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  • 1
    Language: English
    In: Hydrology and Earth System Sciences, 2016, Vol.20(10), pp.4017-4030
    Description: Prediction and modeling of localized flow processes in macropores is of crucial importance for sustaining both soil and water quality. However, currently there are no reliable means to predict preferential flow due to its inherently large spatial variability. The aim of this study was to investigate the predictive performance of previously developed empirical models for both water and air flow and to explore the potential applicability of X-ray computed tomography (CT)-derived macropore network characteristics. For this purpose, 65 cylindrical soil columns (6#xE2;#x80;#xAF;cm diameter and 3.5#xE2;#x80;#xAF;cm height) were extracted from the topsoil (5#xE2;#x80;#xAF;cm to 8.5#xE2;#x80;#xAF;cm depth) in a 15#xE2;#x80;#xAF;m#xE2;#x80;#xAF;#xE2;#x80;#x89;#xC3;#x97;#xE2;#x80;#x89;#xE2;#x80;#xAF;15#xE2;#x80;#xAF;m grid from an agricultural field located in Silstrup, Denmark. All soil columns were scanned with an industrial X-ray CT scanner (129#xE2;#x80;#xAF;#xC2;#xB5;m resolution) and later employed for measurement of saturated hydraulic conductivity, air permeability at -30 and -100#xE2;#x80;#xAF;cm matric potential, and gas diffusivity at -30 and -100#xE2;#x80;#xAF;cm matric potential. Distribution maps for saturated hydraulic conductivity, air permeability, and gas diffusivity reflected no autocorrelation irrespective of soil texture and organic matter content. Existing empirical predictive models for saturated hydraulic conductivity and air permeability showed poor performance, as they were not able to realistically capture macropore flow. The tested empirical model for gas diffusivity predicted measurements at -100#xE2;#x80;#xAF;cm matric potential reasonably well, but failed at -30#xE2;#x80;#xAF;cm matric potential, particularly for soil columns with biopore-dominated flow. X-ray CT-derived macroporosity matched the measured air-filled porosity at -30#xE2;#x80;#xAF;cm matric potential well. Many of the CT-derived macropore network characteristics were strongly interrelated. Most of the macropore network characteristics were also significantly correlated with saturated hydraulic conductivity, air permeability, and gas diffusivity. The predictive Ahuja et al.#xC2;#xA0;(1984) model for saturated hydraulic conductivity, air permeability, and gas diffusivity performed reasonably well when parameterized with novel, X-ray CT-derived parameters such as effective percolating macroporosity for biopore-dominated flow and total macroporosity for matrix-dominated flow. The obtained results further indicate that it is crucially important to discern between matrix-dominated and biopore-dominated flow for accurate prediction of macropore flow from X-ray CT-derived macropore network characteristics.
    Keywords: Hydrogeology – Analysis ; Permeability – Analysis ; Porosity – Analysis ; Cat Scans – Analysis;
    ISSN: Hydrology and Earth System Sciences
    ISSN: 10275606
    E-ISSN: 1607-7938
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Language: English
    In: Hydrology and Earth System Sciences , 495-506., 2006
    Description: A classical transport experiment was performed in a field plot of 2.5 m2 using the dye tracer brilliant blue. The measured tracer distribution demonstrates the dominant role of the heterogeneous soil structure for solute transport. As with many other published experiments, this evidences the need of considering the macroscopic structure of soil to predict flow and transport. We combine three different approaches to represent the relevant structure of the specific situation of our experiment: i) direct measurement, ii) statistical description of heterogeneities and iii) a conceptual model of structure formation. The structure of soil layers was directly obtained from serial sections in the field. The sub-scale heterogeneity within the soil horizons was modelled through correlated random fields with estimated correlation lengths and anisotropy. Earthworm burrows played a dominant role at the transition between the upper soil horizon and the subsoil. A model based on percolation theory is introduced that mimics the geometry of earthworm burrow systems. The hydraulic material properties of the different structural units were obtained by direct measurements where available and by a best estimate otherwise. From the hydraulic structure, the 3-dimensional velocity field of water was calculated by solving Richards' Equation and solute transport was simulated. The simulated tracer distribution compares reasonably well with the experimental data. We conclude that a rough representation of the structure and a rough representation of the hydraulic properties might be sufficient to predict flow and transport, but both elements are definitely required.
    Keywords: Beauce ; Centre ; Calcisol;Dye Tracer;Soil Structure;Percolation ; Expérimentation Au Champ ; Structure Du Sol ; Île De France ; Transfert Hydrique
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
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  • 3
    Language: English
    In: Hydrology and Earth System Sciences , 495-506., 2006
    Description: A classical transport experiment was performed in a field plot of 2.5 m2 using the dye tracer brilliant blue. The measured tracer distribution demonstrates the dominant role of the heterogeneous soil structure for solute transport. As with many other published experiments, this evidences the need of considering the macroscopic structure of soil to predict flow and transport. We combine three different approaches to represent the relevant structure of the specific situation of our experiment: i) direct measurement, ii) statistical description of heterogeneities and iii) a conceptual model of structure formation. The structure of soil layers was directly obtained from serial sections in the field. The sub-scale heterogeneity within the soil horizons was modelled through correlated random fields with estimated correlation lengths and anisotropy. Earthworm burrows played a dominant role at the transition between the upper soil horizon and the subsoil. A model based on percolation theory is introduced that mimics the geometry of earthworm burrow systems. The hydraulic material properties of the different structural units were obtained by direct measurements where available and by a best estimate otherwise. From the hydraulic structure, the 3-dimensional velocity field of water was calculated by solving Richards' Equation and solute transport was simulated. The simulated tracer distribution compares reasonably well with the experimental data. We conclude that a rough representation of the structure and a rough representation of the hydraulic properties might be sufficient to predict flow and transport, but both elements are definitely required.
    Keywords: Beauce ; Centre ; Calcisol;Dye Tracer;Soil Structure;Percolation ; Expérimentation Au Champ ; Structure Du Sol ; Île De France ; Transfert Hydrique
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
    Library Location Call Number Volume/Issue/Year Availability
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