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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/gmd-2017-124
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Model description paper
30 May 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Geoscientific Model Development (GMD).
Soil Methanotrophy Model (MeMo v1.0): a process-based model to quantify global uptake of atmospheric methane by soil
Fabiola Murguia-Flores1, Sandra Arndt1,a, Anita L. Ganesan1, Guillermo N. Murray-Tortarolo2,b, and Edward R. C. Hornibrook3,c 1School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, UK
2University of Exeter, Devon, EX4, UK
3School of Earth Sciences, University of Bristol, Bristol, BS8 1RJ. UK
acurrent address: Department of Geosciences, Environment and Society, Université Libre de Bruxelles, Brussels, Belgium
bcurrent address: Instituto de Investigaciones en Ecosistemas y Sustentabilidad (IIES), UNAM
ccurrent address: Earth, Environmental and Geographic Sciences, The University of British Columbia, Okanagan Campus, Kelowna, BC, Canada V4V 1C7
Abstract. Soil bacteria known as methanotrophs are the sole biological sink for atmospheric methane (CH4), a powerful greenhouse gas that is responsible for ~ 20 % of the human-driven increase in radiative forcing since pre-industrial times. Soil methanotrophy is controlled by a plethora of different factors, including temperature, soil texture and moisture or nitrogen content, resulting in spatially and temporally heterogeneous rates of soil methanotrophy. As a consequence, the exact magnitude of the global soil sink, as well as its temporal and spatial variability remains poorly constrained. We developed a process-based model (Methanotrophy Model; MeMo v1.0) to simulate and quantify the uptake of atmospheric CH4 by soils on the global scale. MeMo builds on previous models by Ridgwell et al. (1999) and Curry (2007) by introducing several advances, including: (1) a general analytical solution of the one-dimensional diffusion-reaction equation in porous media, (2) a refined representation of nitrogen inhibition on soil methanotrophy, and (3) updated factors governing the influence of soil moisture and temperature on CH4 oxidation rates. We show that the improved representation of these key drivers of soil methanotrophy resulted in a better fit to observational data. A global simulation of soil methanotrophy for the period 1990–2009 using MeMo yielded an average annual sink of 34.3 ± 4.3 Tg CH4 yr−1. Warm and semiarid regions (tropical deciduous forest, dense and open shrubland) had the highest CH4 uptake rates of 630 and 580 mg CH4 m−2 y−1, respectively. In these regions, favorable annual soil moisture content (~ 20 % saturation) and low seasonal temperature variations (variations < ~ 6 ºC) provided optimal conditions for soil methanotrophy and soil-atmosphere gas exchange. In contrast to previous model analyses, but in agreement with recent observational data, MeMo predicted low fluxes in wet tropical regions because of refinements in describing the influence of excess soil moisture on methanotrophy. Tundra and boreal forest had the lowest simulated CH4 uptake rates of 179 and 187 mg CH4 m−2 y−1, respectively, due to their marked seasonality driven by temperature. Soil uptake of atmospheric CH4 was attenuated by up to 10 % in regions receiving high rates of nitrogen deposition. Globally, nitrogen deposition reduced soil uptake of atmospheric CH4 by 0.34 Tg y−1, which is an order of magnitude lower than reported previously. In addition to improved characterisation of the contemporary soil sink for atmospheric CH4, MeMo provides an opportunity to quantify more accurately the relative importance of soil methanotrophy in the global CH4 cycle in the past and its capacity to contribute to reduction of atmospheric CH4 levels under future global change scenarios.

Citation: Murguia-Flores, F., Arndt, S., Ganesan, A. L., Murray-Tortarolo, G. N., and Hornibrook, E. R. C.: Soil Methanotrophy Model (MeMo v1.0): a process-based model to quantify global uptake of atmospheric methane by soil, Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2017-124, in review, 2017.
Fabiola Murguia-Flores et al.
Fabiola Murguia-Flores et al.
Fabiola Murguia-Flores et al.

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Short summary
Soil bacteria known as methanotrophs are the only biological sink for atmospheric methane (CH4). Their activity depends on climatic and edaphic conditions, thus varies spatially and temporarily. Based on this, we developed a model (MeMo v1.0) to assess the global CH4 consumption by soils.The global CH4 uptake was 34.3 Tg CH4 yr−1 for the period 1990–2009, with an increasing trend of 0.1 Tg CH4 yr−2. The regional analysis proved that warm and semiarid regions represent the most efficient CH4 sink.
Soil bacteria known as methanotrophs are the only biological sink for atmospheric methane (CH4)....
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