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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-2019-385
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-385
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 14 Oct 2019

Submitted as: research article | 14 Oct 2019

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

The carbon footprint of a Malaysian tropical reservoir: measured versus modeled estimates highlight the underestimated key role of downstream processes

Cynthia Soued and Yves T. Prairie Cynthia Soued and Yves T. Prairie
  • Groupe de Recherche Interuniversitaire en Limnologie et en Environnement Aquatique (GRIL), Département des Sciences Biologiques, Université du Québec à Montréal, Montréal, H2X 3X8,Canada

Abstract. Reservoirs are important sources of greenhouse gases (GHG) to the atmosphere and their number is rapidly increasing, especially in tropical regions. Accurately predicting their current and future emissions is essential but hindered by fragmented data on the subject, which often fail to include all emission pathways (diffusion, ebullition, degassing, and downstream emissions) and the high spatial and temporal flux variability. Here we conducted a comprehensive sampling of Batang Ai reservoir (Malaysia), and compared field-based versus modeled estimates of its annual carbon footprint for each emission pathway. Carbon dioxide (CO2) and methane (CH4) diffusive fluxes were higher in upstream reaches. Reducing spatial and temporal sampling resolution resulted in up to 64 and 28 % change in flux estimate respectively. Most GHGs present in discharged water were degassed at the turbines, and the remainder were gradually emitted along the outflow river, leaving time for CH4 to be partly oxidized to CO2. Overall, the reservoir emitted 2639 g CO2 eq m−2 yr−1, with 90 % occurring downstream of the dam, mostly in the form of CH4. These emissions, largely underestimated by predictions, are mitigated by CH4 oxidation upstream and downstream of the dam, but could have been drastically reduced by slightly raising the water intake elevation depth. CO2 diffusion and CH4 ebullition were lower than predicted, whereas modeled CH4 diffusion was accurate. Investigating latter discrepancies, we conclude that exploring morphometry, soil type, and stratification patterns as predictors can improve modeling of reservoir GHG emissions at local and global scales.

Cynthia Soued and Yves T. Prairie
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Status: open (until 06 Dec 2019)
Status: open (until 06 Dec 2019)
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Cynthia Soued and Yves T. Prairie
Cynthia Soued and Yves T. Prairie
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Short summary
Freshwater reservoirs emit greenhouse gases (GHG) due to organic matter decay after landscape flooding. In order to better understand this phenomenon, we performed a comprehensive carbon footprint assessment of a tropical reservoir. Contrary to predictions, 90% of measured emissions occurred downstream of the dam. Comparing predicted versus measured emissions revealed weaknesses in our current modeling framework and insights to improve our ability to quantify and reduce reservoir GHG emissions.
Freshwater reservoirs emit greenhouse gases (GHG) due to organic matter decay after landscape...
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