Abstract
Abstract. The understanding of biochemical feed-back 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 days period during autumn 2010 (21 October–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 were obtained with the Danish Ammonia MOdelling System (DAMOS). 57.7% of the fluxes measured showed emission and 19.5% showed deposition. The mean NH3 flux was 0.087 ± 0.19 μg NH3-N m−2 s−1. A clear tendency of the flux going from negative (deposition) to positive (emission) fluxes of up to 0.96 ± 0.40 μg NH3-N m−2 s−1 throughout the measurement period was found. In the leaf fall period (23 October–8 November), an increase in the atmospheric NH3 concentrations was related to the increasing forest NH3 flux. The modelled concentration from DAMOS fits well the measured concentrations before leaf fall. 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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Claims 9
Claim · model-written summary
The mean NH3 flux from the beech forest was 0.087 ± 0.19 μg NH3-N m−2 s−1.
Verbatim
e1“for the Danish beech forest, Lille Bøgeskov”
e2“The mean NH3 flux was 0.087 ± 0.19 μg NH3-N m−2 s−1”
Claim · model-written summary
Emission was measured in 57.7% of the NH3 fluxes.
Verbatim
e1“for the Danish beech forest, Lille Bøgeskov”
e3“57.7% of the fluxes measured showed emission”
Claim · model-written summary
Deposition was measured in 19.5% of the NH3 fluxes.
Verbatim
e1“for the Danish beech forest, Lille Bøgeskov”
e4“19.5% showed deposition”
Claim · model-written summary
An increase in atmospheric NH3 concentrations in the leaf fall period was related to increasing beech forest NH3 flux.
Verbatim
e1“for the Danish beech forest, Lille Bøgeskov”
e5“In the leaf fall period (23 October–8 November), an increase in the atmospheric NH3 concentrations was related to the increasing forest NH3 flux”
Claim · model-written summary
Modelled NH3 concentrations from DAMOS fit the measured concentrations before leaf fall.
Verbatim
e1“for the Danish beech forest, Lille Bøgeskov”
e6“The modelled concentration from DAMOS fits well the measured concentrations before leaf fall”
Claim · model-written summary
Modelled NH3 concentrations are too low during and after leaf fall.
Verbatim
e1“for the Danish beech forest, Lille Bøgeskov”
e6“The modelled concentration from DAMOS fits well the measured concentrations before leaf fall”
e7“During and after leaf fall, the modelled concentrations are too low”
Claim · model-written summary
Diurnal variations in measured NH3 concentrations were related to meteorological conditions and forest phenology.
- Taxon
- beech foreste1
- Treatment
- meteorological conditionse2
- Outcome
- diurnal variations in the measured NH3 concentrationse2
Not reportedDirection
Verbatim
e1“for the Danish beech forest, Lille Bøgeskov”
e2“diurnal variations in the measured NH3 concentrations were related to meteorological conditions, forest phenology and the spatial distribution of local anthropogenic NH3 sources”
Claim · model-written summary
Emissions from deciduous forests should be included in model calculations of atmospheric NH3.
Verbatim
e2“We therefore conclude that emissions from deciduous forests are important to include in model calculations of atmospheric NH3 for forest ecosystems”
Claim · model-written summary
An accurate description of ammonia fluxes over forest ecosystems requires a dynamic description of atmospheric and vegetation processes.
Verbatim
e2“an accurate description of ammonia fluxes over forest ecosystems requires a dynamic description of atmospheric and vegetation processes”