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  • 1
    Language: English
    In: Vadose Zone Journal, 2013, Vol.12(4), p.0
    Description: The hydraulic behavior of soil is determined by its hydraulic properties and their variability in space. In agricultural soils, this heterogeneity may stem from tillage or may have natural origin. The root distribution of plants will adapt to some extent to this soil heterogeneity. However, the combined impact of soil heterogeneity and root water uptake (RWU) on long-term soil water budgets has not received much attention. Numerical experiments helped identify how soil heterogeneity affects plant transpiration, soil evaporation, and groundwater recharge. Two-dimensional virtual soils with hierarchical heterogeneity, both natural and tillage induced, served as a basis for modeling soil water dynamics for a 10-yr climate record from two weather stations in Germany that vastly differ in annual precipitation. The complex interactions between soil and vegetation were explored by (i) comparing different RWU strategies (depth-, structure-, and time-dependent root profiles), (ii) land use types (perennial grass and annual winter crops), (iii) a combination of textures (silt above sand and sand above loam), and (iv) RWU with or without a compensation mechanism. The simulations were repeated with one-dimensional, effective representations of these virtual soils. In the framework of hydropedology, this study shed some light on the interaction between plants and pedological features and its impact on the macroscopic soil water budget. We demonstrated that land use has a major impact on the annual water balance through the partitioning of evapotranspiration into bare soil evaporation and plant transpiration. Compensational RWU becomes important for the annual water balance when the root zone comprises contrasting materials with respect to water holding capacity. Soil heterogeneity has in fact a minor impact on long-term soil water budgets. As a consequence, the relative contribution of plant transpiration, soil evaporation, and groundwater recharge to the total soil water loss was well reproduced by simulations in one-dimensional effective soil profiles. This advocates the application of one-dimensional soil-atmosphere-vegetation transfer (SVAT) models at larger scales. These findings only hold for assumptions made in our numerical simulations including flat area without lateral flow and no macropore flow.
    Keywords: Environmental Geology ; Soils ; Atmosphere ; Boundary Conditions ; Central Europe ; Eastern Germany ; Europe ; Field Studies ; Germany ; Grain Size ; Heterogeneity ; Hydrodynamics ; Hydrology ; Hydropedology ; Julicher Borde Germany ; Land Use ; Magdeburg Germany ; Mapping ; North Rhine-Westphalia Germany ; Numerical Models ; One-Dimensional Models ; Rhizosphere ; Saxony-Anhalt Germany ; Scale Factor ; Size Distribution ; Soil-Atmosphere-Vegetation Transfer ; Soils ; Topography ; Two-Dimensional Models ; Unsaturated Zone ; Vegetation ; Water Balance ; Western Germany;
    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
    Library Location Call Number Volume/Issue/Year Availability
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  • 3
    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
    Library Location Call Number Volume/Issue/Year Availability
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