This session welcomes research that advances the current understanding of the vadose zone hydro-biogeochemical functioning across multiple scales, including experimental or modeling approaches, and field or simulation studies. In particular, we encourage researchers to participate with contributions on the following topics:
• Monitoring of water flow, solute transport, and biochemical reactions from the pore scale to the field scale
• Experimental investigation and numerical modeling of the reactive transport of emerging contaminants in variably-saturated porous media
• Influence of static and dynamically changing soil structures (e.g., heterogeneity) on water flow and reactive solute transport
• Transport of water and contaminants in/from the rhizosphere into the plant
• Development of novel modeling approaches to predict water and chemical transport in the vadose zone
• Novel techniques for model appraisal, including calibration, sensitivity analysis, uncertainty assessment, and surrogate-based modeling for hydro-biogeochemical vadose zone modeling.
Soil structure is shaped by the dynamic interaction of physical, chemical, and biological processes, functioning across a wide range of spatial and temporal scales. Alterations in soil structure can, in turn, regulate essential soil processes such as the transport and reactivity of solutes, evaporation and water fluxes, microbial activity, etc., ultimately influencing biogeochemistry in soils and ecosystem functioning. However, the majority of modern widely used predictive models do not account for these dynamics and treat soil structure and thus soil hydraulic properties (SHP) as static. Recently, Jarvis et al. introduced the USSF model, a framework designed to integrate dynamic changes in soil structure and the consequent evolution of SHP. In this contribution, we build on the hydrological component of the USSF model to enhance its flexibility and enable a more accurate representation of SHP in both the soil matrix and structural part.
The USSF model simulates soil matrix water flow using the Brooks–Corey formulation, which assumes a non-zero residual water content at oven-dry matric potentials and exhibits physically inconsistent variability in the extremely dry region of the water retention curve. The soil structural domain is represented through an empirical macropore model with fixed boundaries of the structural pore size distribution. We introduce a more flexible and physically consistent description of matrix SHP based on the Brunswick model, coupled with a fracture-domain hydraulic formulation derived from the Tuller-Or model to represent structural pore flow.
The extended model was evaluated for two contrasting agricultural management strategies: direct seeding (DS) and conventional tillage (CT), with both systems initialized using a 10-year conventional tillage warm-up period. For both systems, soil organic matter was the primary driver of long-term porosity dynamics, with the direct seeding system reaching equilibrium within 10 years in the former plough layer, at 0-25 cm depth. The simulated SHP profiles aligned with published data, capturing a transient post-tillage increase in saturated hydraulic conductivity (Ksat) under CT, followed by rapid structural settling. Under DS temporal Ksat variability was lower. The Ksat depth profile within the plough layer remained vertically uniform in CT, whereas DS showed a systematic decline of Ksat with depth. The model enables realistic reconstruction of how agricultural operations will affect structural porosity and SHP. Future development will couple the extended model with a broader soil-crop-atmosphere system model and focus on improving the process description, particularly regarding seasonal dynamics.
How to cite: Vdovenko, D., Leuther, F., and Diamantopoulos, E.: Modeling the effects of soil structure dynamics on soil hydraulic properties. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1244, https://doi.org/10.5194/egusphere-egu26-1244, 2026.
Direct atmospheric water vapor absorption by structureless soils in coastal deserts has been the subject of various field studies, usually carried out with micro-lysimeters (ML’s). In one of these studies the absorption patterns of loess and sand were studied. Given the larger surface area of the loess soil, it was hypothesized that the loess soil would absorb more water vapor than the sand. The results, when the natural crust present on both soils was removed, were surprisingly similar and contrary to expectation.
We hypothesize that one of the reasons for these results was the different pore size distribution of both substrates, the larger pores of the sand allowing deeper penetration of downwelling eddies, thus directly exposing a thicker soil layer to the atmospheric water vapor concentration and hence to enhanced absorption or desorption.
To test this hypothesis, it is necessary to obtain data on the soil water distribution dynamics within the soil profiles of MLs whose soils have different pore size distribution.
In the present study we report the response of two aggregate sizes of two substrates (aggregated soil and quartz) to the daily fluctuations of atmospheric conditions.
The field study was carried out at the Wadi Mashash Experimental Farm in the Negev Desert, Israel, using four MLs. The MLs were instrumented with six temperature and relative humidity (RH) sensors (MX2302A, HOBO) inserted at depths of 0.5, 2, 5, 10, 20 and 45 cm. Water retention curves were obtained using a vapor sorption analyzer (Aqualab, Addium) for the driest part of the curve and standard pressure plate for the wetter parts of the curve. Data from soil and meteorological sensors and scales were recorded every 15 minutes and collected for six successive days during late summer.
The ML with large soil aggregates absorbed significantly more atmospheric water than the one with smaller aggregates, while the opposite trend was observed for the quartz particles. The absorption of both quartz MLs was, however, significantly lower than that of the small aggregate ML.
The temporal changes in soil water content distribution with depth were estimated by using temperature and RH to compute the thermodynamic soil water potential and transforming the latter into water contents via the water retention curves obtained for each soil and size fraction. The computed total water absorption and release patterns of the soil profiles within each of the MLs corresponded very well with the total recorded mass changes.
The depth of eddy penetration was indirectly estimated by comparing the fluctuations of water vapor concentration within the soil at various depths to the one measured simultaneously five cm. above the soil surface. Penetration depth was larger for the large quartz particles when compared to the small ones, but this effect was not so clear for the soil aggregates.
These results highlight the importance of inter- and intra- pore size distribution in determining water vapor absorption and desorption patterns in bare soils.
How to cite: Berliner, P., Eyni Nezah, H., and Agam, N.: The effect of particle size and mineralogy of soils on the diurnal cycle of atmospheric water absorption , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13886, https://doi.org/10.5194/egusphere-egu26-13886, 2026.
Soil hydraulic behavior is fundamental for determining water flow dynamics within the soil–plant–atmosphere continuum. Soil Hydraulic Properties, SHP, govern essential processes, including soil water storage within the root zone and the entire soil profile, evapotranspiration, plant water and nutrient uptake, runoff generation, deep percolation, groundwater recharge, as well as the transport of solutes and contaminants. There are several laboratory and field methods to characterize SHP. Laboratory measurements are generally more straightforward than field tests. However, their reliability depends on the selection of sample sizes that adequately represent the present heterogeneity in natural soils. In-situ methods for determining SHP are often labor-intensive and time-consuming due to the need for detailed spatial and temporal data. Because SHP exhibit significant spatial variability, many measurements are required to accurately characterize the SHP. This variability highlights the need for faster and more efficient methods to characterize SHP across multiple sites. This study proposes a fast in-situ method for SHP characterization called TDR-2D. It combines Time-Domain Reflectometry (TDR) with soil water modelling in a wetted bulb under a dripper. The TDR-2D method was simultaneously applied to multiple sites across an experimental field to estimate their SHP. The same sites were characterized using the Tension Infiltrometer Method, TIM. The soil hydraulic parameters estimated by TDR-2D were evaluated by comparing them to those obtained by TIM. Parameter correlation matrices were employed to assess uncertainty in parameter estimation. An additional sensitivity analysis was conducted to evaluate the influence of different dripper nominal flow rates (2, 4, and 6 l/h) on parameter estimation. The results indicate that the TDR-2D method reliably estimates soil water retention parameters across all tested flow rates. Estimation of the saturated hydraulic conductivity (K0) was particularly accurate at flow rates of 2 and 4 l/h whereas accuracy declined at 6 l/h. Furthermore, model output sensitivity to soil hydraulic parameters decreased with increasing dripper flow rate. Overall, for the soils investigated, the findings suggest that the TDR-2D method performs optimally at a nominal flow rate of 4 l/h, providing accurate SHP estimates while minimizing parameter uncertainty. Since the TDR-2D and TIM methods yield Russo–Gardner (RG) and van Genuchten–Mualem (vGM) parameters, respectively, direct comparison required conversion between the two parameter sets. The results demonstrate that conversion from vGM to RG parameters is generally feasible, whereas the reverse conversion is less straightforward and should be approached with caution.
How to cite: Coppola, A., Hassan, S. B. M., Dragonetti, G., and Comegna, A.: A New Fast in-Situ Soil Hydraulic Characterization Method Combining 2D Soil Water Flow Modelling and Time-Domain Reflectometry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6956, https://doi.org/10.5194/egusphere-egu26-6956, 2026.
Standard ecohydrological analyses typically frame soil moisture dynamics as direct responses to discrete rainfall episodes. However, this “forcing-first” perspective implicitly assumes that subsurface response timescales are synchronized with atmospheric intermittency—an assumption that breaks down when soil moisture dynamics bridge multiple storms or when storage depletion occurs within shorter timescales. Here, we demonstrate that relying on meteorological event definitions leads to a fundamental mischaracterization of the temporal organization of soil storage. By applying an anomaly-based signal analysis to multi-year, profile-resolved field observations, we decoupled subsurface storage dynamics from rainfall timing to isolate observable patterns of soil response. The analysis reveals two critical dynamics that event-based logic obscures. First, antecedent wetness is associated with a distinct regime-dependent transition in response structure: broadly distributed, multi-day storage anomalies in dry conditions contract into rapid, sub-day drainage pulses in wet conditions. This effectively decouples the subsurface response duration from the rainfall duration. Second, soil moisture dynamics frequently integrate multiple distinct precipitation episodes into single, coherent observed storage trajectories, particularly in deeper layers. These findings show that the temporal organization of soil moisture is governed by the interplay of forcing and antecedent state, not merely by rainfall timing. We conclude that forcing-based definitions are insufficient for capturing effective system memory, and that accurately characterizing ecohydrological function requires defining events by their subsurface response rather than their atmospheric input.
How to cite: Luo, G., Chang, L., Hannah, D. M., and Krause, S.: Antecedent state and the temporal organization of soil moisture response to episodic rainfall , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21575, https://doi.org/10.5194/egusphere-egu26-21575, 2026.
Water fluxes in the critical zone are driven by various environmental variables. For example, soil water is rapidly replenished during precipitation events and is slowly emptied during periods of transpiration at rates which are mainly driven by diurnal solar radiation and vapor pressure deficit. Precipitation, solar radiation and vapor pressure deficit correlate, which complicates proper disentanglement of their individual effects on tree physiology and tree-mediated water fluxes. Here, we use Ensemble Rainfall-Runoff Analysis (ERRA) to disentangle how different environmental variables contribute to ecosystem water fluxes (net soil water and tree water recharge and sapflow) measured at the ‘WaldLab Forest Experimental Site’ in Zurich. The methodology is data‐driven and relies on non-linear and non-stationary deconvolution of time series to infer impulse-response functions. These impulse-response functions quantify the intensity and the time lag in the responses of tree-mediated water fluxes to precipitation, solar radiation and vapor pressure deficit, and account for any covariation effects among these drivers. The results are based on five years of sub-daily sapflow and dendrometer measurements on three beech and spruce trees, respectively, and show the immediate response of tree water fluxes at the field site. Notably, the response of sapflow and tree water recharge towards solar radiation is more pronounced then the response towards vapor pressure deficit, reflecting the higher importance of radiation (a physiological necessity) compared to vapor pressure deficit (a hydraulic boundary condition) in driving transpiration. Beech and spruce trees differ in the duration of the response, with spruce trees showing responses lasting longer then beech, reflecting the higher hydraulic capacitance of spruce trees. Our study highlights how this novel impulse-response approach helps identifying soil-plant-atmosphere relations that complement our understanding of how forest ecosystems work.
How to cite: Martinetti, S., Molnar, P., Kirchner, J. W., and Floriancic, M. G.: Disentangling hydrological responses of forest ecosystems to impulses of precipitation, VPD and solar radiation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18333, https://doi.org/10.5194/egusphere-egu26-18333, 2026.
Twenty-seven percent of the world’s terrestrial area is classified as arid or hyper-arid, regions that are second only to oceans in the sparsity of measurement sites. Contrary to popular perception, these desert areas are dynamic ecosystems that respond sensitively to changes in water availability, temperature, and carbon dioxide levels. Efforts to understand the dynamics and feedback mechanisms between the main players affecting desert weather and climate can be divided, by-and-large, into two groups: (1) addressing the most pressing knowledge gaps of desert weather and climate systems; and (2) exploring processes that have not previously been considered but are hypothesized to be more important than presumed, representing a realm of "unknown unknowns". One example to the “unknown unknowns” realm is related to non-rainfall water inputs (i.e., fog, dew, and atmospheric water vapor adsorption). Traveling between the Negev, Namib, and Sahara deserts, we will look into this largely overlooked phenomenon. We will point to the similarities between these deserts and ask how widespread this phenomenon may be and why should we care.
How to cite: Agam, N., Kool, D., and Bekin, N.: It’s time to start tuning for deserts!, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10216, https://doi.org/10.5194/egusphere-egu26-10216, 2026.
The SWIM² framework (Hendrickx et al., 2025) integrates a soil water balance model with in situ sensor data and soil moisture samples through Bayesian inverse modelling. The calibrated model then generates probabilistic 10-day soil moisture forecasts, enabling real-time, site-specific irrigation advice. SWIM² was validated in a real-time setup for 18 vegetable cropping cycles on agricultural fields in Flanders, Belgium, with reliable precipitation data. Although using minimal prior knowledge and despite sensor bias, SWIM² achieves robust soil moisture predictions for a 7-day horizon, with accuracies comparable to sensor measurements. We also assessed the impact of model parameter and weather forecast uncertainty on SM prediction uncertainty, water stress prediction and irrigation advice by integrating the calibrated model ensemble with ensemble-based probabilistic weather forecasts, resulting in high detection rate and accuracy in predicting water stress triggering the irrigation threshold.
Time series of vegetation indices such as NDVI and LAI from Sentinel-2 optical remote sensing as well as LST from Sentinel-3 contain much information on crop growth and crop evapotranspiration. Additionally, the new NISAR mission is promising for high-resolution surface soil moisture observations. We assess relations between in situ measurements and model outputs (crop growth curve, actual ET and SWC), and the remote sensing data, and we discuss opportunities of these data to improve soil moisture and ETa predictions.
Reference: Hendrickx, M.G.A., Vanderborght, J., Janssens, P., Laloy, E., Bombeke, S., Matthyssen, E., Waverijn, A., Diels, J. (2025). Field-scale soil moisture predictions in real time using in situ sensor measurements in an inverse modeling framework: SWIM². Authorea Preprints, doi:10.22541/ESSOAR.175103915.57413983/V1.
How to cite: Hendrickx, M., Vanderborght, J., Janssens, P., and Diels, J.: Probabilistic soil moisture predictions at field scale using in situ data in a Bayesian inverse modelling framework SWIM² and the potential of remote sensing, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4996, https://doi.org/10.5194/egusphere-egu26-4996, 2026.
Groundwater, the world’s largest accessible freshwater resource, supports billions of people but is increasingly threatened by excessive abstraction rates that exceed natural groundwater recharge (GWR). Sustainable groundwater management requires establishing an accurate balance between extraction and recharge. Hydrological models are commonly used to estimate GWR; these models are typically calibrated to historical data and then assumed to remain valid for future projections under the notion of stationarity, that is, the assumption that the conditions used for model training will remain representative in the future. However, under projected climate change, this assumption is likely to be violated in many regions. In this study, soil water content observations from the International Soil Moisture Network (ISMN) were used to calibrate both bucket-type and Richards’ equation models for estimating GWR across multiple sites, using the DREAM algorithm. For each location, the most appropriate model structure was selected based on the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC). Future climate projections from GCMs under the SSP5–8.5 scenario were then summarized as annual rainfall totals for all sites. Subsequently, site pairs were identified in which historical annual rainfall totals at one location resemble future projected totals at another location, while also exhibiting similar soil hydraulic properties. This framework enables testing whether the model method selected under historical conditions remains valid under future climates. Overall, the proposed approach offers a systematic method for determining the complexity of unsaturated flow models and is expected to reduce uncertainty in GWR estimates.
How to cite: Turkeltaub, T.: Selecting Unsaturated Flow Model Complexity for Groundwater Recharge Estimation Under Climate Change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16297, https://doi.org/10.5194/egusphere-egu26-16297, 2026.
Land surface models (LSMs) play a central role in simulating land-atmosphere interactions by representing coupled soil, vegetation, and energy-water-carbon processes. In most current LSMs, soil hydraulic and thermal properties are treated independently and are coupled only indirectly through soil moisture content, without an explicit linkage between the underlying parameters that define the shape of the curves characterising hydro-thermal properties. Although several independent studies have demonstrated strong correlations between soil hydraulic properties (SHPs) and soil thermal properties (STPs), these relationships have not yet been incorporated into land surface models to assess their impacts on land-surface states and fluxes.
For the present study, we developed a unified hydro-thermal framework for ecLand that explicitly integrates soil hydraulic and thermal properties, thereby improving the representation of coupled soil moisture and heat transport and associated land–atmosphere interactions. First, the van Genuchten (1980) soil water retention curve (SWRC) was replaced by formulations that explicitly represent adsorbed and capillary water components (e.g. Lu, 2016; Peters-Durner-Iden, 2024), leading to a more physically consistent description of soil hydraulic properties, particularly under dry soil conditions. Second, the thermal conductivity formulation of Peters-Lidard et al. (1998), currently used in ecLand, was replaced by an approach that directly links thermal conductivity to SWRC parameters (Lu & McCartney, 2024), ensuring a consistent coupling between soil hydraulic and thermal properties.
We first quantified the impacts of these developments on soil states (soil moisture and soil temperature at multiple depths) and land-surface fluxes (latent and sensible heat) using a series of controlled sensitivity experiments. These experiments were designed to isolate the response of the coupled hydro-thermal system to variations in soil texture, soil depth and discretization, and climatic regimes with an emphasis on more arid conditions. Through this sensitivity analysis, we examined how the unified hydro-thermal framework influences moisture–temperature feedbacks, vertical heat transport, and surface energy partitioning across contrasting hydro-climatic environments. The performance of the unified framework was then evaluated at selected in situ sites by comparing simulations from the original and updated ecLand configurations against observations of soil moisture, soil temperature, and latent and sensible heat fluxes. We find substantial differences between the two formulations in the simulated surface energy fluxes, particularly for soils with high sand content, where discrepancies in latent and sensible heat reach approximately 40 W m-2 for loamy sand. Future work will focus on implementing this framework in global ecLand simulations to assess impacts on near-surface land states and surface fluxes, and subsequently in fully coupled land-atmosphere simulations within IFS to evaluate potential improvements in near-surface atmospheric variables (e.g. 2 m air temperature and relative humidity) and the reliability of ECMWF’s sub-seasonal to seasonal forecasts.
How to cite: Kandala, R., Verhoef, A., Gupta, S., Paulus, S., Boussetta, S., Rosnay, P. D., Rüdiger, C., Zeng, Y., and Black, E.: Advancing Land-Surface Modelling in ecLand Through a Unified Hydro-Thermal Framework, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16547, https://doi.org/10.5194/egusphere-egu26-16547, 2026.
Soil moisture memory (SMM) is a primary driver of land-atmosphere coupling, hydrological predictability, and the response of ecosystems to climate variability. Although machine learning-based algorithms have recently been shown to predict soil moisture with a high degree of accuracy, it is unclear whether these models can predict SMM and SMR effectively. In this study, we assess whether better state estimation results in enhanced representation of SMM. To achieve this, we use six years (2013–2018) of daily grassland lysimeter observations from Rollesbroich, Germany (50°37'12" N, 6°18'15" E), including multi-depth soil moisture (10, 30, and 50 cm), through which a depth-averaged root-zone soil moisture is calculated (see Figure 1). In addition to the observational data, we also estimated soil moisture at different depths and then computed root zone soil moisture according to the upper and lower boundary fluxes (i.e., precipitation, drainage, and actual evapotranspiration), using two modelling methodologies: (i) a physics-based Richards equation model (HYDRUS-1D, calibrated against observations) and (ii) a physics-informed neural network (PINN), which was trained on the same dataset (see Figure 1). We analyze, then, the SMM structure in the simulated and observed time series using a Linear Integro-Differential Equations (LIDE) framework, which quantifies the accumulation of memory at different timescales, e.g., fast memory (τF), slow memory with short-term (τS), intermediate (τI), and long-term (τL) components, and memory saturation timescale (τ∞). The results show that the PINN model is much more accurate than the HYDRUS-1D model at simulating observed soil moisture states (root mean square error, RMSE = 0.003 vs 0.018; Nash-Sutcliffe Efficiency, NSE = 0.997 vs 0.881). However, the fast memory timescale (τF) is slightly underpredicted by PINN (with τF ~ 4.5 days) and is slightly better approximated by HYDRUS-1D (with τF ~ 5.9 days) compared to observations (with τF ~ 7.6 days), reflecting stronger physical damping in HYDRUS-1D. While the short-term slow-memory timescale (τS) could not be identified using either measured or modeled data, the intermediate slow-memory timescale (τI) of measured data (with τI ≈ 4 months) could be robustly recovered using either model. The long-term slow-memory timescale (τL) and the saturation timescale (τ∞) are, respectively, underestimated and overestimated by the PINN (with τL ~ 9 months and τ∞ ~ 10.6 years), resulting in weaker persistence and a narrower window for re-emergence compared to the observed values (with τL ~ 9.5 months and τ∞ ~ 8.96 years). In contrast, HYDRUS-1D better resolves the long-term memory dynamics (with τL ~ 9.7 months and τ∞ ~ 8.26 years). These findings highlight that strong prediction skills for state variables do not necessarily equate to a good representation of their hidden memory structure. According to these results, we suggest that memory-based diagnostics can probably serve as a complementary indicator to analyze the performance of simulated soil moisture dynamics alongside traditional performance measures and can provide a critical benchmark for evaluating physics-based and machine learning hydrological models.
How to cite: Rahmati, M., Song, W., Montzka, C., Vanderborght, J., and Vereecken, H.: Beyond Accuracy: Can Physics-Informed Neural Networks Reproduce Root-Zone Soil Moisture Memory?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10088, https://doi.org/10.5194/egusphere-egu26-10088, 2026.
Actively heated distributed temperature sensing (AH-DTS) has been widely applied for soil moisture monitoring over distances ranging from a few centimeters to several hundred meters; however, few studies have explored this method for investigating transient soil water behavior during rainfall events.
Here, a soil column (75 cm high and 30 cm in diameter) was constructed in the laboratory, where an active fiber-optic cable was helically wrapped around a central supporting element with a 5-cm bending radius. Repacked sandy clay loam soil filled the column with three compaction levels: loose (1.35 g cm-3, 0–25 cm), medium (1.44 g cm-3, 25–50 cm), and dense (1.51 g cm-3, 50–75 cm). Sprinkler nozzles simulated a rainfall event of 40 mm hr-1 lasting 4 hours in the soil profile, during which the fiber-optic cable was continuously heated with a power input of 5 W m-1. A DTS unit collected temperature data at a vertical sampling resolution of 1.25 cm, while 14 soil moisture sensors regularly distributed throughout the column measured changes in soil water content.
The results showed that wetting front arrival at different soil depths was detected by the fiber-optic as cooling pulses. The magnitude and temporal stability of the cooling were inversely related to soil depth and bulk density. From the moment the front was detected, the superficial soil layer exhibited more pronounced and longer-lasting negative thermal anomalies, whereas anomalies in the deepest layer were smaller in magnitude and less persistent. These findings suggest the dominance of thermal advection in the loose soil layer and thermal conduction in the dense layer, while the medium-density layer exhibited transitional behavior. With respect to instrumentation, good agreement was observed between time of detection of the wetting front arrival obtained from the moisture sensors and the optical fiber (root mean square error of 6.2 minutes).
Overall, the results contributed to the understanding of thermal regimes in unsaturated flow and further shed light on the use of temperature as a tracer for soil water infiltration and percolation processes. Ongoing research aims to investigate soil thermal behavior with AH-DTS across a broader range of rainfall intensities and contrasting soil textures.
How to cite: Bertotto, L., Reis, A., Neto, E., Tsuha, C., Wendland, E., and Bour, O.: Can AH-DTS detect wetting front movement in soil columns during rainfall events? First impressions from experimental investigations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11083, https://doi.org/10.5194/egusphere-egu26-11083, 2026.
Plant growth-promoting bacteria (PGPB) are vital for sustainable agriculture as they mobilize key nutrients, boost stress tolerance, and encourage plant growth. Despite their benefits, delivering PGPB effectively into soil is challenging due to strong bacterial adsorption, limited movement, and variable soil conditions that hinder bacterial mobility and decrease bioavailability in the rhizosphere. Consequently, inoculated bacteria often stay near the application site and struggle to colonize roots effectively. Surfactants have shown potential in improving microbial transport through porous media by altering bacterial–soil and water–soil surface interactions. They lower surface tension and modify electrostatic and hydrophobic forces, reducing bacterial attachment to soil particles and facilitating cell detachment and movement. This research investigates how surfactants (Triton-100, rhamnolipid, and Tween-80) influence the mobility of two model PGPB, Azospirillum brasilense and Bacillus subtilis, in soil columns. It also assesses surfactants toxicity through standardized growth inhibition tests. Toxicity testing revealed that Tween-80 is non-inhibitory. Bacterial transport experiments were conducted in packed soil columns under controlled hydraulic conditions, both with and without surfactant, and bacterial breakthrough curves (BTCs) were generated by continuously monitoring bacterial concentrations in the column influent and effluent as a function of pore volumes to quantify transport behavior. Tween-80 improved bacterial breakthrough and decreased the bacteria deposition rate compared to controls, demonstrating enhanced bacterial transport. These findings suggest that non-toxic surfactants can significantly improve PGPB mobility, offering a promising approach for effective microbial inoculation in sustainable farming.
How to cite: Kiros, H. G. and Arye, G.: Effect of Surfactants on the Transport and Availability of Plant Growth-Promoting Bacteria in Soil., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5226, https://doi.org/10.5194/egusphere-egu26-5226, 2026.
Geochemical aging can alter the chemical structure of biochar (BC), resulting in the release of nano sized BC (ranging from 200 nm to 500 nm). Although, several studies have revealed the adsorption and immobilization of pesticides on BC, little is known regarding the mobility and retention of pesticides sorbed on nano particles. Thus, column tests were conducted to investigate organophosphate pesticide (chlorpyrifos) transport using nano biochar (NBC) as amended in sand column and use Hydrus 1D model to simulate the result. The findings demonstrated that NBC amended sand increased chlorpyrifos retention by 60% to 70% when nanoparticles were incorporated. Additionally, the chlorpyrifos simulated kd value (sorption coefficient) increased from 1.64 L/g to 2.10 L/g. Also, the proportion of equilibrium adsorption sites (f) decreased from 0.25 to 6.78 ×10-6 after amendment. This study shows that Nanoparticles maximizes the efficiency of biochar in controlling environmental pollution by improving its adsorption capacities and modulating its ability to prevent pesticide migration to groundwater.
Keywords: Organophosphate transport, HYDRUS-1D, soil column, non-equilibrium equation, adsorption
How to cite: Monika, and Sonkar, I.: Influence of Nano biochar on the fate and transport of chlorpyrifos, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7207, https://doi.org/10.5194/egusphere-egu26-7207, 2026.
Despite the well-known influence of hydrological conditions within the vadose zone on Micro and nano plastic (MnPs) transport, the effect of soil moisture and flow regime remain poorly understood, since most studies have been conducted under saturated conditions.
In this study, we combined laboratory column experiments with numerical modelling to investigate the MnPs transport in gravel soils under contrasting saturation conditions and two flow regimes (steady vs transient). We used commercial 1µm Polystyrene (PS) fluorescent spherical particles in coarse granular media, under both saturated and unsaturated conditions. The chosen material is representative of some parts (lithofacies) of the glaciofluvial deposits exploited for drinking water supply in the region of Lyon. Unsaturated experiments were conducted at different initial soil moisture contents (from 8% to 52%) and under steady and transient flow regimes to assess the influence of the flow hydrodynamics on the MnPs transport. The PS effluent concentration at the column outlets was determined by using fluorescence spectrophotometry, while conservative tracer experiments were used to constrain flow and transport parameters.
Under saturated conditions, transport was highly reproducible, with an average MnPs recovery of 85%, a maximum relative concentration of 0.11, a peak breakthrough arriving at 0.79 pore volumes (PV). In contrast, unsaturated conditions showed bigger variability, with recovery rates ranging from 44-98%, maximum relative concentrations from 0.07 to 0.25 and peak breakthrough occurring between 0.59 and 1.13 PV, depending on experimental conditions. Numerical models using Hydrus reproduced the observed differences and showed differences in water fractions characterised by the tracer. These finding emphasize the need to account for the vadose zone-specific flows and sorption air-water dynamics when assessing the fate of microplastics and the potential impacts on groundwater quality. This study demonstrates the crucial roles of specific flow conditions and air–water interfacial sorption in controlling microplastic transport within the vadose zone, with important implications for groundwater vulnerability assessments and for interpreting spatiotemporal variations in groundwater microplastic concentrations.
This project has received funding from European Union’s HORIZON EUROPE research and innovation program GA N°101072777-PlasticUnderground HEUR-MSCA-2021-DN-01
How to cite: Cardoza-Pedroza, L., Lassabatére, L., Mourier, B., and Volatier, L.: How soil moisture and flow regime drive microplastic transport in the vadose zone: insight from modelling and column experiments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5527, https://doi.org/10.5194/egusphere-egu26-5527, 2026.
Predicting transport of per- and polyfluoroalkyl substances (PFAS) through the vadose zone is essential for contamination risk assessment, yet the reliability of available models remains poorly understood. This study compared five available models by exploring their conceptual and technical differences, and assessing the alignment of model capabilities against current theoretical understanding of reactive transport of PFAS. We evaluated predictive performance by forward modeling two column experiments and conducting one virtual field-scale simulation across different PFAS compounds and soil types. While all models agreed well with short-term column experiments (NSE ≥ 0.82), they diverged substantially at field-scale, with mid-point breakthrough times differing by multiple years despite identical parameterization.
Quantification of the air-water interface (AWI) emerged as the primary source of inter-model variability and remains the most disputed aspect in theoretical reactive transport understanding of PFAS transport. Existing approaches compute systematically different AWI values as functions of saturation and soil physical parameters, whilst likely underestimating the interfacial area by neglecting surface roughness of grains and pore-scale complexity.
All examined models employ simplified and empirically-derived solid-phase sorption parameters that do not account for soil-specific behavior, solution chemistry, and soil heterogeneity. Important processes including precursor transformation, competitive sorption, and desorption hysteresis remain largely unimplemented, fundamentally constraining predictive reliability. Hence, comprehensive multi-year field validation datasets across diverse hydrogeological settings are urgently needed to quantify prediction uncertainty and establish robust parameterization strategies.
How to cite: de Rijk, V., Lutz, S., and Griffioen, J.: Modeling PFAS transport through the vadose zone – a comparison of model codes for column and field-scale experiments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1723, https://doi.org/10.5194/egusphere-egu26-1723, 2026.
The widespread use and extreme persistence of per- and polyfluoroalkyl substances (PFAS) present significant risks to vulnerable hydrologic systems, yet the fate of these compounds originating from diffuse urban runoff remains poorly understood. This study investigates the transport and fate of 25 PFAS compounds within a pilot-scale nature-based infiltration facility, utilizing a multi-parameter in-situ monitoring network to track concentrations across the runoff-soil-groundwater continuum. Through the analysis of three representative rain events across different seasons, results reveal a sharp contrast in PFAS dynamics between environmental compartments. While a pronounced "first flush" effect was observed in surface runoff with peak concentrations of 656 ng/L rapidly decreasing to 5 ng/L the soil matrix acted as a significant geochemical buffer, moderating vadose zone percolate to a narrow range of 26 to 55 ng/L. Interestingly, background PFAS levels in the broader aquifer remained consistently higher (169 - 226 ng/L) than those measured in the vadose zone, suggesting that pre-existing legacy contamination exerts a more dominant influence on groundwater quality than contemporary leaching from the infiltration site. Furthermore, a temporary dilution effect observed in downgradient monitoring wells during rainfall events indicates that urban infiltration practices may locally mitigate groundwater contamination levels. Multivariate analysis identifies low pH and high total organic carbon (TOC) as the primary physicochemical drivers associated with elevated PFAS mobility. Ultimately, this research demonstrates that while urban runoff introduces new PFAS loads, the primary risk at this site stems from background aquifer contamination, providing a strong scientific basis for the promotion of urban infiltration as a sustainable and potentially remedial stormwater management strategy.
How to cite: Bouarafa, S., Khaska, S., Le Gal La Salle, C., Soukrate, I., Lemoine, M., and Côme, J.-M.: Field-scale PFAS transport dynamics in a small urban catchment: Insights from Stormwater, Vadose Zone and Groundwater monitoring in a nature-based Infiltration facility., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17385, https://doi.org/10.5194/egusphere-egu26-17385, 2026.
Zero-tillage (ZT) is a conservation soil management approach which relies more heavily on herbicide application for weed control than in ploughed soil. Changes in soil management can influence the structure and organisation of pore space in soil, which drives changes in the transport of particulates and dissolved substances. Formulation of pesticides can be used to change the delivery of active ingredients to soil; however, it is currently unknown how changing the formulation of an herbicide can influence the transport properties between ZT vs. ploughing. We investigated the bioefficacy of two formulations of the herbicide atrazine, a pre- and post-emergence herbicide that inhibits photosystem II. Bioefficacy was assessed using physical measures and survival analysis of an early photosynthesis-dependent weed species, Amaranthus retroflexus L., over time, and soil pore network structure was assessed by analysing three-dimensional images produced by X-ray Computed Tomography. Increasing the herbicide application rate generally improved bioefficacy, though it was reduced in soils managed under ZT. Under herbicide-treated ZT samples, survival time was higher, ranging from 13.4 to 18.2 days compared with 12.6 to 15.4 days in ploughed samples, the mean dry plant mass was higher, ranging from 0.5 to 2.5 mg compared with 0.05 to 0.68 mg in ploughed samples, and the mean total plant length was higher, ranging from 1.73 to 12.1 mm compared with 0.2 to 5.45 mm in ploughed samples. Changes in the soil pore network previously demonstrated to be indicators of preferential transport were correlated with measures of bioefficacy, including pore thickness and connectivity density. Reduced atrazine efficacy under ZT is problematic considering the inherent reliance on chemical methods for weed control, we suggest that pursuing formulation strategies to alleviate potential risks of loss via preferential transport may be fruitful.
How to cite: Wardak, D., Padia, F., DeHeer, M., Sturrock, C., and Mooney, S.: Zero-Tillage Induces Reduced Bio-Efficacy Against Weed Species Amaranthus retroflexus L. Dependent on Atrazine Formulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17420, https://doi.org/10.5194/egusphere-egu26-17420, 2026.
Soil salinization is a major constraint on the sustainable development of global agriculture. As an effective technique for reclaiming saline soils, subsurface pipe drainage often exhibits limited drainage and salt removal efficiency under complex soil conditions characterized by low-permeability layers. To enhance drainage and salt removal efficiency, this study proposes a sand-column–assisted subsurface pipe drainage system, in which sand columns are installed directly above subsurface pipes and between adjacent pipes to establish stable vertical percolation pathways. Based on two years of field experiments and HYDRUS-3D numerical simulations, the regulatory effects of sand-column–assisted subsurface pipe drainage on the spatiotemporal variation of profile salinity, drainage and salt removal capacity, and groundwater dynamics were systematically evaluated, and comparisons were conducted with conventional subsurface pipe drainage under fixed-quota and fixed-time irrigation schemes focusing on drainage capacity, desalination efficiency, and economic benefits. The results indicated that over the two-year experimental period, soil salinity in the 0-40 cm plough layer of plots with sand-column-assisted subsurface pipe drainage declined from 15.48 g/kg to 8.53 g/kg, achieving a desalination rate of 44.85%, and no salt accumulation was observed in deeper soil layers. Under both fixed-quota and fixed-time irrigation conditions, sand-column–assisted subsurface pipe drainage exhibited superior groundwater control performance compared with conventional subsurface pipe drainage. Under the same irrigation amount, sand-column–assisted subsurface pipe drainage was more suitable for rapidly reducing surface soil salinity in the plough layer, whereas conventional subsurface pipe drainage showed more pronounced advantages in total salt removal and sustained salt discharge capacity. The average salt removal rate of sand-column–assisted subsurface pipe drainage was 49.23% higher than that of conventional subsurface pipe drainage at 1.5 d, whereas the cumulative salt removal of conventional subsurface pipe drainage was on average 16.19% higher than that of sand-column–assisted subsurface pipe drainage at 15 d. Under identical irrigation durations, the cumulative salt discharge of sand-column–assisted subsurface pipe drainage was generally higher than that of conventional subsurface pipe drainage. At a pipe spacing of 10 m, the per-hectare infiltrated water volumes for conventional subsurface pipe drainage and sand-column–assisted subsurface pipe drainage were 1399.95 m³ and 2128.05 m³, respectively, with salt removal by sand-column–assisted subsurface pipe drainage being 9.40% higher than that under conventional subsurface pipe drainage. Comprehensive economic evaluations under the two operating scenarios indicated that under fixed-quota irrigation leaching conditions, sand-column–assisted subsurface pipe drainage system with sand columns installed only above subsurface pipes showed overall economic advantages in terms of EIRR, ENPV, EBCR, and payback period. Under fixed-time irrigation leaching conditions, conventional subsurface pipe drainage exhibited superior overall economic benefits compared with sand-column–assisted subsurface pipe drainage with sand column uniformly installed both above the pipes and between adjacent pipes, whereas sand-column–assisted subsurface pipe drainage with sand columns installed only above the pipes exhibited better economic performance than conventional subsurface pipe drainage.
How to cite: Jin, M., Meng, Z., Tao, Y., Wang, S., Guan, X., Niu, Y., and Liu, H.: Evaluation of Water–Salt Regulation and Economic Performance of Sand-Column–Assisted Subsurface Pipe Drainage in Saline–Alkali Soils Containing Low-Permeability Layers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17845, https://doi.org/10.5194/egusphere-egu26-17845, 2026.
Flooding and subsequent saltwater intrusion from rising sea levels pose significant concerns for shore-front areas, particularly agricultural lowlands and coastal forests. Changes in soil salinity, driven by both vertical infiltration from high tides and lateral seawater intrusion from storm surges, are documented to produce ghost forests and render agricultural soils unsuitable for cultivation. This study explores the sensitivity of geophysical methods to the exchange of water between trees and soil in white oak (Quercus alba) trees on the upper Delmarva Peninsula. High-frequency ground-penetrating radar (GPR) was employed to image root structures, identifying the depth of highest root density at approximately 0.3 m. This data provided critical geometry for Hydrus-1D evapotranspiration models. Small-scale 3D time-lapse electrical resistivity tomography (ERT) can be used to image the root zone and base of the trees. Initial work with ERT shows variability in the rainfall infiltration patterns but there are issues regarding sensitivity at the base of the tree. To assess tree physiology, vertical arrays of true self-potential (SP) non-polarizing electrodes were installed on tree trunks; SP measurements are a passive electrical method typically used in soil to measure streaming potential which is voltage values which are generated by the movement of water through porous media or capillary action. There have been attempts to use SP electrodes on trees before but the information has been ambiguous as a result of polarization effects as proper SP electrodes were not used, leading to misinterpreted data. The SP electrodes are deployed alongside more traditional sap flow sensors for validation of the collected data. In instances where in-situ sap flux data were unavailable, transpiration rates modeled using Hydrus-1D were utilized as a proxy of sap flux values. Wavelet analysis of the SP data revealed distinct diurnal cycles with strong 24-hour peaks that correlated with both the available sap flow measurements and the modeled transpiration. These results confirm that SP is a viable proxy for monitoring soil-tree moisture dynamics. This strategy may offer a novel framework for monitoring tree health and verifying subsurface water dynamics in coastal ecosystems threatened by saltwater intrusion.
How to cite: Pesonen, D., Hess, R., Terra, C., Slater, L., Gedan, K., and Michael, H.: Geophysical Monitoring of Oak Trees in a Marsh-Forest Upland Transect, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3586, https://doi.org/10.5194/egusphere-egu26-3586, 2026.
Abstract
Accurate characterization of transient heat transport in layered subsurface media is fundamental to a wide range of environmental and hydrological applications, including groundwater recharge assessment, land-atmosphere interaction analysis, and climate signal detection in soils. This study presents a fully analytical solution for one-dimensional transient heat transfer in a two-layer soil system subjected to realistic, time-dependent surface temperature forcing associated with diurnal variations. The governing advection-conduction equation is solved using the Generalized Integral Transform Technique, which enables an exact treatment of interlayer thermal interactions while avoiding numerical inversion or interface-matching complexities. The resulting formulation yields a computationally efficient and stable solution that is well suited for both forward simulation and inverse analysis. The analytical solution is rigorously validated through comparison with high-resolution numerical simulations, demonstrating excellent agreement for both homogeneous and stratified soil configurations over a wide range of hydrothermal conditions. The inverse modeling capability of the framework is further demonstrated by coupling the analytical solution with a genetic algorithm to estimate vertical water flux from field-measured temperature data, highlighting its potential for non-invasive hydrological characterization. This work introduces a scalable, computationally efficient, and physically consistent framework for simulating and interpreting transient heat transport in layered subsurface systems. Owing to its generality, the proposed methodology is readily extendable to other diffusion-dominated transport processes, such as solute transport in stratified geological media, thereby enhancing its applicability across a broad range of geoscientific problems.
Keywords: Transient heat transport, Layered subsurface media, Analytical solution, Generalized Integral Transform Technique, Inverse modelling
How to cite: Bashist, V., Sarmah, R., and Sonkar, I.: Analytical and Invertible Model for Transient Heat Transport in Layered Subsurface Media, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7146, https://doi.org/10.5194/egusphere-egu26-7146, 2026.
In irrigated agricultural regions, remotely sensed soil moisture and evapotranspiration data are widely used to calibrate unsaturated zone models, specifically those employing the Richards equation and van Genuchten-Mualem (VG) relationships. However, this often leads to a critical forcing-observation mismatch. While remote sensing products capture both rainfall and irrigation signatures, standard meteorological datasets typically include only rainfall. Calibrating models against irrigation-influenced observations without accounting for irrigation as an input flux is likely to introduce significant parameter bias. The present study attempts to analyze this effect for an experimental site at IIT Kanpur during a wheat growing season. Subplot specific leaf area index, root zone depth, irrigation amounts, and rainfall were recorded separately for four subplots. Soil moisture and water retention curves were measured at 10, 25, 50, and 80 cm depths covering root zone of these subplots. Meteorological variables from an onsite automatic weather station were used to estimate crop evapotranspiration. For analysis, two calibration schemes that minimize root zone soil moisture simulation errors were formulated, a) RET: considers rainfall as the input flux (ignoring irrigation) along with evapotranspiration, and b) RIET: considers both rainfall and irrigation fluxes along with evapotranspiration. Four VG-parameters (θs, α, n, and Ks) were calibrated using mean soil moisture (µθ) and evapotranspiration data within a genetic algorithm framework. The analysis was further extended to (µθ-σ) and (µθ+σ) dataset to analyze the performance of the proposed framework in identifying the parameters with drier and wetter soil moisture data, respectively. The RIET scheme yields substantially lower relative errors than RET for Ks (~36% compared to ~66%), n (~4.7% compared to ~5.9%), and θs(~9.2% compared to ~17.7%), whereas both schemes achieve comparable high accuracy for α (~1–2% relative error). Soil moisture estimates obtained using the optimal parameters from the RIET scheme exhibit 2 to 3 times lower RMSE compared to those from the RET scheme. These findings underscore the need for considering irrigation in model forcing during calibration for reliable parameter estimation.
How to cite: Pandey, A. and Ojha, R.: Impact of irrigation forcing on parameter estimation of 1-D Richards equation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7930, https://doi.org/10.5194/egusphere-egu26-7930, 2026.
Describing the transport of nutrients and contaminants as well as temperature and other scalars in hydrogeological systems presents both computational and modeling challenges due to the heterogeneity of the media themselves, of the resulting flows, and of the flowing phase distributions. Random walk particle tracking methods involve discretizing transported plumes into point masses that undergo random motion, such that the probability density of particle positions corresponds to the concentration field that typical grid-based Eulerian methods solve for. Particle tracking methods for transport are not affected by the instabilities that Eulerian methods are prone to in advection-dominated systems, and they mitigate numerical dispersion because they do not implicitly homogenize concentrations over an underlying grid. From a computational standpoint, since particles represent possible physical trajectories, computational power is naturally localized where mass is present, and locally-adaptive time steps can be employed. These reasons mean particle tracking methods are well suited for resolving plume structures for scalar concentration fields that are relatively localized in space but exhibit complex structure.
So far, the application of random walk particle tracking methods to heterogeneous media has been mainly restricted to time-independent conditions. In the presence of more than one fluid phase, such as air and water, if a chemical species is restricted to a specific phase, moving phase configurations lead to moving interfaces that present challenges for particle tracking. We propose an extension of particle tracking methods to fully time-dependent, two-phase flow conditions, where the restriction of a transported species to one of the fluid phases is handled through the application of a chemical potential that takes a lower value in the carrier phase. Particles feel an effective drift near the fluid-fluid interface that is proportional to the potential difference between the two phases, leading to a concentration ratio that follows Henry's law at equilibrium. By increasing this potential difference, the amount of mass that crosses the interface can be made arbitrarily small. This formulation avoid explicit reconstruction of phase boundaries and does not require direct computation of particle reflection at fluid-fluid interfaces. We illustrate the application of the method to the simulation of solute fronts in heterogeneous media under two-phase-flow conditions where the solute is restricted to a single phase, and we discuss the possibility of extending the method to more complex interactions between the transported scalar and the fluid-fluid interface.
How to cite: Aquino, T. and Linga, G.: Particle tracking in time-dependent two-phase flows, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8318, https://doi.org/10.5194/egusphere-egu26-8318, 2026.
Flow and transport in fractured systems are a major challenge in understanding contaminant transport in the vadose zone. Chalk, a carbonate rock, is characterized by a high porosity and very low hydraulic conductivity. However, this rock can be intersected by fractures that may act as highly permeable pathways that dominate the migration of water, solutes, and particulate matter. Unsaturated conditions further introduce additional complexities, as chalk systems are characterized by heterogeneity, capillary effects, and changes in saturation. Despite significant progress in this field, our understanding of the interaction between transport processes and dynamic flow behavior at different initial water saturation and across different flow rates remains limited. Therefore, this work studies the transport and dynamics of a dyed conservative tracer in a fractured chalk system under two saturation conditions (98% and 40%) and at two flow rates (0.1 and 1.1 mL/min). Laboratory experiments were conducted using a novel system containing a half-cylindrical fractured chalk core, drilled from the Eocene-age Avdat Group (northwestern Negev Desert), with a 5 mm artificial vertical fracture and a transparent wall enabling direct visualization of flow patterns. Time-lapse images of the tracer migration along the fracture surface were acquired using a digital camera, and flow and transport behavior were investigated under controlled laboratory conditions using a combination of traditional breakthrough curves (BTCs) and time-resolved image processing in Python to characterize tracer movement along the fracture surface.
Results show that, under near-saturated conditions, the flow rate has no effect on the mass balance: the recovered mass is similar at both low and high flow rates, with an average of 51%. BTCs obtained under these conditions show early tracer arrival and a higher peak at both flow rates. However, the effect of initial saturation level at low flow rate is observed: the average recovered mass under near-saturated conditions is approximately 2.5 times higher than under unsaturated conditions, where the BTCs show delayed tracer arrival and lower peak concentrations. Image-based analysis indicates that increasing the flow rate from 0.1 mL/min to 1.1 mL/min at near-saturated conditions significantly affects the tracer distribution on the fracture surface. At low rates, narrow channels covering ~20% of the fracture surface developed. However, at higher rates, flow channels covered ~50% of the fracture surface. Under unsaturated conditions (low rate), the flow is characterized by an initial wetting front, followed by the formation of channels that cover up to 20% of the fracture surface.
How to cite: Ougazdamou, H., Klein-BenDavid, O., De Falco, N., and Weisbrod, N.: Effects of Flow Rate and Initial Saturation on Solute Transport and Flow Dynamics in Fractured Chalk, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9247, https://doi.org/10.5194/egusphere-egu26-9247, 2026.
Soil moisture dynamics in unsaturated soils of agricultural fields are driven by the complex interplay of hydraulic heterogeneity, root water uptake (RWU), and atmospheric forcing; however, the specific conditions under which each process becomes dominant are not yet fully understood. We propose a regime-based framework to identify the dominant flow mechanisms in an agricultural field, using the wheat cropping season as a primary case study. For this, 3-D Richard’s equation simulations were performed for silty loam soil, considering crop-specific data and atmospheric conditions from an experimental site at IIT Kanpur. Simulations comparing homogeneous and heterogeneous soil profiles (spatial heterogeneity in van Genuchten parameters, Ks and α) reveal that near-surface layers (10–25 cm) exhibit higher early-season variability and faster post-irrigation responses than deeper layers (50 cm), with heterogeneity effects diminishing over depth and time. Sensitivity profiles based on the ratio of RWU to vertical flux divergence indicate stronger near surface control, with values close to one during irrigation periods and declining with depth, reflecting reduced influence of vertical flux divergence in deeper soil. Variance-based dominance diagnostics, evaluated against variability in both and , reveal a distinct transition in governing processes. As the ratio of soil moisture variance to heterogeneity variance decreases from approximately 0.30 near the surface during early growth to below 0.15 at greater depths and later stages, the system shifts from a heterogeneity-dominated behavior to an RWU-dominated regime. Collectively, these diagnostics categorize the subsurface into four distinct regimes: heterogeneity-dominated, RWU-dominated, atmospheric demand-dominated, and transition zones. This classification provides a physically interpretable framework for analyzing process dominance and refining model selection in structured agricultural soils.
How to cite: Songa, U. M. R. and Ojha, R.: A Regime-Based Framework for Understanding the Dominant Mechanisms of Flow in Heterogeneous Agricultural Soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10402, https://doi.org/10.5194/egusphere-egu26-10402, 2026.
Vegetation characteristics are among the primary factors that influence soil water storage dynamics. Thus, this study aims to determine the interception capacity of urban trees and how differences in effective rainfall beneath these trees regulate soil water dynamics. To achieve this objective, interception capacity was estimated from measured throughfall. The soil water budget elements (including transpiration, soil evaporation, soil water storage, and deep percolation) were simulated using the HYDRUS-1D model. Model inputs include gross rainfall or effective rainfall (throughfall for under-tree soils), volumetric water content (VWC) of the soil, potential evapotranspiration (PET), leaf area index (LAI), and soil hydraulic parameters.
The study was carried out in a small urban park in the City of Ljubljana, Slovenia, between September 2024 and July 2025. The experimental plot includes various tree species, such as deciduous - birch (Betula pendula) and maple (Acer negundo), and evergreen - black pine (Pinus nigra), white pine (Pinus strobus), and yew (Taxus baccata). A tipping-bucket rain gauge was installed in the open area to measure gross rainfall. Throughfall beneath the birch and pine canopies was measured using a V-shaped steel trough collectors equipped with tipping-bucket flow gauges. Throughfall under other tree types was monitored using the same equipment to record open-area rainfall, but positioned under tree canopies. Each instrument was equipped with an automatic data logger that recorded data every 5 minutes. Additionally, soil VWC was monitored in the open area and beneath tree canopies (e.g., pine and birch) using TEROS 10 sensor probes. The probes were positioned horizontally at three successive depths within the soil profile (i.e., top: 16-20 cm, middle: 51-54 cm, and bottom: 74-76 cm). They were connected to data loggers programmed to record VWC at 5-minute intervals, enabling continuous monitoring of moisture variations across the soil profile. Meteorological variables (wind speed, solar radiation, air humidity, air temperature, rainfall, etc.) required to compute PET were collected from a remote weather monitoring station installed in the open area of the experimental site and recorded at 5-minute intervals. The LAI was measured using an LAI-2200C plant canopy analyzer at least twice per week to capture vegetation dynamics during the study period. The soil hydraulic parameters (saturated and residual VWC, saturated hydraulic conductivity, relative saturation, and shape parameters) under each tree were determined in the laboratory. Simulations were executed at an hourly timestep to capture short-term variations in the various water-balance components.
The calibrated HYDRUS-1D model was subsequently used to simulate soil water balance components across different tree species, using different effective rainfall as model input and employing different soil characteristics. The results show that rainfall interception, which defines effective rainfall beneath tree canopies, differs among trees. Thus, it impacts the various soil water budget parameters and soil water dynamics. The analyses conducted indicate the inter-relationship of rainfall interception processes and soil water dynamics.
Acknowledgment: The work was supported through the Ph.D. grant of the first author, which is financially supported by the Slovenian Research and Innovation Agency (ARIS). This study is also part of ongoing research programme P2-0180.
How to cite: Ogunfolaji, Y. O., Alivio, M. B., Golob, N., Zupanc, V., and Bezak, N.: Impact of urban trees' rainfall interception on soil water dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11746, https://doi.org/10.5194/egusphere-egu26-11746, 2026.
Understanding the transport of microplastics (MPs) in the unsaturated zone (UZ) is essential for assessing their environmental impact, particularly regarding groundwater contamination. MPs are increasingly detected in groundwater systems; however, their transport mechanisms through the UZ remain poorly understood, and field-scale experimental evidence is scarce.
This study presents a field-based methodological approach using lysimeter experiments to investigate MP migration under realistic environmental conditions. Four lysimeters, each designed as a vertical column with a diameter of 0.6 metres, were installed outdoors to closely simulate natural UZ environments. The columns were packed with 16 cm of sand and gravel of known granulometric fractions, incorporating variable grain sizes to represent diverse porous media and hydraulic properties. Comprehensive granulometric analyses and infiltration tests were conducted to characterise the physical properties of the columns. Commercial Polypropylene (PP) MPs of different shapes (fibres, fragments, and spheres) were applied as tracers, alongside deuterium oxide (D₂O) as a conservative tracer for hydraulic characterisation.
This experimental approach provides valuable data on MP transport under controlled yet realistic conditions, reducing uncertainties associated with laboratory-only studies. The experimental design allows for the quantification of retention and breakthrough behaviour of MPs under variable hydraulic regimes. Furthermore, the integration of multiple tracer shape-types facilitates the differentiation between physical transport processes, providing a robust framework for future modelling efforts.
How to cite: Mali, N., Colmenarejo Calero, E., and Kovač Viršek, M.: Field Lysimeter Experiments for Tracing Microplastics Transport in the Unsaturated Zone, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12273, https://doi.org/10.5194/egusphere-egu26-12273, 2026.
Forests are essential for the regulation of Earth’s climate both locally and globally. Their ecosystems are dependent on a number of nutrients from mineral sources, which are derived from the underlying rocks and incorporated into clays and oxides in a process referred to as chemical weathering. Streams are ideal indicators of nutrient cycling at the catchment scale, and by extension an indicator of nutrient provision and stresses. As streams collect water from subsurface pathways including water from the root zone, their geochemical signals can be used to quantify nutrient uptake at the catchment scale.
Non-traditional stable isotopes offer opportunities to enhance our understanding of nutrient cycles in the Critical Zone. Biogeochemical processes cause measurable fractionation between metal isotopes, creating fingerprints for their pathway through the ecosystem. In this regard, the micronutrient boron presents an ideal tracer. At the catchment scale the B isotope signature is controlled by inorganic processes such as chemical weathering, atmospheric deposition and transport as dissolved species, but also by vegetational cycling. This can lead to significant deviation between the B-isotopic composition of Critical Zone compartments, in particular in streams, compared to its mineral sources. However, the understanding of the translation of B isotopic signals from the soil-plant system to streams needs to be further investigated in order to develop them as a catchment-scale proxy of nutrients.
Here we present B-isotopic data from the Quaraze instrumented catchment at the Mt. Lozère Critical Zone Observatory, Southern France, a long-term instrumented site covered by a mixed tree forest, which is experiencing water stress in summer. Stream samples were collected along the river profile from the outlet to the source over the course of four trips in April, June, August and October. Additionally, we collected groundwater from piezometers at 20m depth and solutions in the unsaturated zone from -2 to -10m depth. Generally, the stream displays strongly elevated δ11B compositions between 34.80‰ and 43.54‰, compared to the local groundwater (10.64‰ to 26.21‰) and soil solutions (11.75‰ to 38.41‰). Major changes in δ11B are observed from the stream source to the outlet, with the largest difference in August (43.52‰ at the source, 37.92‰ at the outlet). This behavior is exhibiting a strong seasonal dependency, since notably the source and outlet are identical within the analytical error in the month of October (40.55‰ and 40.39‰).
This dataset demonstrates that the B isotope signature is highly dynamic, both temporally and spatially, and sensitive to variations in source inputs. This in turn implies that nutrient provision is impacted by small changes in the ecosystem. Vegetational cycling might be playing a key role in explaining elevated stream δ11B compositions [Gaillardet and Lemarchand, 2018]. Using these data, a modelling framework will be applied to estimate the relative roles of recycled organic matter vs. chemical weathering as nutrient sources in this catchment.
How to cite: Janecke, H., Bouchez, J., Druhan, J., Rigoussen, D., Osorio-Leon, I., Ayral, P.-A., Domergue, J.-M., Wendling, V., and Gaillardet, J.: Probing the Nutrient Cycle in Forests using the Boron Isotopic Composition of Streams, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14361, https://doi.org/10.5194/egusphere-egu26-14361, 2026.
An unseen threat of increasing drought stress in forests emerges from below ground: the lack of deep soil water storage refilling between seasons. However, the reliance of trees on deep soil water is not well understood. Depth-dependent root water uptake (RWU) can be estimated with stable water isotopes, though these estimates are prone to uncertainty and the measurements are typically sparse and labor-intensive to collect. Additionally, soil water potential sensors can provide estimates of tree water stress but are also limited in vertical resolution. Soil-vegetation-atmosphere-transfer (SVAT) models can fill this gap and provide a mechanistic link between soil water availability and tree stress. Currently, SVAT models are limited in their ability to describe plant-level water status through leaf water potential or stem water storage. In this project, we enhance an existing SVAT model (LWFBrook90.jl) with plant water capacity and capacitance to simulate diurnal and seasonal variation in plant water pools. These sub-daily cycles of stem shrinkage and refilling are effectively captured by high-precision, point dendrometers, which measure micrometer-scale stem radius variations, and derived through tree water deficit (TWD) which can serve as a drought stress proxy. By comparing modelled plant water storage to TWD, we benefit from a simple, integrated measure of tree water stress that allows the partitioning of root water uptake into transpiration and refilling plant stores. We apply the updated model to a field site in Valais, Switzerland, located within a dry inner-alpine valley, where a long-term irrigation experiment has been ongoing in the Pfynwald, a 100-year-old Scots pine forest. Multiple field campaigns have collected a suite of observational data for model calibration, including soil water content and potential, soil and xylem isotopes, sap flow, and tree water deficit. Model results indicate that peak transpiration is sourced from an average of 50 cm depth, while deeper water sources are unable to compensate for late-summer water demand, contributing minimally to RWU. Irrigation considerably modified the ecosystem water balance and shifted root water uptake to shallow layers in the top 20 cm, while the legacy effects of irrigation after it was stopped show an alleviation of stress that allows more efficient RWU from deep soils, consistent with sustained root investment developed under long-term irrigation.
How to cite: Graup, L., Bernhard, F., Peters, R., Carminati, A., and Meusburger, K.: Enhancing above-belowground coupling for predictive modelling of tree water stress under deep soil water depletion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17667, https://doi.org/10.5194/egusphere-egu26-17667, 2026.
Rapid urbanization has expanded impervious surfaces, enhancing pollutant buildup and the transport of Persistent Mobile (PMT) substances through stormwater runoff. Green infrastructure, which is designed for flood mitigation and aquifer recharge, can inadvertently transfer polar contaminants into the soil–groundwater systems. As climate change drives more intense storms, measurements of higher-throughput stormwater are necessary. Understanding their limits in removing dissolved PMTs and metals is essential to improve current mitigation strategies.
To investigate these hydraulic and geochemical performance constraints, we conducted a series of controlled fixed-bed column experiments simulating diverse green infrastructure operating conditions. Different PMT loadings, adsorbent dosage, competitive interactions with co-solutes (dissolved metals and dissolved organic matter, DOM) under three infiltration-rate regimes (4.5 – 25.5 cm·h-1) were tested. Columns were packed with a mixture of sandy-loam soil and granular activated carbon (0.5, 2, and 5 %wt.; (GAC) to evaluate the breakthrough behaviour and adsorption capacity towards 8 representative PMTs with different physicochemical molecular properties. Our preliminary results show that at high flow rates, associated with low residence times, substantially decrease adsorption performance, particularly under high inorganic contaminant loads with DOM. Although the 5% GAC amendment achieved the highest overall removal capacity towards the studied PMTs regardless experimental conditions, it also introduces hydraulic limitations, producing pronounced tailing effect driven by micropore diffusion and extended intra-particle residence times.
To interpret the observations from experiments, HYDRUS will be applied to simulate reactive solute transport, enabling inverse calibration of hydraulic properties and solute transport parameters from column breakthrough data. Subsequently, HYDRUS-derived parameters, together with experimental variables, will be integrated into a machine learning framework to identify key removal predictors, and forecast the removal of challenging PMTs under different stormwater conditions.
How to cite: Xu, J., Badia, S., Brunetti, G., Cama, J., and Teixido, M.: Rethinking Green Infrastructure Performance: PMT removal in GAC-Amended Column Experiments under Extreme Operating Conditions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7956, https://doi.org/10.5194/egusphere-egu26-7956, 2026.
