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Berlin Brandenburg

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  • 1
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(3), p.0
    Description: Recently, a new approach was introduced to directly measure unsaturated hydraulic conductivity in flux-controlled experiments--the multistep flux experiment. Thereby an overshoot in matric potential h (sub m) across drainage and infiltration fronts was observed. We extended this experimental approach to simultaneously measure the volumetric water content Theta within the sample and applied the method to a sand and a clay loam soil. The detailed trajectories within the h (sub m) -Theta space were obtained during a number of decreasing and increasing steps in infiltration rate. This clearly demonstrates the type and magnitude of hydraulic nonequilibrium under transient conditions where water content and matric potential deviate from a well-defined static relation. We also compared the directly measured hydraulic conductivities with those obtained from classical multistep outflow experiments and found that nonequilibrium dynamics might lead to an underestimation of hydraulic conductivity when obtained from an inverse solution of Richards" equation. We provide a qualitative explanation of nonequilibrium that depends on the structure of the material and the type and magnitude of external forcing. The new experimental setup is considered to be a valuable tool to actually quantify nonequilibrium effects. This will make it possible to represent this relevant phenomenon in future modeling concepts.
    Keywords: Hydrogeology ; Aquifers ; Climate Forcing ; Discharge ; Drainage ; Experimental Studies ; Ground Water ; Hydraulic Conductivity ; Hydrodynamics ; Hysteresis ; Infiltration ; Models ; Richards Equation ; Saturation ; Soil Mechanics ; Solute Transport ; Transport ; Unsaturated Zone;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 2
    Language: English
    In: Advances in Water Resources, August 2012, Vol.44, pp.101-112
    Description: ► New averaging approach that conserves hydraulic non-equilibrium during rapid infiltration of water. ► New indicators to describe hydraulic non-equilibrium quantitatively. ► Direct link between front morphology and hydraulic non-equilibrium. ► Insights into how structural connectivity affects hydraulic non-equilibrium. ► Shortcomings of an upscaled Richards model extended by hydraulic non-equilibrium. Water infiltration into heterogeneous, structured soil leads to hydraulic non-equilibrium across the infiltration front. That is, the water content and pressure head are not in equilibrium according to some static water retention curve. The water content increases more rapidly in more conductive regions followed by a slow relaxation towards an equilibrium state behind the front. An extreme case is preferential infiltration into macropores. Since flow paths adapt to the structural heterogeneity of the porous medium, there is a direct link between structure and non-equilibrium. The aim of our study is to develop an upscaled description of water dynamics which conserves the macroscopic effects of non-equilibrium and which can be directly linked to structural properties of the material. A critical question is how to define averaged state variables at the larger scale. We propose a novel approach based on flux-weighted averaging of pressure head, and compare its performance to alternative methods for averaging. Further, we suggest some meaningful indicators of hydraulic non-equilibrium that can be related to morphological characteristics of infiltration fronts in quantitative terms. These methods provide a sound basis to assess the impact of structural connectivity on hydraulic non-equilibrium. We demonstrate our approach using numerical case studies for infiltration into two-dimensional heterogeneous media using three different structure models with distinct differences in connectivity. Our results indicate that an increased isotropic, short-range connectivity reduces non-equilibrium, whereas anisotropic structures that are elongated in the direction of flow enforce it. We observe a good agreement between front morphology and effective hydraulic non-equilibrium. A detailed comparison of averaged state variables with results from an upscaled model that includes hydraulic non-equilibrium outlines potential improvements in the description of non-equilibrium dynamics including preferential flow in simplified, upscaled models based on Richards equation.
    Keywords: Transient Flow ; Upscaling ; Pressure Head Averaging ; Hydraulic Non-Equilibrium ; Preferential Flow ; Connectivity ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 3
    In: Soil Science, 2012, Vol.177(1), pp.1-11
    Description: ABSTRACT: It is important to understand the impact of texture and organic carbon (OC) on soil structure development. Only few studies investigated this for silt-dominated soils. In this study, soil physical properties were determined on samples from a controlled experiment (Static Fertilization Experiment, Bad Lauchstädt, Germany) on a loess soil that started more than 100 years ago with six different combinations of organic and mineral fertilizers. The parameters measured include soil texture, water retention curve, air-connected porosity, gas diffusion coefficient, air permeability, and saturated hydraulic conductivity. The management resulted in a distinct gradient in OC. A bulk density gradient developed from differences in amount of clay not complexed with OC. This gradient in bulk density mainly affected content of pores larger than 3 μm. The air-connected porosity measured by a pycnometer was highly similar to the total air-filled porosity calculated from gravimetric water content. For all six treatments, diffusivities and permeabilities were quite similar; both suggested that air-filled pore space was inactive for gas transport for air saturation below 0.1, but became highly connected around 0.2 to 0.25. Furthermore, diffusion data from intact cores compared well with data from repacked samples measured at low air-filled porosities and another high-silt soil (Yolo silt loam, USA) measured at higher air-filled porosities. A two-parameter fitting model was used to analyze gas diffusion coefficient data; the model pore-connectivity factor was fairly constant, whereas the water blockage factor was markedly different. Water and air parameters both implied that change in bulk density was the major driver for diffusive and convective parameters in the experiment.
    Keywords: Soil Sciences ; Physical Properties ; Carbon ; Porosity ; Diffusion;
    ISSN: 0038-075X
    E-ISSN: 15389243
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  • 4
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(3), p.0
    Description: The rhizosphere has a controlling role in the flow of water and nutrients from soil to plant roots; however, its hydraulic properties are not well understood. As roots grow, they change the pore size distribution of the surrounding soil. Roots release polymeric substances such as mucilage into their rhizosphere. Microorganisms living in the rhizosphere feed on these organic materials and release other polymeric substances into the rhizosphere. The presence of these organic materials might affect the water retention properties and the hydraulic conductivity of the rhizosphere soil during drying and rewetting. We used neutron radiography to monitor the dynamics of water distribution in the rhizosphere of lupin (Lupinus albus L.) plants during a period of drying and rewetting. The rhizosphere was shown to have a higher water content than the bulk soil during the drying period but a lower one during the subsequent rewetting. We evaluated the wettability of the bulk soil and the rhizosphere soil by measuring the contact angle of water in the soil. We found significantly higher contact angles for the rhizosphere soil than the bulk soil after drying, which indicates slight water repellency in the rhizosphere. This explains the lower soil water content in the rhizosphere than the bulk soil after rewetting. Our results suggest that the water holding capacity of the rhizosphere is dynamic and might shift toward higher or lower values than those of the surrounding bulk soil, not affected by roots, depending on the history of drying and rewetting cycles.
    Keywords: Soils ; Hydrogeology ; Absorption ; Carbohydrates ; Compactness ; Concentration ; Ecology ; Habitat ; Hydraulic Conductivity ; Hydrologic Cycle ; Hydrology ; Hydrophobic Materials ; Imagery ; Lipids ; Lupinus Albus ; Measurement ; Microorganisms ; Moisture ; Nuclear Magnetic Resonance ; Nutrients ; Organic Compounds ; Physical Properties ; Plantae ; Polymers ; Polysaccharides ; Porosity ; Rhizosphere ; Roots ; Soil Profiles ; Soil-Water Balance ; Soils ; Spectroscopy ; Tomography ; Wettability ; X-Ray Data;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 5
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(4), p.0
    Description: The hydraulic behavior of soil is determined by the spatial heterogeneity of its hydraulic properties. The interplay among parent material, pedogenesis, and tillage leads to characteristic structures in cultivated soils. Tillage-induced features like a loosely aggregated seed bed, a compacted plow pan, and soil compaction beneath tractor ruts overlay natural features such as facies and horizons. Assessing the impact of such structural components on vadose zone hydrology requires an observation scale of several meters and a resolution in the range of centimeters, which is not feasible with experimental setups. An alternative solution is the generation of synthetic but realistic structures and their hydraulic properties as a basis for modeling the hydraulic behavior in response to different boundary conditions. With such "virtual soils" at hand, comparative studies are possible that help explore the relation between soil architecture and soil function. We developed a structure generator that provides great flexibility in the design of virtual soils with nested heterogeneity. Virtual soils with increasing complexity were generated to explore scenarios of precipitation and evaporation for a period of several months. The simulations demonstrated that the structure and the hydraulic properties close to the soil surface originating from tillage clearly govern atmospheric boundary fluxes, while the impact of heterogeneity on groundwater recharge is more complex due to threshold effects, hydraulic nonequilibrium, and the interaction with atmospheric forcing. A comparison with one-dimensional, effective representations of these virtual soils demonstrated that upscaling of soil water dynamics becomes inaccurate when lateral fluxes become relevant at the scale of observation.
    Keywords: Hydrogeology ; Soils ; Agriculture ; Air ; Aquifers ; Boundary Conditions ; Ground Water ; Heterogeneity ; Hydraulic Conductivity ; Hydrodynamics ; Moisture ; Morphology ; Recharge ; Simulation ; Soil-Atmosphere Interface ; Soils ; Tillage ; Topsoil ; Unsaturated Zone ; Virtual Reality ; Water;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 6
    Text Resource
    Text Resource
    Universitäts- und Landesbibliothek Sachsen-Anhalt
    Description: Fluss und Transport in natürlichen porösen Medien werden durch die Strukturheterogenität des Untergrunds bestimmt. Konnektivität ist ein wichtiger Aspekt jener Strukturheterogenität, der richtig erfasst werden muss, um Modelvorhersagen zu verschiedenen physikalischen Prozessen zu ermöglichen oder zu verbessern. Die vorliegende Arbeit präsentiert neue Erkenntnisse über die quantitative Beschreibbarkeit von Strukturkonnektivität und die komplexe Beziehung zwischen struktureller und funktionaler Konnektivität in Bezug auf die Hydrologie der ungesättigten Zone. Funktionale Konnektivität beschreibt dabei das effektive hydraulische Verhalten in Bezug auf stationären Fluss, Stofftransport und hydraulisches Ungleichgewicht. Numerische Simulationen zeigen, dass eine gute Reproduktion von Strukturkonnektivität auch zu einer guten Reproduktionen funktionaler Konnektivität führt. Strukturkonnektivität beeinflusst jedoch effektiven Fluss, Transport und hydraulisches Ungleichgewicht auf unterschiedliche Weise. Funktionale Konnektivität muss daher als ein prozess- und zustandsabhängiges Konzept aufgefasst werden.... ; Flow and transport in the subsurface are determined by the structural heterogeneity of natural porous media. Connectivity is known to be an important facet of structural heterogeneity that has to be captured adequately in order to facilitate or improve model predictions on diverse physical processes in porous formations. This thesis presents some novel insights into the approaches to quantify structural connectivity and the complex relationship between structural and functional connectivity in the realm of vadose zone hydrology. Functional connectivity is expressed as effective hydraulic behavior with respect to stationary flow, solute transport and hydraulic non-equilibrium during infiltration. Numerical simulations demonstrate that a good reproduction of structural connectivity also entails a good reproduction of functional connectivity metrics. However, structural connectivity affect upscaled flow, transport and hydraulic non-equilibrium behavior differently. Thus, functional connectivity has to be considered as a process and state-dependent concept....
    Keywords: Bodenphysik ; Stoffübertragung ; Online-Publikation ; Hochschulschrift ; Konnektivitätsmaße; Stochastische Rekonstruktion; Stationärer Fluss; Stofftransport; Hydraulisches Ungleichgewicht; Upscaling ; Connectivity Metrics; Stochastic Reconstruction; Stationary Flow; Solute Transport; Hydraulic Nonequilibrium; Upscaling ; Ddc::600 Technik, Medizin, Angewandte Wissenschaften::630 Landwirtschaft::631 Technik, Ausstattung, Materialien
    Source: DataCite
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