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ENV East Doctoral Training Partnership

 

Applications to the EnvEast Doctoral Training Partnership are now closed.

Below you can browse some of the PhD projects we have previously funded; if you would like to be informed when applications open, or if you have any questions about EnvEast and our application process, please email us.

Projects previously funded by EnvEast

HISCOCK_U14EE

Determination and control of nitrate leaching losses in intensive arable farming

Project description

Over the last century there has been a dramatic perturbation of the global nitrogen budget which has led to a doubling of reactive nitrogen in the environment.  Reactive nitrogen of anthropogenic origin now equals that derived from natural terrestrial nitrogen fixation, and is predicted to exceed it by 2020 [1].  The majority of the anthropogenic budget is due to fertiliser production, reflecting changes over the last 50 years in agricultural practices to increase food production.  However, the accumulation of reactive nitrogen in the environment results in detrimental effects including increased aquatic biomass productivity leading to hypoxia, eutrophication and a loss of species diversity [2].

Reactive nitrogen may be removed from the terrestrial environment and transformed to N2 gas through microbially-mediated denitrification.  While some of the removal and storage of reactive nitrogen occurs within the landscape, a significant proportion is thought to occur within rivers and groundwater [3].  The hyporheic zone represents the interface between groundwater and surface water within the fluvial sediments below a river, and is a reactive zone supporting intense microbial activity, including denitrification [4]. This denitrification in the hyporheic zone is considered to provide a major contribution to the reduction of riverine nitrogen exports [5]. 

This PhD study will apply the dual stable isotopes of nitrogen and oxygen with solute flux mass-balance calculations to determine the composition and nitrogen species concentrations of the main sources of flow in a lowland river draining an agriculturally impacted catchment.  The principal aim is to identify and quantify nitrate removal during soil water infiltration and in groundwater-supported baseflow in the hyporheic zone.  A second aim is to determine whether changes in cultivation practices from deep inversion (ploughing) with no cover cropping in autumn to minimum cultivation (e.g. strip tillage) with cover cropping can mitigate the impact of diffuse nitrate pollution from arable agriculture.  The study area is located in the Blackwater sub-catchment of the River Wensum and is part of the Defra Wensum Demonstration Test Catchment Project.  Previous work at UEA in the River Wensum using the combined stable dual isotope and mass balance methodology [5, 6] has calculated that about 30% of leached nitrogen is removed in the microbiologically active hyporheic zone. 

References:

[1] Millennium Ecosystem Assessment Ecosystems and Human Well-Being: Findings of the Condition and Trends Working Group. Volume 1: Current State and Trends, Millennium Ecosystem Assessment; Island Press: 2005.

[2] Vitousek, P. M., Aber, J. D., Howarth, R. W., Likens, G. E., Matson, P. A., Schindler, D. W., Schlesinger, W. H., Tilman, D. G. (1997) Human alteration of the global nitrogen cycle: sources and consequences. Ecol.  Appl 7, 737-750.

[3] Seitzinger, S., Harrison, J. A., Bohlke, J. K., Bouwman, A. F., Lowrance, R., Peterson, B. J., Tobias, C., Van Drecht, G. (2006) Denitrification across landscapes and waterscapes: a synthesis. Ecol. Appl. 16, 2064-2090.

[4] Boulton, A. J., Findlay, S., Marmonier, P., Stanley, E. H., Valett, H. M. (1998) The functional significance of the hyporheic zone in streams and rivers. Annu. Rev. Ecol. Syst. 29, 59-81.

[5] Wexler, S.K., Hiscock, K.M., Dennis, P.F. (2011) Catchment-scale quantification oh hyporheic denitrification using an isotopic and solute flux approach. Env. Sci. Technol. 45, 3967-3973.

[6] Wexler, S.K., Hiscock, K.M., Dennis, P.F. (2012) Microbial and hydrological influences on nitrate isotopic composition in an agricultural lowland catchment. J. Hydrol., 468-469, 85-93.

Co-Supervisors
Dr Alina Marca
  • Start date 1 October 2014