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• 1
Article
Language: English
In: Transport in Porous Media, 2013, Vol.96(2), pp.271-294
Description: The 3D description of the soil structure at the pore scale level can help to elucidate the biological functioning of soil. The water–air distribution in the 3D-pore space is of particular interest because it determines the diffusion pathways of nutrients and the localisation of active soil microorganisms. We used the Shan–Chen interparticle-potential approach to simulate spontaneous phase separation in complex academic and real 3D-porous media using the advanced TRT lattice Boltzmann scheme. The equation of state and phase diagram were calculated and the model was verified using hydrostatic laws. The 3D pattern of water/air interface in two complex academic pore geometries was accurately computed. Finally, 3D maps of static liquid–gas distribution were simulated in a real 3D X-ray computed tomography image obtained from an undisturbed soil column sampled in a silty clay loam soil. The simulated soil sample of 1.7 cm 3 was described at a voxel-resolution of 60 μm. The range of the simulated saturations (from 0.5 to 0.9) was in a good agreement with the expected saturations calculated from the phase diagram.
Keywords: Lattice Boltzmann method ; Water meniscus ; TRT ; Shan–Chen ; Porous media
ISSN: 0169-3913
E-ISSN: 1573-1634
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• 2
Article
Language: English
In: Journal of Hydrology, December 2017, Vol.555, pp.253-256
Description: In the last decade, X-ray computed tomography (CT) has become widely used to characterize the geometry and topology of the pore space of soils and natural porous media. Regardless of the resolution of CT images, a fundamental problem associated with their use, for example as a starting point in simulation efforts, is that sub-resolution pores are not detected. Over the last few years, a particular type of modeling method, known as "Grey" or "Partial Bounce Back" Lattice-Boltzmann (LB), has been adopted by increasing numbers of researchers to try to account for sub-resolution pores in the modeling of water and solute transport in natural porous media. In this short paper, we assess the extent to which Grey LB methods indeed offer a workable solution to the problem at hand. We conclude that, in spite of significant computational advances, a major experimental hurdle related to the evaluation of the penetrability of sub-resolution pores, is blocking the way ahead. This hurdle will need to be cleared before Grey LB can become a credible option in the microscale modeling of soils and sediments. A necessarily interdisciplinary effort, involving both modelers and experimentalists, is needed to clear the path forward.
Keywords: Computer Modeling ; Transport Processes ; Image Resolution ; Measurement ; Interdisciplinary Research ; Geography
ISSN: 0022-1694
E-ISSN: 1879-2707
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• 3
Article
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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• 4
Article
Language: English
In: Science of the Total Environment, 01 July 2018, Vol.628-629, pp.1508-1517
Description: Conservation tillage practices mainly based on cover crops and no-tillage with accumulation of crop residues at the soil surface (mulch) modify the environmental fate of pesticides. However, only few pesticide fate models are able to consider mulch of crop residues as well as the effect of intermediate cover crops. Thus, the objective was to develop an approach to model the effects of crop residues left at the soil surface and cover crops on the fate of pesticides. This approach consisted in (1) considering the crop residues as a soil layer with specific physical, hydrodynamic and pesticide-reactivity properties close to that of a high organic content soil layer, and (2) introducing a correction factor of the potential evapotranspiration, estimated through a calibration step, to take into account the reduction of soil evaporation by the presence of a mulch. This approach was developed using MACRO as support pesticide model. To assess the model performances, we used the data from a field experiment designed in an irrigated maize monoculture under conservation tillage. Soil water content, water percolates, soil temperature and S-metolachlor herbicide concentrations in the leachate at 1 m depth were measured during two years. The approach chosen to simulate the mulch effects allowed MACRO to make acceptable predictions of the observed water percolation, soil temperature and to a less extent herbicide leaching. However, it showed a poor performance to simulate the soil water content. Results are discussed in terms of further modelling options to better assess the environmental risks of pesticides under conservation tillage. This approach remains to be tested against various soils, crops, pesticides and types of mulch.
Keywords: Pesticide Fate Model ; Macro ; Crop Residue ; Cover Crop ; Field Experiment ; Pesticide ; Environmental Sciences ; Biology ; Public Health
ISSN: 0048-9697
E-ISSN: 1879-1026
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• 5
Article
Language: English
In: Ecological Modelling, 2018, Vol.383, pp.10-22
Description: Soil respiration causes the second largest C flux between ecosystems and the atmosphere. Emerging soil carbon dynamics models consider the complex interplay of microscale interactions between the physical and biological drivers of soil organic...
Keywords: Life Sciences ; Uncertainty Analysis ; Sensitivity Analysis ; Lattice–Boltzmann Model ; Soil Architecture ; Carbon ; Bacteria ; Environmental Sciences ; Ecology
ISSN: 0304-3800
E-ISSN: 1872-7026
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• 6
Article
Language: English
In: Soil Biology and Biochemistry, November 2014, Vol.78, pp.189-194
Description: Modelling carbon mineralisation in natural soils is a major topic in soil and climate research. Current models need to be improved to include soil structure as an influencing factor to better predict C fluxes between pedosphere and atmosphere and to estimate carbon sequestration potentials. Geometry-based mechanistic modelling approaches have recently been developed to systematically study the effect of soil structure on carbon decomposition. Such models require spatially explicit input parameters describing the architecture of the pore space and the heterogeneous distribution of microbes and organic matter as decomposable substrate. The latter is very difficult to determine , resulting in increased uncertainty in the models. To obtain more realistic input data, we have developed a novel approach to locate soil organic matter (SOM) in undisturbed aggregates of soil using a combination of synchrotron-based X-ray microtomography and osmium as a staining agent for SOM. Here, we present the first results using 5 mm sized soil aggregate samples with contrasting C-contents in which we obtained maps of organic matter distributions in relation to the pore networks at the aggregate scale.
Keywords: Soil Organic Matter ; Soil Structure ; Carbon Sequestration ; Synchrotron Microtomography ; Staining ; Agriculture ; Chemistry
ISSN: 0038-0717
E-ISSN: 1879-3428
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• 7
Article
Language: English
In: Geoderma, 15 April 2016, Vol.268, pp.29-40
Description: Compost amendments and tillage practices can modify soil structure and create heterogeneities at the local scale. Tillage affects soil physical properties and consequently water and solute transport in soil, while compost addition to soil influences pesticide sorption and degradation processes. Based on the long-term field experiment QualiAgro (a INRA–Veolia partnership), a modeling study was carried out using HYDRUS-2D to evaluate how two different compost types combined with the presence of heterogeneities due to tillage affect water and isoproturon dynamics in soil compared to a control plot. A municipal solid waste compost (MSW) and a co-compost of sewage sludge and green wastes (SGW) have been applied to experimental plots. In each plot, wick lysimeters, TDR probes, and tensiometers were installed to monitor water and solute dynamics. In the plowed layer, four zones differing in their structure were identified: compacted clods, non-compacted soil, interfurrows, and the plow pan. From 2004 to 2010, the unamended control (CONT) plot had the largest cumulative water outflow (1388 mm) compared to the MSW plot (962 mm) and SGW plot (979 mm). After calibration, the model was able to describe cumulative water outflow for the whole 2004–2010 period with a model efficiency value of 0.99 for all three plots. The CONT plot had the largest isoproturon cumulated leaching (21.31 μg) while similar cumulated isoproturon leaching was measured in the SGW (0.663 μg) and MSW (0.245 μg) plots. The model was able to simulate isoproturon leaching patterns except for the large preferential flow events that were observed in the MSW and CONT plots. The timing of these preferential flow events could be reproduced by the model but not their magnitude. Modeling results indicate that spatial and temporal variations in pesticide degradation rate due to tillage and compost application play a major role in the dynamics of isoproturon leaching. Both types of compost were found to reduce isoproturon leaching on the 6 year duration of the experiment.
Keywords: Soil Heterogeneity ; Compost Amendments ; Conventional Tillage ; Water Flow ; Isoproturon ; Hydrus-2d ; Agriculture
ISSN: 0016-7061
E-ISSN: 1872-6259
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• 8
Article
Language: English
In: Geoderma, April 2015, Vol.243-244, pp.18-28
Description: Temporal variations in soil physical properties are rarely recorded in field experiments or considered when modeling water and solute dynamics in agricultural soils. This study aimed at (a) quantifying the temporal variations in soil physical properties, such as the saturated hydraulic conductivity ( ), bulk density ( ) and soil water retention during the growing season of an irrigated maize crop conventionally tilled with a moldboard plow, and (b) modeling the observed water dynamics. For modeling, the effect of temporal variations of soil properties was explored and compared to results with constant values of soil properties during the simulation period and with results after an optimization of soil parameters by inverse modeling. Field and laboratory experiments were performed to measure the soil physical properties of five soil compartments (defined according to the position relative to crop row and the depth) at three dates during the maize season (sowing, flowering and just before harvest). During the maize season, values ranged from 1.21 to 1.56 g cm and increased with time (by 15–25% of the initial value). values, ranging from 2.9 to 56.3 mm h , significantly decreased with time (by a factor of 3 to 6) according to the soil compartment, and were negatively correlated with . In the first step to model water dynamics, the initial values of soil physical properties (measured at maize sowing) were used as constant input parameters for the model HYDRUS-2D during the maize season. This simulation led to a poor description of soil water potentials and water content dynamics, without any drainage at 100 cm depth during the maize season. After an optimization of soil physical parameters, the description of the water dynamics was significantly improved, but optimized parameters, especially and , were not within the range of field measurements. In a last modeling step, the simulation period was divided into three periods with a specific parameterization of soil physical properties for each period. The description of the water dynamics was improved compared to the simulation with constant values for soil physical properties. Such results argue for taking into account time-variable soil physical properties in modeling to correctly assess the water and solute dynamics in soils.
Keywords: Hydraulic Potential ; Volumetric Water Content ; Hydrus-2d ; Drainage ; Saturated Hydraulic Conductivity ; Agriculture
ISSN: 0016-7061
E-ISSN: 1872-6259
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• 9
Article
Language: English
In: Frontiers in Microbiology, 2018, Vol.9, p.1583
Description: There is still no satisfactory understanding of the factors that enable soil microbial populations to be as highly biodiverse as they are. The present article explores in silico the hypothesis that the heterogeneous distribution of soil organic...
Keywords: Life Sciences ; Bacteria ; Resource Allocation ; Organic Matter ; Pore Scale ; Soil ; Biodiversity ; Agent-Based Modeling ; Biology
ISSN: 1664-302X
E-ISSN: 1664-302X
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• 10
Article
Language: English
In: Transport in Porous Media, 2017, Vol.116(3), pp.975-1003
Description: Hydrogen gas migration modeling through water-saturated engineering barriers and the host rock of a deep geological repository for radioactive waste is of concern for safety assessment of such facilities. A two-phase two-relaxation-time lattice Boltzmann model using the Rothman and Keller approach was parallelized on graphic processing units to simulate hydrogen gas migration in a 3D image obtained by X-ray microtomography of Opalinus clay microfractures. A dimensional analysis combined with a grid refinement analysis was carried out to set the model parameters to reproduce the realistic viscous, capillary and inertial forces of the natural system. Relative permeabilities curves were first calculated in a simple regular fracture with different initial two-phase configurations. We observed that segmented gas flow configurations led to a drop in the relative gas permeability by two orders of magnitude as compared to parallel flow configuration. The model was then applied to 4 $$\times$$ × refined 3D images. For lower water saturation values ( $$0.5 \le S_\mathrm{w} 〈 0.7$$ 0.5 ≤ S w 〈 0.7 ), hydrogen gas migrated through continuous gas paths oriented in the flow direction. At high water saturation values ( $$S_\mathrm{w}\ge 0.7$$ S w ≥ 0.7 ), the relative gas permeability dropped to zero because the hydrogen phase segmented into gas pockets that were stuck in local narrow throats of the clay fracture. The study pointed out that the high capillary forces prevented the gas bubbles from distorting themselves to pass through these narrow paths.
Keywords: LBM ; Two-phase flow ; Relative permeability ; RK ; TRT ; GPU
ISSN: 0169-3913
E-ISSN: 1573-1634
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