Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern Borneo
<p>Nitrous oxide (<span class="inline-formula">N<sub>2</sub>O</span>) and methane (<span class="inline-formula">CH<sub>4</sub></span>) are atmospheric trace gases which play important roles in the climate and atmospheric chemi...
| Main Authors: | , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-11-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/16/4321/2019/bg-16-4321-2019.pdf |
| _version_ | 1818337794049703936 |
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| author | H. W. Bange C. H. Sim D. Bastian J. Kallert A. Kock A. Mujahid M. Müller |
| author_facet | H. W. Bange C. H. Sim D. Bastian J. Kallert A. Kock A. Mujahid M. Müller |
| author_sort | H. W. Bange |
| collection | DOAJ |
| description | <p>Nitrous oxide (<span class="inline-formula">N<sub>2</sub>O</span>) and methane (<span class="inline-formula">CH<sub>4</sub></span>) are atmospheric trace gases
which play important roles in the climate and atmospheric chemistry of the
Earth. However, little is known about their emissions from rivers and
estuaries, which seem to contribute significantly to the atmospheric budget
of both gases. To this end concentrations of <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CH<sub>4</sub></span> were
measured in the Rajang, Maludam, Sebuyau and Simunjan rivers draining
peatland in northwestern (NW) Borneo during two campaigns in March and
September 2017. The Rajang River was additionally sampled in August 2016 and
the Samunsam and Sematan rivers were additionally sampled in March 2017. The
Maludam, Sebuyau, and Simunjan rivers are typical “blackwater” rivers with
very low pH (3.7–7.8), very high dissolved organic carbon (DOC)
concentrations (235–4387 mmol L<span class="inline-formula"><sup>−1</sup></span>) and very low <span class="inline-formula">O<sub>2</sub></span>
concentrations (31–246 <span class="inline-formula">µ</span>mol L<span class="inline-formula"><sup>−1</sup></span>; i.e. 13 %–116 % <span class="inline-formula">O<sub>2</sub></span>
saturation). The spatial and temporal variability of <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CH<sub>4</sub></span>
concentrations (saturations) in the six rivers or estuaries was large and
ranged from 2.0 nmol L<span class="inline-formula"><sup>−1</sup></span> (28 %) to 41.4 nmol L<span class="inline-formula"><sup>−1</sup></span> (570 %) and
from 2.5 nmol L<span class="inline-formula"><sup>−1</sup></span> (106 %) to 1372 nmol L<span class="inline-formula"><sup>−1</sup></span> (57 459 %),
respectively. We found no overall trends of <span class="inline-formula">N<sub>2</sub>O</span> with <span class="inline-formula">O<sub>2</sub></span> or
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M22" 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="23164037a5a41a281ec2bd2a6e11aeb2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4321-2019-ie00001.svg" width="25pt" height="16pt" src="bg-16-4321-2019-ie00001.png"/></svg:svg></span></span>, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</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="28c795146b952e4d8389bf50a28441ff"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4321-2019-ie00002.svg" width="25pt" height="16pt" src="bg-16-4321-2019-ie00002.png"/></svg:svg></span></span> or <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M24" 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="ae42caf6f031f0c6641dd1d09f6cb28c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4321-2019-ie00003.svg" width="24pt" height="15pt" src="bg-16-4321-2019-ie00003.png"/></svg:svg></span></span>, and there were no trends of
<span class="inline-formula">CH<sub>4</sub></span> with <span class="inline-formula">O<sub>2</sub></span> or dissolved nutrients or DOC. <span class="inline-formula">N<sub>2</sub>O</span> concentrations
showed a positive linear correlation with rainfall. We conclude, therefore,
that rainfall is the main factor determining the riverine <span class="inline-formula">N<sub>2</sub>O</span>
concentrations since <span class="inline-formula">N<sub>2</sub>O</span> production or consumption in the blackwater rivers themselves seems to be low because of the low pH. <span class="inline-formula">CH<sub>4</sub></span>
concentrations were highest at salinity <span class="inline-formula">=</span> 0 and most probably result from
methanogenesis as part of the decomposition of organic matter under anoxic
conditions. <span class="inline-formula">CH<sub>4</sub></span> in the concentrations in the blackwater rivers showed
an inverse relationship with rainfall. We suggest that <span class="inline-formula">CH<sub>4</sub></span> oxidation in
combination with an enhanced river flow after the rainfall events might be
responsible for the decrease in the <span class="inline-formula">CH<sub>4</sub></span> concentrations. The rivers and
estuaries studied here were an overall net source of <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CH<sub>4</sub></span>
to the atmosphere. The total annual <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CH<sub>4</sub></span> emissions were
1.09 Gg <span class="inline-formula">N<sub>2</sub>O</span> yr<span class="inline-formula"><sup>−1</sup></span> (0.7 Gg N yr<span class="inline-formula"><sup>−1</sup></span>) and 23.8 Gg <span class="inline-formula">CH<sub>4</sub></span> yr<span class="inline-formula"><sup>−1</sup></span>, respectively. This represents about 0.3 %–0.7 % of the global
annual riverine and estuarine <span class="inline-formula">N<sub>2</sub>O</span> emissions and about 0.1 %–1 % of
the global riverine and estuarine <span class="inline-formula">CH<sub>4</sub></span> emissions. Therefore, we conclude
that rivers and estuaries in NW Borneo – despite the fact their water area
covers only 0.05 % of the global river/estuarine area – contribute
significantly to global riverine and estuarine emissions of <span class="inline-formula">N<sub>2</sub>O</span> and
<span class="inline-formula">CH<sub>4</sub></span>.</p> |
| first_indexed | 2024-12-13T15:00:52Z |
| format | Article |
| id | doaj.art-4fca33e1bedc47ef9c364d4a63aceec1 |
| institution | Directory Open Access Journal |
| issn | 1726-4170 1726-4189 |
| language | English |
| last_indexed | 2024-12-13T15:00:52Z |
| publishDate | 2019-11-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Biogeosciences |
| spelling | doaj.art-4fca33e1bedc47ef9c364d4a63aceec12022-12-21T23:41:08ZengCopernicus PublicationsBiogeosciences1726-41701726-41892019-11-01164321433510.5194/bg-16-4321-2019Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern BorneoH. W. Bange0C. H. Sim1D. Bastian2J. Kallert3A. Kock4A. Mujahid5M. Müller6Marine Biogeochemistry Research Division, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, GermanyFaculty of Engineering, Computing and Science, Swinburne University of Technology, Kuching, Sarawak, MalaysiaMarine Biogeochemistry Research Division, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, GermanyMarine Biogeochemistry Research Division, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, GermanyMarine Biogeochemistry Research Division, GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, GermanyDepartment of Aquatic Science, Faculty of Resource Science & Technology, University Malaysia Sarawak, Kota Samarahan, Sarawak, MalaysiaFaculty of Engineering, Computing and Science, Swinburne University of Technology, Kuching, Sarawak, Malaysia<p>Nitrous oxide (<span class="inline-formula">N<sub>2</sub>O</span>) and methane (<span class="inline-formula">CH<sub>4</sub></span>) are atmospheric trace gases which play important roles in the climate and atmospheric chemistry of the Earth. However, little is known about their emissions from rivers and estuaries, which seem to contribute significantly to the atmospheric budget of both gases. To this end concentrations of <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CH<sub>4</sub></span> were measured in the Rajang, Maludam, Sebuyau and Simunjan rivers draining peatland in northwestern (NW) Borneo during two campaigns in March and September 2017. The Rajang River was additionally sampled in August 2016 and the Samunsam and Sematan rivers were additionally sampled in March 2017. The Maludam, Sebuyau, and Simunjan rivers are typical “blackwater” rivers with very low pH (3.7–7.8), very high dissolved organic carbon (DOC) concentrations (235–4387 mmol L<span class="inline-formula"><sup>−1</sup></span>) and very low <span class="inline-formula">O<sub>2</sub></span> concentrations (31–246 <span class="inline-formula">µ</span>mol L<span class="inline-formula"><sup>−1</sup></span>; i.e. 13 %–116 % <span class="inline-formula">O<sub>2</sub></span> saturation). The spatial and temporal variability of <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CH<sub>4</sub></span> concentrations (saturations) in the six rivers or estuaries was large and ranged from 2.0 nmol L<span class="inline-formula"><sup>−1</sup></span> (28 %) to 41.4 nmol L<span class="inline-formula"><sup>−1</sup></span> (570 %) and from 2.5 nmol L<span class="inline-formula"><sup>−1</sup></span> (106 %) to 1372 nmol L<span class="inline-formula"><sup>−1</sup></span> (57 459 %), respectively. We found no overall trends of <span class="inline-formula">N<sub>2</sub>O</span> with <span class="inline-formula">O<sub>2</sub></span> or <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M22" 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="23164037a5a41a281ec2bd2a6e11aeb2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4321-2019-ie00001.svg" width="25pt" height="16pt" src="bg-16-4321-2019-ie00001.png"/></svg:svg></span></span>, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</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="28c795146b952e4d8389bf50a28441ff"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4321-2019-ie00002.svg" width="25pt" height="16pt" src="bg-16-4321-2019-ie00002.png"/></svg:svg></span></span> or <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M24" 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="ae42caf6f031f0c6641dd1d09f6cb28c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4321-2019-ie00003.svg" width="24pt" height="15pt" src="bg-16-4321-2019-ie00003.png"/></svg:svg></span></span>, and there were no trends of <span class="inline-formula">CH<sub>4</sub></span> with <span class="inline-formula">O<sub>2</sub></span> or dissolved nutrients or DOC. <span class="inline-formula">N<sub>2</sub>O</span> concentrations showed a positive linear correlation with rainfall. We conclude, therefore, that rainfall is the main factor determining the riverine <span class="inline-formula">N<sub>2</sub>O</span> concentrations since <span class="inline-formula">N<sub>2</sub>O</span> production or consumption in the blackwater rivers themselves seems to be low because of the low pH. <span class="inline-formula">CH<sub>4</sub></span> concentrations were highest at salinity <span class="inline-formula">=</span> 0 and most probably result from methanogenesis as part of the decomposition of organic matter under anoxic conditions. <span class="inline-formula">CH<sub>4</sub></span> in the concentrations in the blackwater rivers showed an inverse relationship with rainfall. We suggest that <span class="inline-formula">CH<sub>4</sub></span> oxidation in combination with an enhanced river flow after the rainfall events might be responsible for the decrease in the <span class="inline-formula">CH<sub>4</sub></span> concentrations. The rivers and estuaries studied here were an overall net source of <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CH<sub>4</sub></span> to the atmosphere. The total annual <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CH<sub>4</sub></span> emissions were 1.09 Gg <span class="inline-formula">N<sub>2</sub>O</span> yr<span class="inline-formula"><sup>−1</sup></span> (0.7 Gg N yr<span class="inline-formula"><sup>−1</sup></span>) and 23.8 Gg <span class="inline-formula">CH<sub>4</sub></span> yr<span class="inline-formula"><sup>−1</sup></span>, respectively. This represents about 0.3 %–0.7 % of the global annual riverine and estuarine <span class="inline-formula">N<sub>2</sub>O</span> emissions and about 0.1 %–1 % of the global riverine and estuarine <span class="inline-formula">CH<sub>4</sub></span> emissions. Therefore, we conclude that rivers and estuaries in NW Borneo – despite the fact their water area covers only 0.05 % of the global river/estuarine area – contribute significantly to global riverine and estuarine emissions of <span class="inline-formula">N<sub>2</sub>O</span> and <span class="inline-formula">CH<sub>4</sub></span>.</p>https://www.biogeosciences.net/16/4321/2019/bg-16-4321-2019.pdf |
| spellingShingle | H. W. Bange C. H. Sim D. Bastian J. Kallert A. Kock A. Mujahid M. Müller Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern Borneo Biogeosciences |
| title | Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern Borneo |
| title_full | Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern Borneo |
| title_fullStr | Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern Borneo |
| title_full_unstemmed | Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern Borneo |
| title_short | Nitrous oxide (N<sub>2</sub>O) and methane (CH<sub>4</sub>) in rivers and estuaries of northwestern Borneo |
| title_sort | nitrous oxide n sub 2 sub o and methane ch sub 4 sub in rivers and estuaries of northwestern borneo |
| url | https://www.biogeosciences.net/16/4321/2019/bg-16-4321-2019.pdf |
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