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ORE agro-hydrosystèmes

Zone de texte éditable et éditée

PhD defense by Michael Bell

December 2017, the 18th

Michael Bell will defend his PhD thesis entitled "Emission, dispersion and deposition of ammonia, from plot scale to landscape scale"

On Monday the 18th of December, 2:00 pm in AgroCampus Ouest Rennes

The jury members are:

Edith Le Cadre, Professeur Agrocampus

Claire Delon, Laboratoire d’Aerologie Toulouse

Karine Sartelet,  CEREA, École des Ponts ParisTech

Christof Ammann,Agroscope Zürich

François Gautier, INERIS, Verneuil-en-Halatte

Benjamin Loubet, INRA-ECOSYS Grignon, Director

Pierre Cellier, INRA-ECOSYS, Grignon

Chris Flechard, INRA-SAS, Supervisor


Emissions of ammonia (NH3) to the atmosphere have been implicated in a web of harmful environmental impacts, from pollution of sensitive terrestrial and aquatic ecosystems to worsening of urban air quality and the indirect emissions of nitrous oxide (N20). Originating overwhelmingly from livestock, NH3 emissions and its impacts are extremely variable in space, from the perspective of an individual farm source through to the regional or continental scale. In part, this spatial heterogeneity is due to the solubility and reactivity of the NH3 molecule and effective deposition processes, leading to a very short atmospheric lifetime. The complexities of NH3 emissions therefore necessitate investigation at the smallest practical scale measurement, which may be a single field or livestock barn. However, the composite nature of livestock operations can be a considerable challenge when integrating to the scale of a whole farm or a landscape containing multiple farms.

The application of atmospheric measurements and inverse dispersion modelling may be unique in providing a singular methodology which can quantify emissions of NH3 to the atmosphere from almost any source. However, there are various measurement and modelling techniques and options which may be implemented within the inverse dispersion method, which can be optimised for specific sources. The special case of NH3 in the context of NH3 in the context of inverse dispersion presents a number of measurement and modelling challenges, all related to the reactive and “sticky” nature of the molecule.

This thesis features six experiments carried out in three countries, in which NH3 emissions were quantified from multiple sources across a broad range of scales and system complexities - from the simple case of circular plots applied with slurry to an entire agricultural landscape containing multiple farm scale sources of varying intensity. In each case the inverse dispersion method was adapted to the specific nature of the source being investigated and the uncertainties of NH3 measurement and modelling, where local deposition must be considered. The experiments were undertaken with an emphasis on methodological evaluation, in which novel techniques were developed and alternative methods are compared.

This thesis ultimately expands the scope of the inverse dispersion method applied for NH3 to the landscape scale, connecting with integrated nitrogen assessments and budgeting which may bring forth new understanding into cascade of reactive nitrogen to the environment.