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Dynamics of ammonia exchange with cut grassland: synthesis of results and conclusions of the GRAMINAE Integrated Experiment

Sutton, M.A.; Nemitz, E.; Milford, C.; Campbell, C.; Erisman, J.W.; Hensen, A.; Cellier, P.; David, M.; Loubet, B.; Personne, E.; Schjoerring, J.K.; Mattsson, M.; Dorsey, J.R.; Gallagher, M.W.; Horváth, L.; Weidinger, T.; Mészáros, R.; Dämmgen, U.; Neftel, A.; Herrmann, B.; Lehman, B.E.; Flechard, C.; Burkhardt, J.. 2009 Dynamics of ammonia exchange with cut grassland: synthesis of results and conclusions of the GRAMINAE Integrated Experiment. Biogeosciences Discussions, 6. 1121-1184. 10.5194/bgd-6-1121-2009

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Abstract/Summary

Improved data on biosphere-atmosphere exchange are fundamental to understanding the production and fate of ammonia (NH3) in the atmosphere. The GRAMINAE Integrated Experiment combined novel measurement and modelling approaches to provide the most comprehensive analysis of the interactions to date. Major inter-comparisons of micrometeorological parameters and NH3 flux measurements using the aerodynamic gradient method and relaxed eddy accumulation (REA) were conducted. These showed close agreement, though the REA systems proved insufficiently precise to investigate vertical flux divergence. Grassland management had a large effect on fluxes: Emissions increased after grass cutting (−50 to 700 ng m−2 s−1 NH3) and after N-fertilization (0 to 3800 ng m−2 s) compared with before the cut (−60 to 40 ng m−2 s. Effects of advection and air chemistry were investigated using horizontal NH3 profiles, acid gas and particle flux measurements. Inverse modelling of NH3 emission from an experimental farm agreed closely with inventory estimates, while advection errors were used to correct measured grassland fluxes. Advection effects were caused both by the farm and by emissions from the field, with an inverse dispersion-deposition model providing a reliable new approach to estimate net NH3 fluxes. Effects of aerosol chemistry on net NH3 fluxes were small, while the measurements allowed NH3-induced particle growth rates to be calculated and aerosol fluxes to be corrected. Bioassays estimated the emission potential Γ=[NH4+]/[H+] for different plant pools, with the apoplast having the smallest values (30–1000). The main sources of NH3 emission appeared to be leaf litter and the soil surface, with Γ up to 3 million and 300 000, respectively. Cuvette and within-canopy analyses confirmed the role of leaf litter NH3 emission, which, prior to cutting, was mostly recaptured within the canopy. Measured fluxes were compared with three models: an ecosystem model, a soil vegetation atmosphere transfer model and a dynamic leaf chemistry model. The simulations highlighted the importance of canopy temperature, interactions with ecosystem nitrogen cycling and the role of leaf surface chemistry. The dynamics of ammonia emission from leaf litter are identified as a priority for future research. [abstract from: http://www.biogeosciences-discuss.net/6/1121/2009/bgd-6-1121-2009.html]

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.5194/bgd-6-1121-2009
Programmes: CEH Programmes pre-2009 publications > Biogeochemistry
CEH Sections: Billett
Additional Information. Not used in RCUK Gateway to Research.: Full text access is available via the Official URL link. Open access journal.
NORA Subject Terms: Atmospheric Sciences
Date made live: 17 May 2010 14:55
URI: http://nora.nerc.ac.uk/id/eprint/9463

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