Ammonia fluxes in relation to cutting and fertilization of an intensively managed grassland derived from an inter-comparison of gradient measurements

Milford, C.; Theobald, M.R.; Nemitz, E.; Hargreaves, K.J.; Horvath, L.; Raso, J.; Dammgen, U.; Neftel, A.; Jones, S.K.; Hensen, A.; Loubet, B.; Cellier, P.; Sutton, M.A.. 2009 Ammonia fluxes in relation to cutting and fertilization of an intensively managed grassland derived from an inter-comparison of gradient measurements. Biogeosciences, 6. 819-834.

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Quantification of ammonia (NH3) land-atmosphere exchange is required for atmospheric modelling and assessment of nitrogen deposition, yet flux measurement methods remain highly uncertain. To address this issue, a major inter-comparison of ammonia fluxes over intensively managed grassland was conducted during the GRAMINAE Integrated Experiment held in Braunschweig, Germany. In order to provide a robust dataset of ammonia exchange with the vegetation, four independent continuous flux gradient systems were operated. Three independently operated continuous wet denuders systems (AMANDA) were compared with a Wet Effluent Diffusion Denuder (mini-WEDD) system. Measurements were made at two distances from an adjacent livestock farm, allowing effects of advection to be quantified in a real landscape setting. Data treatment included filtering for instrument failure, disturbed wind sectors and unsuitable micrometeorological conditions, with corrections made for storage and advection errors. The inter-comparison demonstrated good agreement in measured ammonia concentrations and fluxes (relative standard error <20%) for some periods, although the performance of the ammonia analyzers were variable, with much poorer agreement on particular days. However, by using four systems, the inter-comparison was able to provide a robust mean estimate of continuous ammonia fluxes through the experiment. The observed fluxes were: a) small bi-directional fluxes prior to cutting (−64 to 42 ng NH3 m−2 s−1), b) larger diurnally-varying emissions following cutting (−49 to 703 ng NH3 m−2 s−1) and c) much larger emissions following fertilizer application (0 to 3820 ng NH3 m−2 s−1). The results are a salutary reminder of the uncertainty in unreplicated ammonia flux measurements, while the replication of the present study provides a uniquely robust dataset for the evaluation of ammonia exchange processes. It is clear that consistently reliable determination of ammonia concentrations remains the major measurement challenge. [Abstract from: ]

Item Type: Publication - Article
Programmes: CEH Programmes pre-2009 publications > Biogeochemistry
UKCEH and CEH Sections/Science Areas: Billett (to November 2013)
ISSN: 1726-4170
Additional Information. Not used in RCUK Gateway to Research.: Paper published in Biogeosciences 6 (Special Issue): Processes controlling the exchange of ammonia between grassland and the atmosphere (GRAMINAE), edited by K.Pilegaard, J.K. Schjoerring and M.A. Sutton. Open access journal.
NORA Subject Terms: Atmospheric Sciences
Date made live: 23 Sep 2009 13:19 +0 (UTC)

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