Forest–atmosphere exchange of reactive nitrogen in a remote region – Part I: Measuring temporal dynamics
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Published:2022-01-25
Issue:2
Volume:19
Page:389-413
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ISSN:1726-4189
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Container-title:Biogeosciences
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language:en
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Short-container-title:Biogeosciences
Author:
Wintjen Pascal, Schrader Frederik, Schaap Martijn, Beudert Burkhard, Brümmer ChristianORCID
Abstract
Abstract. Long-term dry deposition flux measurements of reactive nitrogen based on the
eddy covariance or the aerodynamic gradient method are scarce. Due to the
large diversity of reactive nitrogen compounds and high technical requirements
for the measuring devices, simultaneous measurements of individual reactive
nitrogen compounds are not affordable. Hence, we examined the exchange
patterns of total reactive nitrogen (ΣNr) and
determined annual dry deposition budgets based on measured data at a mixed
forest exposed to low air pollution levels located in the Bavarian Forest
National Park (NPBW), Germany. Flux measurements of
ΣNr were carried out with the Total Reactive
Atmospheric Nitrogen Converter (TRANC) coupled to a chemiluminescence
detector (CLD) for 2.5 years. The average ΣNr concentration was 3.1 µg N m−3. Denuder measurements with DELTA samplers and chemiluminescence
measurements of nitrogen oxides (NOx) have shown that NOx has the
highest contribution to ΣNr (∼51.4 %), followed by ammonia (NH3) (∼20.0 %),
ammonium (NH4+) (∼15.3 %), nitrate NO3- (∼7.0 %), and nitric acid (HNO3) (∼6.3 %). Only
slight seasonal changes were found in the ΣNr
concentration level, whereas a seasonal pattern was observed for the
contribution of NH3 and NOx. NH3 showed highest
contributions to ΣNr in spring and summer,
NOx in autumn and winter. We observed deposition fluxes at the measurement site with median fluxes
ranging from −15 to −5 ngNm-2s-1 (negative fluxes
indicate deposition). Median deposition velocities ranged from 0.2 to
0.5 cm s−1. In general, highest deposition velocities were
recorded during high solar radiation, in particular from May to September. Our
results suggest that seasonal changes in composition of
ΣNr, global radiation (Rg), and
other drivers correlated with Rg were most likely influencing
the deposition velocity (vd). We found that from May to
September higher temperatures, lower relative humidity, and dry leaf surfaces
increase vd of ΣNr. At the
measurement site, ΣNr concentration did not
emerge as a driver for the ΣNrvd. No significant influence of temperature, humidity, friction velocity, or wind
speed on ΣNr fluxes when using the
mean-diurnal-variation (MDV) approach for filling gaps of up to 5 days was
found. Remaining gaps were replaced by a monthly average of the specific
half-hourly value. From June 2016 to May 2017 and June 2017 to May 2018, we
estimated dry deposition sums of 3.8 and 4.0 kgNha-1a-1,
respectively. Adding results from the wet deposition measurements, we
determined 12.2 and 10.9 kgNha-1a-1 as total nitrogen
deposition in the 2 years of observation. This work encompasses (one of) the first long-term flux measurements of
ΣNr using novel measurements techniques for
estimating annual nitrogen dry deposition to a remote forest ecosystem.
Funder
Umweltbundesamt Bundesministerium für Bildung und Forschung
Publisher
Copernicus GmbH
Subject
Earth-Surface Processes,Ecology, Evolution, Behavior and Systematics
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