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| Titel |
Soil–atmosphere exchange of ammonia in a non-fertilized grassland: measured emission potentials and inferred fluxes |
| VerfasserIn |
G. R. Wentworth, J. G. Murphy, P. K. Gregoire, C. A. L. Cheyne, A. G. Tevlin, R. Hems |
| 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 ; 11, no. 20 ; Nr. 11, no. 20 (2014-10-16), S.5675-5686 |
| Datensatznummer |
250117642
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| Publikation (Nr.) |
 copernicus.org/bg-11-5675-2014.pdf |
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| Zusammenfassung |
| A 50-day field study was carried out in a semi-natural, non-fertilized
grassland in south-western Ontario, Canada during the late summer and early
autumn of 2012. The purpose was to explore surface–atmosphere exchange
processes of ammonia (NH3) with a focus on bi-directional fluxes
between the soil and atmosphere. Measurements of soil pH and ammonium
concentration ([NH4+]) yielded the first direct quantification of
soil emission potential (Γsoil = [NH4+]/[H+])
for this land type, with values ranging from 35 to 1850 (an average of
290). The soil compensation point, the atmospheric NH3 mixing ratio
below which net emission from the soil will occur, exhibited both a seasonal
trend and diurnal trend. Higher daytime and August compensation points were
attributed to higher soil temperature. Soil–atmosphere fluxes were estimated
using NH3 measurements from the Ambient Ion Monitor Ion Chromatograph
(AIM-IC) and a simple resistance model. Vegetative effects were ignored
due to the short canopy height and significant Γsoil. Inferred
fluxes were, on average, 2.6 ± 4.5 ng m−2 s−1 in August
(i.e. net emission) and −5.8 ± 3.0 ng m−2 s−1 in September
(i.e. net deposition). These results are in good agreement with the only
other bi-directional exchange study in a semi-natural, non-fertilized
grassland. A Lagrangian dispersion model (Hybrid Single-Particle Lagrangian Integrated Trajectory – HYSPLIT) was used to calculate air
parcel back-trajectories throughout the campaign and revealed that NH3
mixing ratios had no directional bias throughout the campaign, unlike the
other atmospheric constituents measured. This implies that soil–atmosphere
exchange over a non-fertilized grassland can significantly moderate
near-surface NH3 concentrations. In addition, we provide indirect
evidence that dew and fog evaporation can cause a morning increase of
[NH3]g. Implications of our findings on current NH3
bi-directional exchange modelling efforts are also discussed. |
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