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| Titel |
Dynamics of ammonia exchange with cut grassland: synthesis of results and conclusions of the GRAMINAE Integrated Experiment |
| VerfasserIn |
M. A. Sutton, E. Nemitz, C. Milford, C. Campbell, J. W. Erisman, A. Hensen, P. Cellier, M. David, B. Loubet, E. Personne, J. K. Schjoerring, M. Mattsson, J. R. Dorsey, M. W. Gallagher, L. Horvath, T. Weidinger, R. Meszaros, U. Dämmgen, A. Neftel, B. Herrmann, B. E. Lehman, C. Flechard, J. Burkhardt |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 6, no. 12 ; Nr. 6, no. 12 (2009-12-10), S.2907-2934 |
| Datensatznummer |
250004221
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| Publikation (Nr.) |
 copernicus.org/bg-6-2907-2009.pdf |
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| Zusammenfassung |
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−1)
compared with before the cut (−60 to 40 ng m−2 s−1).
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 within-canopy 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 ammonia fluxes were compared with three models: an ecosystem model
(PaSim), a soil vegetation atmosphere transfer model (SURFATM-NH3) and
a dynamic leaf chemistry model (DCC model). The different models each
reproduced the main temporal dynamics in the flux, highlighting the
importance of canopy temperature dynamics (Surfatm-NH3), interactions
with ecosystem nitrogen cycling (PaSim) and the role of leaf surface
chemistry (DCC model). Overall, net above-canopy fluxes were mostly
determined by stomatal and cuticular uptake (before the cut), leaf litter
emissions (after the cut) and fertilizer and litter emissions (after
fertilization). The dynamics of ammonia emission from leaf litter are
identified as a priority for future research. |
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