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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-222
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-222
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 11 Jun 2019

Submitted as: research article | 11 Jun 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Nitrous oxide (N2O) and methane (CH4) in rivers and estuaries of northwestern Borneo

Hermann W. Bange1, Chun Hock Sim2, Daniel Bastian1, Jennifer Kallert1, Annette Kock1, Aazani Mujahid3, and Moritz Müller2 Hermann W. Bange et al.
  • 1GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 2Swinburne University of Technology, Faculty of Engineering, Computing and Science, Kuching, Sarawak, Malaysia
  • 3Department of Aquatic Science, Faculty of Resource Science & Technology, University Malaysia Sarawak, Kota Samarahan, Sarawak, Malaysia

Abstract. Nitrous oxide (N2O) and methane (CH4) are atmospheric trace gases which play important roles of 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 N2O and CH4 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 Samusam and Sematan Rivers were additionally sampled in March 2017. The Maludam, Sebuyau, and Simunjan Rivers are typical "blackwater" rivers with very low pH, very high dissolved organic carbon (DOC) concentrations and very low O2 concentrations. The spatial and temporal variability of N2O and CH4 concentrations (saturations) in the six rivers/estuaries was large and ranged from 2.0 nmol L−1 (28 %) to 41.4 nmol L−1 (570 %) and from 2.5 nmol L−1 (106 %) to 1372 nmol L−1 (57,459 %), respectively. We found no overall trends of N2O with O2 or NO3, NO2, NH4+ and there were no trends of CH4 with O2 or dissolved nutrients or DOC. N2O concentrations showed a positive linear correlation with rainfall. We conclude, therefore, that rainfall is the main factor determining the riverine N2O concentrations since N2O production/consumption in the "blackwater" rivers themselves seems to be unlikely because of the low pH. In contrast CH4 concentrations showed an inverse relationship with rainfall. CH4 concentrations were highest at salinity = 0 and most probably result from methanogenesis as part of the decomposition of organic matter under anoxic conditions. We speculate that CH4 oxidation, which can be high when the water discharge is high (e.g. after rainfall events), is responsible for the decrease of the CH4 concentrations along the salinity gradients. The rivers and estuaries studied here were an overall net source of N2O and CH4 to the atmosphere. The total annual N2O and CH4 emissions were 1.09 Gg N2O yr-1 (0.7 Gg N yr-1) and 23.8 Gg CH4 yr-1, respectively. This represents about 0.3–0.7 % of the global annual riverine and estuarine N2O emissions and about 0.1–1 % of the global riverine and estuarine CH4 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 N2O and CH4.

Hermann W. Bange et al.
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Status: final response (author comments only)
Status: final response (author comments only)
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Hermann W. Bange et al.
Hermann W. Bange et al.
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Short summary
Nitrous oxide (N2O) and methane (CH4) are atmospheric trace gases which play important roles of the climate and atmospheric chemistry of the Earth. However, little is known about their emissions from rivers and estuaries. To this end concentrations of N2O/CH4 were measured duirng a seasonal study in six rivers and estuaries in northwestern Borneo. The concentrations of both gases were mainly driven rainfall events. The rivers and estuaries were an overall net ource of atmospheric N2O/CH4.
Nitrous oxide (N2O) and methane (CH4) are atmospheric trace gases which play important roles of...
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