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  • 1
    Language: English
    In: Geoderma, 15 April 2019, Vol.340, pp.269-278
    Description: Soil-born exudates such as mucilage are known to affect soil physicochemical properties. Characterization of the gel properties of mucilage at the pore-scale is necessary to gain mechanistic understanding of the underlying processes leading to changes of soil properties. Yet, mucilage intrinsic properties' complicate its - detection. Longitudinal and transverse magnetic relaxation rates measured with H Nuclear Magnetic Resonance (NMR) relaxometry have the potential to study mucilage-water interactions - as they are sensitive to restricted molecular motion of water protons in biohydrogels. However, the relations between water mobility and biohydrogel properties in porous media have remained unknown until now. In this study, the mobility of water molecules in chia seed mucilage in porous systems was systematically investigated by means of H NMR relaxometry. Chia seed mucilage was used as it has hydrogel properties shared by a range of biological hydrogels found in soil. Glass beads of several sizes were used to study the influence of the pore size on the NMR signal. A conceptual model based on the equations describing the relaxation of water protons in porous media was developed to integrate these gel effects into the NMR parameters. The increased rigidity of the polymer network and its organization in the pore space, which depended on the particle size and the mucilage concentration, were assessed as the gel effects significantly affecting the bulk relaxation. Our approach, which combines the use of NMR along with other imaging methods, is a promising strategy to detect and characterize the properties of biohydrogel in porous media.
    Keywords: Mucilage ; Pore Size ; 1h NMR Relaxometry ; Gel Effect ; Water Mobility ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 2
    Language: English
    In: Journal of Hydrology, December 2015, Vol.531, pp.792-801
    Description: The major groundwater resources of the Arabian Peninsula are stored in the large sedimentary basins in its eastern part. Evaporation from continental salt pans (playas) is an important process in water resources assessments of its upper principal aquifers – the Upper Mega Aquifer system – as it constitutes a significant sink. However, literature values on evaporation rates vary widely and usually report about coastal salt pans where seawater evaporation is assumed. The present study applies different methods to provide a comprehensive picture of groundwater evaporation from salt pans of the Upper Mega Aquifer system. A remote sensing approach provided the spatial distribution and total salt pan area of about 36,500 km . Hydrochemical and isotopic investigations revealed that from about 10% (3600 km ± 1600 km ) of the mapped salt pan area seawater evaporates. To estimate the groundwater evaporation rate from continental salt pans a laboratory column experiment was set up, implying a mean annual evaporation rate of about 42 mm ± 13 mm. In-situ analysis of water table fluctuations in the field suggested about 3 mm a originate from recently infiltrated rainwater leading to an annual net groundwater evaporation of 39 mm ± 13 mm. Relating this number to the mapped salt pan area, from which groundwater evaporates, provides a total annual groundwater loss of 1.3 km ± 0.5 km for the Upper Mega Aquifer system.
    Keywords: Evaporation ; Salt Pan ; Playa ; Sabkha ; Remote Sensing ; Column Experiment ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: Portuguese
    In: Scientia Agricola, 01 April 2011, Vol.68(2), pp.160-166
    Description: The understanding of the preferential water flow and solute transport is important with regard to losses of nutrients and pesticides that affect the quality of the groundwater or surface water resources. Experiments using the brilliant blue dye tracer, a tension infiltrometer (TI) and a double square infiltrometer (DI) were carried out in the experimental field site located around 15 km southeast of the city of Rostock (North-Eastern Germany) on arable land in a Pleistocene lowland landscape where corn (Zea mays L.) and barley (Hordeum spp.) had been cultivated. One day after dye the infiltration, a pit was dug and vertical profiles were prepared in the TI and DI sites to assess the dye pathways in the subsoil of a Gleyic Luvisol. We wanted to examine if the mottled red and white (bleached) colour-pattern of the Gleyic Luvisol subsoil resulting from temporally stagnant water could be related to flow paths as visualized by dye tracing and if the soil colour could be related to other physical soil properties. Biogenic soil structures were the main transport routes conducting water and solutes into great depth in short time. These pathways had lower bulk density and less cone resistance than the adjacent red or white (bleached) areas of the Gleyic Luvisol subsoil. The red areas were involved in transport because their water contents increased after as compared to before infiltration. However, the measured physical soil properties did not differ between white and red areas. We assume that red areas participate in transport at least by imbibing water from the adjacent biogenic flow paths.
    Keywords: Agriculture, Multidisciplinary ; Umidade Do Solo ; Densidade Do Solo ; Resistência ; Soil Water Content ; Bulk Density ; Cone Resistance ; Agriculture
    ISSN: 1678-992X
    ISSN: 01039016
    E-ISSN: 1678-992X
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  • 4
    Language: English
    In: Journal of Hydrology, 2004, Vol.289(1), pp.239-257
    Description: A tile-drained agricultural field can be regarded as a "field-scale" lysimeter that may be used to study soil water and chemical transport under relatively natural conditions. Tile discharge and effluent bromide concentrations measured in a previous field tracer experiment for a structured clayey loam at Bokhorst, Northern Germany, indicated strong preferential flow. Simulation using single domain HYDRUS numerical flow and transport model could nevertheless explain water outflow, however, completely failed to describe tile-drain leaching patterns of the conservative tracer. The objective of this paper was to analyze whether the nonequilibrium-type dual-permeability model concept could better capture soil structure related principle mechanisms of preferential leaching in the unsaturated soil at that study site. The dual-permeability model (DUAL) describes for soil matrix and fracture pore systems Darcian flow with coupled Richards' equations and convective-dispersive (CD) solute transport with coupled CD equations. The hydraulic parameters of the dual-permeability model were obtained from standard soil hydraulic measurements by adopting a bimodal fitting procedure, whereas transport parameters were inferred from soil column tracer experiments and geometrical transfer term parameters were derived using qualitative soil structure descriptions. The hydraulic conductivity K (sub a) in the inter-domain water transfer term and the effective diffusion coefficient D (sub a) in the solute mass transfer term were calibrated by comparing simulated with measured tile flow and effluent concentrations. The DUAL approach described water flow similarly well as the single-domain model. Bromide concentrations in the tile effluent could be approximated with DUAL when decreasing the K (sub a) and D (sub a) values by three orders of magnitude compared with the values of the soil matrix domain. The dual-permeability approach seems to reflect nonequilibrium transport mechanisms at this structured soil since it not only predicts concentration peaks in initial leaching phases during early time events of the experiment but also the observed reverse reaction of decreased effluent concentrations in initial phases of leaching events during later times of the experiment. The latter occurs when bromide-free infiltrating water is diluting bromide concentrations in the fracture domain such that less concentrated water is preferentially draining from tiles in initial phases of infiltration. Bromide effluent concentrations gradually increase in later phases since vertical flow velocities decrease while "diffusive" solute transfer from the soil matrix continues. Mass transfer restrictions (e.g. due to soil aggregate coatings) may effectively be controlling preferential leaching at this site.
    Keywords: Preferential Flow ; Bromide Tracer ; Dual-Permeability Model ; Mass Transfer ; Subsurface Drains ; Tile Effluent ; Glacial Till ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 5
    Language: English
    In: Journal of Hydrology, 2011, Vol.403(1), pp.141-156
    Description: ► A surface-subsurface flow model with multi-objective global optimization is presented. ► The model performance was evaluated using bench-scale flow experiments. ► Inverse parameter estimation required observations at different spatial positions. ► The Pareto trade-off and model mismatch suggest lateral flow in soil layers. ► The model system is versatile for studying soil water and overland flow. A comprehensive description of water flow in environmental and agricultural systems requires an account of both surface and subsurface pathways. We present a new model which combines a 1D overland flow model and the 2D subsurface flow HYDRUS-2D model, and uses the multi-objective global search method AMALGAM for inverse parameter estimation. Furthermore, we present data from bench-scale flow experiments which were conducted with two 5-m long replicate soil channels. While rainfall was applied, surface runoff was recorded at the downstream end of the soil channel, subsurface drainage waters were sampled at three positions equally spaced along the channels, and pressure heads were recorded at five depths. The experimental observations were used to evaluate the performance of our modeling system. The complexity of the modeling approach was increased in three steps. First, only runoff and total drainage were simulated, then drainage flows from individual compartments were additionally evaluated, and finally a surface crust and immobile soil water were also considered. The results showed that a good match between measured and observed surface runoff and total drainage does not guarantee accurate representation of the flow process. An inspection of the Pareto results of different multiobjective calibration runs revealed a significant trade-off between individual objectives, showing that no single solution existed to match spatial variability in the flow. In spite of the observed crust formation, its consideration in the more complex model structure did not significantly improve the fit between the model and measurements. Accounting for immobile water regions only slightly improved the fit for one of the two replicate soil channels. Discrepancies between relatively complex model simulations and seemingly simple soil channel experiments suggest the presence of additional unknowns, such as heterogeneity of the soil hydraulic properties. Nevertheless, with its versatile subsurface options and powerful inverse method, the model system shows promise for studying hillslope flow problems involving both surface runoff and subsurface flow.
    Keywords: Overland Flow ; Surface Runoff ; Multi-Objective Global Parameter Optimization ; Mobile–Immobile Model ; Simulation ; Flow Channel Experiment ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 6
    Language: English
    In: Vadose Zone Journal, 2011, Vol.10(3), p.1082
    Description: Predicting solute transport through structured soil based on observable structural properties of the material has not been accomplished to date. We evaluated a new approach to predicting breakthrough curves (BTCs) of dissolved chemicals in intact structured soil columns based on attributes of the pore structure at hierarchical spatial scales. The methodology centers on x-ray computed microtomography of a hierarchic suite of undisturbed soil samples (diameters 1, 4.6, 7.5, and 16 cm) to identify the network of pores 〉10 mu m in diameter. The pore structure was quantified in terms of pore size distribution, interface area density, and connectivity. The pore size distribution and pore connectivity were used to set up an equivalent pore network model (PNM) for predicting the BTCs of Br (super -) and Brilliant Blue FCF (BB) at unsaturated, steady-state flux. For a structured silt loam soil column, the predictions of Br (super -) tracer breakthrough were within the variation observed in the column experiments. A similarly good prediction was obtained for Br (super -) breakthrough in a sandy soil column. The BB breakthrough observed in the silt loam was dominated by a large variation in sorption (retardation factors between R = 2.9 and 24.2). The BB sorption distribution coefficient, k (sub d) , was measured in batch tests. Using the average k (sub d) in the PNM resulted in an overestimated retardation (R = 28). By contrast, breakthrough of BB in the sandy soil (experimental R = 3.3) could be roughly predicted using the batch test k (sub d) (PNM simulation R = 5.3). The prediction improved when applying a sorption correction function accounting for the deviation between measured interface area density distribution and its realization in the network model (R = 4.1). Overall, the results support the hypothesis that solute transport can be estimated based on a limited number of characteristics describing pore structure: the pore size distribution, pore topology, and pore-solid interfacial density.
    Keywords: Soils ; Bad Lauchstadt Germany ; Boundary Conditions ; Breakthrough Curves ; Bromine ; Central Europe ; Central Germany ; Chemical Dispersion ; Chernozems ; Computed Tomography ; Convection ; Density ; Dye Tracers ; Equations ; Europe ; Experimental Studies ; Fuhrberg Germany ; Germany ; Halogens ; Image Analysis ; Laboratory Studies ; Lower Saxony Germany ; Microtomography ; Minckowski Functions ; Morphology ; Networks ; Podzols ; Porosity ; Quantitative Analysis ; Saxony-Anhalt Germany ; Simulation ; Soils ; Solute Transport ; Spectra ; Tomography ; Topology ; Transport ; X-Ray Spectra;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
    Source: CrossRef
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  • 7
    In: Water Resources Research, November 2018, Vol.54(11), pp.9033-9044
    Description: Structural hierarchy is a fundamental characteristic of natural porous media. Yet it provokes one of the grand challenges for the modeling of fluid flow and transport since pore‐scale structures and continuum‐scale domains often coincide independent of the observation scale. Common approaches to represent structural hierarchy build, for example, on a multidomain continuum for transport or on the coupling of the Stokes equations with Darcy's law for fluid flow. These approaches, however, are computationally expensive or introduce empirical parameters that are difficult to derive with independent observations. We present an efficient model for fluid flow based on Darcy's law and the law of Hagen‐Poiseuille that is parameterized based on the explicit pore space morphology obtained, for example, by X‐ray μ‐CT and inherently permits the coupling of pore‐scale and continuum‐scale domain. We used the resulting flow field to predict the transport of solutes via particle tracking across the different domains. Compared to experimental breakthrough data from laboratory‐scale columns with hierarchically structured porosity built from solid glass beads and microporous glass pellets, an excellent agreement was achieved without any calibration. Furthermore, we present different test scenarios to compare the flow fields resulting from the Stokes‐Brinkman equations and our approach to comprehensively illustrate its advantages and limitations. In this way, we could show a striking efficiency and accuracy of our approach that qualifies as general alternative for the modeling of fluid flow and transport in hierarchical porous media, for example, fractured rock or karstic aquifers. A model for the simulation of pore‐scale and continuum‐scale flow in hierarchically structured porous media is developed Explicit pore space morphology obtained by image analysis of X‐ray micro‐CT images is used for parameterization Predictions of solute breakthrough obtained by particle tracking perfectly match observations
    Keywords: Darcy'S Law ; Particle Tracking ; Column Experiments ; X‐Ray Μ‐Ct ; Pore Space Morphology ; Image Analysis
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 8
    Language: English
    In: Journal of Hydrology, 2006, Vol.321(1), pp.390-408
    Description: Systematically tile drained field sites have been recognized as one major source for surface water contamination with agrochemicals. To study the effects of tile drainage and physical non-equilibrium on solute transport in structured soil, bromide (Br ) transport experiments were carried out on three plots (A, B, C) with different tile drain depths (128, 101, 96 cm) and spacings (16, 18 and 12 m) at the Infeld experimental field site (North–West Germany). Tile drain outflow along with Br concentrations were monitored over a half-year period. For all three plots, fast Br breakthrough was observed with Br concentrations fluctuating around levels below 6 mg/L during the experiment without a distinct concentration maximum. Experimental observations of plot B were analyzed using one-dimensional (1D) and two-dimensional (2D) single-porosity model (SPM) and mobile-immobile model (MIM) approaches. All SPM and MIM parameters were obtained from independent measurements, except for the calibrated MIM water and solute transfer coefficients. Water flow and Br transport were then predicted for the A and C plots using the model parameters as obtained for plot B. Measured plateau-like Br concentrations could only be consistently calibrated (plot B) and predicted (A and C) using the 2D-MIM approach, while the 1D-MIM, 2D-SPM, and 1D-SPM approaches (in this order) increasingly deviated from the experimental data. The MIM simulations suggested that solute transfer into the immobile region represented more than 60% of the surface applied Br . Non-equilibrium transport with advective and diffusive mass transfer increased early mass loss and entailed extended, slower leaching as compared to equilibrium transport. Furthermore, model simulations suggested that the two-dimensional flow field as induced by tile drains enhanced Br dispersion and accelerated Br appearance in the drain. This study showed that both the variably-saturated 2D flow field and physical non-equilibrium transport should be explicitly accounted for in physically based model simulations of solute transport in tile-drained structured field soils.
    Keywords: Field-Scale Experiment ; Subsurface-Drainage ; Physical Non-Equilibrium ; Preferential Flow and Transport ; Mobile-Immobile Model ; Two-Dimensional Modeling ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 9
    Language: English
    In: Geoderma, 01 September 2018, Vol.325, pp.37-48
    Description: Organic particles including microorganisms are a significant fraction of the mobile organic matter (MOM) pool that contributes to initial pedogenesis. Still, the dynamics and the interplay of the multitude of processes that control the mobilization, transport, and retention of MOM are vastly unclear. We studied this interplay using an ‘artificial soil’ as model for a young, unstructured soil with defined initial composition employing a novel two-layer column experiment. The upstream layer was composed of a mixture of well-defined mineral phases, a sterile organic matter source and a diverse, natural microbial inoculant mimicking an organic-rich topsoil. The downstream layer, mimicking the subsoil, was composed of the mineral phases, only. Columns were run under water-unsaturated flow conditions with multiple flow interruptions to reflect natural flow regimes and to detect possible non-equilibrium processes. Pore system changes caused by flow were inspected by scanning electron microscopy and computed micro-tomography. MOM-related physicochemical effluent parameters and bacterial community diversity and abundance were assessed by molecular analysis of the effluent and the solid phase obtained after the long-term irrigation experiment (75 d). Tomographic data showed homogeneous packing of the fine-grained media (sandy loam). During flow, the initially single-grain structured artificial soil showed no connected macropores. In total, 6% of the initial top layer organic matter was mobile. The release and transport of particulate (1.2%) and dissolved organic matter (4.8%) including bacteria were controlled by non-equilibrium conditions. Bacterial cells were released and selectively transported to downstream layer resulting in a depth-dependent and selective establishment of bacterial communities in the previously sterile artificial soil. This study underlines the importance of bacterial transport from the surface or topsoil for colonization and maturation of downstream compartments. This initial colonization of pristine surfaces is the major step in forming biogeochemical interfaces - the prominent locations of intensive biological activity and element turnover that seem to play a major role for the functioning of soil.
    Keywords: Mobile Organic Matter ; Unsaturated Two-Layer Column Experiment ; Experimental Pedogenesis ; Artificial Soil ; Computed Micro-Tomography ; Molecular Analysis ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 10
    Language: English
    In: Vadose Zone Journal, 2005, Vol.4(3), p.866
    Description: Soil water suction cups used in laboratory solute transport studies may cause undesired perturbations of the flow field. The twofold objective of this study was to test mini suction cups, and to assess the effects of pore water- extraction rate and cup size on preferential water flow and bromide (Br super(-)) breakthrough. Porous ceramic cups of 0.25-cm outer diameter and 1-cm length could extract 1 cm super(3) of pore water within 17 (34, 38) min from 100% (85%, 70%) saturated loam soil by applying 0.1 (0.3, 0.5) bar suction. The corresponding sampling times for larger cups (0.6-cm diam., 2-cm length) were 3.3, 4.6, and 5.7 min. The smaller cups were subsequently tested for solution extraction of 1-cm super(3) samples every 20 min out of the matrix and preferential flow path (PFP) of a large soil column (24-cm diam., 80-cm high) during a Br super(- ) transport experiment. Numerical simulations were used (i) to describe the Br super(-) transport experiment and (ii) to evaluate how preferential Br super(-) transport would be affected by pore solution extraction at different locations in the matrix and the PFP of a loam soil block (20 by 20 by 20 cm super(3)) subject to wet and dry initial conditions. Three-dimensional water flow and solute transport were simulated using the Richards and convection-dispersion equations. The experimental and simulation results revealed a dilemma: while fast solution extraction using larger cups altered the flow field and preferential Br super(-) breakthrough for wet and particularly for dry initial conditions, slower solution extraction using small cups caused negligible perturbation of the flow field, but yielded insufficient resolution of the preferential Br super(-) breakthrough. Sampling in the matrix did not considerably affect Br super(-) transport, and gave sufficient resolution of the matrix Br super(-) peak. This study showed that the use of suction cups for measuring solute transport may be problematic in case of preferential flow.
    Keywords: Ceramics ; Soil ; Pore Water ; Loam ; Simulation ; Water Flow ; Testing Procedures ; Pores ; Soil Water Suction ; Bromides ; Solute Transport ; Laboratories ; Soil Columns ; Flow Discharge ; Interstitial Water ; Sampling ; Loam ; Preferential Flow ; Testing Procedures ; Pores ; Soil Water Suction ; Bromides ; Solute Transport ; Laboratories ; Soil Columns ; Flow Discharge ; Interstitial Water ; Sampling ; Loam ; Preferential Flow ; Sources and Fate of Pollution ; Monitoring and Analysis of Water and Wastes ; Freshwater Pollution;
    ISSN: Vadose Zone Journal
    E-ISSN: 1539-1663
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