Journal cover Journal topic
Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
doi:10.5194/hess-2017-30
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
07 Mar 2017
Review status
This discussion paper is under review for the journal Hydrology and Earth System Sciences (HESS).
Hydrological controls on DOC : nitrate resource stoichiometry in a lowland, agricultural catchment, southern UK
Catherine M. Heppell1, Andrew Binley2, Mark Trimmer3, Tegan Darch1,2, Ashley Jones1,2, Ed Malone1,2, Adrian L. Collins4, Penny J. Johnes5, Jim E. Freer5, and Charlotte E. M. Lloyd6 1School of Geography, Queen Mary University of London, Mile End Road, London E1 4NS, UK
2Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
3School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK
4Sustainable Soils and Grassland Systems Department, Rothamsted Research, North Wyke, Okehampton, EX20 2SB, UK
5School of Geographical Sciences, University of Bristol, University Road, Bristol BS8 1SS, UK
6School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK
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, yet important to assess given the potential changes to production and delivery of DOC and nitrate arising from climate change. 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 Baseflow Index (BFI) and DOC : nitrate molar ratios across contrasting geologies (Chalk, Greensand and clay). We found a significant positive relationship between nitrate and Baseflow Index (p < 0.0001), and a significant negative relationship between DOC and Baseflow Index (p < 0.0001), resulting in a non-linear negative correlation between DOC : nitrate molar ratio and Baseflow Index. In the Hampshire Avon, headwater reaches which are underlain by clay and characterised 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 Baseflow Index 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 storm events in sub-catchments underlain by Chalk and Greensand, and autumn events in drained, clay sub-catchments) when DOC : nitrate molar ratios are low, suggesting low potential for in-stream uptake of inorganic forms of nitrogen. Future work should determine whether the results reported here are transferable to other agricultural, lowland catchments, and seek to understand the generalised hydrological controls on the availability of DOC transported through such landscapes.

Citation: 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.: Hydrological controls on DOC : nitrate resource stoichiometry in a lowland, agricultural catchment, southern UK, Hydrol. Earth Syst. Sci. Discuss., doi:10.5194/hess-2017-30, in review, 2017.
Catherine M. Heppell et al.
Catherine M. Heppell et al.

Data sets

Hampshire Avon: Daily discharge, stage and water chemistry data from four tributaries (Sem, Nadder, West Avon, Ebble).
C. M. Heppell and A. Binley
doi:10.5285/0dd10858-7b96-41f1-8db5-e7b4c4168af5
Hampshire Avon: Vertical head gradient, saturated hydraulic conductivity and pore water chemistry data from six river reaches.
C. M. Heppell and A. Binley
doi:10.5285/d82a04ce-f04d-40b4-9750-1a2bf7dc29a3
Catherine M. Heppell et al.

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Short summary
The role that hydrology plays in controlling the interplay between dissolved organic carbon (DOC) and nitrogen in rivers of lowland, agricultural landscapes is poorly understood, yet important to assess given the potential changes to production and delivery of DOC and nitrate arising from climate change. We measured DOC and nitrate concentrations in river water of the lowland River Hampshire Avon (Wiltshire, southern UK) revealing significant seasonal variations in DOC : nitrate transport.
The role that hydrology plays in controlling the interplay between dissolved organic carbon...
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