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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-2020-5
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-5
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 31 Jan 2020

Submitted as: research article | 31 Jan 2020

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This preprint is currently under review for the journal BG.

Mineralization of organic matter in boreal lake sediments: Rates, pathways and nature of the fermenting substrates

François Clayer1,3, Yves Gélinas2,3, André Tessier1, and Charles Gobeil1,3 François Clayer et al.
  • 1INRS-ETE, Université du Québec, 490 rue de la Couronne, Québec (QC), Canada G1K 9A9
  • 2Concordia University, Department of Chemistry and Biochemistry, 7141 Sherbrooke Street West, Montreal (QC), Canada H4B 1R6
  • 3Geotop, Interuniversity research and training centre in geosciences, 201 Président-Kennedy Ave., Montréal (QC), Canada H2X 3Y7

Abstract. The complexity of organic matter (OM) degradation mechanisms represents a significant challenge for developing biogeochemical models to quantify the role of aquatic sediments in the climate system. The common representation of OM by carbohydrates formulated as CH2O in models comes with the assumption that its degradation by fermentation produces equimolar amounts of methane (CH4) and dissolved inorganic carbon (DIC). To test the validity of this assumption, we modeled using reaction-transport equations vertical profiles of the concentration and isotopic composition (δ13C) of CH4 and DIC in the top 25 cm of the sediment column from two lake basins, one whose hypolimnion is perennially oxygenated and one with seasonal anoxia. Our results reveal that methanogenesis only occurs via hydrogenotrophy in both basins. Furthermore, we calculate, from CH4 and DIC production rates associated with methanogenesis, that the fermenting OM has an average carbon oxidation state (COS) below −0.9. Modeling solute porewater profiles reported in the literature for four other seasonally anoxic lake basins also yields negative COS values. Collectively, the mean (±SD) COS value of −1.4 ± 0.3 for all the seasonally anoxic sites is much lower than the value of zero expected from carbohydrates fermentation. We conclude that carbohydrates do not adequately represent the fermenting OM and that the COS should be included in the formulation of OM fermentation in models applied to lake sediments. This study highlights the need to better characterize the labile OM undergoing mineralization to interpret present-day greenhouse gases cycling and predict its alteration under environmental changes.

François Clayer et al.

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François Clayer et al.

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Latest update: 25 Feb 2020
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Short summary
In this study, we quantified the production of methane and carbon dioxide in lake sediments to better characterize the nature of the organic matter at the origin of these two greenhouse gases. We demonstrate that the current representation of this greenhouse gas production in models is not adequate for the six studied lake basins. We finally propose to improve the representation of organic matter degradation reactions in current models for predicting greenhouse gas cycling in aquatic sediments.
In this study, we quantified the production of methane and carbon dioxide in lake sediments to...
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