Structure‐Dependent Water‐Induced Linear Reduction Model for Predicting Gas Diffusivity and Tortuosity in Repacked and Intact Soil

Møldrup, Per; Deepagoda, T.K.K. Chamindu; Hamamoto, Shoichiro; Komatsu, Toshiko; Kawamoto, Ken; Rolston, Dennis E.; Jonge, Lis Wollesen de

doi:10.2136/vzj2013.01.0026

Cited by 96 publications

(74 citation statements)

References 37 publications

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“…Our exponential model relating effective CH 4 diffusivity to soil water content is mathematically equivalent to an exponential fit of diffusivity to air-filled pore space (Richter et al, 1991) when total porosity is treated as a constant. Our model results were in good agreement with other commonly used physical models of soil gas diffusion for total porosities near 0.6 (Buckingham, 1904;Ghanbarian and Hunt, 2014;Møldrup et al, 2014) and incorporate site-to-site variability due to local VWC. We calculated cumulative seasonal CH 4 flux (F CH 4 ) for each site by summing the linearly interpolated daily fluxes (29 May-12 September).…”

Section: Soil Gas Measurements and Flux Calculationssupporting

confidence: 83%

Landscape analysis of soil methane flux across complex terrain

2018

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Abstract. Relationships between methane (CH 4 ) fluxes and environmental conditions have been extensively explored in saturated soils, while research has been less prevalent in aerated soils because of the relatively small magnitudes of CH 4 fluxes that occur in dry soils. Our study builds on previous carbon cycle research at Tenderfoot Creek Experimental Forest, Montana, to identify how environmental conditions reflected by topographic metrics can be leveraged to estimate watershed scale CH 4 fluxes from point scale measurements. Here, we measured soil CH 4 concentrations and fluxes across a range of landscape positions (7 riparian, 25 upland), utilizing topographic and seasonal (29 May-12 September) gradients to examine the relationships between environmental variables, hydrologic dynamics, and CH 4 emission and uptake. Riparian areas emitted small fluxes of CH 4 throughout the study (median: 0.186 µg CH 4 -C m −2 h −1 ) and uplands increased in sink strength with dry-down of the watershed (median: −22.9 µg CH 4 -C m −2 h −1 ). Locations with volumetric water content (VWC) below 38 % were methane sinks, and uptake increased with decreasing VWC. Above 43 % VWC, net CH 4 efflux occurred, and at intermediate VWC net fluxes were near zero. Riparian sites had nearneutral cumulative seasonal flux, and cumulative uptake of CH 4 in the uplands was significantly related to topographic indices. These relationships were used to model the net seasonal CH 4 flux of the upper Stringer Creek watershed (−1.75 kg CH 4 -C ha −1 ). This spatially distributed estimate was 111 % larger than that obtained by simply extrapolating the mean CH 4 flux to the entire watershed area. Our results highlight the importance of quantifying the space-time variability of net CH 4 fluxes as predicted by the frequency distribution of landscape positions when assessing watershed scale greenhouse gas balances.

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Section: Soil Gas Measurements and Flux Calculationssupporting

confidence: 83%

Landscape analysis of soil methane flux across complex terrain

2018

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“…Our 15 exponential model relating effective CH4 diffusivity to soil water content is mathematically equivalent to an exponential fit of diffusivity to air-filled pore space (Richter et al, 1991) when total porosity is treated as a constant. Our model results were in good agreement with other commonly used physical models of soil gas diffusion for total porosities near 0.6 (Buckingham, 1904;Ghanbarian and Hunt, 2014;Møldrup et al, 2014), and incorporate site to site variability due to local VWC. We calculated cumulative seasonal CH4 flux (FCH4) for each site (May 29 th -September 12 th ) by summing the linearly interpolated 20 daily fluxes.…”

Section: Soil Gas Measurements and Flux Calculationssupporting

confidence: 83%

Landscape analysis of soil methane flux across complex terrain

Kaiser¹,

McGlynn²,

Dore³

2018

Preprint

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“…The soil structure factor (G soil ) accounts for the effects of pore size, connectivity and tortuosity on gaseous diffusion and is determined according to the parameterization of Moldrup et al (1996Moldrup et al ( , 2013:…”

Section: Soil Ch 4 Diffusivity D Chmentioning

confidence: 99%

Soil Methanotrophy Model (MeMo v1.0): a process-based model to quantify global uptake of atmospheric methane by soil

et al. 2018

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Abstract. Soil bacteria known as methanotrophs are the sole biological sink for atmospheric methane (CH 4 ), a potent greenhouse gas that is responsible for ∼ 20 % of the humandriven increase in radiative forcing since pre-industrial times. Soil methanotrophy is controlled by a plethora of factors, including temperature, soil texture, moisture and 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 CH 4 by soils at 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, (3) updated factors governing the influence of soil moisture and temperature on CH 4 oxidation rates and (4) the ability to evaluate the impact of autochthonous soil CH 4 sources on uptake of atmospheric CH 4 . We show that the improved structural and parametric representation of key drivers of soil methanotrophy in MeMo results 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 33.5 ± 0.6 Tg CH 4 yr −1 . Warm and semi-arid regions (tropical deciduous forest and open shrubland) had the highest CH 4 uptake rates of 602 and 518 mg CH 4 m −2 yr −1 , respectively. In these regions, favourable annual soil moisture content (∼ 20 % saturation) and low seasonal temperature variations (variations < ∼ 6 • C) 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 formulation of the influence of excess soil moisture on methanotrophy. Tundra and mixed forest had the lowest simulated CH 4 uptake rates of 176 and 182 mg CH 4 m −2 yr −1 , respectively, due to their marked seasonality driven by temperature. Global soil uptake of atmospheric CH 4 was decreased by 4 % by the effect of nitrogen inputs to the system; however, the direct addition of fertilizers attenuated the flux by 72 % in regions with high agricultural intensity (i.e. China, India and Europe) and by 4-10 % in agriculture areas receiving low rates of N input (e.g. South America). Globally, nitrogen inputs reduced soil uptake of atmospheric CH 4 by 1.38 Tg yr −1 , which is 2-5 times smaller than reported previously. In addition to improved characterization of the contemporary soil sink for atmospheric CH 4 , MeMo provides an opportunity to quantify more accurately the relative importance of soil methanotrophy in the global CH 4 cycle in the past and its capaci...

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Structure‐Dependent Water‐Induced Linear Reduction Model for Predicting Gas Diffusivity and Tortuosity in Repacked and Intact Soil

Cited by 96 publications

References 37 publications

Landscape analysis of soil methane flux across complex terrain

Landscape analysis of soil methane flux across complex terrain

Landscape analysis of soil methane flux across complex terrain

Soil Methanotrophy Model (MeMo v1.0): a process-based model to quantify global uptake of atmospheric methane by soil

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