Hydrological controls on DOC : nitrate resource stoichiometry in a lowland, agricultural catchment, southern UK

A - Papers appearing in refereed journals

Heppell, C. M., Binley, A., Trimmer, M., Darch, T., Jones, A., Malone, E., Collins, A. L., Johnes, P. J., Freer, J. E. and Lloyd, C. E. M. 2017. Hydrological controls on DOC : nitrate resource stoichiometry in a lowland, agricultural catchment, southern UK. Hydrology And Earth System Sciences. 21 (9), pp. 4785-4802.

AuthorsHeppell, C. M., Binley, A., Trimmer, M., Darch, T., Jones, A., Malone, E., Collins, A. L., Johnes, P. J., Freer, J. E. and Lloyd, C. E. M.
Abstract

The role that hydrology plays in governing the interactions
between dissolved organic carbon (DOC) and nitrogen
in rivers draining lowland, agricultural landscapes is
currently poorly understood. In light of the potential changes to the production and delivery of DOC and nitrate to rivers arising from climate change and land use management, there is a pressing need to improve our understanding of hydrological controls on DOC and nitrate dynamics in such catchments. We measured DOC and nitrate concentrations in river water of six reaches of the lowland river Hampshire Avon (Wiltshire, southern UK) in order to quantify the relationship between BFI (BFI) and DOC: nitrate molar ratios across contrasting geologies (Chalk, Greensand, and clay). We found a significant positive relationship between nitrate and BFI (p < 0:0001), and a significant negative relationship between DOC and BFI (p < 0:0001), resulting in a non-linear negative correlation between DOC: nitrate molar ratio and BFI. In the Hampshire Avon, headwater reaches which are underlain by clay and characterized by a more flashy hydrological regime are associated with DOC: nitrate ratios >5 throughout the year, whilst groundwater-dominated reaches
underlain by Chalk, with a high BFI have DOC: nitrate ratios
in surface waters that are an order of magnitude lower
(<0.5). Our analysis also reveals significant seasonal variations in DOC: nitrate transport and highlights critical periods of nitrate export (e.g. winter in sub-catchments underlain by Chalk and Greensand, and autumn in drained, clay subcatchments) when DOC: nitrate molar ratios are low, suggesting low potential for in-stream uptake of inorganic forms of nitrogen. Consequently, our study emphasizes the tight relationship between DOC and nitrate availability in agricultural catchments, and further reveals that this relationship is controlled to a great extent by the hydrological setting.

Keywords
Year of Publication2017
JournalHydrology And Earth System Sciences
Journal citation21 (9), pp. 4785-4802
Digital Object Identifier (DOI)doi:10.5194/hess-21-4785-2017
Open accessPublished as ‘gold’ (paid) open access
Funder project or codeNE/J012106/I
NE/J011738/I
Sustainability
Provision of Demonstration test Catchments: LM0304
FunderNatural Environment Research Council
Publisher's versionhess-21-4785-2017.pdf
Output statusPublished
Publication dates
Online27 Sep 2017
Publication process dates
Accepted27 Jul 2017
Copyright licenseCC BY
PublisherCopernicus Gesellschaft Mbh
ISSN1027-5606

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