SSS6.1

EDI
Measurement and modeling of soil processes in different scales

Water, energy, and solute transport in the vadose zone occur in a variety of scales. How the processes occurring at the small scale control and constrain the large scale responses is a long-standing challenge in vadose zone hydrology. Description of several processes such as evaporation, infiltration, soil-root-water interactions as well as soil characteristics such as conductivity and mechanical impedance rely on small scale measurement which are used to model processes occurring at scales much larger than the measurement scales. The utilization of advanced experimental and modelling tools are required to close the hierarchical gap present in different scales. Within this context, the focus of this session is on measurement or modeling approaches to parametrize or conceptualize soil physical, thermal, hydraulic, and mechanical properties across different spatial and temporal scales and resolutions from the size of a pore to the sample or field scale. We invite contributions related to:
- Measuring soil physical and chemical properties in the lab, field, or watershed utilizing a variety of tools ranging from micro-scale imaging to local measurement by soil sensors, drowns, radars, remote sensing, etc.
- Analytical, empirical, statistical, or numerical modeling approaches that link soil processes across scales, upscaling and downscaling experiences to tackle heterogeneity challenges for the description of vadose zone processes such as evaporation, infiltration, land-atmosphere interactions, and subsurface mass and energy fluxes.
- Modeling or measurement campaigns concerning the spatiotemporal changes of vadose zone properties at different scales induced naturally or by human activities such as freezing-thawing circles, climate change, heavy agricultural machinery, and agricultural practices.

Convener: Mahyar Naseri | Co-conveners: Paolo Nasta, Nima Shokri, Martine van der Ploeg, Wolfgang Durner
Presentations
| Mon, 23 May, 10:20–11:47 (CEST), 13:20–13:59 (CEST)
 
Room -2.47/48

Presentations: Mon, 23 May | Room -2.47/48

Chairpersons: Mahyar Naseri, Martine van der Ploeg, Nima Shokri
10:20–10:23
10:23–10:29
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EGU22-757
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Virtual presentation
Tobias Karl David Weber and the ISMC Working Group: Pedotransfer functions

Hydro-pedotransfer functions (hyPTF) are used to relate available knowledge about soil properties to soil hydraulic properties and parameters of interest for applications in process models. At least more than four decades have been invested to derive such relationships. However, while models, methods, data storage capacity, and computational efficiency have advanced, there are fundamental issues related to the scope and adequacy of current hyPTFs, particularly when applied to parameterise models at the field scale and beyond. Much of the hyPTF development process has focussed on refining and advancing the methods, while fundamental questions remain largely unanswered, namely i) how should hyPTFs be built (methods) for maximum prediction confidence, ii) which processes/properties need to be predicted to move beyond the van Genuchten-Mualem based parameterisation of the Richards equation, iii) which new datasets and data coverage are needed, iv) how does the measurement process of soil hydraulic properties determine the construction of hyPTFs and at which scale, iv) what is the implication of diverging scales (lab measurements/field to regional scale of application), v) what scaling/modulation/constraining strategies are required to make hyPTF predictions at field-to-regional scale appropriate and physically meaningful, and vi) what is the spatial representativeness? These questions have been addressed in a joint effort by the members of the International Soil Modelling Consortium (ISMC) Pedotransfer Functions Working Group with the aim to systematise hyPTF research and provide a roadmap guiding both scientists and reviewers.

How to cite: Weber, T. K. D. and the ISMC Working Group: Pedotransfer functions: Hydro-pedotransfer functions: A roadmap for future development       , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-757, https://doi.org/10.5194/egusphere-egu22-757, 2022.

10:29–10:35
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EGU22-11106
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Virtual presentation
Mats Larsbo, Jumpei Fukumasu, and Johannes Koestel

Sub-resolution pore space is increasingly being accounted for in Lattice-Boltzmann models of water flow and solute transport. However, robust methods to estimate the permeability and porosity of sub-resolution voxels in 3D X-ray images, which are needed for model parameterization are lacking. The grey-value of a voxel in a 3D X-ray tomography image is approximately proportional to the density. Since the density in a voxel depends on the volume fractions of solids, air and water, and the densities of these phases, a grey-value cannot be directly translated to a porosity value. The objective of this study was to develop a reliable method for 3D estimation of sub-resolution porosity in undisturbed soil samples using data obtained from standard industrial X-ray tomography images. To achieve this we used the differences in X-ray attenuation between samples saturated with water and saturated with a potassium iodide (KI) solution.

We collected ten intact soil cores (5.5 cm high, 6.5 cm diameter) in aluminium cylinders from the topsoil of an arable field in south-west Sweden. The samples had a large variations both in soil texture and organic carbon content. The samples were scanned using X-ray tomography after being slowly saturated with water from the bottom. The water was then replaced by a KI solution (30 g I L-1) with a larger X-ray attenuation than water, and the samples were scanned a second time. The grey-values of the resulting 3D images were scaled by the known densities of air, water and aluminium and the images were registered (i.e. spatially aligned). Macropores, sand grains and gravel were then removed from the images. The difference in attenuation between the two final images was then used to calculate the sub-resolution porosity (i.e. the degree of saturation) in all voxels in the remaining image of the soil matrix. Average porosities for individual samples, which were in the range 0,34­–0.45, were significantly correlated to matrix porosities estimated from soil water retention measurements.

How to cite: Larsbo, M., Fukumasu, J., and Koestel, J.: A method for 3D mapping of sub-resolution porosity from X-ray tomography images, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11106, https://doi.org/10.5194/egusphere-egu22-11106, 2022.

10:35–10:41
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EGU22-12291
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ECS
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Presentation form not yet defined
Rong Qu, Hu Zhou, and Paul Hallett

Soil aggregates fracture through the coalescence of internal macropores (cracks), forming smaller fragments that change pore structure characteristics. Many studies have measured soil aggregate fracture with laboratory tests, but the impact of internal pore structure has remained elusive in the black box of soil.  This study, which is the first of its kind, uses Xray micro-CT imaging, mechanical measurement experiments and finite element simulations to investigate the relationship between soil pore-scale topology and aggregate mechanical properties including fracture energy. The soil aggregates came from a red soil (Acrisols) experimental field in Jiangxi, China that had been amended with different amounts of manure and lime. From Xray micro-CT, quantitative topology analysis extracted the pore network extraction method. Then the strain-stress relationship and fracture energy of the scanned aggregate were measured using a loading frame. The micro-CT images are used as geometry inputs to perform finite element methods to calculate effective Young’s modulus and detailed strain-stress distribution at micrometers. The experimental results showed that adding manure increased the elastic stiffness and fracture energy of the aggregate. The pore scale strain-stress distribution analysis from finite element simulations found these properties at aggregate scale were weakly correlated to bulk porosity but driven by the stress intensity distribution of the aggregates, agreeing with previous research on model soil structures.

How to cite: Qu, R., Zhou, H., and Hallett, P.: Micron-scale mechanical properties of soil aggregates amended with manure: experimental evidence and image-based finite element simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12291, https://doi.org/10.5194/egusphere-egu22-12291, 2022.

10:41–10:47
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EGU22-4330
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On-site presentation
Agnieszka Szypłowska, Arkadiusz Lewandowski, Marcin Kafarski, Justyna Szerement, Andrzej Wilczek, Jacek Majcher, and Wojciech Skierucha

Dielectric properties of soil are often utilized for the purpose of soil moisture measurement. However, the relations between soil complex dielectric permittivity and volumetric water content depend also on other factors, such as the operating frequency of the sensor, soil texture, and temperature. The goal of the presented work is to examine the impact of temperature in the 0.5 – 40°C range on the complex dielectric permittivity spectrum of two soils of silt loam and loamy sand textures. The permittivity spectra were measured in a coaxial transmission-line cell system with the use of a Copper Mountain R60 one-port vector-network-analyzer in the frequency range from 20 MHz to 3 GHz. The relations between the real part of dielectric permittivity and soil volumetric water content were modeled at each examined frequency and the temperature dependence of the applied model parameters was determined. In the future research steps, the obtained relations will be applied and tested with the use of a prototype field soil moisture probe operating in a broadband frequency range.

 

The research has been supported by the Polish National Agency for Academic Exchange under Grant No. PPI/APM/2018/1/00048/U/001. The soil dielectric spectra have been obtained in the scope of the project No. 2014/15/D/ST10/04000 financed by the Polish National Science Centre (NCN).

How to cite: Szypłowska, A., Lewandowski, A., Kafarski, M., Szerement, J., Wilczek, A., Majcher, J., and Skierucha, W.: The influence of temperature on soil complex dielectric permittivity in the 0.02 – 3 GHz frequency range, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4330, https://doi.org/10.5194/egusphere-egu22-4330, 2022.

10:47–10:53
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EGU22-13065
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On-site presentation
Michal Snehota, John Koestel, Andreas Pohlmeier, Tomas Princ, Martina Sobotkova, Milena Cislerova, and Jan Sklenar

Magnetic resonance imaging (MRI) of the freezing and thawing process was performed on a series of repacked samples of sand, soil, and sand-soil mixture. The freezing/thawing is performed in the sample container placed inside the vertical bore MRI scanner within the 66 mm inner diameter of the radiofrequency coil. The sample container was vacuum insulated from the sides and bottom to allow for the minimum thickness of the insulation layer. The vacuum was constantly maintained by a vacuum pump. The sample assembly was built from PMMA and other nonmetallic - MRI compatible materials. A porous material in the sample container was cooled at the top by the flow of cold gaseous nitrogen released from the liquid nitrogen stored in the Dewar flask. The cooling took place across the glass plate positioned at the top of the sample in the headspace above the sample. The temperature of the gas that was delivered to the headspace and leaving the headspace was monitored. Additionally, the temperature was monitored in the headspace above the glass disk and directly in the glass disk by fiber optics temperature probes. A 4.7 T magnet at the FZJ was used for MRI. Multiple-Slice Spin-Echo and Zero Echo Time pulse sequences were utilized. The contrast between the frozen and unfrozen water is given by the difference in T1 and T2 relaxation times. The time-lapse 3D imaging was done during the entire course of the experiment. Once the freezing front reached the bottom of the sample, the thawing process was induced. The small changes in sand structure as a consequence of volumetric ice-water changes were studied. The spatiotemporal analysis of the freezing front advancement and frozen water volume has been performed. The data are available for the development of two-phase ice-water simulation models.

How to cite: Snehota, M., Koestel, J., Pohlmeier, A., Princ, T., Sobotkova, M., Cislerova, M., and Sklenar, J.: Dynamics of freezing and thawing of water in saturated sand and soil: Magnetic resonance imaging study, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13065, https://doi.org/10.5194/egusphere-egu22-13065, 2022.

10:53–10:59
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EGU22-6597
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On-site presentation
Scott B. Jones, Chieh-Yun Chang, Juan D. González-Teruel, David A. Robinson, Shmulik P. Friedman, Agnieszka Szyplowska, and Wojciech Skierucha

Electromagnetic (EM)-based sensors used for water content determination are now being widely used across the globe in research, environmental monitoring networks, weather stations, irrigation management, feed and grain quality control in addition to a host of other applications. The multi-million-dollar EM sensor market continues to expand and yet lacks test standards and is generally lacking in information about sensor quality and performance. Decades of past sensor assessments have presented mixed testing approaches and a commensurate measure of mixed results. Confusion regarding EM sensor-function, -failure rate and -value, stems from testing results that often use non-standard targets including inhomogeneous (variable density and water content) and complex materials (e.g., soils) that may not be widely available for subsequent testing and verification by others. Electromagnetic sensors employ time- or frequency-domain measurements to estimate real (and sometimes including imaginary) permittivity and electrical conductivity, with different sensors measuring at varied and often unknown frequencies. Sensor output is affected by environmental impacts on circuitry (temperature) combined with effects of porous medium temperature, electrical conductivity, interfacial polarization and dielectric relaxation, all of which often combine to alter the apparent permittivity and resulting water content. Although a few attempts have been made to standardize testing, more work and research is required before an international standard can be recognized and adopted. Here we point to standardizing 1) granular porous test media, 2) media packing approaches and 3) permittivity-water content calibration functions with examples and comparison of different EM sensors.  

How to cite: Jones, S. B., Chang, C.-Y., González-Teruel, J. D., Robinson, D. A., Friedman, S. P., Szyplowska, A., and Skierucha, W.: A Framework for Standardizing Electromagnetic Water Content Sensor Assessment using Granular Porous Media, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6597, https://doi.org/10.5194/egusphere-egu22-6597, 2022.

10:59–11:05
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EGU22-2914
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ECS
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On-site presentation
Juan D. González-Teruel, Scott B. Jones, David A. Robinson, Jaime Giménez-Gallego, Raúl Zornoza, and Roque Torres-Sánchez

Soil moisture is of major relevance in agricultural and environmental monitoring, having a direct impact in crop growth and yield, and playing an important role in soil conservation and landscape management. Several well-known techniques are widely used to determine soil moisture, but dielectric methods are notable for their automation potential and integration in monitoring and irrigation control systems. Measurement of dielectric properties in moist porous substances, such as soils, has been shown to provide reliable estimation of water content. However, frequency domain dielectric spectroscopy seems to reveal information about other useful physicochemical properties of soils. Dielectric spectroscopy measurements are normally restricted to laboratory setups and limited for low budgets due to the high cost, bulk and weight of the equipment. We evaluated the performance of a low-cost, handheld, open-source VNA (Vector Network Analyzer) for the measurement of the complex permittivity of soils in the 1 MHz to 900 MHz frequency range. The tested device was compared with a commercial model using a low-cost, self-manufactured, open-ended coaxial probe to measure the broadband dielectric properties of organic liquids. An empirical method based on known dielectric properties of standard fluids was used to calibrate the probe. The tested low-cost VNA paired with the experimental probe was found to provide accurate and reliable measurements of the broadband complex permittivity from 50 to 700 MHz. The broadband complex permittivity of mineral soils of varied textures was obtained for a range of bulk densities and water contents from dry to water-saturated conditions.

How to cite: González-Teruel, J. D., Jones, S. B., Robinson, D. A., Giménez-Gallego, J., Zornoza, R., and Torres-Sánchez, R.: Assessment of a low-cost Handheld Vector Network Analyzer to Measure the Broadband Complex Permittivity of Soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2914, https://doi.org/10.5194/egusphere-egu22-2914, 2022.