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| Titel |
Modelling the dynamic chemical interactions of atmospheric ammonia with leaf surface wetness in a managed grassland canopy |
| VerfasserIn |
J. Burkhardt, C. R. Flechard, F. Gresens, M. Mattsson, P. A. C. Jongejan, J. W. Erisman, T. Weidinger, R. Meszaros, E. Nemitz, M. A. Sutton |
| 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. 1 ; Nr. 6, no. 1 (2009-01-13), S.67-84 |
| Datensatznummer |
250003316
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| Publikation (Nr.) |
 copernicus.org/bg-6-67-2009.pdf |
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| Zusammenfassung |
Ammonia exchange fluxes between grassland and the atmosphere were modelled on
the basis of stomatal compensation points and leaf surface chemistry, and
compared with measured fluxes during the GRAMINAE intensive measurement
campaign in spring 2000 near Braunschweig, Germany. Leaf wetness and dew
chemistry in grassland were measured together with ammonia fluxes and
apoplastic NH4+ and H+ concentration, and the data were used to
apply, validate and further develop an existing model of leaf surface
chemistry and ammonia exchange. Foliar leaf wetness which is known to affect
ammonia fluxes may be persistent after the end of rainfall, or sustained by
recondensation of water vapour originating from the ground or leaf
transpiration, so measured leaf wetness values were included in the model. pH
and ammonium concentrations of dew samples collected from grass were compared
to modelled values.
The measurement period was divided into three phases: a relatively wet phase
followed by a dry phase in the first week before the grass was cut, and a
second drier week after the cut. While the first two phases were mainly
characterised by ammonia deposition and occasional short emission events,
regular events of strong ammonia emissions were observed during the post-cut
period. A single-layer resistance model including dynamic cuticular and
stomatal exchange could describe the fluxes well before the cut, but after
the cut the stomatal compensation points needed to numerically match measured
fluxes were much higher than the ones measured by bioassays, suggesting
another source of ammonia fluxes. Considerably better agreement both in the
direction and the size range of fluxes were obtained when a second layer was
introduced into the model, to account for the large additional ammonia source
inherent in the leaf litter at the bottom of the grass canopy. Therefore,
this was found to be a useful extension of the mechanistic dynamic chemistry
model by keeping the advantage of requiring relatively little site-specific
information. |
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