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  • 1
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    Online Resource
    Gas Transport Parameters in the Vadose Zone: Gas Diffusivity in Field and Lysimeter Soil Profiles
    Wiley ; 2006
    In:  Vadose Zone Journal Vol. 5, No. 4 ( 2006-11), p. 1194-1204
    Details
    In: Vadose Zone Journal, Wiley, Vol. 5, No. 4 ( 2006-11), p. 1194-1204
    Abstract: The main soil‐gas transport parameters, gas diffusivity and air permeability, and their variations with soil type and air‐filled porosity play a key role in soil‐gas emission problems including volatilization of toxic chemicals at polluted sites and the production and emission of greenhouse gases. Only limited information on soil‐gas transport parameters across the vadose zone is available, especially for soil layers below the root zone. In a series of studies, we developed new data for the soil‐gas transport parameters in different soil profiles and tested existing and new predictive models. In this first study, we measured gas diffusivity at different soil‐water matric potentials on undisturbed soil samples for three lysimeter soil profiles down to 1.4‐m depth and for two field soil profiles down to 5.6‐m depth, representing a total of 22 different soil layers with soil texture ranging from sand to sandy clay loam. Five commonly used predictive gas diffusivity models were tested. The three‐porosity model (TPM) performed best for both shallow and deep soil layers. The tortuosity–connectivity parameter X in the TPM varied with soil texture and pore size distribution, and the TPM predicted well the depth distributions of measured soil‐gas diffusivities. The TPM also requires less detailed information on the soil‐water characteristic curve than other well‐performing predictive models, and is therefore recommended for predicting variations in soil‐gas diffusivity within the vadose zone.
    Type of Medium: Online Resource
    ISSN: 1539-1663 , 1539-1663
    URL: Article
    DOI: 10.2136/vzj2006.0014
    Language: English
    Publisher: Wiley
    Publication Date: 2006
    detail.hit.zdb_id: 2088189-7
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  • 2
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    Diffusion Aspects of Designing Porous Growth Media for Earth and Space
    Wiley ; 2012
    In:  Soil Science Society of America Journal Vol. 76, No. 5 ( 2012-09), p. 1564-1578
    Details
    In: Soil Science Society of America Journal, Wiley, Vol. 76, No. 5 ( 2012-09), p. 1564-1578
    Type of Medium: Online Resource
    ISSN: 0361-5995
    URL: Article
    DOI: 10.2136/sssaj2011.0438
    RVK:
    RA 4845
    Language: English
    Publisher: Wiley
    Publication Date: 2012
    detail.hit.zdb_id: 241415-6
    detail.hit.zdb_id: 2239747-4
    detail.hit.zdb_id: 196788-5
    detail.hit.zdb_id: 1481691-X
    SSG: 13
    SSG: 21
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  • 3
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    Gas Transport Parameters in the Vadose Zone: Development and Tests of Power‐Law Models for Air Permeability
    Wiley ; 2006
    In:  Vadose Zone Journal Vol. 5, No. 4 ( 2006-11), p. 1205-1215
    Details
    In: Vadose Zone Journal, Wiley, Vol. 5, No. 4 ( 2006-11), p. 1205-1215
    Abstract: The soil‐air permeability ( k a ) and its dependency on air‐filled porosity (ε) govern convective air and gas transport in soil. For example, accurate prediction of k a (ε) is a prerequisite for optimizing soil vapor extraction systems for cleanup of soils polluted with volatile organic chemicals. In this study, we measured k a at different soil‐water matric potentials down to 5.6‐m depth, totaling 25 differently textured soil layers. Comparing k a and soil‐gas diffusivity ( D p / D 0 ) measurements on the same soil samples suggested an analogy between how the two soil‐gas transport parameters depend on ε. The exponent in a power‐law model for k a (ε) was typically smaller than for D p (ε)/ D 0 , however, probably due to the influence of soil structure and large‐pore network being more pronounced for k a than for D p / D 0 In analogy to recent gas diffusivity models and in line with capillary tube models for unsaturated hydraulic conductivity, two power‐law k a (ε) models were suggested. One k a (ε) model is based on the Campbell pore‐size distribution parameter b and the other on the content of larger pores (ε 100 , corresponding to the air‐filled porosity at −100 cm H 2 O of soil‐water matric potential). Both new models require measured k a at −100 cm H 2 O ( k a,100 ) as a reference point to obtain reasonably accurate predictions. If k a,100 is not known, two expressions for predicting k a,100 from ε 100 were proposed but will cause at least one order of magnitude uncertainty in predicted k a The k a (ε) model based on only ε 100 performed well in the model tests and is recommended together with a similar model for gas diffusivity for predicting variations in soil‐gas transport parameters in the vadose zone.
    Type of Medium: Online Resource
    ISSN: 1539-1663 , 1539-1663
    URL: Article
    DOI: 10.2136/vzj2006.0030
    Language: English
    Publisher: Wiley
    Publication Date: 2006
    detail.hit.zdb_id: 2088189-7
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  • 4
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    PREDICTIVE-DESCRIPTIVE MODELS FOR GAS AND SOLUTE DIFFUSION COEFFICIENTS IN VARIABLY SATURATED POROUS MEDIA COUPLED TO PORE-SIZE DISTRIBUTION : I. GAS DIFFUSIVITY IN REPACKED SOIL
    Ovid Technologies (Wolters Kluwer Health) ; 2005
    In:  Soil Science Vol. 170, No. 11 ( 2005-11), p. 843-853
    Details
    In: Soil Science, Ovid Technologies (Wolters Kluwer Health), Vol. 170, No. 11 ( 2005-11), p. 843-853
    Type of Medium: Online Resource
    ISSN: 0038-075X
    URL: Article
    DOI: 10.1097/01.ss.0000196769.51788.73
    Language: English
    Publisher: Ovid Technologies (Wolters Kluwer Health)
    Publication Date: 2005
    detail.hit.zdb_id: 204569-2
    detail.hit.zdb_id: 2046289-X
    SSG: 13
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  • 5
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    RESPONSE TO THE LETTER TO THE EDITOR
    Ovid Technologies (Wolters Kluwer Health) ; 1995
    In:  Soil Science Vol. 160, No. 6 ( 1995-12), p. 444-448
    Details
    In: Soil Science, Ovid Technologies (Wolters Kluwer Health), Vol. 160, No. 6 ( 1995-12), p. 444-448
    Type of Medium: Online Resource
    ISSN: 0038-075X
    URL: Article
    DOI: 10.1097/00010694-199512000-00011
    Language: English
    Publisher: Ovid Technologies (Wolters Kluwer Health)
    Publication Date: 1995
    detail.hit.zdb_id: 204569-2
    detail.hit.zdb_id: 2046289-X
    SSG: 13
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  • 6
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    Online Resource
    Variable Pore Connectivity Factor Model for Gas Diffusivity in Unsaturated, Aggregated Soil
    Wiley ; 2008
    In:  Vadose Zone Journal Vol. 7, No. 2 ( 2008-05), p. 397-405
    Details
    In: Vadose Zone Journal, Wiley, Vol. 7, No. 2 ( 2008-05), p. 397-405
    Abstract: The soil gas diffusion coefficient ( D p ) and its variations with soil air content (ε) and soil water matric potential (ψ) control vadose zone transport and emissions of volatile organic chemicals and greenhouse gases. This study revisits the 1904 Buckingham power‐law model where D p is proportional to ε X , with X characterizing the tortuosity and connectivity of air‐filled pore space. One hundred years later, most models linking D p (ε) to soil water retention and pore size distribution still assume that the pore connectivity factor, X , is a constant for a given soil. We show that X varies strongly with both ε and matric potential [given as pF = log(−ψ, cm H 2 O)] for indivi dual soils ranging from undisturbed sand to aggregated volcanic ash soils (Andisols). For Andisols with bimodal pore size distribution, the X –pF function appears symmetrical. The minimum X value is typically around 2 and was observed close to ψ of −1000 cm H 2 O (pF 3) when interaggregate voids are drained. To link D p with bimodal pore size distribution, we coupled a two‐region van Genuchten soil water retention model with the Buckingham D p (ε) model, assuming X to vary symmetrically around a given pF. The coupled model well described D p as a function of both ε and ψ for both repacked and undisturbed Andisols and for other soil types. By merely using average values of the three constants in the proposed symmetrical X –pF expression, predictions of D p were better than with traditional models.
    Type of Medium: Online Resource
    ISSN: 1539-1663 , 1539-1663
    URL: Article
    DOI: 10.2136/vzj2007.0058
    Language: English
    Publisher: Wiley
    Publication Date: 2008
    detail.hit.zdb_id: 2088189-7
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  • 7
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    Comparison of Air and Water Permeability between Disturbed and Undisturbed Soils
    Wiley ; 2005
    In:  Soil Science Society of America Journal Vol. 69, No. 5 ( 2005-09), p. 1361-1371
    Details
    In: Soil Science Society of America Journal, Wiley, Vol. 69, No. 5 ( 2005-09), p. 1361-1371
    Abstract: Although soil structure and pore geometry characteristics largely control flow and transport processes in soils, there is a general lack of experiments that study the effects of soil structure and pore‐space characteristics on air and water permeability. Our objective was to determine the dependency of soil permeability on fluid content for both water and air, and compare results for both disturbed (D) and undisturbed (UD) soils. For that purpose, we first measured the water permeability ( k w ) and air permeability ( k a ) for several intact UD soil samples. Subsequently, the same samples were crushed and repacked into the same soil cores to create the D equivalent for the same soil material. Measurements showed large differences between D and UD samples, confirming the enormous impact of soil structure and pore‐space characteristics on flow. The permeability of both fluid phases (air and water) was greatly reduced for the D samples, especially for soil air permeability due to its greater dependency on soil aggregation and structure. Soil water retention and permeability data were fitted to Campbell's and Mualem's pore‐size distribution model, respectively. Regardless of soil disturbance, we showed that the tortuosity–connectivity parameter, l , for the water permeability ( l 1 ) and air permeability ( l 2 ) were different. This is in contrast to the general practice of using the same parameter value for both functions. The relation between l 1 and l 2 was largely controlled by soil structure and associated macroporosity properties.
    Type of Medium: Online Resource
    ISSN: 0361-5995 , 1435-0661
    URL: Article
    DOI: 10.2136/sssaj2004.0332
    RVK:
    RA 4845
    Language: English
    Publisher: Wiley
    Publication Date: 2005
    detail.hit.zdb_id: 241415-6
    detail.hit.zdb_id: 2239747-4
    detail.hit.zdb_id: 196788-5
    detail.hit.zdb_id: 1481691-X
    SSG: 13
    SSG: 21
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  • 8
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    Online Resource
    Unified Measurement System for the Gas Dispersion Coefficient, Air Permeability, and Gas Diffusion Coefficient in Variably Saturated Soil
    Wiley ; 2009
    In:  Soil Science Society of America Journal Vol. 73, No. 6 ( 2009-11), p. 1921-1930
    Details
    In: Soil Science Society of America Journal, Wiley, Vol. 73, No. 6 ( 2009-11), p. 1921-1930
    Abstract: The transport of gaseous compounds in soil takes place by gas diffusion, advection, and dispersion. Gas transport processes are influenced by the soil‐gas diffusion coefficient ( D p ), air permeability ( k a ) and soil‐gas dispersion coefficient ( D H ), respectively. Of three gas transport parameters, D H is the least understood, especially how it is correlated to soil type, moisture conditions, and other transport parameters (i.e., D p and k a ). In this study, a unified measurement system (UMS) that enables sequential measurement of D p , k a , and D H on the same soil core was developed. The experimental sequence is based on a two‐chamber measurement of D H and k a , followed by a one‐chamber measurement of D p Gaseous oxygen concentration and air pressure sensors are located in inlet and outlet chambers as well as at multiple points along the soil column. Using different particle‐size fractions of non‐aggregated (Toyoura sand) and aggregated (Nishi‐Tokyo loam) soils, the effects of soil structure, particle (aggregate) size, and column scale (5‐cm i.d. and 30‐cm or 60‐cm length) on the three gas transport parameters were investigated. For both soils, D H linearly increased with increasing pore‐air velocity. For Toyoura sand, gas dispersivity (λ = D H / u 0 ) decreased with increasing soil‐air content, while for Nishi‐Tokyo loam, gas dispersivity decreased with increasing soil‐air content to a minimum value when inter‐aggregate pores were drained and increased again when the pores inside the soil aggregates started to act as tortuous air‐filled pathways. In the arterial pore region (corresponding to the total pore volume for Narita sand and the inter‐aggregate pore volume for Nishi‐Tokyo loam), a linear relation between tortuosity of the air‐filled pore network ( T , calculated from D p ) and the gas dispersivity (λ) was observed.
    Type of Medium: Online Resource
    ISSN: 0361-5995 , 1435-0661
    URL: Article
    DOI: 10.2136/sssaj2009.0012
    RVK:
    RA 4845
    Language: English
    Publisher: Wiley
    Publication Date: 2009
    detail.hit.zdb_id: 241415-6
    detail.hit.zdb_id: 2239747-4
    detail.hit.zdb_id: 196788-5
    detail.hit.zdb_id: 1481691-X
    SSG: 13
    SSG: 21
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  • 9
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    Online Resource
    Hierarchical, Bimodal Model for Gas Diffusivity in Aggregated, Unsaturated Soils
    Wiley ; 2010
    In:  Soil Science Society of America Journal Vol. 74, No. 2 ( 2010-03), p. 481-491
    Details
    In: Soil Science Society of America Journal, Wiley, Vol. 74, No. 2 ( 2010-03), p. 481-491
    Abstract: The soil gas diffusion coefficient ( D p ) and its dependency on soil air content, ε, and tortuosity–connectivity of the air‐filled pore networks control the transport and fate of gaseous‐phase contaminants in variably saturated soil. The bimodality in pore size distribution of structured soil often yields a variation of D p with ε in the intraaggregate pore region that is distinctly different from that in the interaggregate region. Data imply a highly nonlinear behavior of soil gas diffusivity, D p (ε)/ D o (where D o is the gas diffusion coefficient in free air), in the interaggregate region of aggregated soils similar to that of structureless soils with a unimodal pore size distribution, probably due to diffusion‐limiting effects by connected water films at low ε. In contrast, for the intraaggregate region, we show that the impedance factor F * (= D p /ε D o ) and tortuosity factor T [= (1/ F *) 1/2 ] are approximately constant for most soil media. We suggest a typically well‐defined separation between the two pore regions at the minimum for the pore connectivity factor X * [= log( D p / D o )/log(ε)], at which point the interaggregate pores are devoid of water while the intraaggregate pore region is water saturated. Based on this, a hierarchical two independent region (TIR) D p / D o model was developed by applying a cumulative series of Buckingham–Currie power‐law functions, F ε X A nonlinear, water‐content‐dependent expression for F best described the measured D p / D o in the interaggregate region, while constant F (around 0.5) and X (around 1) generally sufficed for the intraaggregate region. The TIR model better predicted gas diffusivities for both aggregate fractions and highly structured soils across the entire range of moisture conditions with RMSE reduced by two to five times compared with traditional predictive D p (ε)/ D o models.
    Type of Medium: Online Resource
    ISSN: 0361-5995 , 1435-0661
    URL: Article
    DOI: 10.2136/sssaj2009.0055
    RVK:
    RA 4845
    Language: English
    Publisher: Wiley
    Publication Date: 2010
    detail.hit.zdb_id: 241415-6
    detail.hit.zdb_id: 2239747-4
    detail.hit.zdb_id: 196788-5
    detail.hit.zdb_id: 1481691-X
    SSG: 13
    SSG: 21
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  • 10
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    Online Resource
    Three‐Porosity Model for Predicting the Gas Diffusion Coefficient in Undisturbed Soil
    Wiley ; 2004
    In:  Soil Science Society of America Journal Vol. 68, No. 3 ( 2004-05), p. 750-759
    Details
    In: Soil Science Society of America Journal, Wiley, Vol. 68, No. 3 ( 2004-05), p. 750-759
    Abstract: The soil gas diffusion coefficient ( D P ) and its dependency on air‐filled porosity (ε) govern most gas diffusion‐reaction processes in soil. Accurate D P (ε) prediction models for undisturbed soils are needed in vadose zone transport and fate models. The objective of this paper was to develop a D P (ε) model with lower input parameter requirement and similar prediction accuracy as recent soil‐type dependent models. Combining three gas diffusivity models: (i) a general power‐law D P (ε) model, (ii) the classical Buckingham (1904) model for D P at air saturation, and (iii) a recent macroporosity dependent model for D P at −100 cm H 2 O of soil–water matric potential (ψ), yielded a single equation to predict D P as a function of the actual ε, the total porosity (Φ), and the macroporosity (ε 100 ; defined as the air‐filled porosity at ψ = −100 cm H 2 O). The new model, termed the three‐porosity model (TPM), requires only one point (at −100 cm H 2 O) on the soil–water characteristic curve (SWC), compared with recent D P (ε) models that require knowledge of the entire SWC. The D P (ε) was measured at different ψ on undisturbed soil samples from dark‐red Latosols (Brazil) and Yellow soils (Japan), representing different tillage intensities. The TPM and five other D P (ε) models were tested against the new data (17 soils) and data from the literature for additional 43 undisturbed soils. The new TPM performed equally well (root mean square error [RMSE] in relative gas diffusivity 〈 0.027) as recent SWC‐dependent D P (ε) models and better than typically used soil type independent models.
    Type of Medium: Online Resource
    ISSN: 0361-5995 , 1435-0661
    URL: Article
    DOI: 10.2136/sssaj2004.7500
    RVK:
    RA 4845
    Language: English
    Publisher: Wiley
    Publication Date: 2004
    detail.hit.zdb_id: 241415-6
    detail.hit.zdb_id: 2239747-4
    detail.hit.zdb_id: 196788-5
    detail.hit.zdb_id: 1481691-X
    SSG: 13
    SSG: 21
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