Ammonia fluxes in relation to cutting and fertilization of an intensively managed grassland derived from an inter-comparison of gradient measurements C. Milford1,*, M. R. Theobald1, E. Nemitz1, K. J. Hargreaves1, L. Horvath2, J. Raso2, U. Dämmgen3, A. Neftel4, S. K. Jones1,4, A. Hensen5, B. Loubet6, P. Cellier6, and M. A. Sutton1 1Centre for Ecology and Hydrology (Edinburgh Research Station), Bush Estate, Penicuik, Midlothian, EH26 0QB, UK 2Institute of Atmospheric Physics, P.O. Box 39, 1675 Budapest, Hungary 3Institut für Agrarökologie, Bundesforschungsanstalt für Landwirtschaft (FAL), Bundesallee 50, 38116 Braunschweig, Germany 4Agroscope Reckenholz-Tänikon Research Station ART, Reckenholzstrasse 191, 8046 Zurich, Switzerland 5Energy research Centre of the Netherlands (ECN), Postbus 1, 1755 ZG Petten, The Netherlands 6Institut National de la Recherche Agronomique (INRA), UMR Environnement et Grandes Cultures, Thiverval-Grignon, 78850, France *now at: Institute of Earth Sciences "Jaume Almera", CSIC, C/Lluis Solé i Sabarís s/n, Barcelona, 08028, Spain
Abstract. 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.
Citation: Milford, C., Theobald, M. R., Nemitz, E., Hargreaves, K. J., Horvath, L., Raso, J., Dämmgen, U., Neftel, A., Jones, S. K., Hensen, A., Loubet, B., Cellier, P., and Sutton, M. A.: 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, doi:10.5194/bg-6-819-2009, 2009.