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Observations et modélisation in-situ du carbone des sols boréaux et des émissions de méthane associées

Abstract : The methane is one of the most powerful greenhouse gases in the atmosphere, with the carbon dioxyde and the water vapour. At the global scale, most of natural methane emissions come from high latitude wetlands and permafrosts. These regions accounts for a large part of terrestrial carbon stocks. In a climate change context, their future is highly uncertain, like the associated greenhouse gas emissions. Understanding the biogoechemical processes leading to methane fluxes and their interactions with surface processes is therefore important. One of the objectives of this thesis is to represent methane fluxes from these regions within the land surface model ISBA. To do so, we developped a biogeochemical model that represents explicitely gases, their production, consumption and transport within the soil column. This model is coupled with a new dynamic soil carbon model, vertically discretized, also developed during this thesis. The new biogeochemical model represents correctly methane and carbon dioxyde fluxes on three distinct arctic sites, with or without permafrost. The representation of underground biogeochemical processes is also satisfying. Nevertheless, some parameters remain uncertain and the model is very sensitive to hydrological conditions. We also measured soil carbon stocks and profiles in one of the Greenlandic studied fen. Comparing these stocks and profiles with the modelled carbon stocks shows some shortcomings of the new discretized soil carbon model : CENTURY original structure and parametrisation is not perfectly suited for high-latitudes wetlands, and the representation of carbon vertical dynamics needs improvements.
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Xavier Morel. Observations et modélisation in-situ du carbone des sols boréaux et des émissions de méthane associées. Interfaces continentales, environnement. Université Paul Sabatier - Toulouse III, 2018. Français. ⟨NNT : 2018TOU30347⟩. ⟨tel-02484763⟩

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