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- Title
Ammonia fluxes in relation to cutting and fertilization of an intensively managed grassland derived from an inter-comparison of gradient measurements.
- Authors
Milford, C.; Theobald, M. R.; Nemitz, E.; Hargreaves, K. J.; Horvath, L.; Raso, J.; Dämmgen, U.; NefteI, A.; Jones, S. K.; Hensen, A.; Loubet, B.; CeIIier, P.; Sutton, M. A.
- 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 hi-directional fluxes prior to cutting (-64 to 42ng NH3 m-2s-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.
- Subjects
BRAUNSCHWEIG (Germany); GERMANY; AMMONIA; AGRICULTURE; MICROMETEOROLOGY; ATMOSPHERIC models; GRASSLANDS
- Publication
Biogeosciences, 2009, Vol 6, Issue 5, p819
- ISSN
1726-4170
- Publication type
Article
- DOI
10.5194/bg-6-819-2009