Understanding the fate and transport of PFAS in the subsurface is essential for groundwater and contaminated site management. Most international studies focused on the transport in homogeneous sands, while other hydrogeological settings are less well studied. In this contribution, we investigate the impact of different glacial geological settings typically found in the Northern Hemisphere, possibly containing fractures and heterogeneities, on PFAS leaching through unsaturated glacial sediments.
We have implemented a vertical cross-section model that simulates transient groundwater flow and PFAS transport through the variably-saturated zone, accounting for sorption to the solid phase and to air-water interfaces. The model was tested on measured breakthrough curve data from saturated and unsaturated laboratory column experiments considering PFAS with different chain lengths. Model parameters were obtained from a comprehensive literature review, laboratory studies, and field investigations of contaminated sites.
The model was used to investigate the leaching of PFAS with different chain lengths through different setups with glacial sediment. We observed that the hydrogeological setting determines the magnitude of the air-water interfacial area and, thus, the retention of surface-active PFAS like PFOS and PFOA. Further, the model outcomes demonstrated a chromatographic separation of PFAS with different chain lengths due to different retention mechanisms. The longer-chained PFAS were retained more strongly in the unsaturated zone, while shorter-chained compounds were mobile.
Low-permeability clay-rich layers and inclusions generally provided less retention for surface-active PFAS due to a typically higher water saturation and, thus, smaller interfacial area compared to high-permeability media like sands. Fractures and heterogeneities may lead to the formation of preferential flow paths and thereby a potential bypassing of the unsaturated zone, where sorption to the air-water interface could occur. On the other hand, matrix diffusion may slow the rate of plume expansion by retaining PFAS in low-permeability layers. Over time, back diffusion from the matrix can result in long-term release to the groundwater.
The modeling investigations based on realistic data conducted in this study led to an improved understanding of the transport of short- and longer-chained PFAS in variably saturated glacial geological settings. Our findings allowed analyzing the influence of key parameters and processes on PFAS fate and transport.
How to cite: Mosthaf, K., Morsing, L., Bilic, N., Wienkenjohann, H., Fjordbøge, A. S., and Bjerg, P. L.: Modeling investigations of PFAS transport through variably-saturated glacial sediments, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18846, https://doi.org/10.5194/egusphere-egu25-18846, 2025.
Microplastic pollution in terrestrial environments poses significant risks to soil health, groundwater quality, and ecosystem functionality. This study integrates findings from laboratory and field experiments to elucidate the dynamics of microplastic transport and retention in soils under various conditions. Laboratory experiments examined the fate of low-density polyethylene (LDPE), polybutylene adipate terephthalate (PBAT), and starch-based biodegradable microplastics in sandy loam and loamy sand soils under controlled rainfall intensities (22 mm/h and 35 mm/h). Effluent and soil analyses, coupled with microplastic balance assessments, revealed recovery rates between 64% and 104%, underscoring the reliability of the experimental approach. Transport varied with soil type, rainfall intensity, and polymer characteristics, with loamy sand exhibiting higher wash-off rates. LDPE consistently showed greater mobility than biodegradable polymers, particularly under higher rainfall intensities. Field studies complemented these findings, using loamy sand soil columns subjected to natural precipitation and fluctuating groundwater levels over 6- and 12-month periods. Retention profiles and particle size analyses highlighted distinct behaviors: LDPE persisted across soil depths, PBAT exhibited moderate redistribution due to partial biodegradation and starch-based microplastics underwent significant fragmentation and deeper transport. The field's natural precipitation and wet-dry cycles enhanced microplastic mobilization and degradation compared to laboratory conditions. HYDRUS-1D modeling was employed across both settings. Laboratory simulations showed depth-dependent deposition, particularly in upper soil layers, while field models reflected material-specific degradation and redistribution. Notably, LDPE exhibited stable retention parameters, whereas biodegradable polymers demonstrated declining attachment and detachment coefficients over time, indicating their biodegradability. These findings underscore the critical roles of soil type, rainfall intensity, polymer properties, and environmental conditions in shaping microplastic behavior in soils. Integrating controlled laboratory experiments and long-term field studies provides a comprehensive understanding of microplastic fate, offering essential insights for modeling and mitigating their impact on terrestrial ecosystems.
Keywords: microplastic transport, soil contamination, soil column experiment, HYDRUS-1D
How to cite: Soltani Tehrani, R., Yang, X., and van Dam, J.: Understanding microplastic transport and retention in soil: insights from laboratory and field studies, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6306, https://doi.org/10.5194/egusphere-egu25-6306, 2025.
Stable isotopes of nitrate (δ15N-NO3- and δ18O-NO3-) are powerful tools for tracing nitrogen sources and understanding transformation processes in soil-water systems. The isotopic composition of nitrogen and oxygen evolves due to isotope effects, which characterize processes such as nitrification and denitrification whilst offering insights into the environmental factors driving these reactions. Although isotope effects are often derived from laboratory experiments under controlled conditions, this study aims to derive them in situ within a dynamic natural system, where varying redox conditions, inflows, and substrate availability introduce complexities absent in controlled environments.
Combining high-resolution hydrochemical and stable isotopic monitoring of nitrate and water with numerical modeling and particle tracking using HYDRUS, we investigate the spatial variability of nitrogen transformations within an agricultural soil profile. Preliminary results indicate that nitrification, with nitrate concentrations exceeding 200 mg·l-1, is prominent in the upper soil layers and exhibits isotopic signatures (δ15N = 4.2‰ ±0.9‰) characteristic of soil nitrogen, likely derived from the immobilization of applied fertilizer. Denitrification, reducing concentrations to as low as 0.2 mg·l-1, occurs primarily within the capillary fringe, generating a linear Δδ18O:Δδ15N trajectory with a slope of 0.79 and a field based apparent isotopic enrichment factor for nitrogen of ε = -4.8‰. Below this zone, regions dominated by nitrification on denitrification exhibit curved Δδ18O:Δδ15N trajectories, highlighting the incorporation of oxygen from ambient water during re-nitrification.
How to cite: Richard-Cerda, J. C., Schulz, S., and Knöller, K.: Using in-situ monitoring and modeling to characterize isotope effects in nitrate cycling at an agricultural site, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18992, https://doi.org/10.5194/egusphere-egu25-18992, 2025.
In soils contaminated with petroleum hydrocarbons (PHCs), water table fluctuations (WTFs) affect the kinetics of PHC biodegradation and the generation and transport of carbon dioxide (CO2) and methane (CH4). Thus, understanding the impacts of WTFs on natural source zone depletion processes is critical for environmental risk assessment and the design of soil remediation strategies. In this study, a 300 day-long column experiment was conducted to simulate the effects of water table fluctuations on the aerobic and anaerobic PHC biodegradation pathways and rates. Eight columns were each filled with 45 cm of soil from undisturbed cores collected at a site formerly contaminated with PHCs. Four columns simulating fluctuating water table conditions were subjected to three successive 6-week cycles of drainage and imbibition. The remaining four columns remained fully saturated over the period of the experiment, simulating a static water table. Except for the controls, the columns received injections of ethanol or ethanol plus naphthalene after 111 days of pre-equilibration. Over the duration of the experiment, soil moisture, soil surface CO2 and CH4 effluxes, dissolved CO2 and CH4 concentrations, δ13C compositions of CO2 and CH4, dissolved naphthalene concentrations, and ancillary geochemical parameters were monitored. The remaining naphthalene depth distributions in the soil columns were also measured at the end of the experiment. A reactive transport model representing 13 biogeochemical reaction pathways was verified against the acquired data. The experimental and modeling results confirmed that the prevailing pathway generating CH4 shifted from hydrogen-based to acetate-based methanogenesis in the ethanol and ethanol plus naphthalene spiked columns, while CH4 oxidation played a key role in controlling the CH4 efflux during the drainage periods. Compared to the static water table columns, the WTF columns exhibited significantly faster naphthalene attenuation while the cumulative CO2 and CH4 effluxes were about twice as high. These observations were attributed to the periodic incursion of air during the WTFs, which increased the porewater-air interface area for gas transfer while also accelerating the aerobic degradation of soil organic matter and naphthalene. Overall, our study advances the quantitative modeling of the biogeochemical reaction network in PHC contaminated soils under WTFs, including the role of methanogenic pathways.
How to cite: Rezanezhad, F., Ramezanzadeh, M., Slowinski, S., Ye, J., Vandergriendt, M., and Van Cappellen, P.: Effects of Water Table Fluctuations on Natural Source Zone Depletion of Petroleum Hydrocarbons in Contaminated Soils, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10142, https://doi.org/10.5194/egusphere-egu25-10142, 2025.
Evaporation from porous media is a key phenomenon in the terrestrial environment and is linked to soil salinization, degradation and weathering of building materials. Column-scale experiments could extend our understanding of the complex processes affecting saline water evaporation. In this context, the current study aims at investigating solute accumulation near evaporating surfaces and the resulting implications for time to salt crust formation. Previous numerical studies with REV-scale simulations predict the development of local instabilities due to density differences during saline water evaporation in case of saturated porous media with high permeability, eventually causing density-driven downward flow through fingering. To experimentally investigate this process on the column-scale, we performed evaporation experiments on two types of porous media: medium sand (F36) and fine sand/silt (W3) saturated with NaCl solution. The intrinsic permeability of the two packings differed by two orders of magnitude, i.e. 29×10-12 m2 for F36 and 0.56×10-12 m2 for W3. Using magnetic resonance imaging (23Na-MRI), we monitored solute accumulation at the surface and subsequent downward redistribution of salt in time-lapse scans during evaporation with a continuous supply of water from below (wicking). Results showed key differences between the enrichment patterns of Na for the two types of porous media. Density-driven downward flow only occurred in F36, initially manifested by fingering, and resulted eventually in redistribution of Na throughout the sample. For W3, solute accumulated at the thin region at the surface with a thickness of a few mm. Despite similar average evaporation rates for both porous media, the concentration at the top reached the saturation limit (6.13 mol/L) for W3, whereas it remained relatively low (2.5 mol/L) for F36 due to the redistribution. This different behavior suggests that time-to-crust formation is longer for higher permeability porous media under similar evaporation conditions applied in our experiments.
To investigate crust formation in more detail, additional column-scale evaporation experiments with wicking conditions were performed on three sands WS1, WS2 and WS3 with particle sizes ranging between 0.1 to 0.3 mm, 0.3 to 0.5 mm and 0.71 to 1.0 mm, respectively. To achieve well-controlled evaporation conditions, experiments were performed in a wind tunnel maintaining a constant wind speed of 5 ms-1. Surface time-lapse imaging with a digital camera was performed to observe the onset time of crust formation as well as the resulting crust morphology after initiation. The results showed that for the relatively coarser WS2 sand, onset of crust took twice as long (40 hours) in comparison to the finer WS1 sand (20 hours). The significantly larger particle size of WS3 sand led to air entry, partially saturated conditions and an almost instantaneous crust formation. The crust formation affected also the evaporation rate of each sand, which is attributed to the formation of a new porous layer (crust) and its wetting-drying dynamics. These findings encourage further investigation into effects on crust development for heterogeneous porous media, redistribution and precipitation of different salt types, and the coupling of experimental results to numerical modelling.
How to cite: Chaudhry, M. A., Kiemle, S., Jannesarahmadi, S., Pohlmeier, A., Helmig, R., Shokri, N., and Huisman, J. A.: Solute redistribution during saline water evaporation in porous media and its effects on the onset of salt crust formation , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11280, https://doi.org/10.5194/egusphere-egu25-11280, 2025.
Infiltration and evaporation processes in porous media are crucial for understanding the hydrologic cycle and managing water resources, particularly in the context of climate change. Studying these processes requires models that accurately represent experimental and field measurements.
This work focuses on understanding flow and transport during water infiltration and evaporation cycles, considering factors such as soil heterogeneity, the non-linearity of its properties, and the formation of gravity fingers. We aim to improve the modeling of infiltration and evaporation processes in soils to accurately predict water flow and solute transport behavior, and to characterize the impact of soil heterogeneity, non-linear properties, and gravity fingers on these processes.
To address the effect of these factors, we simulate water infiltration and evaporation cycles, and solute transport in unsaturated soil. Two modeling approaches are compared: the traditional Richards’ equation and the fourth-order derivative in space model proposed by Cueto-Felgueroso and Juanes (2009), which is able to reproduce the formation of fingers and preferential flow during water infiltration. The flow and transport problems are solved using the finite element library FEniCS.
Soil heterogeneity is represented by Gaussian random permeability fields, with different correlation lengths and variance. To evaluate how heterogeneity affects dispersion and mixing during the solute transport, we analyze solute breakthrough curves at different depths, we calculate dispersion coefficients, concentration distribution and segregation index.
Keywords: infiltration and evaporation cycles, unsaturated flow, heterogeneity, gravity fingers, finite element method, solute transport, mixing.
References:
Cueto-Felgueroso, L., and R. Juanes (2009). A phase field model of unsaturated flow. Water Resources Research, 45, W10409. https://doi.org/10.1029/2009WR007945
How to cite: Castillo, Y., Hidalgo, J., and Dentz, M.: Unsaturated Flow and Solute Transport During Infiltration and Evaporation Cycles: Influence of Soil Heterogeneity and Gravity Fingers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9139, https://doi.org/10.5194/egusphere-egu25-9139, 2025.
The source-responsive method (SRM), which accounts for film flow in macropores and matrix absorption phenomena, is an advanced dual-domain modeling framework and has been successfully applied in catchment scale. It also provides a parameter-predictive approach by introducing a parameter, M, to represent macropore area density. However, the capability of this parameter to accurately reflect macropore structure remains unclear. In this study, a 1-D infiltration model based on SRM was developed to simulate soil water dynamics across six experiments, and obtained calibrated M values. The results demonstrate that the SRM performs well (NSE>0.88) in most cases, except for two artificial-macropore experiments with low M values. Measured M values were extracted from horizontal image slices of dyeing experiments. In experiments with good infiltration simulation performance, the measured values align closely with calibrated values (RE<35%), though they are consistently slightly higher. Conversely, in poorly simulated experiments, significant deviations were observed, with RE exceeding one order of magnitude. Further analysis using HYDRUS-2D revealed that limited lateral water propagation from macropore walls contributed to poor simulation accuracy when M values were excessively low.
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How to cite: Shen, X., Liu, J., Vereecken, H., and Rahmati, M.: The potential of Source-responsive Method in representing macropore structural characteristics within soil profiles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4980, https://doi.org/10.5194/egusphere-egu25-4980, 2025.
Frozen soils are typically considered impermeable due to their reduced infiltration capacity. During rainfall, water behavior depends on whether the soil thaws, allowing infiltration, or remains frozen, causing surface runoff that may lead to flooding or debris flows.
Open macropores, such as cracks, root channels, and wormholes, act as preferential flow paths, significantly altering these dynamics. Understanding these processes is crucial for improving hydrological models, evaluating slope stability, and assessing natural hazard risks in cold regions.
To investigate these mechanisms, a novel large-scale experimental setup has been developed, which is up to ten times larger than previous experiments and surpasses them in complexity.
The setup features a tiltable design, adjustable up to 20°, allowing the system to replicate natural slope conditions. An advanced irrigation system ensures automated and uniform rainfall distribution across the surface. Controlled climate conditions are maintained via a sophisticated climate chamber, enabling precise and realistic freezing processes. A macropore pattern plate facilitates the creation of a reproducible macropore network, ensuring consistency across experiments. Additionally, advanced sensors enable 3D visualization of soil temperature and moisture distribution, providing detailed insights into the internal processes during freezing and thawing.
This innovative approach reduces the gap between simplified small-scale experiments and the complexity of real-world scenarios.
Experimental results demonstrate that open macropores, despite their small volume fraction within the soil body, significantly facilitate infiltration and accelerate thawing of frozen slopes, directly influencing the hydrological cycle and slope stability.
The findings provide essential data for validating numerical models under climate-relevant freeze-thaw scenarios.
With the increasing frequency of freeze-thaw cycles driven by climate change, this research is essential for assessing infrastructure risks, managing groundwater resources, and mitigating natural hazards in cold and transitional regions.
How to cite: Bauer, J., Müller, S., and Baselt, I.: Macropore-Driven Infiltration in Frozen Slopes: Large-Scale Experimental Insights with Hydrological and Geotechnical Implications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6622, https://doi.org/10.5194/egusphere-egu25-6622, 2025.
Non-uniform infiltration is a very common observation and one manifestation of non-diffusive physics in soil-water processes. It is posing a fundamental challenge to conventional Darcy-scale approaches in soil-water processes, revealing limitations in our current understanding of complex soil-water interactions. While infiltration is fundamental to many ecohydrologic and hydropedologic aspects, its manifestation through structured soil and dynamically connected flow paths demands a more sophisticated system description.
Through a series of plot-scale irrigation experiments, we characterized infiltration flow fields based on observed soil moisture, tracers and time-lapse GPR data. Based on these data we conceptualised a thermodynamic representation for characterizing soil-water dynamics and their interactions. We observe celerity distributions in flow fields shifting to higher values with higher antecedent soil moisture. We also see shifting soil reconfigurations in precipitation events.
In the view of soil water dynamics as dissipative processes, we propose that these dynamic soil configurations systematically adapt to meet the system's dissipation demands. The thermodynamic perspective offers new insights into the physical constraints governing soil-water dynamics and provides a theoretical foundation for improved and scaleable prediction of non-uniform flow processes. Our results contribute to an advanced understanding of soil-water constitutive laws under non-equilibrium conditions and may help bridge the gap between observed soil-water dynamics and their representation in models.
How to cite: Jackisch, C., Hoffmeister, S., Stephan, S. M., and Zehe, E.: Thermodynamic Controls on Dynamic Soil Configuration and Non-uniform Infiltration Processes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18870, https://doi.org/10.5194/egusphere-egu25-18870, 2025.
Networks of subsurface pipes are widely used in humid regions to facilitate rapid removal of surface ponding and effectively decrease groundwater tables. Their application is also extended to arid regions as a strategic approach for mitigating soil salinization. Currently available subsurface pipe layout design methods require updating to properly incorporate salt discharge in such contexts. Numerical modeling is then a key tool for effective optimization of design parameters of such subsurface drainage systems. One of the challenges in subsurface drainage simulation is the inherent multiscale nature of the setting. A substantial scale disparity can be evidenced between millimeter-scale dimensions of subsurface drainage pipes and the meter-scale size of available field-scale soil profiles. Gradients of water potential and solute concentration near a subsurface pipe are typically high, thus challenging accuracy of numerical simulations targeting water and salt content across the soil-water system. To achieve accurate and computationally efficient simulations of water flow and solute transport in soil-water system within which subsurface drainage systems are in place, implementation of local grid refinement strategies is critical. In this context, we proposed (Qian et al., 2024) a soil water flow and solute transport model based on a vertex- centered finite volume method (VCFVM). The model has virtually no limitations on the cell shape as well as the number of neighbor cells, and strictly ensures local mass conservation. Here, we start by rigorously assessing the accuracy and efficiency of the algorithm upon considering test scenarios characterized by various soil textures and diverse boundary conditions. Our results show the that accurate solutions can be obtained upon relying on a grid whose number of nodes is only 5% of that of globally refined grid of the kind that are typically employed. The model is then further integrated with drainage equations to accurately simulate subsurface drainage process, so that the effect of placement of subsurface pipes can be effectively included. Our study suggests that the proposed model can accurately simulate soil water content, solute concentration, and subsurface drainage amount using a typical (globally refined) gridding procedure. Otherwise, it can save about 95% of CPU time by using nonmatching grids. Finally, a novel, user-friendly framework for the optimization of subsurface pipe layouts and corresponding leaching quota is proposed and demonstrated on a series of exemplary scenarios.
Reference:
Yingzhi Qian, Xiaoping Zhang, Yan Zhu, Lili Ju, Alberto Guadagnini, Jiesheng Huang, 2024, A novel vertex-centered finite volume method for solving Richards' equation and its adaptation to local mesh refinement, Journal of Computational Physics, 501, 112766,
https://doi.org/10.1016/j.jcp.2024.112766.
How to cite: Qian, Y., Zhu, Y., Zhang, X., Guadagnini, A., and Huang, J.: A multiscale algorithm for soil water flow and solute transport simulations and its application in subsurface drainage system optimization, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4935, https://doi.org/10.5194/egusphere-egu25-4935, 2025.
Estimating areal groundwater recharge (GWR) rates is crucial to assess the sustainability of groundwater resource use. Estimation methods, including physical measurements, water budget approaches, numerical methods and tracer methods each have their strength and limitations. Jointly, monitoring of different hydrological dynamics (e.g. shallow and deep soil moisture, GW levels) and the simulation of the complex process interactions between groundwater, soil, plants and the atmosphere can lead to a more accurate quantitative and scale-relevant estimation.
Influenced by soil hydraulic properties and meteorological conditions, soil moisture plays a crucial role in controlling water flux partitioning into evapotranspiration (ET) and seepage, which can ultimately contribute to groundwater recharge (GWR). For better understanding the soil moisture dynamics, cosmic ray neutron sensing (CRNS) is an increasingly popular method for continuous SM monitoring beyond the point scale over a footprint of (150-300 m radius) over the depth of the root zone (down to 30-50 cm). Soil water isotopes are natural tracers and, for several decades form part of the toolkit for assessing water fluxes in the vadose zone. The general usefulness of both observations has been evaluated separately and successfully in the dedicated modules of the widely used vadose zone model (HYDRUS 5) in previous studies. However, their combined value is yet to be assessed in tracking quantities and timing of GWR.
Therefore, the overall aim of the present study is to evaluate the usefulness of combining field-scale CRNS based soil moisture information with soil water isotopes (δ2H and δ18O) measurements in HYDRUS 5 to evaluate GWR dynamics in a highly instrumented agricultural hillslope in NE Germany. The study period focuses on two distinct hydrological years, a relatively drier (October 1st, 2022 – September 30th, 2023) and a relatively wetter one with considerable snow input in winter (October 1st, 2023 – September 30th, 2024).
We parameterize the vadose zone model for two locations on a hillslope with contrasting distances to the GW table. These differences are expected to directly influence GWR travel times and GW contribution to ET. The upslope location has deeper GW table of 4-6 m below surface and the downslope one features shallow GW table, 0.8 – 2.5m, respectively. On the one hand, we employ field-scale SM estimates resulting from a combination of CRNS and adjacent profile SM (down to 100 cm) timeseries at each location, to estimate site-specific transport parameters. Timeseries of groundwater level measurements are additionally used to constrain the bottom boundary of the model. Secondly, we use profiles of bulk soil water isotopes collected along the hillslope on three occasions (May 2023, January 2024 and May 2024) to constrain transport parameters. The calibrated models are then used to track the fate of infiltrated rainfall to estimate GWR travel times and compare dynamics (quantity and timing of GWR) between the dry and wet year.
The insights gained from this modelling exercise will inform future efforts in GWR estimation and drought monitoring networks in NE Germany and evaluate the usefulness of complementing these with dedicated tracer measurements for better understanding hydrological processes driving GWR.
How to cite: Dimitrova Petrova, K., Stumpp, C., Scheiffele, L., Tombraegel, A., and Oswald, S.: Evaluating the combined value of cosmic ray neutron sensing and water isotopes to track and quantify groundwater recharge and soil moisture dynamics in vadose zone modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10991, https://doi.org/10.5194/egusphere-egu25-10991, 2025.
Rhizoliths, cylindrical concretions formed mostly by CaCO3 accumulation around plant roots, serve as valuable indicators of environmental conditions and ecosystem dynamics such as carbon sequestration and water balance. Despite increasing attention to rhizolith formation, there remains a lack of numerical, laboratory, and field experiments. For the first time, we developed a dynamic model of rhizolith formation in CaCO3-containing loess soils, considering water fluxes toward roots, Ca2+ and CO32- concentration in soil solution, and potential evapotranspiration rates (ETo). Using numerical simulations with the HYDRUS-1D model, we explored the interplay between these factors and their impacts on rhizolith development. Hydraulic fluxes facilitate Ca2+ (simulated at 0.13, 0.15, 0.3, and 1 mmol L-1) transport towards the rhizosphere as a function of root water uptake at low (ETo = 0.03 cm d-1) and high (ETo = 1 cm d-1) water flow rates under initial optimal (ho = -100 cm) and intermediate (ho = -1000 cm) moisture conditions. An extensive simulation run was critical for achieving zero-suction gradient (dh/dz =0) in the model, which was attained at 374-year run (Tԑ), with equilibrium water content Ɵԑ of 0.089 cm3 cm-3 and yields 0.23 cm3 cm-3 threshold porosity for calcite saturation ɸ Casat, equivalent to 72% of the loess porosity ɸ of 0.32 cm3 cm-3. The equilibrium properties at Tԑ enabled differentiation between hydraulic constraints and jamming of the porous medium by calcite saturation as the causes of the standstill in the calcification function. On top of that, our work unfolds root encasement and reliquary varieties with their concomitant physical and biogeochemical mechanisms underlying rhizolith transformations. At intermediate soil-water conditions with 1 mmol L-1 Ca2+, tempo-sequential evolution of rhizoliths of radii 0.2, 1, 2, and 3 cm occurs in respectively 1.5, 9.5, 85, and 150 years. Each rhizolith layer harbors CaCO3 constituents (namely, δ18O, δ13C, 44Ca, 46Ca, and 48Ca), organic biomarker compounds from root (e.g., lignin), and clumped isotopes (Δ⁴⁷) among others which are preserved across time into the future. Therefore, this work conceptualizes rhizolith as a ‘time-capsule’ with each CaCO3 layer encapsulating a snapshot of vital environmental proxies, providing a window into otherwise inaccessible historic ecosystem dynamics.
How to cite: Tetteh, K.: Rhizoliths formation: mechanistic models and implications for paleoenvironmental reconstructions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2288, https://doi.org/10.5194/egusphere-egu25-2288, 2025.
Soils exhibit considerable variability in their physical and hydraulic properties, which can change both spatially and temporally. Research on the temporal variability and especially the internal variability of hydraulic and physical properties within the shallow topsoil itself remains scarce. In this one-year study (2023–2024), we investigated seasonal changes in the physical and hydraulic properties of post-tillage bare topsoil at the plot scale, hypothesizing significant temporal variability and heterogeneity within topsoil. The study was conducted in Czechia in a continental humid climate on agricultural soils. Monthly sampling was carried out on a 16 m² plot during the growing season, focusing on the 12 cm thick topsoil layer, which was divided into the upper section (0–5 cm) and the deeper section (7–12 cm). A total of 28 disturbed and 107 undisturbed samples were collected, 40 soil water retention curves (SWRC) were measured. Robust statistical analyses were performed, including normality tests (Shapiro-Wilk, Kolmogorov-Smirnov, Anderson-Darling, and Lilliefors tests) and variability tests (Kruskal-Wallis, Dunn test, LOWESS, and MANOVA). The results revealed a . For instance, the overall mean of the n parameter in the upper section was 1.404 ± 0.126, exhibiting greater variability compared to the deeper section, which had a mean of 1.254 ± 0.103. The mean α parameter showed similar overall variability in the deeper section (0.075 ± 0.024) and the upper section (0.060 ± 0.019). The contrasting patterns of variability highlight the importance of thoroughly evaluating both datasets. Relying solely on statistical results of the van Genuchten parameters or the SWRC data alone risks overlooking important temporal and vertical variations, emphasizing the need for comprehensive analyses.
How to cite: Kubát, J.-F., Vrána, M., Babuljak, A., and Zumr, D.: A Year Lond Study: Bare Topsoil Temporal and Vertical Variability in Hydraulic Properties, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2850, https://doi.org/10.5194/egusphere-egu25-2850, 2025.
It is by now well known that pore-scale heterogeneity can lead to mass transfer limitations, resulting in incomplete solute mixing and thereby decreasing reaction rates when compared to laboratory batch experiments. The mixing state of the plume, and therefore the reaction rates, result from a complex interplay of deformation by fluid flow, diffusion, and reactive depletion or production. In partially-saturated systems, such as the vadose zone, the simultaneous presence of air and water further enhances structural heterogeneity, leading to broad flow velocity distributions and resulting in qualitatively different transport dynamics. Despite significant advances in modeling pore-scale reactive mixing, the role of partial saturation in reaction dynamics remains poorly understood. In this work, we focus on linear decay of a transported species upon contact with the water-solid interface. Among other processes, this type of reaction models antibiotic degradation through redox reaction with a mineral phase. We simulate steady-state water flow subject to a frozen spatial configuration of air and water phases obtained experimentally in quasi-2D media. The solid phase is composed of cylindrical pillars with variable radii, characterized by different spatial correlation structures. The flow is simulated using Eulerian methods, while reactive transport simulations employ Lagrangian particle tracking. We find that, while solute dispersion and breakthrough curve width increase dramatically, overall reaction rates are largely insensitive to saturation. We discuss the origins of this counter-intuitive result and how it can be used to model reactive breakthrough. These findings provide new insights into the role of saturation in transport subject to surface reaction, and open up new questions regarding the role of flow structure and reaction kinetics.
How to cite: Aquino, T., Sole-Mari, G., Borgman, O., Delouche, N., Hanna, K., and Le Borgne, T.: Fluid-solid reaction in partially-saturated media at the pore scale, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11393, https://doi.org/10.5194/egusphere-egu25-11393, 2025.
Denitrification is an important process in the soil that leads to the degradation of nitrate into nitrous oxide or dinitrogen. It prevents the leaching of nitrate from the soil into groundwater. For this reason, denitrification is implemented in many models. However, most of the models only consider the root zone in their calculations. Denitrification below the root zone (deep vadose zone or drainage zone) is overlooked. The current state of research is that most of the denitrification takes place in the root zone. The lack of organic carbon and oxic conditions probably prevent denitrification in the drainage zone, with the exception of microsites with high organic carbon content. Nevertheless, due to the potentially large thickness of the drainage zone and the associated long travel time of the nitrate, some nitrate could be degraded on its way to the groundwater.
To date, there is no model that can accurately predict denitrification in the drainage zone. Most models completely ignore the fact that nitrate could be degraded in this zone. The few models that do consider denitrification in the drainage zone rely on knowledge from the topsoil. Due to the differences between the root zone and the underlying drainage zone, this approach may be overestimate denitrification rates in the drainage zone. Therefore, there is a need for a model that simulates denitrification in the drainage zone. In the DeniDrain project, we will adapt existing models to the conditions in the drainage zone using actual denitrification rates from soils across Germany.
How to cite: Schoner, D., Westphal, J., Well, R., Buchen-Tschiskale, C., and Stange, F.: The demand for an accurate model of the denitrification process in the drainage zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11713, https://doi.org/10.5194/egusphere-egu25-11713, 2025.
In soils exhibiting bi-modal porosity, such as shrink-swell clays, understanding the impact of seasonal variability on water movement is crucial for stakeholders. These clay soils alter their structure based on moisture content, bulging and swelling at higher moisture levels or shrinking and cracking during drier periods.
Within soil water models, this seasonal variation of soil parameters is not captured. Saturated hydraulic conductivity and porosity are considered as fixed values. Our hypothesis is that during the winter season simpler modelling approaches, such as single porosity models, can be applied using focused parameterisation and that more complex modelling approaches may be overfitting. During summer, when cracking of these soils is more prevalent, dual permeability approaches should be more adequate and capture the system complexity required. Evaluating the adequacy of these models is vital for identifying critical system controls and for scaling up findings to broader catchment models.
To test this hypothesis, we calibrated and validated single-porosity, dual-porosity, and dual-permeability mass transfer models under dry and wet conditions across three sites using HYDRUS-2D/3D. Volumetric soil moisture data was collected using Delta-T PR2 SDI-12 probes to a depth of 1 m. Parameterization involved field sampling of intact soil cores to 60 cm depth in summer and winter, analysed using laboratory methods (KSAT and HYPROP-2, METER). Additional parameters for dual-permeability models were derived through inverse estimation modelling from field infiltration tests. To determine which model is better able to represent the physical reality under dry and wet conditions, we jointly assessed their performance and complexity/parsimony using Bayesian approaches as parameters are not independent.
This study provides insights into the behaviour of the shrink-swell clay soils in these catchments, offering guidance on their conceptualization and model adjustments to better capture seasonal variability. In catchments such as the River Beane, up to 35% of soils are classified Hanslope clay overlying chalk. These chalk aquifers are critical for drinking water supply and sustaining river baseflows. Therefore, the project outputs are essential for understanding seasonal recharge and support effective water resource management.
How to cite: Pitt, M., Momblanch, A., Simmons, R., Leggatt, A., and Coffey, D.: Understanding seasonal variability in shrink-swell clay soils and the impact on parameterisation of soil-water mass transfer models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16677, https://doi.org/10.5194/egusphere-egu25-16677, 2025.
Pesticides applied in agriculture often infiltrate into the vadose zone, and flushing events due to rainfall and irrigation can enhance their percolation to groundwater. Understanding the transport dynamics and persistence of these substances in soil is essential, as these compounds can contaminate aquifers, and thus threatening groundwater quality.
This study investigates pesticide mobility, sorption and degradation at a cash crop sites within the Hessian Ried, located south of Frankfurt in Germany.
To study the fate of pesticides, two high-resolution monitoring stations were established on agricultural fields. Soil water samples are collected at varying depths (10 cm, 20 cm, 50 cm, 150 cm, and shallow groundwater) using glass suction cups. This depth-resolved sampling approach will provide insights into the movement and persistence of pesticides in the soil and their possible infiltration into the groundwater. Furthermore, major ions and trace elements concentrations are measured in the unsaturated zone and in groundwater in eight different depths ranging from 2.30 m b.g.l. to 3.35 m b.g.l. Soil water content is measured using a soil water content profile sensor, while groundwater level and temperature are monitored through a 4-meter-deep hand-drilled well.
The findings help understanding the extent of contamination risks, allowing to design better management practices to protect groundwater quality in the region.
How to cite: Hillmann, S., Bockstiegel, M., Richard-Cerda, J. C., and Schulz, S.: Event-based high-resolution monitoring of pesticides at a cash crop site, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18847, https://doi.org/10.5194/egusphere-egu25-18847, 2025.
Due to the immense complexity of porous structure of soils, a proper level of complexity reduction is fundamental to any continuum modeling approach, ranging from one parameter characteristics, such as the Darcy law, to the overwhelming virtual representations, such as pore network models or even full-pore-space geometry characterisations. The role of various levels of reduced descriptions is crucial not only for the practical purpose of representing and simulating the particular functional behavior of given soil based on measurable properties, but also because they may inspire our understanding of the processes involved and, in particular, the changes and interaction of various soil properties.
We are interested in non-Newtonian porosimetry approach, introduced previously by other authors, which allows quantifying the functional pore size distribution of porous medium based on saturated flow experiments using (yield-stress and/or) shear-thinning fluids, such as xanthan gum aqueous solutions. The functional pore size distribution has been defined by the capillary bundle model of the flow through the porous medium and is related to various other (saturated and unsaturated) hydrological properties of the soil. The framework offers interesting potential applications both in the laboratory and in field, as it allows for nondestructive measurements that are not restricted to very small samples. In the poster, we focus on the method introduced previously by (Abou Najm, Atallah, 2016). We will discuss some interesting aspects of the concept (such as the relation to different definitions of pore size) along with some related issues (such as the sensitivity of the inverse problem to the measurement errors or the observed polymer entrapment). We will also touch on more potential applications, such as (Slavík, Lanzendörfer, 2024).
Abou Najm, M.R., Atallah, N.M., 2016. Vadose Zone Journal 15. https://doi.org/10.2136/vzj2015.06.0092
Slavík, M., and Lanzendörfer, M. 2024. Hydrology 11(9):133. https://doi.org/10.3390/hydrology11090133
How to cite: Lanzendörfer, M., Slavík, M., and Safari Anarkouli, S.: Towards functional characterization of soil pore size distribution using shear-thinning fluids: challenges and prospects , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18536, https://doi.org/10.5194/egusphere-egu25-18536, 2025.
Transport in porous media on the Darcy scale can be both Fickian and non-Fickian, an outcome dependent on the degree of homogeneity of the hydraulic conductivity pattern, as well as the boundary conditions and flow rate. The non-Fickian manifestation promotes the formation of preferential pathways that funnel the transport, which occurs in both weakly and strongly heterogeneous domains. We model Darcy-scale transport in a lognormally distributed conductivity field with varying hetrogeneity. We find that the resulting preferential pathways tend to split into more pathways (bifurcations), leaving regions into which particles do not invade, which we refer to as “under sampled regions” (USR), while forming a tortuous path. The fraction of bifurcations decreases downstream, reaching an asymptotic value, with a trend that can be fitted as a power-law of the variance. We show that the same power-law exponent relating the bifurcations to the variance holds true for the USR fraction, tortuosity, and fractal dimension with the same variance. An extension of our work is also presented for varying correlation length of the conductivity spatial distribution. We further expand our analysis to a case of impermeable fraction in a uniform conductivity field and show that the power-law fit still holds. We accompany this analysis with a Shannon entropy on the flow and find that there is a correlation between the scaling parameters and entropy change in the field.
How to cite: Edery, Y. and Dagan, A.: Bifurcating paths: the relation between preferential pathways, channel splitting, under-sampled regions, and tortuosity on the Darcy scale, and their relation to flow entropy. , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15378, https://doi.org/10.5194/egusphere-egu25-15378, 2025.
Air-sparging refers to the injection of air below the groundwater table. Air-sparging can facilitate the volatilization of organic pollutants or form a hydraulic barrier for the remediation or confinement of polluted groundwater. However, evaluating and modeling the flow and distribution of air is limited by the complicated physics of unstable multiphase flow. These complexities drive researchers to search for empirical relations and rules of thumb to design air-sparging systems.
Yet, despite these complexities, good agreement has been found when comparing analytical solutions of the classical flow physics' steady air injection problem to experimental results. Building on these results, adjusted analytical solutions and a phase decoupling framework can be set as a fast, robust, and parameters-parsimonious method for the design of air injection systems.
How to cite: Ben-Noah, I.: Air sparging analysis through the continuum approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1787, https://doi.org/10.5194/egusphere-egu25-1787, 2025.
Rice is one of the world’s most important staple foods and it is typically grown in rice paddies which are usually flooded for much of the growing season, causing significant percolation through the soil profile. The amount of water percolated depends on the ponding water level and on the hydrological properties of the soil, which in paddy fields is mainly articulated into a rooted soil horizon (muddy layer), a hardpan, and a subsoil. In addition, the percolation can be affected (reduced) by a shallow water table depth, which is commonly present in many rice growing areas.
In the models proposed to compute rice field water fluxes, three approaches are mostly used to simulate the vertical percolation: fixed percolation rate set by the user (e.g. implemented in YIELD, Cropwat and ORYZA models), Richard’s equation (e.g. in Hydrus, SWAP, FLOWS), or the Darcy’s law (e.g. SAWAH, WatPad introduced by Facchi et al., 2018). The fixed percolation approach is suitable when information on average percolation is available and percolation is known to be roughly constant along the season. On the opposite side, the application of the Richard’s equation requires the knowledge of the thicknesses and the soil properties (i.e. parameters of the soil water retention curve and unsaturated conductivity curves) of all soil horizons in the profile. Somehow in the middle of the two previous approaches, the Darcy-based models require only a few soil parameters; WatPad only needs the thickness of muddy and hardpan layers and saturated hydraulic conductivity of the hardpan. Obviously, both the Darcy and Richard’s approaches need the groundwater level if the water table is close to the soil surface.
The use of a Darcy’s model allows data collection to be focused on a small number of highly relevant soil characteristics, and this can be particularly useful when considering modelling applications over large spatial areas. However, this type of model lacks theoretical support for calculating water fluxes during periods when fields are in unsaturated conditions and, more importantly, for defining water potential values under the hardpan, especially when the water table is far from the soil surface. If the unsaturated flow is often very small or even negligible, errors in defining the soil water potential under the hardpan can lead to significant errors undermining the Darcy-based models.
A series of comparisons were made between the WatPad model and the SWAP model, considering deep groundwater table conditions. Results show that the two models gave nearly overlapping vertical percolations when in the Darcy’s model: i) the atmospheric pressure is set at the lower side of the hardpan and ii) the head loss due to the muddy layer is neglected. Indeed, these two simplifications affect the estimated percolation with similar errors and different signs, almost canceling each other out.
This research has been developed in the context of the PROMEDRICE project (https://promedrice.org/).
How to cite: Rienzner, M., Gilardi, G. L. C., and Facchi, A.: Applicability of Darcy-based models to predict vertical water fluxes in paddy fields, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11331, https://doi.org/10.5194/egusphere-egu25-11331, 2025.
Nature-based Solutions (NbS) are becoming very popular in literature as a promising strategy for adapting to climate change and manage stormwater in urban environment with numerous beneficial synergies. Although the benefits of using NbS, these systems are not as widespread as they should be because the water flow and solute transport dynamics are strongly dependent on the hydro dispersive properties of the medium which are not easy to determine.
In this way, this work presents several experimental investigations coupled with numerical analysis to define the hydro-dispersive properties of two soil substrates usually used in the drainage packages of Nbs.
Thus, to define the Soil Water Retention Curve (SWRC) and the Unsaturated Hydraulic Conductivity Curve (UHCC) the Hyprop device based on the modified evaporation method has been used. The traditional constrained van Genuchten-Mualem model has been used to fit the experimental points measured from the evaporation method.
Results from this experiment shown the goodness of the estimated hydraulic parameters values assessed with the traditional constrained van Genuchten-Mualem model, and this was confirmed by the low uncertainties of the individual parameters, indicated by the 95% confidence limits for the parameter values obtained, which were narrow as well as the curves goodness of fit described by the Root Mean Square Error (RMSE) which was very low.
Solute transport in the soil is governed by two main processes: advection and dispersion, both of which are essential for understanding the dynamics of contamination and solute mobility. In this way, to determine the longitudinal dispersivity (DL) of the investigated porous media, which is a key factor in solute transport dynamics, two saturated soil columns were injected with a natural tracer (deuterium) to characterize non-reactive solute transport in the substrates. Results from these experiments show a complex interaction between a mobile and an immobile domain, as indicated by the breakthrough curves' notable tailing. Finally, the inverse parameter estimation of the HYDRUS-1D model was applied to the experimental data obtained from the soil column experiment to assess the DL. The inverse optimization results have shown that the equilibrium models used in the optimization phase remained dependable in this instance, despite the breakthrough curves displaying notable tailing behaviour, indicating the presence of a complex interaction between the mobile and immobile flow domains.
How to cite: Presta, L., Turco, M., Brunetti, G., Stumpp, C., and Piro, P.: The assessment of the hydro-dispersive properties of a Nature-based Solutions porous media, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13103, https://doi.org/10.5194/egusphere-egu25-13103, 2025.
Posters virtual: Mon, 28 Apr, 14:00–15:45 | vPoster spot A
EGU25-2901 | Posters virtual | VPS8
Simulation of Salt and Moisture Dynamics in Agricultural Fields Using HYDRUS: Insights from a Sensor-Based CalibrationMon, 28 Apr, 14:00–15:45 (CEST) | vPA.20
The sustainable management of soil moisture and salinity is a critical challenge for semi-arid regions like the Mahabad Plain in northwestern Iran. This study applies the HYDRUS-1D model, calibrated using sensor-based data, to simulate water and salt dynamics in a 4 HA sugar beet field. The Mahabad Plain, covering 249 km², experiences annual precipitation of 402 mm and evaporation rates of 1,560 mm. Despite its fertile soils, the region faces persistent challenges such as waterlogging, salinity, and unsustainable irrigation practices, exacerbated by agricultural expansion and climate variability. Sensor data were collected every other day from four soil depths (0–25 cm, 25–50 cm, 50–75 cm, and 75–100 cm) in a single sugar beet field between late June 2024 and late July 2024. These measurements were used to calibrate the HYDRUS-1D model, optimizing parameters such as residual and saturated water content, hydraulic conductivity, and dispersion coefficients. Calibration metrics, including RMSE and Nash-Sutcliffe efficiency, confirmed the reliability of the simulations in replicating observed conditions. The results revealed critical inefficiencies in irrigation practices. Over-irrigation was observed, particularly in deeper soil layers, where moisture levels exceeded the optimal range of 18–25% for sugar beet cultivation. Surface layers (0–25 cm) also exhibited frequent waterlogging after irrigation events, with moisture levels surpassing 25%. Electrical conductivity (EC) levels, however, remained within the safe range of 0.6–1.3 dS/m, indicating effective salt leaching and no immediate risk to crop health. Simulations demonstrated that increasing irrigation intervals by 1–2 days could reduce water consumption by 15–30%, prevent excessive soil saturation, and promote healthier root growth. This approach ensures that soil moisture remains within the optimal range while maintaining crop yield and quality. This study is the first of its kind for the Mahabad Plain, offering a novel application of sensor-calibrated HYDRUS-1D modeling. It provides actionable recommendations for addressing water scarcity and improving agricultural sustainability. By integrating field observations with advanced modeling, the research bridges gaps in water resource management and offers replicable solutions for semi-arid agricultural systems worldwide. The findings are especially relevant as the region faces increasing agricultural demands and environmental challenges, including efforts to restore Lake Urmia. By improving irrigation efficiency and reducing agricultural water consumption, more water can be directed toward Lake Urmia, contributing to its restoration and the broader ecological balance of the region.
How to cite: Hossaini Baheri, M. and Tajrishy, M.: Simulation of Salt and Moisture Dynamics in Agricultural Fields Using HYDRUS: Insights from a Sensor-Based Calibration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2901, https://doi.org/10.5194/egusphere-egu25-2901, 2025.
EGU25-20587 | ECS | Posters virtual | VPS8
Physics-Informed Deep Learning for Soil Water DynamicsMon, 28 Apr, 14:00–15:45 (CEST) | vPA.21
The prediction of soil moisture movement remains challenging due to the complexity of underground flow processes and the availability of accurate soil parameters. There have been attempts to overcome this issue with parametric models and inverse modeling, but it remains challenging because it requires knowledge of initial and boundary conditions. While deep learning offers a solution, the one significant constraint remains not to violate the physical constraints. I present a novel physics-informed neural network (PINN) framework that integrates the soil moisture movement governing equation constraints with deep learning to predict soil moisture dynamics. The new approach follows mass conservation principles and soil hydraulic properties into the neural network's loss function. The model ensures physically consistent predictions. The framework simultaneously learns soil hydraulic parameters and water content distributions, adapting to heterogeneous soil conditions through a hybrid optimization strategy. The model incorporates the Van Genuchten parameterization within the physics-informed architecture to ensure consistency and accuracy. This methodology bridges the gap between computationally intensive traditional numerical solutions and pure data-driven approaches, offering a new paradigm for modeling soil water dynamics.
How to cite: Pathak, V. S.: Physics-Informed Deep Learning for Soil Water Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20587, https://doi.org/10.5194/egusphere-egu25-20587, 2025.
