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  • 1
    Online Resource
    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
    Online Resource
    Online Resource
    Field Application of a Portable Air Permeameter to Characterize Spatial Variability in Air and Water Permeability
    Wiley ; 2003
    In:  Vadose Zone Journal Vol. 2, No. 4 ( 2003-11), p. 618-626
    Details
    In: Vadose Zone Journal, Wiley, Vol. 2, No. 4 ( 2003-11), p. 618-626
    Abstract: The saturated hydraulic conductivity ( K s ) is an essential parameter for modeling water and chemical transport in the vadose zone. Since in situ measurements of K s are complex and time‐consuming, indirect methods that are dependable, fast, and inexpensive with regard to assessing magnitude and spatial variability in K s at the field scale are needed. In situ measurements of air permeability ( k a,in situ ) may fulfill these criteria. In this study, a portable insertion‐type air permeameter was used to measure k a,in situ in the Ap and B horizons at five agricultural field sites in Denmark with soil types ranging from sand to sandy loam. Around 100 k a,in situ measurements were performed within 2 d at each field site. The data showed spatial correlation in k a,in situ at three out of five sites, with correlation distances between 30 and 〉 120 m. On the basis of additional laboratory measurements on large, undisturbed soil samples (6280 cm 3 ), a log‐log linear relationship between air permeability ( k a ) measured at the actual soil‐water content (close to field capacity) and K s was found. The K s – k a relation was in agreement with an earlier predictive relationship based on undisturbed 100‐cm 3 samples from nine other field sites. Using pedotransfer functions for K s based only on soil texture yielded an unrealistic narrow range in predicted K s values whereas pedotransfer functions based on k a,in situ yielded a more realistic prediction range. Measurements of k a,in situ constitute a promising indirect method for assessing spatial variability in K s at the field scale.
    Type of Medium: Online Resource
    ISSN: 1539-1663 , 1539-1663
    URL: Article
    DOI: 10.2136/vzj2003.6180
    Language: English
    Publisher: Wiley
    Publication Date: 2003
    detail.hit.zdb_id: 2088189-7
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  • 3
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    Online Resource
    Two-Region Extended Archie's Law Model for Soil Air Permeability and Gas Diffusivity
    Wiley ; 2011
    In:  Soil Science Society of America Journal Vol. 75, No. 3 ( 2011-05), p. 795-806
    Details
    In: Soil Science Society of America Journal, Wiley, Vol. 75, No. 3 ( 2011-05), p. 795-806
    Type of Medium: Online Resource
    ISSN: 0361-5995
    URL: Article
    DOI: 10.2136/sssaj2010.0207
    RVK:
    RA 4845
    Language: English
    Publisher: Wiley
    Publication Date: 2011
    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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  • 4
    Online Resource
    Online Resource
    Linking Soil Microbial Activity to Water- and Air-Phase Contents and Diffusivities
    Wiley ; 2003
    In:  Soil Science Society of America Journal Vol. 67, No. 1 ( 2003), p. 156-
    Details
    In: Soil Science Society of America Journal, Wiley, Vol. 67, No. 1 ( 2003), p. 156-
    Type of Medium: Online Resource
    ISSN: 1435-0661
    URL: Article
    DOI: 10.2136/sssaj2003.0156
    Language: English
    Publisher: Wiley
    Publication Date: 2003
    detail.hit.zdb_id: 241415-6
    detail.hit.zdb_id: 196788-5
    detail.hit.zdb_id: 1481691-X
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  • 5
    Online Resource
    Online Resource
    Water‐Dispersible Colloids: Effects of Measurement Method, Clay Content, Initial Soil Matric Potential, and Wetting Rate
    Wiley ; 2004
    In:  Vadose Zone Journal Vol. 3, No. 2 ( 2004-05), p. 403-412
    Details
    In: Vadose Zone Journal, Wiley, Vol. 3, No. 2 ( 2004-05), p. 403-412
    Abstract: The fraction of clay that disperses in water, water‐dispersible clay (WDC), is recognized as an important property with respect to predicting soil erosion and colloid leaching. Using six mineralogically similar soils with 12, 18, 24, 28, 37, and 43% clay, we studied the influence of soil clay content, initial matric potential (IMP; ψ = −2.5, −100, and −15500 hPa), and wetting rate on WDC released in response to infiltration of low–ionic strength rainwater, using a low‐energy input measurement of WDC (LE‐WDC). These results were referenced by WDC obtained by a conventional, high‐energy input measurement based on air‐dried soil (HE‐WDC). The energy input in the dispersion procedure significantly affected the release of WDC. The amount of HE‐WDC increased with clay content, while the amount of LE‐WDC decreased with increasing clay content. The decrease in LE‐WDC was explained by an increase in cohesive strength, reflected by the increase in water‐stable aggregates (≥4 mm). A strong dependency of IMP on LE‐WDC was observed, with maximum release of LE‐WDC from soils that were at −2.5 hPa before measurement. Decreasing soil matric potential in the period before measurement reduced LE‐WDC and also reduced the dependency of soil clay content, with soils incubated at −15500 hPa releasing a low amount of LE‐WDC independent of clay content. The content of particulate organic C (POC) in the LE‐WDC decreased with increasing clay content, and increased after drying to −15500 hPa. Colloid dispersibility changed as a function of time and moisture status, with the main changes occurring during or immediately after adjustment of the moisture content. Increasing the wetting rate resulted in a doubling of the amount of LE‐WDC released from the initially dry soil (−15500 hPa), while no effect of wetting rate was observed at higher initial matric potentials.
    Type of Medium: Online Resource
    ISSN: 1539-1663 , 1539-1663
    URL: Article
    DOI: 10.2136/vzj2004.0403
    Language: English
    Publisher: Wiley
    Publication Date: 2004
    detail.hit.zdb_id: 2088189-7
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  • 6
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    Online Resource
    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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  • 7
    Online Resource
    Online Resource
    Predicting Soil-Water and Soil-Air Transport Properties and Their Effects on Soil-Vapor Extraction Efficiency
    Wiley ; 1999
    In:  Groundwater Monitoring & Remediation Vol. 19, No. 3 ( 1999-08), p. 61-70
    Details
    In: Groundwater Monitoring & Remediation, Wiley, Vol. 19, No. 3 ( 1999-08), p. 61-70
    Type of Medium: Online Resource
    ISSN: 1069-3629
    URL: Article
    DOI: 10.1111/j.1745-6592.1999.tb00225.x
    Language: English
    Publisher: Wiley
    Publication Date: 1999
    detail.hit.zdb_id: 2181890-3
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  • 8
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    Online Resource
    Density‐Corrected Models for Gas Diffusivity and Air Permeability in Unsaturated Soil
    Wiley ; 2011
    In:  Vadose Zone Journal Vol. 10, No. 1 ( 2011-02), p. 226-238
    Details
    In: Vadose Zone Journal, Wiley, Vol. 10, No. 1 ( 2011-02), p. 226-238
    Abstract: Accurate prediction of gas diffusivity ( D p / D o ) and air permeability ( k a ) and their variations with air‐filled porosity (ε) in soil is critical for simulating subsurface migration and emission of climate gases and organic vapors. Gas diffusivity and air permeability measurements from Danish soil profile data (total of 150 undisturbed soil samples) were used to investigate soil type and density effects on the gas transport parameters and for model development. The measurements were within a given range of matric potentials (−10 to −500 cm H 2 O) typically representing natural field conditions in subsurface soil. The data were regrouped into four categories based on compaction (total porosity Φ 〈 0.4 or 〉 0.4 m 3 m −3 ) and soil texture (volume‐based content of clay, silt, and organic matter 〈 15 or 〉 15%). The results suggested that soil compaction more than soil type was the major control on gas diffusivity and to some extent also on air permeability. We developed a density‐corrected (D‐C) D p (ε)/ D o model as a generalized form of a previous model for D p / D o at −100 cm H 2 O of matric potential ( D p , 100 / D o ). The D‐C model performed well across soil types and density levels compared with existing models. Also, a power‐law k a model with exponent 1.5 (derived from analogy with a previous gas diffusivity model) used in combination with the D‐C approach for k a,100 (reference point) seemed promising for k a (ε) predictions, with good accuracy and minimum parameter requirements. Finally, the new D‐C model concept for gas diffusivity was extended to bimodal (aggregated) media and performed well against data for uncompacted and compacted volcanic ash soil.
    Type of Medium: Online Resource
    ISSN: 1539-1663 , 1539-1663
    URL: Article
    DOI: 10.2136/vzj2009.0137
    Language: English
    Publisher: Wiley
    Publication Date: 2011
    detail.hit.zdb_id: 2088189-7
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  • 9
    Online Resource
    Online Resource
    Variable Pore Connectivity Model Linking Gas Diffusivity and Air‐Phase Tortuosity to Soil Matric Potential
    Wiley ; 2012
    In:  Vadose Zone Journal Vol. 11, No. 1 ( 2012-02)
    Details
    In: Vadose Zone Journal, Wiley, Vol. 11, No. 1 ( 2012-02)
    Abstract: Soil‐gas diffusivity ( D p / D o ) and its dependency on soil matric potential (ψ) is important when taking regulative measures (based on accurate predictions) for climate gas emissions and also risk‐mitigating measures (based on upper‐limit predictions) of gaseous‐phase contaminant emissions. Useful information on soil functional pore structure, e.g., pore network tortuosity and connectivity, can also be revealed from D p / D o –ψ relations. Based on D p / D o measurements in a wide range of soil types across geographically remote vadose zone profiles, this study analyzed pore connectivity for the development of a variable pore connectivity factor, X , as a function of soil matric potential, expressed as pF (=log |−ψ|), for pF values ranging from 1.0 to 3.5. The new model takes the form of X = X * ( F / F *) A with F = 1 + pF −1 , where X * is the pore network tortuosity at reference F ( F* ) and A is a model parameter that accounts for water blockage. The X –pF relation can be linked to drained pore size to explain the lower probability of the larger but far fewer air‐filled pores at lower pF effectively interconnecting and promoting gas diffusion. The model with X* = 2 and A = 0.5 proved promising for generalizing D p / D o predictions across soils of wide geographic contrast and yielded results comparable to those from widely used predictive models. The X –pF model additionally proved valuable for differentiating between soils (providing a unique soil structural fingerprint for each soil layer) and also between the inter‐ and intraaggregate pore regions of aggregated soils. We further suggest that the new model with parameter values of X * = 1.7 and A = 0 may be used for upper limit D p / D o predictions in risk assessments of, e.g., fluxes of toxic volatile organics from soil to indoor air at polluted soil sites.
    Type of Medium: Online Resource
    ISSN: 1539-1663 , 1539-1663
    URL: Article
    DOI: 10.2136/vzj2011.0096
    Language: English
    Publisher: Wiley
    Publication Date: 2012
    detail.hit.zdb_id: 2088189-7
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  • 10
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    Online Resource
    Linking Particle and Pore Size Distribution Parameters to Soil Gas Transport Properties
    Wiley ; 2012
    In:  Soil Science Society of America Journal Vol. 76, No. 1 ( 2012-01), p. 18-27
    Details
    In: Soil Science Society of America Journal, Wiley, Vol. 76, No. 1 ( 2012-01), p. 18-27
    Abstract: Accurate estimation of soil gas diffusivity ( D p / D o , the ratio of gas diffusion coefficients in soil and free air) and air permeability ( k a ) from basic texture and pore characteristics will be highly valuable for modeling soil gas transport and emission and their field‐scale variations. From the topsoil of two Danish arable fields representing two natural clay gradients, D p / D o and k a were measured at soil water matric potentials between −1 and −100 kPa on undisturbed soil cores. The Rosin–Rammler particle size distribution parameters α and β (characteristic particle size and degree of sorting, respectively) and the Campbell water retention parameter b were used to characterize particle and pore size distributions, respectively. Campbell b yielded a wide interval (4.6–26.2) and was highly correlated with α, β, and volumetric clay content. Both D p / D o and k a followed simple power‐law functions (PLFs) of air‐filled porosity (ε a ). The PLF tortuosity–connectivity factors ( X *) for D p / D o and k a were both highly correlated with all basic soil characteristics, in the order of volumetric clay content = Campbell b 〉 gravimetric clay content 〉 α 〉 β. The PLF water blockage factors ( H ) for D p / D o and k a were also well (but relatively more weakly) correlated with the basic soil characteristics, again with the best correlations to volumetric clay content and b . As a first attempt at developing a simple D p / D o model useful at the field scale, we extended the classical Buckingham D p / D o model (ε a 2 ) by a scaling factor based on volumetric clay content. The scaled Buckingham model provided accurate predictions of D p (ε a )/ D o across both natural clay gradients.
    Type of Medium: Online Resource
    ISSN: 0361-5995 , 1435-0661
    URL: Article
    DOI: 10.2136/sssaj2011.0125
    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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