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| Titel |
Ammonia emissions from deciduous forest after leaf fall |
| VerfasserIn |
K. Hansen, L. L. Sørensen, O. Hertel, C. Geels, C. A. Skjøth, B. Jensen, E. Boegh |
| 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 ; 10, no. 7 ; Nr. 10, no. 7 (2013-07-09), S.4577-4589 |
| Datensatznummer |
250018331
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| Publikation (Nr.) |
 copernicus.org/bg-10-4577-2013.pdf |
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| Zusammenfassung |
| The understanding of biochemical feedback mechanisms in the climate system is
lacking knowledge in relation to bi-directional ammonia (NH3) exchange
between natural ecosystems and the atmosphere. We therefore study the
atmospheric NH3 fluxes during a 25-day period during autumn 2010
(21 October to 15 November) for the Danish beech forest Lille Bøgeskov to
address the hypothesis that NH3 emissions occur from deciduous forests
in relation to leaf fall. This is accomplished by using observations of
vegetation status, NH3 fluxes and model calculations. Vegetation status
was observed using plant area index (PAI) and leaf area index (LAI). NH3
fluxes were measured using the relaxed eddy accumulation (REA) method. The
REA-based NH3 concentrations were compared to NH3 denuder
measurements. Model calculations of the atmospheric NH3 concentration
were obtained with the Danish Ammonia MOdelling System (DAMOS). The relative
contribution from the forest components to the atmospheric NH3 flux was
assessed using a simple two-layer bi-directional canopy compensation point
model. A total of 57.7% of the fluxes measured showed emission and
19.5% showed deposition. A clear tendency of the flux going from
deposition of −0.25 ± 0.30 μg NH3-N m−2 s−1
to emission of up to
0.67 ± 0.28 μg NH3-N m−2 s−1 throughout the
measurement period was found. In the leaf fall period (23 October to
8 November), an increase in the atmospheric NH3 concentrations was
related to the increasing forest NH3 flux. Following leaf fall, the
magnitude and temporal structure of the measured NH3 emission fluxes
could be adequately reproduced with the bi-directional resistance model; it
suggested the forest ground layer (soil and litter) to be the main
contributing component to the NH3 emissions. The modelled concentration
from DAMOS fits well the measured concentrations before leaf fall, but during
and after leaf fall, the modelled concentrations are too low. The results
indicate that the missing contribution to atmospheric NH3 concentration
from vegetative surfaces related to leaf fall are of a relatively large
magnitude. We therefore conclude that emissions from deciduous forests are
important to include in model calculations of atmospheric NH3 for forest
ecosystems. Finally, diurnal variations in the measured NH3
concentrations were related to meteorological conditions, forest phenology
and the spatial distribution of local anthropogenic NH3 sources. This
suggests that an accurate description of ammonia fluxes over forest
ecosystems requires a dynamic description of atmospheric and vegetation
processes. |
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