Hydrology and Earth System Sciences
Hydrology and Earth System Sciences
HESS
Articles | Volume 21, issue 9
Articles | Volume 21, issue 9
https://doi.org/10.5194/hess-21-4785-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
https://doi.org/10.5194/hess-21-4785-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Articles | Volume 21, issue 9
Research article
 | 
27 Sep 2017
Research article |  | 27 Sep 2017

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

Catherine M. Heppell, Andrew Binley, Mark Trimmer, Tegan Darch, Ashley Jones, Ed Malone, Adrian L. Collins, Penny J. Johnes, Jim E. Freer, and Charlotte E. M. Lloyd

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 sub-catchments) 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.

How to cite. 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., 21, 4785–4802, https://doi.org/10.5194/hess-21-4785-2017, 2017.
Received: 19 Jan 2017 – Discussion started: 07 Mar 2017 – Revised: 10 Jul 2017 – Accepted: 27 Jul 2017 – Published: 27 Sep 2017
Download
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.
Read more