Forest–atmosphere exchange of reactive nitrogen in a remote region – Part I: Measuring temporal dynamics
<p>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 indiv...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-01-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/19/389/2022/bg-19-389-2022.pdf |
| Summary: | <p>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 (<span class="inline-formula">ΣN<sub>r</sub></span>) 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
<span class="inline-formula">ΣN<sub>r</sub></span> were carried out with the Total Reactive
Atmospheric Nitrogen Converter (TRANC) coupled to a chemiluminescence
detector (CLD) for 2.5 years.</p>
<p>The average <span class="inline-formula">ΣN<sub>r</sub></span> concentration was 3.1 <span class="inline-formula">µg N m<sup>−3</sup></span>. Denuder measurements with DELTA samplers and chemiluminescence
measurements of nitrogen oxides (NO<span class="inline-formula"><sub><i>x</i></sub></span>) have shown that NO<span class="inline-formula"><sub><i>x</i></sub></span> has the
highest contribution to <span class="inline-formula">ΣN<sub>r</sub></span> (<span class="inline-formula">∼51.4 %</span>), followed by ammonia (<span class="inline-formula">NH<sub>3</sub></span>) (<span class="inline-formula">∼20.0 %</span>),
ammonium (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="8cff18dc7544e09830abea500d71300b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-389-2022-ie00001.svg" width="24pt" height="15pt" src="bg-19-389-2022-ie00001.png"/></svg:svg></span></span>) (<span class="inline-formula">∼15.3 %</span>), nitrate <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="9712381780fcc4de6c4d72f703a8771c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-389-2022-ie00002.svg" width="25pt" height="16pt" src="bg-19-389-2022-ie00002.png"/></svg:svg></span></span> (<span class="inline-formula">∼7.0 %</span>), and nitric acid (<span class="inline-formula">HNO<sub>3</sub></span>) (<span class="inline-formula">∼6.3 %</span>). Only
slight seasonal changes were found in the <span class="inline-formula">ΣN<sub>r</sub></span>
concentration level, whereas a seasonal pattern was observed for the
contribution of <span class="inline-formula">NH<sub>3</sub></span> and NO<span class="inline-formula"><sub><i>x</i></sub></span>. <span class="inline-formula">NH<sub>3</sub></span> showed highest
contributions to <span class="inline-formula">ΣN<sub>r</sub></span> in spring and summer,
NO<span class="inline-formula"><sub><i>x</i></sub></span> in autumn and winter.</p>
<p>We observed deposition fluxes at the measurement site with median fluxes
ranging from <span class="inline-formula">−</span>15 to <span class="inline-formula">−</span>5 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M25" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">ng</mi><mspace width="0.125em" linebreak="nobreak"/><mi mathvariant="normal">N</mi><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">m</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">s</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="61pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="15c7f58df3083e15bb72b02ec9cf128e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-389-2022-ie00003.svg" width="61pt" height="15pt" src="bg-19-389-2022-ie00003.png"/></svg:svg></span></span> (negative fluxes
indicate deposition). Median deposition velocities ranged from 0.2 to
0.5 <span class="inline-formula">cm s<sup>−1</sup></span>. 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
<span class="inline-formula">ΣN<sub>r</sub></span>, global radiation (<span class="inline-formula"><i>R</i><sub>g</sub></span>), and
other drivers correlated with <span class="inline-formula"><i>R</i><sub>g</sub></span> were most likely influencing
the deposition velocity (<span class="inline-formula"><i>v</i><sub>d</sub></span>). We found that from May to
September higher temperatures, lower relative humidity, and dry leaf surfaces
increase <span class="inline-formula"><i>v</i><sub>d</sub></span> of <span class="inline-formula">ΣN<sub>r</sub></span>. At the
measurement site, <span class="inline-formula">ΣN<sub>r</sub></span> concentration did not
emerge as a driver for the <span class="inline-formula">ΣN<sub>r</sub><i>v</i><sub>d</sub></span>.</p>
<p>No significant influence of temperature, humidity, friction velocity, or wind
speed on <span class="inline-formula">ΣN<sub>r</sub></span> 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 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M36" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">kg</mi><mspace width="0.125em" linebreak="nobreak"/><mi mathvariant="normal">N</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">ha</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">a</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="65pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="3d622f083d7beee7f925678d6e6c6af0"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-389-2022-ie00004.svg" width="65pt" height="15pt" src="bg-19-389-2022-ie00004.png"/></svg:svg></span></span>,
respectively. Adding results from the wet deposition measurements, we
determined 12.2 and 10.9 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M37" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">kg</mi><mspace width="0.125em" linebreak="nobreak"/><mi mathvariant="normal">N</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">ha</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">a</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="65pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="0aedb55a7f2c97ea5ca5cfc118929278"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-19-389-2022-ie00005.svg" width="65pt" height="15pt" src="bg-19-389-2022-ie00005.png"/></svg:svg></span></span> as total nitrogen
deposition in the 2 years of observation.</p>
<p>This work encompasses (one of) the first long-term flux measurements of
<span class="inline-formula">ΣN<sub>r</sub></span> using novel measurements techniques for
estimating annual nitrogen dry deposition to a remote forest ecosystem.</p> |
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| ISSN: | 1726-4170 1726-4189 |