA
Faculty of Science > School of Environmental Sciences
UEA Research Groups: Faculty of Science > Research Groups > Geosciences
Faculty of Social Sciences > Research Centres > Water Security Research Centre
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Depositing User: LivePure Connector
Date Deposited: 11 Mar 2024 16:31
Last Modified: 18 Mar 2024 09:30
DOI: 10.1016/j.jhydrol.2024.130982


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