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Berlin Brandenburg

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  • 1
    Language: English
    In: Vadose Zone Journal, 2016, Vol.15(4), p.0
    Description: 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.
    Keywords: Agriculture;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 2
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(1), p.0
    Description: Gas diffusion is a dominant transport mechanism for climate and regulated gases in the vadose zone. Soil-gas diffusion is governed by the gas diffusion coefficient (D (sub p) , m (super 2) s (super -1) ) which is highly dependent on soil texture, such as sand, silt, clay, and organic matter contents, as well as soil physical properties such as soil-air content (epsilon , m (super 3) m (super -3) ) or total porosity (Phi , m (super 3) m (super -3) ). Soil organic matter is a key contributor to the formation of the soil pore structure (i.e., total porosity and air-filled pore tortuosity), and it highly affects D (sub p) behavior under variably saturated conditions. In this study, based on numerous D (sub p) data sets across soil types including sands, loamy clay soils, volcanic ash soils, and organic soils, predictive D (sub p) models incorporating a percolation threshold (epsilon (sub th) , m (super 3) m (super -3) ) and pore tortuosity factor (X') are proposed. The observed relations between either epsilon (sub th) or X' and either Phi or volumetric organic matter fraction (OMF, m (super 3) m (super -3) ) were embedded in the proposed D (sub p) model. The proposed D (sub p) models, coupled with predictive epsilon (sub th) and OMF models, performed well against the measured D (sub p) data across soil types. Finally, a sensitivity analysis of the OMF in relation to the D (sub p) and pore-network tortuosity (T) showed a reduction in D (sub p) and increase in T with increasing OMF under the same epsilon conditions.
    Keywords: Soils ; Asia ; Diffusion ; Far East ; Gases ; Grain Size ; Hokkaido ; Honshu ; Hydrology ; Japan ; Loam ; Memuro Japan ; Moisture ; Nishi-Tokyo Japan ; Organic Compounds ; Percolation ; Permeability ; Physical Properties ; Porosity ; Power Law ; Saitama Japan ; Saturation ; Size Distribution ; Soil Gases ; Soils ; Statistical Analysis ; Tortuosity ; Transport ; Unsaturated Zone ; Volcanic Soils ; Water;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 3
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(1), p.0
    Description: Bench testing of petroleum biodegradation rates in vadose zone soils is typically associated with errors because transport conditions in laboratory systems are different from those found in the vadose zone. This work addressed the effect of soil structure and gas transport properties on hydrocarbon biodegradation in the unsaturated zone and we present a novel method for measuring biodegradation rates in intact and undisturbed soil columns of 100 cm (super 3) . To determine whether soil structure and gas diffusivity, defined as the ratio of the gas diffusion coefficient in soil to that in free air (D (sub p) /D (sub 0) ), influence the outcome of aerobic benzene biodegradation experiments, measurements using identical sandy soils were performed on (i) undisturbed 100-cm (super 3) core samples; (ii) sieved (2-mm) and repacked 100-cm (super 3) core samples; and (iii) soil samples (10 g) prepared as slurry microcosms. While slurry reactor experiments changed the first-order rate constant (k (sub w,1) ) significantly compared with undisturbed core samples, this was not the case for soil cores that had been sieved and repacked. This suggests that soil structure on a millimeter scale does not affect aerobic biodegradation in relatively unstructured sandy soils. Within differently textured soil cores, the biodegradation rate was found to increase with gas diffusivity when D (sub p) /D (sub 0) 〈0.02. This establishes gaseous O (sub 2) and petroleum vapor diffusion and distribution in soil profiles as a controlling factor for natural biodegradation of petroleum vapors.
    Keywords: Environmental Geology ; Aromatic Hydrocarbons ; Bacteria ; Benzene ; Biodegradation ; Biota ; Btex ; Cores ; Denmark ; Diffusivity ; Ethylbenzene ; Europe ; Experimental Studies ; Gas Transport ; Gases ; Hjorring Denmark ; Hydrocarbons ; Jutland ; Laboratory Studies ; Moisture ; Morphology ; Nyborg Denmark ; Organic Compounds ; Petroleum Products ; Pollution ; Sampling ; Scandinavia ; Slurries ; Soils ; Toluene ; Transport ; Unsaturated Zone ; Western Europe ; Xylene;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 4
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(1), p.0
    Description: Soil thermal conductivity (lambda ) and heat capacity (C) control heat transport and the thermal environment for biogeophysical processes in the vadose zone. Accurate lambda and C predictions for peaty soils with high organic contents are particularly important for assessing emissions of greenhouse gases formed during microbial activity in wetlands. In this study, we measured the lambda and C at different soil-water matric potentials on undisturbed samples for three peaty soil profiles at the Hokkaido Bibai marsh in Japan, representing a total of 10 different soil horizons. The thermal properties under air-dried conditions, lambda (sub dry) and C (sub dry) , were measured separately at changing volumetric solids contents (sigma ). For each sample, volume shrinkage was observed to varying degrees during the drying process. Measured lambda and C increased linearly with increasing volumetric water content (theta ). Applying the concept of a three-phase mixing model and incorporating the lambda -theta or C-theta and the lambda (sub dry) -sigma or C (sub dry) -sigma relations, predictive lambda and C models were developed as functions of sigma and theta . The new mixing model is represented by lambda = lambda (sub dry) +f (sub lambda ) theta lambda (sub w) and C = C (sub dry) +f (sub C) {theta}C (sub w) , where lambda (sub w) and C (sub w) are the thermal conductivity and heat capacity of water, respectively, and f is an impedance factor that takes into account the liquid-phase tortuosity. The new mixing model predicted literature lambda -theta data on peaty and highly organic soils under variable saturation well. The probable ranges of lambda and C under variable saturation were proposed based on the sensitivity analysis.
    Keywords: Soils ; Asia ; Bibai Marsh ; Biogenic Processes ; Bogs ; Carbon ; Equations ; Far East ; Ground Water ; Heat Capacity ; Heat Flow ; Heat Transport ; Hokkaido ; Horizons ; Hydrologic Cycle ; Hydrology ; Impedance ; Japan ; Liquid Phase ; Mires ; Organic Carbon ; Peat ; Physicochemical Properties ; Retention ; Sediments ; Sensitivity Analysis ; Soils ; Statistical Analysis ; Thermal Conductivity ; Thermal Properties ; Transport ; Unsaturated Zone ; Water Table ; Wetlands;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 5
    Language: English
    In: Vadose Zone Journal, 2015, Vol.14(7), p.0
    Description: A new parameter for representing the matrix bulk density, computed tomography (CT) number derived matrix density, was used in studying preferential flow and transport in an agricultural soil. Results illustrate that CT number derived matrix density provides useful information regarding the initiation of macropore flow and the magnitude of preferential flow. Preferential flow and transport in structured soils can be intimately linked to numerous environmental problems. Surface-applied chemicals are susceptible to rapid transport to deeper depths in structural soil pores, thereby potentially contaminating valuable environmental resources and posing risks to public health. This study focused on establishing links between the structural pore space and preferential transport using a combination of standard physical measurement methods for air and water permeabilities, breakthrough experiments, and X-ray computed tomography (CT) on large soil columns. Substantial structural heterogeneity that resulted in significant variations in flow and tracer transport was observed, despite the textural similarity of the investigated samples. Quantification of macropore characteristics with X-ray CT was useful but not sufficient to explain the variability in air permeability, saturated hydraulic conductivity, and solute transport. This was due to the limited CT scan resolution and large structural variability below this resolution. However, CTmatrix, a new parameter derived from the CT number of the matrix excluding stones and large mostly air-filled macropores, was found to be useful for determining the magnitude of preferential flow under boundary conditions of constant, near-saturated flow.
    Keywords: Tracers ; Solutes ; Permeability ; X-Rays ; Soils ; Public Health ; Flow ; Permeability ; Pores ; Variability ; Public Health ; Density ; Standards ; Preferential Flow ; Heterogeneity ; Coastal Zone Management ; General ; CT, Computed Tomography ; Ctmatrix, Computed Tomography Number of the Soil Matrix ; Hu, Hounsfield Units ; Roi, Region of Interest ; Btc, Breakthrough Curve;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 6
    Language: English
    In: Vadose Zone Journal, 2014, Vol.13(1), p.0
    Description: Eminent environmental challenges such as remediation of contaminated sites, the establishment and maintenance of nuclear waste repositories, or the design of surface landfill covers all require accurate quantification of the soil water characteristic (SWC) at low water contents. Furthermore, several essential but difficult-to-measure soil properties, including clay content and specific surface area, are intimately related to water vapor sorption. Until recently, it was a major challenge to measure detailed water vapor sorption isotherms accurately within a reasonable time frame. This priority communication illustrates potential applications of a new, fully automated, and rapid Vapor Sorption Analyzer (VSA) to pertinent issues in vadose zone research. Detailed vapor sorption isotherms for 25 variably textured soils were measured with the VSA within 1 to 3 d. Links between generated isotherms and pesticide volatilization, toxic organic vapor sorption kinetics, and soil water repellency are illustrated. Several methods to quantify hysteresis effects and to derive soil clay content and specific surface area from VSA-measured isotherms are presented. Besides above mentioned applications, potential relationships to percolation threshold for solute diffusion in unsaturated soil and to soil cation exchange capacity are discussed to stimulate new and much-needed vadose zone research.
    Keywords: Soils ; Environmental Geology ; Agriculture ; Asia ; Automated Analysis ; California ; Carbon ; Denmark ; Europe ; Humidity ; Hydrophobic Materials ; Hysteresis ; Isotherms ; Measurement ; Moisture ; Organic Carbon ; Organic Compounds ; Petroleum Products ; Pollution ; Rapid Analysis ; Research ; Scandinavia ; Soil Water Characteristic ; Soils ; Sorption ; Sri Lanka ; Toxic Materials ; United States ; Unsaturated Zone ; Volatile Organic Compounds ; Volatiles ; Volatilization ; Water Vapor ; Western Europe;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 7
    Language: English
    In: Vadose Zone Journal, 2011, Vol.10(4), p.1228
    Description: A series of column experiments was conducted to investigate the transport and deposition of variably charged colloids in saturated porous media. Soil colloids with diameters 〈1 mu m were extracted from a volcanic-ash soil from Nishi-Tokyo (referred to here as VAS colloids) and a red-yellow soil from Okinawa (RYS colloids) in Japan. The VAS colloids exhibited a negative surface charge with a high pH dependency, whereas the RYS colloids exhibited a negative surface charge with less pH dependency. The soil colloids were applied as colloidal suspensions to 10-cm-long saturated sand columns packed with either Narita sand (mean diameter = 0.64 mm) or Toyoura sand (mean diameter = 0.21 mm) at different flow rates, suspension concentrations, and pH conditions. Both sands exhibited a negative surface charge in the measured pH range, but the pH dependency was more pronounced for the Toyoura sand. Breakthrough curves and deposition profiles for soil colloids were strong functions of the hydrodynamics, solution pH, and surface charge of the colloids and sand grains. Greater deposition was typical for lower flow rates and lower pH. The deposition of VAS colloids in both sands under low-pH conditions exhibited depth-dependent retention, with high colloid deposition at the column inlet. The RYS colloids were mainly deposited uniformly along columns, and depth-dependent retention was observed only in Toyoura sand at low pH. Results suggest that decreasing solution pH enhanced surface charge neutralization of both soil colloids and sand grains, thereby increasing colloid deposition. This study emphasizes that the pH-dependent surface charge of both mobile colloids and receiving porous media needs more consideration in models for colloid and colloid-facilitated transport in soil.
    Keywords: Soils ; Asia ; Breakthrough Curves ; Characterization ; Clastic Sediments ; Colloidal Materials ; Deposition ; Derjaguin-Landau-Verwey-Overbeek Theory ; Electrostatic Properties ; Experimental Studies ; Far East ; Heterogeneous Materials ; Honshu ; Japan ; Nakijison Japan ; Nishi-Tokyo Japan ; Okinawa ; Porous Materials ; Red-Yellow Soils ; Ryukyu Islands ; Sand ; Sediments ; Soils ; Surface Charge ; Surface Properties ; Suspended Materials ; Theoretical Studies ; Tokyo Japan ; Transport ; Variable Charge ; Volcanic Soils ; Weathered Materials;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 8
    Language: English
    In: Vadose Zone Journal, 2011, Vol.10(1), p.226
    Description: Accurate prediction of gas diffusivity (D (sub p) /D (sub o) ) and air permeability (k (sub a) ) and their variations with air-filled porosity (epsilon ) 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 (sub 2) O) typically representing natural field conditions in subsurface soil. The data were regrouped into four categories based on compaction (total porosity Phi 〈0.4 or 〉0.4 m (super 3) m (super -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 (sub p) (epsilon )/D (sub o) model as a generalized form of a previous model for D (sub p) /D (sub o) at -100 cm H (sub 2) O of matric potential (D (sub p,100) /D (sub o) ). The D-C model performed well across soil types and density levels compared with existing models. Also, a power-law k (sub 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 (sub a,100) (reference point) seemed promising for k (sub a) (epsilon ) 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.
    Keywords: Environmental Geology ; Agriculture ; Air ; Atmosphere ; Compactness ; Denmark ; Density ; Diffusivity ; Europe ; Forest Soils ; Foulum Denmark ; Gjorslev Denmark ; Hjorring Denmark ; Jutland ; Jyndevad Denmark ; Land Use ; Landfills ; Mammen Denmark ; Midtjylland Denmark ; Moisture ; Nordjylland Denmark ; Organic Compounds ; Permeability ; Porosity ; Poulstrup Denmark ; Ronhave Denmark ; Scandinavia ; Size ; Sjaelland ; Skellingsted Denmark ; Soil Gases ; Soil Profiles ; Soils ; Unsaturated Zone ; Urban Environment ; Western Europe;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 9
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(1), p.0
    Description: Soil-gas diffusivity (D (sub p) /D (sub o) ) and its dependency on soil matric potential (psi ) 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 (sub p) /D (sub o) -psi relations. Based on D (sub p) /D (sub 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 -psi ), for pF values ranging from 1.0 to 3.5. The new model takes the form of X=X (super *) (F/F (super *) ) (super A) with F=1 + pF (super -1) , where X (sub *) is the pore network tortuosity at reference F (F (super *) ) 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 (super *) =2 and A=0.5 proved promising for generalizing D (sub p) /D (sub 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 (super *) =1.7 and A=0 may be used for upper limit D (sub p) /D (sub o) predictions in risk assessments of, e.g., fluxes of toxic volatile organics from soil to indoor air at polluted soil sites.
    Keywords: Soils ; Agriculture ; Alluvial Soils ; Andisols ; Asia ; Brazil ; Central Europe ; Chernozems ; Connectivity ; Cores ; Denmark ; Diffusivity ; Dronninglund Denmark ; Europe ; Far East ; Gaseous Phase ; Honshu ; Japan ; Jutland ; Matric Potential ; Moisture ; Nakskov Denmark ; Nishi-Tokyo Japan ; Poland ; Porosity ; Porous Materials ; Probability ; Rendzinas ; Scandinavia ; Sjaelland ; Soil Gases ; Soil-Water Characteristics ; Soils ; South America ; Statistical Analysis ; Tokyo Japan ; Tortuosity ; Unsaturated Zone ; Water ; Western Europe;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 10
    Language: English
    In: Vadose Zone Journal, 2016, Vol.15(4), p.0
    Description: The characterization of soil pore space geometry is important for explaining fluxes of air, water, and solutes through soil and understanding soil hydrogeochemical functions. X-ray computed tomography (CT) can be applied for this characterization, and in this study CT-derived parameters were used to explain water, air, and solute transport through soil. Forty-five soil columns (20 by 20 cm) were collected from an agricultural field in Estrup, Denmark, and subsequently scanned using a medical CT scanner. Nonreactive tracer leaching experiments were performed in the laboratory along with measurements of air permeability (K (sub a) ) and saturated hydraulic conductivity (K (sub sat) ). The CT number of the matrix (CT (sub matrix) ), which represents the moist bulk density of the soil matrix, was obtained from the CT scans as the average CT number of the voxels in the grayscale image excluding macropores and stones. The CT (sub matrix) showed the best relationships with the solute transport characteristics, especially the time by which 5% of the applied mass of tritium was leached, known as the 5% arrival time (t (sub 0.05) ). The CT-derived macroporosity (pores 〉 1.2 mm) was correlated with K (sub a) and log (sub 10) (K (sub sat) ). The correlation improved when the limiting macroporosity (the minimum macroporosity for every 0.6-mm layer along the soil column) was used, suggesting that soil layers with the narrowest macropore section restricted the flow through the whole soil column. Water, air, and solute transport were related with the CT-derived parameters by using a best subsets regression analysis. The regression coefficients improved using CT (sub matrix) , limiting macroporosity, and genus density, while the best model for t (sub 0.05) used CT (sub matrix) only. The scanning resolution and the time for soil structure development after mechanical activities could be factors that increased the uncertainty of the relationships. Nevertheless, the results confirmed the potential of X-ray CT visualization techniques for estimating fluxes through soil at the field scale.
    Keywords: Soils ; Agriculture ; Air ; Breakthrough Curves ; Carbon ; Computed Tomography Data ; Connectivity ; Denmark ; Density ; Estrup Denmark ; Europe ; Functions ; Hydraulic Conductivity ; Hydrogen ; Image Analysis ; Isotopes ; Jutland ; Leaching ; Organic Carbon ; Pesticides ; Porosity ; Preferential Flow ; Probability ; Probability Density Function ; Radioactive Isotopes ; Scandinavia ; Segmentation ; Size ; Soils ; Solute Transport ; Solutes ; Statistical Analysis ; Transport ; Tritium ; Unsaturated Zone ; Visualization ; Water ; Western Europe ; X-Ray Data;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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