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  • 1
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(4), p.0
    Description: We investigated the feasibility of simultaneous identification of soil hydraulic and root-distribution parameters by inverse simulation of soil water flow in monolithic lysimeters under atmospheric boundary conditions using the Richards equation and a macroscopic root water uptake model. Weighable lysimeters are powerful test systems for this purpose because the boundary fluxes (precipitation, actual evapotranspiration, and seepage across the bottom) can be determined very precisely. We analyzed the amount of information needed for the unique identification of parameters and investigated the magnitude of their uncertainties. First, we examined synthetic data sets for different scenarios and instrumentation campaigns that differed in their information content and complexity of soil properties. Atmospheric boundary conditions as measured at the lysimeter station in Wagna, Austria, were used as forcing data. The results show that for homogeneous profiles, cumulative outflow and profile-averaged water content data contain enough system information to allow the simultaneous estimation of soil hydraulic properties and root-distribution parameters. In contrast, for soil profiles consisting of two layers, unique soil hydraulic parameters and the correct rooting depth could only be estimated if matric potential measurements from both layers were included in the objective function. Finally, soil hydraulic properties of the grass-reference lysimeter in Wagna were estimated using real measurements. Water dynamics in the lysimeter could be described well by an effective parameterization assuming a homogeneous soil profile. Furthermore, the system behavior under different boundary conditions could be predicted adequately with the estimated parameters. This demonstrates the usefulness of the identified system properties for predictive modeling.
    Keywords: Soils ; Hydrogeology ; Austria ; Boundary Conditions ; Cambisols ; Central Europe ; Europe ; Field Studies ; Hydrodynamics ; Inverse Problem ; Lysimeters ; Moisture ; Numerical Models ; Richards Equation ; Roots ; Simulation ; Soil Profiles ; Soils ; Spatial Distribution ; Statistical Analysis ; Styria Austria ; Synthetic Data ; Unsaturated Zone ; Wagna Austria;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 2
    Language: English
    In: Vadose Zone Journal, 2013, Vol.12(3), p.0
    Description: Soils are structured on multiple spatial scales, originating from inhomogeneities of the parent material, pedogenesis, soil organisms, plant roots, or tillage. This leads to heterogeneities that cause variability of local measurements of hydraulic state variables and affects the flow behavior of water in soil. Whereas in real-world systems, the true underlying structures can never be absolutely known, it is appealing to employ synthetic or "virtual" experiments for assessing general properties of flow in porous media and grasping the main physical mechanisms. With this aim, three two-dimensional virtual realities with increasing structural complexity, representing cultivated soils with hierarchical spatial heterogeneity on multiple scales were constructed by the interdisciplinary research group Virtual Institute of the Helmholtz Association (INVEST). At these systems, numerical simulations of water dynamics including a heavy rain, a redistribution, and a long-lasting evaporation period were performed. The technical aspects of the construction of the virtual soils and results of the forward simulations have been presented in a paper by Schluter et al. (2012). In this follow-up paper, we use inverse modeling to investigate measurements in virtual vertical soil profiles, mimicking typical field monitoring campaigns with moisture content and matric potential sensors placed at five depths. Contrary to the real situation, we can interpret observed data, their variability, estimated hydraulic properties, and predicted water balance in the light of the known truth. Our results showed that measurements, particularly those of water contents, varied strongly with measuring position. Using data from single profiles in systems similar to our virtual soils thus will lead to very different estimates of the soil hydraulic properties. As a consequence, the correct calculation of the water balance is rather a lucky coincidence than the rule. However, the average of the predicted water balances obtained from the one-dimensional simulations, and the estimated soil hydraulic properties agreed very well with those attained from the two-dimensional systems.
    Keywords: Soils ; Hydrogeology ; Boundary Interactions ; Evaporation ; Grain Size ; Heterogeneous Materials ; Hydrodynamics ; Infiltration ; Interpretation ; Inverse Problem ; Irrigation ; Matric Head ; Measurement ; Moisture ; One-Dimensional Models ; Quantitative Analysis ; Simulation ; Size Distribution ; Soils ; Spatial Distribution ; Tdr Data ; Two-Dimensional Models ; Unsaturated Zone ; Van Genuchten-Mualem Parameters ; Water ; Water Balance;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 3
    Language: English
    In: Procedia Environmental Sciences, 2013, Vol.19, pp.564-573
    Description: Weighable lysimeters are powerful measurement systems for identifying soil hydraulic processes and properties, because the boundary fluxes (precipitation, actual evapotranspiration, and seepage across the bottom) can be determined very precisely. However, root water uptake by plants and the soil water flux are interrelated. Thus, the simultaneous estimation of root water uptake parameters and soil hydraulic parameters from macroscopic state observations is a challenge. In this study we investigated the possibility of simultaneously estimating root water uptake and soil hydraulic parameters by inverse simulation of soil water flow in monolithic lysimeters under atmospheric boundary conditions. We used the Richards equation and a macroscopic root water uptake model to simulate the processes. The amount of information needed for the unique identification of parameters was analyzed and the magnitude of their uncertainties was investigated. To check the principal feasibility of our approach, we first examined synthetic data sets for different scenarios and instrumentation campaigns that differed in their information content and complexity of soil properties. The investigations of synthetic data showed that for homogeneous profiles, cumulative outflow and profile-averaged water content data contained enough system information to allow the simultaneous estimation of soil hydraulic properties and root-distribution parameters. In contrast, for soil profiles consisting of two layers, unique soil hydraulic parameters and the correct rooting depth could only be estimated if matric potential measurements from both layers were included in the objective function. To test the procedure with real data, soil hydraulic properties of the grass-reference lysimeter at Wagna (Austria) were estimated using actual measurements. Water dynamics in the lysimeter could be described well by an effective parameterization assuming a homogeneous soil profile. Furthermore, the system behavior under different boundary conditions could be predicted adequately with the estimated parameters.
    Keywords: Soil Hydraulic Properties ; Inverse Modeling ; Root Water Uptake ; Environmental Sciences
    ISSN: 1878-0296
    E-ISSN: 1878-0296
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  • 4
    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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