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Berlin Brandenburg

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  • 1
    Language: English
    In: Soil Science Society of America journal, 2010, Vol.74(4), pp.1084-1091
    Description: Solute diffusion controls important processes in soils: plant uptake of nutrients, sorption–desorption processes, degradation of organic matter, and leaching of radionuclides through clay barriers. We developed a new method for measuring the solute diffusivity (solute diffusion coefficient in the soil relative to water) in intact soil samples (the Multiple Tracer, Filter Separated half-cell method using a Dynamic Model for parameter estimation [MT-FS-DM]). The MT-FS-DM method consists of half-cell diffusion of two pairs of counterdiffusing anionic tracers and a parameter estimation scheme that allows diffusion coefficients for tracers in the two half-cells to be estimated on the basis of two concentration profiles in each sample. The parameter estimation scheme uses a fully dynamic (time-resolved) simulation model. From sensitivity and uncertainty analyses of the dynamic model, we found that the MT-FS-DM method provided reliable results. We compared diffusivities measured on a sandy loam soil using the MT-FS-DM method with diffusivities from six sandy loam test soils from the literature. The new method can be used to estimate solute diffusivity in intact structured soil and provides a more confident estimate for solute diffusion due to the use of two tracer profiles in the same soil sample. Especially when we are interested in determining the diffusivity of a single intact soil sample, such as when relating solute diffusivity to other properties of the soil (e.g., microbial activity), this method will be an improvement over existing methods. ; Includes references ; p. 1084-1091.
    Keywords: Soil Transport Processes ; Labeling Techniques ; Diffusion ; Soil Water Content ; Soil Solution ; Solutes ; Accuracy ; Methodology ; Sandy Loam Soils ; Measurement ; Diffusivity
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 2
    Language: English
    In: Chemosphere, 2011, Vol.83(11), pp.1475-1479
    Description: Photodegradation on dried loamy sand was measured for OTNE and triclosan, and the shading effect was proved to be important and related to soil properties. ► Photodegradation of chemical compounds on dried loamy sand surfaces was measured. ► Photodegradation was not restricted by diffusion in soil but by the shading effect of light. ► The shading effect was quantified from the concentration decrease profile. Fragrances such as OTNE (marketed as Iso-E-Super®) and bactericides such as triclosan (marketed as Igrasan) are present in waste water and thus finally sorbed to sewage sludge. With that sludge they can reach agricultural fields where they potentially can undergo photodegradation processes. In this study the photodegradation of OTNE and triclosan on dried loamy sand was measured under artificial sunlight conditions in laboratory experiments. These compounds were artificially added with concentrations of 1 μg g on pre-rinsed dried loamy sand. The decrease in concentration with light irradiation was measured for 32 d in comparison to soil samples without light irradiation. The estimated light source intensity was 27 W m . Within the experiment, the apparent half-life was 7 and 17 d for OTNE and triclosan respectively. The decrease did not simply follow first-order kinetics. The apparent rate constant decreased in the latter stage of reaction, suggesting that part of the chemicals were inaccessible for degradation. Two models, i.e., a diffusion-limited model, and a light penetration-limited model, were used in comparison to the measured data to explain the observed degradation limitations in the latter stages of the experiments. Comparing the hereby obtained model parameters with estimated physico-chemical parameters for the soil and the two chemical compounds, the light penetration-limited model, in which the degradation in the soil surface layer is assumed to be limited due to the shading effect of light in the upper thin soil layer, showed to be the most realistic in describing the photodegradation.
    Keywords: Otne ; Triclosan ; Soil ; Photodegradation ; Chemistry ; Ecology
    ISSN: 0045-6535
    E-ISSN: 1879-1298
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  • 3
    Language: English
    In: Journal of Hazardous Materials, 2010, Vol.179(1), pp.573-580
    Description: Quantifying the spatial variability of factors affecting natural attenuation of hydrocarbons in the unsaturated zone is important to (i) performing a reliable risk assessment and (ii) evaluating the possibility for bioremediation of petroleum-polluted sites. Most studies to date have focused on the shallow unsaturated zone. Based on a data set comprising analysis of about 100 soil samples taken in a 16 m-deep unsaturated zone polluted with volatile petroleum compounds, we statistically and geostatistically analysed values of essential soil properties. The subsurface of the site was highly layered, resulting in an accumulation of pollution within coarse sandy lenses. Air-filled porosity, readily available phosphorous, and the first-order rate constant ( ) of benzene obtained from slurry biodegradation experiments were found to depend on geologic sample characterization ( 〈 0.05), while inorganic nitrogen was homogenously distributed across the soil stratigraphy. Semivariogram analysis showed a spatial continuity of 4–8.6 m in the vertical direction, while it was 2–5 times greater in the horizontal direction. Values of displayed strong spatial autocorrelation. Even so, the soil potential for biodegradation was highly variable, which from autoregressive state-space modeling was partly explained by changes in soil air-filled porosity and gravimetric water content. The results suggest considering biological heterogeneity when evaluating the fate of contaminants in the subsurface.
    Keywords: Biological Heterogeneity ; Petroleum Vapors ; Spatial Variability ; Semivariogram Analysis ; State-Space Modeling ; Engineering ; Law
    ISSN: 0304-3894
    E-ISSN: 1873-3336
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  • 4
    Language: English
    In: Soil Science Society of America Journal, Sept-Oct, 2013, Vol.77(5), p.1517(12)
    Description: Time domain reflectometry (TDR) is used widely for measuring soil-water content. New TDR coil probe technology facilitates the development of small, nondestructive probes for simultaneous measurement of soil-water content (?) and soil-water potential (?). In this study we developed mini tensiometer-time domain reflectometry (T-TDR) coil probes, 6-mm wide and 32-mm long. The coil probes were calibrated against a conventional three-rod probe and were used for measuring ? for a aggregated volcanic ash soil (VAS) and a uniform sand. A commonly-used dielectric mixing model did not accurately describe the measured relation between the dielectric constant of the T-TDR coil probe (?coil) and ?, and a new calibration model for ?coil (?) was proposed instead. The new model assumes single-region behavior for sand and two-region behavior for aggregated VAS, when plotting the normalized dielectric constant of the coil probe (?coil-? dry; where ?dry is the dielectric constant of the T-TDR coil probe for air-dried material) as a function of ?. The new calibration model accurately described the (?coil-? dry)-? relations measured by 7 T-TDR coil probes on both sand and VAS. Additionally, there was a good agreement between measured soil-water retention curves (? 〉 -100 cm H2O) by the new T-TDR coil probes and independent measurements by the hanging water column method.
    Keywords: Reflectometers -- Usage ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 5
    Language: English
    In: Journal of Geotechnical and Geoenvironmental Engineering, July, 2011, Vol.137(7), p.653(10)
    Description: Landfill sites have been implicated in greenhouse warming scenarios as a significant source of atmospheric methane. In this study, the effects of extreme compaction on the two main soil-gas transport parameters, the gas diffusion coefficient ([D.sub.p]) and the intrinsic air permeability ([k.sub.a]), and the cumulative methane oxidation rate in a landfill cover soil were investigated. Extremely compacted landfill cover soil exhibited negligible inactive soil-air contents for both [D.sub.p] and ka. In addition, greater [D.sub.p] and [k.sub.a] were observed as compared with normal compacted soils at the same soil-air content ([epsilon]), likely because of reduced water-blockage effects under extreme compaction. These phenomena are not included in existing predictive models for [D.sub.p]([epsilon]) and ka([epsilon]). On the basis of the measured data, new predictive models for [D.sub.p]([epsilon]) and ka([epsilon]) were developed with model parameters (representing air-filled pore connectivity and water-blockage effects) expressed as functions of dry density ([[rho].sub.b]). The developed [D.sub.p] ([epsilon]) and [k.sub.a] (e) models together with soil-water retention data for soils at normal and extreme compaction ([[rho].sub.b] = 1.44 and 1.85 g [cm.sup.-3]) implied that extremely compacted soils will exhibit lower [D.sub.p] and [k.sub.a] at natural field-water content (-100 cm [H.sub.2]O of soil-water matric potential) because of much lower soil-air content. Numerical simulations of methane gas transport, including a first-order methane oxidation rate, were performed for differently compacted soils by using the new predictive [D.sub.p]([epsilon]) model. Model results showed that compaction-induced difference in soil-air content at a given soil-water matric potential condition is likely the most important parameter governing methane oxidation rates in extremely compacted landfill cover soil. DOI: 10.1061/(ASCE)GT.1943-5606.0000459. CE Database subject headings: Landfills; Coverings; Gas; Parameters; Methane. Author keywords: Landfill final cover soil; Gas transport parameters; Compaction.
    Keywords: Atmospheric Carbon Dioxide -- Analysis ; Waste Management -- Analysis ; Methane -- Analysis ; Permeability -- Analysis ; Natural Gas Transmission -- Analysis
    ISSN: 1090-0241
    E-ISSN: 19435606
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  • 6
    Language: English
    In: Waste Management, 2011, Vol.31(12), pp.2464-2472
    Description: ► The effects of soil physical properties on gas transport parameters were investigated. ► Higher values of and exhibited in the ‘+gravel’ than the ‘−gravel’ fraction at same soil–air content ( ). ► Recent power law models for (WLR) and (RPL) were modified. ► Model parameters were linearly related to easily measurable dry bulk density ( ). Landfill sites are emerging in climate change scenarios as a significant source of greenhouse gases. The compacted final soil cover at landfill sites plays a vital role for the emission, fate and transport of landfill gases. This study investigated the effects of dry bulk density, , and particle size fraction on the main soil–gas transport parameters – soil–gas diffusivity ( / , ratio of gas diffusion coefficients in soil and free air) and air permeability ( ) – under variably-saturated moisture conditions. Soil samples were prepared by three different compaction methods (Standard and Modified Proctor compaction, and hand compaction) with resulting values ranging from 1.40 to 2.10 g cm . Results showed that and values for the ‘+gravel’ fraction (〈35 mm) became larger than for the ‘−gravel’ fraction (〈2 mm) under variably-saturated conditions for a given soil–air content ( ), likely due to enhanced gas diffusion and advection through less tortuous, large-pore networks. The effect of dry bulk density on and was most pronounced for the ‘+gravel’ fraction. Normalized ratios were introduced for all soil–gas parameters: (i) for gas diffusivity / , the ratio of measured to in total porosity ( ), (ii) for air permeability / , the ratio of measured to at 1235 kPa matric potential (=pF 4.1), and (iii) for soil–air content, the ratio of soil–air content ( ) to total porosity ( ) (air saturation). Based on the normalized parameters, predictive power-law models for ( / ) and ( / ) models were developed based on a single parameter (water blockage factor for and for ). The water blockage factors, and , were found to be linearly correlated to values, and the effects of dry bulk density on and for both ‘+gravel’ and ‘−gravel’ fractions were well accounted for by the new models.
    Keywords: Air Permeability ; Gas Diffusivity ; Dry Bulk Density ; Landfill Final Cover ; Engineering ; Chemistry
    ISSN: 0956-053X
    E-ISSN: 1879-2456
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  • 7
    Language: English
    In: Soil Science Society of America Journal, Nov-Dec, 2013, Vol.77(6), p.1944(11)
    Description: The time dependency of water repellency (WR) in hydrophobic porous media plays a crucial role for water infiltration processes after rainfall and for the long-term performance of capillary barrier systems. The contact angle (CA) of hydrophobic media normally decreases with continuous contact with water, eventually allowing water imbibition. However, the effect of the reduction in CA with soil-water contact time on the water retention function of hydrophobic media is not yet fully understood. In this study, water retention characteristics were measured using a hanging water column apparatus equipped with a mini-time domain reflectometry (TDR) coil probe under controlled wetting and drying in a water-repellent volcanic ash soil (VAS) and in sands coated with different hydrophobic agents. The contact angle (CA-SWRC) under imbibition was evaluated based on the inflection points on the water retention curves. For both water-repellent VAS and hydrophobized sand samples, the calculated CA-SWRC increased with increasing WR. This was determined from both the water drop penetration time and the initial contact angle (CAi) by the sessile drop method. Calculated CAuSWRC values ranged from 20[degrees] to 48[degrees] for the water-repellent VAS and from 40[degrees] to 63[degrees] for the hydrophobized sand. The CA reduction with contact time was quantified by relating CA-SWRC and CAi. This gave a significant linear relationship for the hydrophobized sand [CA-SWRC = 0.40CAi +11.3 (30[degrees] 〈 CAi 〈 120[degrees]), R2 = 0.66]. A large difference in water-filled pore distributions under controlled wetting and drying cycles was found on c
    Keywords: Water Repellents -- Usage ; Hydrophobic Effect -- Analysis ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 8
    Language: English
    In: Soil Science Society of America Journal, March, 2013, Vol.77(2), p.362(10)
    Description: Understanding soil-gas phase properties and processes is important for finding solutions to critical environmental problems such as greenhouse gas emissions and transport of gaseous-phase contaminants in soils. Soil-air permeability, ka (?m2), is the key parameter governing advective gas movement in soil and is controlled by soil physical characteristics representing soil texture and structure. Models predicting ka as a function of air-filled porosity (?) often use a reference-point measurement, for example, ka,1000 at ?1000 (where the measurement is done at a suction of -1000 cm H2O). Using ka measurements from two Danish arable fields, each located on natural clay gradients, this study presents a pore tortuosity-disconnectivity analysis to characterize the soil-gas phase. The main objective of this study is to investigate the effect of soil-moisture condition, clay content, and other potential drivers of soil texture and structure on soil-gas phase characteristics based on a ka-based pore tortuosity parameter, Xa [= log(ka/ka,1000)/log(?/?,1000)]. Results showed that Xa did not vary significantly with soil matric potential (in the range of -10 to -1000 cm H2O), but the average Xa across moisture conditions showed a strong linear relation (R2 = 0.74) to clay content. The Xa, further showed promising relations to specific surface area, Rosin-Rammler particle size distribution indices, ? and ? (representing characteristic particle size and degree of sorting, respectively), and the Campbell water retention parameter, b. Considering clay as a main driver of soil-gas phase characteristics, we developed expressions linking clay content and ka,1000 at ?1000 and discussed the effect of clay content on general ka-? behavior.
    Keywords: Grading (Building materials) -- Usage ; Soil Permeability -- Analysis ; Soil Research
    ISSN: 0361-5995
    E-ISSN: 14350661
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  • 9
    Language: English
    In: Soil Science Society of America Journal, 2013, Vol.77(2), pp.403-411
    Description: The influence of clay content in soil-pore structure development and the relative importance of macroporosity in governing convective fluid flow are two key challenges toward better understanding and quantifying soil ecosystem functions....
    Keywords: Life Sciences ; Agricultural Sciences ; GAS ; Models ; Consequences ; Porosity ; Air Permeability ; Parameters ; Transport ; Microtomography ; Quantification ; Agriculture
    ISSN: 0361-5995
    E-ISSN: 1435-0661
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  • 10
    Language: English
    In: Soil Science Society of America journal, 2012, Vol.76(6), pp.1946-1956
    Description: Modeling water distribution and flow in partially saturated soils requires knowledge of the soil water characteristic (SWC). However, measurement of the SWC is challenging and time-consuming and, in some cases, not feasible. This study introduces two predictive models (F(W)–model and A(W)–model) for the SWC, derived from readily available soil properties such as texture and bulk density. A total of 46 undisturbed soils from different horizons at 15 locations across Denmark were used for model evaluation. The F(W)–model predicts the volumetric water content as a function of volumetric fines content (organic matter and clay). It performed reasonably well for the dry-end of SWC (above a pF value of 2.0; pF = log(|ψ|), where ψ is the matric potential in cm), but did not do as well closer to saturated conditions. The A(W)–model predicts the volumetric water content as a function of volumetric content of different particle size fractions (organic matter, clay, silt, and fine and coarse sands). The volumetric content of a particular soil particle size fraction was considered if it contributed to the pore size fraction still occupied with water at the given pF value. Hereby, the A(W)–model implicitly assumes that a given particle size fraction creates an analogue pore size fraction and further this pore size fraction filled with water is corresponding to a certain pF value according to the well-known capillary rise equation. The A(W)–model was found to be quite robust, and it performed exceptionally well for pF values ranging from 0.4 to 4.2 for different soil types. For prediction of the continuous SWC, it is recommended to parameterize the van Genuchten model based on the SWC data points predicted by the A(W)–model. ; p. 1946-1956.
    Keywords: Clay ; Particle Size ; Soil Types ; Bulk Density ; Texture ; Prediction ; Capillarity ; Silt ; Equations ; Organic Matter ; Models ; Water Distribution ; Soil Water Characteristic ; Water Content ; Saturated Conditions
    ISSN: 0361-5995
    E-ISSN: 14350661
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