The exchange flow between preferential flow paths and matrix in soils: from pore to continuum scale with tensors
Final Report Abstract
The exchange of water and solutes between the macropore and the soil matrix is important for the quantification of preferential flow and solute transport, e.g., for predicting contaminant leaching from arable soils. However, a physically adequate pore-scale understanding of this process is still missing. The objective of the collaborative project was to establish a novel class of models, in which the exchange fluxes are informed by pore-scale physics. The group from the RAS (Moscow) focused on pore-scale flow simulations and stochastic reconstruction based on the analyses of X-ray computed tomography (CT) images to compute tensorial properties and upscaling functions. The group from the ZALF (Müncheberg) focused on characterization of macropore surface properties and hydro-mechanic models using the discrete element method (DEM) as well as on experiments for simultaneous 3D X-ray and Neutron CT imaging of dynamic macropore-matrix exchange flow in intact samples with a central earthworm burrow. Mechanic properties of soil with and without burrow coatings were determined using indirect tensile strength test. Bulk density and particle information were used to construct DEM models of soil around the worm burrow that consisted of finer- (coating) and coarser-sized (matrix) porous aggregates. The DEM models were coupled with a two-phase pore finite volume (2PFV) flow model (from RAS group) to simulate structure dynamics (cracking and swell-shrink) as well as changes in strength, water and pressure distributions upon drainage. The coupled hydro-mechanic pore-scale flow simulations of drainage were used for determining up-scaled “effective” soil water retention and hydraulic conductivity functions depending on the specific volume. Experimentally, simultaneous 3D X-ray and Neutron CT imaging of dynamic exchange flow confirmed flow-limiting effects of wall coatings for soil from Bt-horizon. Matrix water absorption during macropore flow was much larger than reverse flow during osmotic induced desiccation. The 2D Neutron radiography images revealed smaller water absorption by coated biopore in Bt- than in C-horizons; deviations in exchange flow as obtained with mini-infiltrometer on the same soils, are pointing to the need for more in-situ characterizing of flow path surfaces all along the course from top- to subsoil. Because of the geopolitical situation, most of the planned collaboration with the group from RAS (Moscow) could not be carried out including the improved flow exchange coefficients. Still, the presented novel coupled hydro-mechanical experiments and modeling for heterogeneous soil around macropores may serve as foundation for more physics-based preferential flow approaches.
Publications
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Macropore–matrix mass transfer of reactive solutes quantified by fluorescence imaging. Vadose Zone Journal, 19(1).
Haas, Christoph; Leue, Martin; Ellerbrock, Ruth H. & Gerke, Horst H.
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Macropore-matrix flow exchange experiments. Institut Laue-Langevin (ILL)
Barbosa L.A.P., K. Berger, H.H. Gerke, N. Kardjilov & A. Tengattini
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Discrete element modeling of aggregate shape and internal structure effects on Weibull distribution of tensile strength. Soil and Tillage Research, 219, 105341.
Barbosa, Luis Alfredo Pires; Gerke, Kirill M.; Munkholm, Lars J.; Keller, Thomas & Gerke, Horst H.
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Hydro-mechanical coupling to uncover stability and permeability of coated biopore on the pore-scale: the way to improve larger-scale modelling. Porous Media for a Green World: Water & Agriculture. InterPore, 30 May – 2 June 2022. 438
Barbosa, L.A.P., Gerke, K.M. & Gerke, H.H.
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Modelling of soil mechanical stability and hydraulic permeability of the interface between coated biopore and matrix pore regions. Geoderma, 410, 115673.
Barbosa, Luis Alfredo Pires; Gerke, Kirill M. & Gerke, Horst H.
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Shrinkage-swelling effect on mass transfer through a pore-scale model of the biopore - matrix interface coupling Discrete Element and Finite Volume.
Pires, Barbosa Luis Alfredo & Gerke, Horst H.
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Structural heterogeneity of soil clods: Correlating Weibull parameters to fracture surface topography. Geoderma, 428, 116161.
Barbosa, Luis Alfredo Pires & Gerke, Horst H.
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A discrete element model for describing coupled hydro-mechanical processes during drying of soils with coated worm burrows.
Barbosa, Luis Alfredo & Gerke, Horst H.
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Characterization of macropore-matrix mass transfer parameters in two-domain preferential flow models.
Gerke, Horst H.
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Continuum and discrete element modelling for describing coupled hydro-mechanical effects of earthworm burrow coatings on soil shrinkage. Geoderma, 435, 116497.
Barbosa, Luis Alfredo Pires & Gerke, Horst H.
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Upscaling the Effect of Micro Parameters of Worm Burrow Coatings on Soil Shrinkage and Hydraulic Properties Through Coupled Hydro-Mechanical Pore-Scale Modelling.
Pires, Barbosa Luis Alfredo & Gerke, Horst H.
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Coupled hydro‐mechanical pore‐scale modeling of biopore‐coated clods for upscaling soil shrinkage and hydraulic properties. Vadose Zone Journal, 23(4).
Barbosa, Luis Alfredo Pires & Gerke, Horst H.
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Hydraulic characterization of earthworm macropore surfaces using miniaturized infiltration data. Soil and Tillage Research, 236, 105954.
Villarreal, Rafael; Lozano, Luis A.; Salazar, María Paz; Polich, Nicolás G.; Bellora, Guido L.; Ellerbrock, Ruth H.; Pires, Barbosa Luis A.; Gerke, Horst H. & Soracco, C. Germán
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Neutron imaging of exchange flow between biopore and matrix for Bt versus C horizons. Vadose Zone Journal, 23(4).
Barbosa, Luis Alfredo Pires; Lima, Fernando Vieira & Gerke, Horst H.
