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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-2020-258
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-258
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  14 Sep 2020

14 Sep 2020

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This preprint is currently under review for the journal BG.

Sources and processes sustaining surface CO2 and CH4 fluxes in a tropical reservoir: the importance of water column metabolism

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. Freshwaters are important emitters of carbon dioxide (CO2) and methane (CH4) to the atmosphere, two potent greenhouse gases (GHG). While aquatic surface GHG fluxes have been extensively measured, there is much less information about their underlying sources. In lakes and reservoirs, surface GHG can originate from horizontal riverine flow, the hypolimnion, littoral sediments, and water column metabolism. These processes are generally studied separately, leading to a fragmented assessment of their relative role in sustaining CO2 and CH4 surface fluxes. In this study, we quantified sources/sinks of CO2 and CH4 in the epilimnion along a hydrological continuum in a permanently stratified tropical reservoir (Borneo Island). Results showed that horizontal inputs are an important source of both CO2 and CH4 (18 to 100 % of surface emissions) in the upstream reservoir branches. However, this contribution fades along the hydrological continuum, becoming negligible in the main basin of the reservoir, where CO2 and CH4 are uncoupled and driven by different processes. In the main basin, vertical CO2 inputs and sediment CH4 inputs contributed to on average 60 and 23 % respectively to the surface fluxes of the corresponding gas. Water column metabolism exhibited wide amplitude and range for both gases, making it the most influential but uncertain component in the epilimnetic gas budgets. Overall our results show that while sources sustaining surface CO2 and CH4 fluxes vary spatially and between the two gases, internal water metabolism remains a dominant driver. However, this study also highlights challenges and knowledge gaps related to estimating ecosystem-scale CO2 and CH4 metabolism, which hinder aquatic GHG flux predictions.

Cynthia Soued and Yves T. Prairie

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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 (CO2 and CH4) to the atmosphere, however, the sources underlying these emissions are numerous and their magnitude is not well known. This study quantifies surface CO2 and CH4 emissions and all their potential sources in a tropical reservoir. Findings show that emissions are mostly influenced by internal metabolic processes rather than external inputs. However, results highlight the challenges and uncertainties related to estimating internal metabolism.
Freshwater reservoirs emit greenhouse gases (CO2 and CH4) to the atmosphere, however, the...
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