Characterization of diffusivity‐based oxygen transport in Arctic organic soil

Soil Science Soc of Amer J

Jayarathne

Clough

et al. 2019

Grazed pastures are recognized as a dominant source of nitrous oxide (N2O), a highly potent greenhouse gas. Studies have examined soil physical controls on N2O emissions, including soil moisture status. Limited attempts to link N2O emissions with soil‐diffusivity (Dp/Do), using repacked soil cores, have shown peak N2O emissions to align with a relatively narrow window of Dp/Do, despite a relatively wide range in water‐filled pore space (WFPS), across a range of soil bulk densities. Such detailed studies have not been performed with intact soil cores. We investigated the effects of soil‐water characteristic (SWC) and Dp/Do on N2O emissions from intact soil samples, retrieved at three depths (0–5, 5–10, 10–15 cm) from three perennial pasture sites that received a KNO3 solution (1800 mg, N mL−1). We observed distinct fingerprints of SWC and Dp/Do, which showed clear effects of soil structure on diffusion‐controlled gas emissions. Depth‐wise variation in soil moisture diminished as the soil was subjected to higher matric potential (> ∼ ‐100 kPa). Variation in Dp/Do, was more pronounced in the dry soil (> ∼ ‐1000 kPa), being largely constrained by soil moisture in wet soil (∼ ‐100 kPa) with little depth‐wise variation. Measured N2O fluxes peaked within narrow ranges of WFPS and Dp/Do, 0.90–0.95 and 0.005–0.01, respectively. The value of Dp/Do can be determined using parametric models and presents a pasture management (e.g., irrigation, soil physical disturbance such as pasture renovation and animal treading)) tool to minimize N2O emissions: soil Dp/Do should be maintained above a range of 0.005–0.01 to minimize N2O emissions. Core Ideas Peak N2O fluxes from intact soil cores occurred when diffusivity ranged from 0.005–0.01 This peak N2O flux diffusivity range was 0.005–0.01 regardless of soil or depth (0–15 cm) The diffusivity range for peak N2O flux equalled that observed in repacked soil cores Diffusivity values are readily determined and add to the suite of soil management tools

Section: Resultssupporting

confidence: 81%

Section: Soil-gas Diffusivity (D P /D O ) and Gaseous Phase Tortuositysupporting

confidence: 71%

Soil‐Gas Diffusivity and Soil‐Moisture effects on N₂O Emissions from Intact Pasture Soils

Soil Science Soc of Amer J

Jayarathne

Clough

et al. 2019

“…and 10-cm height), embedded and glued into a 10-mm-thick plastic bottom plate. A 5-cm-diameter rubber O-ring was inserted into an engraved slot at the top edge of the tube to facilitate sample positioning while ensuring an air-tight joint (Chamindu Deepagoda and Elberling, 2015). A galvanic cell type O 2 sensor (KE-25, Figaro Inc.) was outfitted at the mid-height of the cell wall for O 2 measurements.…”

Section: Methodsmentioning

confidence: 99%

Characterization of Thermal, Hydraulic, and Gas Diffusion Properties in Variably Saturated Sand Grades

Smits

Ramirez

et al. 2016

Vadose Zone Journal

Core Ideas This study provides physical, hydraulic, and thermal properties of five sand grades. An extended three‐region thermal conductivity model is proposed. A gas diffusivity‐based variable tortuosity parameter is examined. Useful parametric functions and descriptive models were tested. Detailed characterization of partially saturated porous media is important for understanding and predicting vadose zone transport processes. While basic properties (e.g., particle‐ and pore‐size distributions and soil‐water retention) are, in general, essential prerequisites for characterizing most porous media transport properties, key transport parameters such as thermal conductivity and gas diffusivity are particularly important to describe temperature‐induced heat transport and diffusion‐controlled gas transport processes, respectively. Despite many experimental and numerical studies focusing on a specific porous media characteristic, a single study presenting a wide range of important characteristics, together with the best‐performing functional relationships, can seldom be found. This study characterized five differently textured sand grades (Accusand no. 12/20, 20/30, 30/40, 40/50, and 50/70) in relation to physical properties, water retention, hydraulic conductivity, thermal conductivity, and gas diffusivity. We used measured basic properties and transport data to accurately parameterize the characteristic functions (particle‐ and pore‐size distributions and water retention) and descriptive transport models (thermal conductivity, saturated hydraulic conductivity, and gas diffusivity). An existing thermal conductivity model was improved to describe the distinct three‐region behavior in observed thermal conductivity–water saturation relations. Applying widely used parametric models for saturated hydraulic conductivity and soil‐gas diffusivity, we characterized porous media tortuosity in relation to grain size. Strong relations among average particle diameter, characteristic pore diameter from soil‐water retention measurements, and saturated hydraulic conductivity were found. Thus, the results of this work are useful toward better describing, linking, and predicting mass transfer and pore network properties in variably saturated porous media.

“…We used a one-chamber diffusion apparatus to measure the diffusion coefficient (Currie, 1960). An air-tight chamber made with a 10-mm thick PVC tube was used as the diffusion apparatus (Chamindu Deepagoda et al, 2015). All three size fractions were packed in 100-cm 3 annular cores by keeping the packing energy constant.…”

Section: Soil-gas Diffusivity (D P /D 0 )mentioning

confidence: 99%

Effects of “soil‐like” particle size on gas transport and water retention properties in aged municipal solid waste from a Sri Lankan open dumpsite

Shanujah

Soil Science Soc of Amer J

Karunarathna

et al. 2020

Open dumps constitute a major source of greenhouse gases (GHGs), predominantly methane and carbon dioxide, in developing countries. In an aged dump, typical waste composition is dominated by the “soil‐like” fraction of which physical, hydraulic and gas transport characteristics markedly affect GHG emissions. This study characterized soil‐gas diffusivity (Dp/D0), soil‐water characteristics (SWC), and particle size distribution in “soil‐like” fractions of aged solid waste retrieved at 2.5–5 m depth from an old open dumpsite situated at Kurunegala, Sri Lanka. The “soil‐like” fraction was proportioned into three groups based on particle size (0–4.75, 4.75–9.5, and 9.5–25 mm) to investigate the particle size effect on Dp/D0 and SWC. The simulated methane concentration profiles in different size groups were also examined using the transport simulator TOUGH2‐EOS7CA based on the multiphase flow of multicomponent gas mixture (methane, water vapour and air) under dry and half‐saturation conditions across a predefined temperature gradient. The results highlighted distinct two‐region characteristics (i.e., inter‐aggregate and intra‐aggregate pore regions) in all three size fractions which could be adequately parameterized with existing and modified bimodal functions. We proposed a useful practical tool for estimating Dp/D0 for known mean particle size and volumetric water content in the absence of direct measurements. The results further revealed that Dp/D0 is particle‐size dependent; however, Dp/D0 remained invariant across all size fractions at the volumetric water content of ∼0.22–0.25 cm3 cm−3. Numerical results further showed a pronounced effect of particle size and soil moisture on gas transport properties.