Understanding chemicals mixing and reactions in porous media is critical for many environmental and industrial applications. In the presence of a non-wetting immiscible phase (e.g., gas) within the pore space, it can remain immobile, giving rise to the so-called unsaturated flow, or it can move, resulting in a multiphase flow. In other cases, the immiscible phase can be permeable, as it occurs with biofilms growing within the pore space. We combine experiments and numerical modeling to assess the impact of saturation (fraction of the pore volume occupied by the wetting phase), multiphase flow (stationary two-phase flow), and the presence of permeable biofilm within the pore space on mixing-driven reactions. The product formation is larger for a given flow rate as saturation decreases, while for a given Peclet, it is the opposite. In multiphase flow conditions, for a given flow rate of the wetting phase, the product formation depends on the flow rate of the non-wetting phase. In the presence of biofilms, the product formation is enhanced compared to their absence and is further enhanced with a heterogeneous permeability within the biofilm.

How to cite: Jimenez-Martinez, J., Zhang, X., Markale, I., Kurz, D., Dou, Z., Carrel, M., Morales, V., and Holzner, M.: Impact of an immobile, mobile and permeable phase on mixing-driven reactions in porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4162, https://doi.org/10.5194/egusphere-egu24-4162, 2024.

Mixing-induced reactions are an essential feature of environmental flow and transport processes. They control many reactive transport processes, including mineral precipitation rates and contaminant remediation processes. Natural porous media are characterized by a strong structural heterogeneity, which impacts solute mixing and, therefore, the resulting chemical reaction rates. Establishing a quantitative link between pore-scale heterogeneity and mixing/reaction rates in saturated and unsaturated conditions remains an open question. Here, we study pore-scale solute mixing using high-resolution experimental measurements to quantify the overall reaction rates and product concentrations. Our goals are to study the impact of structural heterogeneity on 1) reaction rates and products during saturated flow and 2) the spatial arrangement of fluid phases during unsaturated flow and its impact on reaction rates and products.

We use two-dimensional porous media consisting of circular posts in a Hele-Shaw-type flow cell. We control heterogeneity by varying the posts’ diameters disorder and correlation length; increasing this length introduces more structure in the porous medium. We utilize an irreversible oxidation reaction to produce fluorescein from its non-fluorescent form. The Damköhler number is sufficiently larger than unity, so the reaction rate is mixing-controlled. We inject a non-fluorescent tracer pulse into the porous medium sample filled with the oxidating reactant under saturated and unsaturated flow conditions. We analyze periodic fluorescence intensity images to track the evolving solute concentration field. The reaction rates and the total reaction product mass are calculated directly from the concentration images.

Solute concentration images show that increasing the spatial correlation length under saturated flow conditions leads to enhanced reaction front stretching and elongation as the solute travels along preferential pathways. Due to this overall stretching, the reaction front is locally more compressed perpendicular to the elongation direction. In a non-correlated, randomly disordered porous medium, overall stretching is reduced, and the front is less compressed locally. Under unsaturated flow conditions, a main preferential flow path characterizes the correlated porous medium. In contrast, the non-correlated medium is characterized by a higher degree of branching and splitting in the velocity field. Solute pulse focusing in the correlated porous medium sample reduces reaction front stretching compared to the non-correlated porous medium, under unsaturated conditions. Under these conditions, the reaction rate increases more than the saturated case due to the unsaturated flow pattern's enhanced reaction front stretching. This effect is more pronounced for the non-correlated sample, where flow path splitting and reaction front stretching are more significant. This work shows that structural heterogeneity has a considerable effect on reactive solute transport and that this effect depends on the system’s saturation.

How to cite: Borgman, O., Gomez, F., Le Borgne, T., and Méheust, Y.: Mixing-induced reactive transport experiments in heterogeneous and variably saturated porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14907, https://doi.org/10.5194/egusphere-egu24-14907, 2024.

Two-phase flow in geological fractures holds significant relevance in various applications, including subsurface fluid storage and oil and gas exploitation. The pore-scale modelling of such flows is a challenging task influenced by many factors, such as the complex interplay between the viscous, capillary, gravitational and inertial forces, intricate geometries, as well as molecular scale phenomena such as moving contact lines and thin wetting films. Although various modelling approaches have been used to tackle these challenges, the high computational demands required to accurately capture the three-dimensional fluid-fluid interfacial dynamics often render these models impractical for real-world applications. Consequently, from a practical point of view, the simplification of these 3D models may become imperative to facilitate efficient and reasonably accurate predictions of flow quantities.

Depth-integrated two-dimensional modelling is one such approach which enables saving computational time and effort at the expense of not resolving the third dimension. Here, the governing equations are solved in two dimensions, the influence of the third dimension being incorporated through appropriate additional terms. While such models have been used previously, they have so far been restricted to either permanent single-phase flow in rough fractures or two-phase flow in 2D porous media of homogeneous depth. In a rough fracture, the fluid-fluid interface possesses not only an in-plane curvature but also an out-of-plane curvature, which must be accommodated in the 2D depth-integrated model. Therefore, to address the immiscible flows in rough fractures it is essential to reformulate the 2-D depth-integrated approach from the first principles.

To perform the depth integration, we proceed from the traditional direct numerical simulation (DNS) approach, where the Navier-Stokes equations, coupled with an interface capturing technique, which in our case is the Volume of Fluid (VOF), are solved numerically. We integrate the governing flow equations in the vertical direction while expressing the flow fields in terms of 2D depth-averaged flow quantities. To account for the out-of-plane curvature and the wall shear stress arising from the no-slip conditions on the fracture walls, we assume locally a plane Poiseuille configuration (Hele-Shaw). 

The derived 2D depth-integrated model is implemented in the open-source CFD code OpenFOAM. We validate our model using the Saffman-Taylor instability case, comparing predictions with experiments and full 3D model results. We then extend our study to two numerically generated rough fractures with (a) smoothly and periodically varying aperture and (b) a more realistic aperture field with a larger roughness. We investigate drainage (i.e., the displacement of the wetting fluid by the non-wetting fluid) over a range of Capillary numbers spanning more than three orders of magnitude. We compare our 2D model predictions of both, pore-scale and macroscopic flow variables, with those obtained using 3D simulations. Our 2D model accurately estimates key statistical indicators with a tenfold reduction in computation time, offering an excellent compromise between solution accuracy and computational efficiency. We also discuss the limitations of the depth-averaged model depending on flow ranges.

How to cite: Krishna, R., Meheust, Y., and Neuweiler, I.: Depth-integrated Two-dimensional Model for Immiscible Two-phase Flow in Open Rough-walled Fractures with Smoothly Varying Aperture, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7889, https://doi.org/10.5194/egusphere-egu24-7889, 2024.

The kinetic interface-sensitive (KIS) tracer test is a newly developed tracer approach to measure the fluid-fluid interfacial area (IFA) during dynamic two-phase flow in porous media. This new tracer approach can be applied for multiple geological applications, where dynamic two-phase flow is involved, e.g. monitoring the plume during geological storage of carbon dioxide. The obtained concentration breakthrough curves by measuring reacted tracer concentration in water samples are interpreted with a specialized Darcy-scale numerical model to determine the IFA. The previous design of the drainage experiments has one major limitation that the volume of the usable water sample after breakthrough for the measurement is often insufficient. An alternative is to employ KIS tracers in a “push-pull” experimental set-up, i.e. primary drainage is followed by a consequent main imbibition process, with the flow direction being reversed. This study applies both the pore-scale numerical simulation and the core-scale column experiments to study the KIS tracer reactive transport during push-pull processes. The pore-scale numerical simulation is done with a phase-field method-based continuous species transport model. The reactive transport of the tracer and the characteristics of the concentration breakthrough curves are analyzed. The Darcy-scale reactive transport model is validated by comparing it to the pore-scale results. Finally, the new method is applied in the column experiment, where the determined specific interfacial area is found to be close to the literature data.

How to cite: Gao, H., Tatomir, A., Abdullah, H., and Sauter, M.: Reservoir characterization by push-pull tests employing Kinetic Interface Sensitive tracers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9503, https://doi.org/10.5194/egusphere-egu24-9503, 2024.

Contamination with mono-aromatic hydrocarbons, specifically benzene, toluene, and xylenes (BTX), is one of the major concern to groundwater aquifers. BTX have high environmental stability and are harmful to human health and aquifer ecosystem. Thorough assessment and monitoring of the risk posed by BTX in aquifers are essential for the sustainable use of groundwater resources. The biodegradation of BTX in aquifer rely primarily on anaerobic processes. Nitrate-sulfate-reducing assemblages is considered for BTX bioremediation in such anoxic condition. These assemblages act as a terminal electron acceptor for bacterial respiration. The degree of the interaction between combinations of nitrate-sulfate reduction and BTX elimination determines the efficacy of BTX biological degradation. The interactions, however, received limited attention in the existing literature. Hence, the current analysis focuses co-existence of nitrate-sulfate assemblages affecting BTX bioremediation. A multi-component numerical simulation is performed to investigate the potential of nitrate-sulfate-assemblages for bioremediation of BTX in anoxic conditions. A fully implicit finite-difference novel approach is adopted here to solve the proposed numerical model, which is capable of obtaining spatial variation in BTX concentrations. The results suggest that bioremediation is efficient in removing toxic BTX from aquifers under the coexistence of nitrate-sulfate assemblages. This approach, in addition, can be used in deciding the optimum rate of electron acceptor injection and the time required to bring BTX to standard limits. Furthermore, it can help us to plan sustainable bioremediation strategies for mono-aromatic hydrocarbon contaminated aquifers where such reduction assemblages co-exist. This hydrogeobiochemical modelling study also emphasizes the importance of multidisciplinary methods in dealing with challenging environmental issues in the contaminated aquifers.

Keywords: Hydrogeobiochemical modelling; Bioremediation; BTX; Nitrate-sulfate assemblages; Aquifers.

How to cite: Srivastava, A., Valsala, R., and Jagadevan, S.: Hydrogeobiochemical Modelling for Bioremediation of Mono-Aromatic Hydrocarbons Using Nitrate-Sulfate-Reducing Assemblages in Aquifers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4243, https://doi.org/10.5194/egusphere-egu24-4243, 2024.

Mixing is the process that homogenizes initially segregated miscible constituents, increases the volume occupied by a solute, and decreases concentration peaks. It is important for the assessment of contamination levels and biogeochemical reactions in groundwater and soils. Mixing processes are governed by the interplay of fluid advection, molecular diffusion and local-scale dispersion at Darcy scale. Here we study the mechanisms of mixing in three-dimensional Darcy scale porous media with different heterogeneity structure. We analyze the role of medium and flow topology on the mixing and dispersion behavior. To this end, we perform Darcy-scale numerical simulations of incompressible flow and transport in heterogeneous three-dimensional porous media. Hydraulic conductivity is represented as a multi-Gaussian random field with lognormal marginal distribution. We consider isotropic and anisotropic correlation structures and scalar and tensorial conductivity. Flow is solved using a finite volume two-point method and transport using a Lagrangian approach. The flow topology is quantified by the helicity of the velocity field. We consider a planar injection of particles. Dispersion is quantified by the longitudinal and transverse dispersion coefficient, which are determined by the evolution along time of the position’s variance in the respective direction divide by two. It is also quantified by the breakthrough curves, which measure the distribution of arrival times at a given position from the initial one. Mixing is quantified by the ability of the flow to stretch and elongate a fluid strip which enhances diffusion through the creation and sustaining of concentration gradients. Results show that for a helical flow, a finite transverse dispersion coefficient is observed at long times and that the elongation of elemental strips follow an exponential stretching  (for large logK variances). On the contrary, on non-helical flows, transverse dispersion tends asymptotically to zero and the stretching rate is algebraic. The longitudinal dispersion coefficient seems unaffected by the helicity of the flow. These results shed light on the relation between medium structure and flow topology on mixing, making an important step towards the control, upscaling and large scale representation of mixing in porous media

.

How to cite: Feroukas, K., Dentz, M., Hidalgo, J., and Lester, D.: Impact of helicity on mixing in heterogeneous porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18085, https://doi.org/10.5194/egusphere-egu24-18085, 2024.

As heat tracing gains versatility in hydrogeological applications, precise thermal dispersion modeling becomes essential. However, limited experimental data for thermal dispersion, influenced by several factors such as particle size or shape, poses a challenge to the understanding of the relationship between flow velocity and thermal dispersion coefficient. To fill these gaps, the solute and heat tracer experiments were conducted using two different sizes of sand. Thermal and solute dispersion were analyzed by applying analytical models. We also systematically collected and revisited literature data to comprehensively interpret the influences of particle size, shape, and pore-scale heterogeneity on dispersion. The results exhibited that the solute and thermal dispersivity were comparable when the dispersion linearly increased to the velocity. However, within the transition regime (Pe < 5), a departure from linearity was observed (R² < 0.9). The deviation was more pronounced in smaller particle size due to pore-scale heterogeneity arising from the complexity of pore network. Consequently, our findings emphasize the potential necessity for caution when modeling thermal dispersion based on solute dispersion within natural porous materials.

Keywords: Particle size; Thermal dispersion; Pore-scale heterogeneity; Transition regime; Sandbox experiment

Acknowledgements

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2022R1A2C1006696). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MSIT) (No. 2022R1A5A1085103). This work was also supported by the Nuclear Research and Development Program of the National Research Foundation of Korea (NRF-2021M2E1A1085200).

How to cite: Baek, J., Park, B.-H., Rau, G., and Lee, K.-K.: Experimental Investigation on Dispersion Within Porous Media Influenced by Particle sizes and Pore-Scale Heterogeneity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4880, https://doi.org/10.5194/egusphere-egu24-4880, 2024.

The aeration zone (AZ) below the soils sensu stricto is still neglected compartment regarding its structure, diversity of life and habitats, and role for the provision of ecosystem services. Especially in thick AZ of topographic recharge areas, fluid flow dynamics and the exchange of the total mobile inventory (Lehmann et al. 2021) and their roles for the quality-evolution of groundwater are largely unknown. In the low-mountain topographic recharge area of the Hainich Critical Zone Exploratory (central Germany), we study spatiotemporal dynamics of the fluid fluxes and mobile inventory within the shallow (upper) AZ (regolith) and compare their signature with soil seepage and perched groundwater (deeper AZ). Percolates from 20 drainage collectors (DC) covering a diversity of Triassic mixed carbonate-siliciclastic (sedimentary) bedrock, soil types, and installation depths were sampled for more than 3 years on regular (monthly) and event-based basis and analyzed by various physico-/hydrochemical and spectro-microscopic techniques.

On average, the DC captured ~13% of the percolate from the forest topsoil seepage and 2.4% of precipitation. Seepage volume was mainly influenced by the factors soil thickness and sampling month, followed by scarp slope gradient and seasonal differences. In the upper AZ, the mobile inventory exhibited strong seasonality (e.g. EC, pH, nitrate, sulphate, K, Si, Mn, Al, Fe, particle concentration) and were more dependend on seasonal weather conditions and single (extreme) events (e.g., snow melt, rain events) than on lithology, followed by site-specific structural factors (location, slope), or pedological settings (e.g. overburden soil type, soil thickness). Generally, our results show fluid-rock interactions within the upper AZ with a more similar hydrochemical water signature to perched groundwater. Contrastingly, particulate mobile inventory showed a strong connection to soil seepage signature, comprising a diverse spectrum of mineral particles (mainly clay minerals) and mineral- and mineral-organic associations up to 160 µm, including aggregates and microorganisms. The different flow regimes that prevail during different seasons and weather conditions mainly influenced the amount and spectrum of percolate mobile inventory. During summer, dry periods in conjunction with extreme precipitation events favored translocation of small-sized particles. In winter, fast-flow regimes during normal precipitation as well as during snowmelts contributed strongly to the translocation of organic/inorganic carbon and mineral particle through the AZ and to groundwater. We conclude that the AZ is a complex biogeochemical reactor, that severely alters the percolate composition and properties, already preshaping the biogeochemical groundwater quality as well as due to its functions and services (e.g. water-purification and storage). As such, the aeration zone hast to be considered as a crucial compartment for groundwater quality evolution, especially in topographic recharge areas.

Lehmann, K., Lehmann, R., Totsche, K. U. (2021) Event-driven dynamics of the total mobile inventory in undisturbed soil account for significant fluxes of particulate organic carbon. Sci. Total Environ. 756, 143774, doi: https://doi.org/10.1016/j.scitotenv.2020.143774

How to cite: Lehmann, K., Eshvara Arachchige, D., Lehmann, R., and Totsche, K. U.: Dynamics of aeration zone mobile inventory preshape groundwater quality evolution - results from multi-year sampling of regolith seepage , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7503, https://doi.org/10.5194/egusphere-egu24-7503, 2024.

This study experimentally demonstrates the impact of water and solute influx magnitude, and its resulting local distribution, on transport at timescales longer than the influx duration, through a disparate velocity field of a partially saturated domain. In a sand-filled cell, steady-state flow is maintained with a constant horizontal hydraulic head, while the upper part of the cell is partially saturated. The horizontal velocity varies by orders of magnitude from the surface to the saturated zone. An influx of water with a dissolved tracer is applied at the middle of the upper boundary surface, over several minutes, forming a plume that reaches a depth of a few centimeters. This influx disturbs the flow field locally, but after it is terminated, the return to steady-state flow is of the order of magnitude of the influx timescale. Eventually, the solute flows to the saturated zone and out of the cell through a path on the scale of decimeters, over a time scale of days. Employing ICP-MS as a sensitive measurement tool to detect highly diluted concentrations of solute enables tracking of a small influx volume that does not significantly perturb the flow field. This maintains a separation between the distinct spatial-temporal scales of the short-term local infiltration and the long-term system-scale transport. Applying varying influx magnitudes sets the solute plume across different velocity profiles and thus dictates the downstream plume distribution. A low influx relative to the hydraulic conductivity of the partially saturated sand allows solutes to infiltrate farther down compared to a higher influx, so that the plume reaches higher flow velocities but also spans a wider velocity variability. A higher influx relative to the hydraulic conductivity leads to a local increase in saturation, but a shallower depth of infiltration compared to the lower influx, and the system accordingly exhibits a more uniform plume located at a lower velocity region. In downstream solute concentration measurements, these influx variations result in a faster but more smeared breakthrough for the lower influx compared to a slower and more uniform breakthrough for the higher influx, corresponding to their initial distribution after infiltration.

How to cite: Kalisman, D., Dror, I., and Berkowitz, B.: From infiltration to steady-state flow in partially saturated media – bridging solute transport between millimeter-decimeter and minute-day scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5615, https://doi.org/10.5194/egusphere-egu24-5615, 2024.

Assessment of the leaching potential of pesticides and their metabolites is an important part of the authorization procedure for pesticides in Europe. To protect groundwater quality, it must be demonstrated that concentrations of active substances in the upper groundwater do not exceed 0.1 μg/L before a pesticide can be approved for use. For the purpose of exposure assessment, this concentration limit is imposed on the water leaching downward at 1 m depth in the soil profile. For a given substance and application pattern, this leaching concentration can vary in space by several orders of magnitude, due to variation in site conditions, most importantly soil properties and climate. Spatially distributed leaching modelling (SDLM) is a methodology for exposure assessment over large spatial extents, dealing with this spatial variability in a comprehensive way. It involves performing simulations for many parametrizations representative for a spatial region and can be used to generate maps or calculate spatio-temporal percentiles of leaching concentrations. While such tools are already used in exposure assessment at national level in several EU member states, no generally accepted SDLM tool is available at the European level. In 2020, a working group of Society of Environmental Toxicology and Chemistry (SETAC) was formed with the purpose to develop a harmonized framework for SDLM across Europe (EU27 + UK).

A first version of an SDLM—referred to as GeoPEARL-EU—was built around the pesticide leaching model PEARL, a field-scale model of pesticide fate in the soil-plant system. PEARL mechanistically simulates pesticide behaviour in a 1D soil column based on explicit descriptions of transport in the liquid and gas phases, sorption to the solid phase, degradation, volatilisation, and plant-uptake. Soil moisture content and fluxes are provided by the SWAP hydrological model. PEARL is used in regulatory exposure assessment for groundwater and soil. Furthermore, a spatially distributed tool based on PEARL (GeoPEARL) is used for exposure assessment in the Netherlands.

To apply PEARL to Europe, pan-European gridded datasets were collected for several variables, including soil texture, pH, soil organic carbon, weather, irrigation patterns and crop area. These datasets were used to develop a set of parametrizations covering the variability of climate and soil conditions in Europe. To this end, all 1x1 km grid cells for the EU27 + UK were partitioned into approximately 10,000 clusters using k-means clustering, based on several soil- and climate-related variables relevant for leaching vulnerability. Subsequently, a representative grid cell was selected for each cluster, which was used to obtain the data required to parameterize PEARL from the spatial data sets. Pedotransfer functions were used to derive soil hydraulic parameters.

We will present results from GeoPEARL-EU for several test cases with specific attention to the effect of the spatial aggregation approach on the model predictions. Moreover, we discuss how the tool could be used in the tiered approach of the regulatory exposure assessment for groundwater in the EU.

How to cite: Braakhekke, M., Cornelissen, P., Wipfler, L., Tiktak, A., Poot, A., Jene, B., Hoogeweg, G., Ghafoor, A., Klein, J., Stemmer, M., Ritter, A., Sur, R., Spickermann, G., Heuvelink, G., Hughes, G., Marahrens, S., Reichenberger, S., Suciu, N., and Morris, M.: A Spatially Distributed Leaching Model to assess pesticide leaching for exposure assessment at the European level, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19678, https://doi.org/10.5194/egusphere-egu24-19678, 2024.

The movement dynamics of glyphosate (GLY) in soil can be highly complex and challenging to predict, because its high water solubility and strong propensity to soil particle adsorption can interact with agricultural management practices, e.g. tillage operations and water table management. This can make GLY i) sensitive to nonuniform leaching via preferential flow paths into the groundwater before it can degrade, ii) difficult to model according to uniform flows. The aim of this study was to understand GLY dynamics in different agricultural systems of the low-lying Venetian plain, by calibrating a dual permeability model embedded in HYDRUS-1D using a series of GLY experimental data that were collected in the field, and compare it with a dual porosity mobile-immobile approach. Experimental data came from eight drainable lysimeters, where two shallow water table depths (60 cm and 120 cm deep) were compared in conventional (CV) and conservation agriculture (CA) systems as representative of the low-lying Venetian plain conditions (NE Italy). On May 2019, GLY and a tracer (KBr) were applied on bare soil (in CV) and rye that was used as a cover crop, in CA. After the distribution, soil (0-5, 5-15 cm deep) and soil-pore water (15, 30, 60 cm deep) samples were collected for 48 days to follow solutes dynamics. At the same depths, soil moisture and matric potential were monitored using TDR probes and electronic tensiometers. An automated system modulated the suction through matric potential readings combined with an electronic vacuum regulator. The HYDRUS 1-D software package was employed for inverse modelling of soil properties, first through parameterization and matric potential results, while solute movement parameters were calibrated based on GLY and KBr results from soil and water samples. Experimental results showed that GLY was found at different depths, especially soon after its distribution as dependent on intense rainfall events. The MIM model failed to predict any GLY movement, due to its high adsorption coefficient that hindered any GLY exchange between the immobile and mobile phases. In fact, experimental observations revealed that a preferential flow occurred down to the deepest layers (60 cm deep), even in the presence of poorly structured soil and irrespective of both the groundwater level and the cultivation system. In contrast, the dual permeability model provided a more accurate description of GLY dynamics in soil, successfully predicting the observed bypass flow timing experiment. Therefore, dual permeability model seems crucial for describing GLY dynamics in agroecosystems, enabling more accurate predictions of its potential pathways. 

How to cite: Piazzon, G., Longo, M., Rocco, S., Morari, F., and Dal Ferro, N.: Assessing glyphosate movement through different agricultural systems with a shallow water table: insights from an inverse dual permeability model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9159, https://doi.org/10.5194/egusphere-egu24-9159, 2024.

The lead-zinc tailings pond contains a significant concentration of heavy metal pollutants, such as lead, zinc, copper, chromium, cadmium, mercury, and arsenic. These pollutants exist in the form of ions within the tailings. External environmental factors can facilitate the release and transportation of these heavy metal elements from the tailings, resulting in pollution. The factors influencing pollutant release and variations in heavy metal tailings transport across different media were investigated by employing statistical analysis, leaching tests, and heavy metal soil column experiments based on the results of a case study on the Qingshan lead-zinc mining area. The multi-component solute release transport model for tailings to examine the interplay between concentration and seepage fields was constructed by considering hydrodynamics, mass transfer, and chemical reactions. The COMSOL software was performed to develop a customized model for the transport of heavy metal pollutants, wherein specific boundary conditions were set to enable quantitative analysis and interpretation of the release and migration of heavy metal solutes in tailings. The present study establishes a foundation for comprehending the migration patterns, pollution pathways, and mechanisms of heavy metal pollutants in tailings ponds. Furthermore, it provides indispensable technical support for addressing heavy metal contamination in lead-zinc mining regions and developing impermeable systems for tailings ponds.

How to cite: Jin, J., Wu, P., Cui, H., and Zhang, X.: Release and Transport Characteristics of Heavy Metal Pollutants in Tailings Pond, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2753, https://doi.org/10.5194/egusphere-egu24-2753, 2024.

Water flow in the vadose zone is strongly non-linear due to the feedback of water flow, saturation, and the associated hydraulic conductivity. Therefore, the simulation of unsaturated flow at the continuum scale is notoriously complicated. Yet, not only the solution of the non-linear partial differential equation itself is difficult, also the appropriate parameterization of the unsaturated hydraulic conductivity function poses a challenge. Frequently, hydraulic conductivity is estimated from the water retention curve using capillary bundle models such as the well-established Mualem model or from pedotransfer functions that hardly include information on the actual pore space morphology. Here, a novel approach is presented to estimate the full unsaturated hydraulic conductivity function from a morphological analysis of Xray-CT images in the following way. First, the local pore space morphology is evaluated to obtain pore radius, Euclidean distances to the pore wall, and connectivity measures. Then, a local hydraulic conductivity and capillary forces are calculated for individual voxels of the images. This already permits to estimate the water retention curve and the water distribution inside the pore space at different levels of saturation. These configurations are then used to calculate an associated continuum scale hydraulic conductivity from dry to fully saturated conditions. This approach can be implemented in image analysis software, e.g. ImageJ, in a straight-forward way and may provide much better and specific estimates of the unsaturated hydraulic conductivity that sensitively affects the simulation of fluid flow in soils and the vadose zone provided satisfactory pore space acquisition with Xray-CT is possible.

How to cite: Ritschel, T.: Estimation of unsaturated hydraulic conductivity from morphological analysis of Xray-CT images, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14615, https://doi.org/10.5194/egusphere-egu24-14615, 2024.

The power mean is the generalization of the common averaging methods, such as harmonic, geometric and arithmetic mean, but also minimum and maximum. However, it also allows an infinite number of other means between these common means and can therefore be adapted very flexibly to the specific task of upscaling. This will be demonstrated in the contribution by calculating the effective thermal conductivity as the mean of the partial conductivities of soil components (typically of the solid, liquid, and gaseous phase). Soil thermal conductivity is a key factor for the soil heat balance and is widely used in many fields of science. However, it is elaborate to measure thermal conductivity of soils that have different porosities and degrees of saturation. Effective thermal conductivity of soil strongly depends on the arrangement of particles (soil structure) and on the interaction of added water to the solid phase (e.g., menisci).  To improve the prediction of soil thermal conductivity, specific information of soil structure needs to be taken into account. The relationship between the power mean exponents p and the degree of saturation is an indicator of the existing soil structure.

How to cite: Stange, C. F.: On the possibilities of the power mean as an upscaling method using the example of thermal conductivity in soil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3853, https://doi.org/10.5194/egusphere-egu24-3853, 2024.

Drying of building materials filled with salt-containing moisture is a common example of salt weathering [1]. Fluid flow, such as capillary uptake of water, and local climate changes stand out as key factors in salt weathering, substantially impacting the Earth's landscape and building infrastructure [2]. While microbial organisms are known to alter rock surfaces, some exhibit physiological capabilities that beneficially impact rock properties by producing biofilms, biocement and biogas [3]. Environmental factors such as temperature, relative humidity, and ionic strength of the medium influence microbial-induced products [4]. The impact of salt type, concentration, and ionic strength on microbially mediated reactions inside porous media is a largely unexplored phenomenon at the pore scale. Effective addressing of the respective challenges requires understanding the synergistic and counter effects of bacterial interactions and salt crystallization within the internal pore structure of rocks, influencing related pore-scale processes. In this study, we explored the response to the drying process in a range of porous materials, from PDMS transparent micromodels to sedimentary porous rocks containing brine solutions of various compositions in the presence and without bacterial solutions. We used Paracoccus denitrificans bacteria in our experiments. We specifically consider the case where air with different levels of humidity and at a constant temperature is exposed to one side of the porous media, forming a drying front—a defined interface separating liquid-saturated and partially gas-filled domains. High-resolution optical and confocal microscopy, Raman spectroscopy, and X-ray micro-computed tomography (µ-CT) were used to visualize and characterize bacteria-salt aggregates interactions in the porous media. Systematic investigations were carried out to understand how the interactions between salt crystallization and bacterial reactions depend on pore space morphology, type, and ionic strength of salt solutions. The findings highlight the potential of advanced 2D and 3D imaging techniques for enhanced understanding of the transport-crystallization coupling with bacterial activity through in-situ experiments and, hence, for constructing more accurate prediction models and conservation strategies.

Keywords: Salt weathering; Bacteria; Ionic strength; Relative humidity; Evaporation; Imaging techniques.

Acknowledgement: This project has received funding from the Dutch Research Council (NWO) through the BugControl project (project number VI.C.202.074) of the NWO Talent program and from the EU INFRAIA project (H2020) the EXCITE Network.

References

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How to cite: Qajar, J., Reyes Amezaga, A., Selen Ezgi Celik, S. E. C., Godts, S., Schröer, L., Amir Raoof, A. R., and Cnudde, V.: Pore-scale investigations of interactions between microorganisms and ionic strength: Implications for salt crystallization damage in porous media, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20806, https://doi.org/10.5194/egusphere-egu24-20806, 2024.