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Obtaining a comprehensive understanding of solute transport in fractured rocks is crucial for various geoengineering applications, including waste disposal and construction of geo-energy infrastructure. It was realized that solute transport in fractured rocks is controlled by stochastic discrete fracture-matrix systems. However, the impacts and specific uncertainty caused by fracture network structures on solute transport in discrete fracture-matrix systems have yet not been fully understood. In this article, we aim to investigate the influence of fracture network structure on solute transport in stochastic discrete fracture-matrix systems. The fluid flow and solute transport are simulated using a three-dimensional discrete fracture matrix model with considering various values of fracture density and size (i.e., radius). The obtained results reveal that as the fracture density or minimum fracture radius increases, the corresponding fluid flow and solute transport channels increase, and the solute concentration distribution range expands in the matrix. This phenomenon, attributed to the enhanced connectivity of the fracture network, leads to a rise in the effluent solute concentration mean value from 0.422 to 0.704, or from 0.496 to 0.689. Furthermore, when solute transport reached a steady state, the coefficient of variation of effluent concentration decreases with the increasing fracture density or minimum fracture radius in different scenarios, indicating an improvement in the homogeneity of solute transport results. The presented analysis results of solute transport in stochastic discrete fracture-matrix systems can be helpful for uncertainty management in the geological disposal of high-level radioactive waste. [ABSTRACT FROM AUTHOR]

Existing models often face limitations in the understanding and prediction of nitrate nitrogen (NO3−-N) concentrations in karst groundwater. In this study, to tackle this issue, a Gaussian function model was coupled with the Groundwater Modeling System (GMS) to simulate NO3−-N concentration changes in the southwest karst wetland of China. Additionally, fluorescence spectroscopy was employed to measure dissolved organic matter (DOM) components in the groundwater, providing insights into their variation and influence on NO3−-N dynamics. The results demonstrated that coupling the Gaussian curve fitting method with the GMS model accurately simulated NO3−-N concentration changes in the study area. The simulation revealed lower NO3−-N levels in the northern region, with higher concentrations in the central area, peaking at 20.73 mg/L at lower elevations. NO3−-N was primarily distributed in the southwestern region and upper Mudong Lake, exhibiting a diffusion trend from west to east. DOM analysis indicated significant autochthonous contributions, particularly microbial metabolic by-products. The total fluorescence intensity and DOM components increased downstream, with the lowest values at the source and the highest values at river confluences. The humification index (HIX) was correlated with NO3−-N concentrations, where lower NO3−-N levels corresponded to lower HIX values, and higher NO3−-N levels corresponded to higher HIX values. In conclusion, this study provides valuable insights into NO3−-N prediction in groundwater and the role of DOM, offering a reference for groundwater protection in the southwest China karst basin. [ABSTRACT FROM AUTHOR]

Displacement washing of filter cakes is a critical process in various filtration applications and the presence of a top layer of fine particles from preceding cake filtration may influence washing efficiency. To investigate the effect of such a top layer on the displacement washing process, filter cakes with solid volume fractions ranging from 15 % to 33 % are formed from crushed, irregularly shaped limestone particles of about 10 to 250 µm to minimize or induce segregation effects due to sedimentation superimposed on cake filtration. The structural properties of the filter cakes are measured using X‐ray microscopy and dynamic image analysis. To predict the influence of cake structure on displacement washing, an advection–dispersion model is employed. Comparison between prediction and experimental data shows good agreement, highlighting the impact of cake structure on washing efficiency and providing valuable insights for optimizing displacement washing processes in industrial applications. [ABSTRACT FROM AUTHOR]

Understanding the fluid flow and solute transport in karst conduits is significant for preventing pollutants (treated as solutes) in karst areas. This study evaluates the evolution of eddies in semi‐circular rough conduits under different hydrodynamic conditions and their effects on solute transport. As inlet flow velocity increases, the non‐Fickian coefficient (a parameter used for qualifying the tailing of BTCs) increases first then decreases afterward. A critical equilibrium concentration is found when the concentration of the main flow stream and the concentration of the eddy zone reaches the same value, signaling the moment at which the mass transfer (due to diffusion) between the main flow stream and the eddy zone drops to zero. Such a critical equilibrium concentration and its corresponding moment of occurrence are found to follow two distinctive logarithmic functions of the inlet flow velocity. These findings provide crucial technical support for groundwater pollution control in karst areas. Plain Language Summary: Eddies are commonly seen when groundwater moves through highly permeable porous media, fractures, or conduit media, and understanding their effects on pollutants (treated as solutes) transport is crucial. In this study, we designed a semicircular rough conduit to reveal the mechanism of solute transport under different hydrodynamic conditions using a combined experimental and numerical simulation approach. The occurrence of the eddy zone and its influence on solute transport are revealed in great detail by analyzing the breakthrough curves (BTCs). This study provides a scientific basis for groundwater pollution control, especially in karst areas, demonstrating the relevance and applicability of our research to the field of geophysical fluid dynamics. Key Points: The non‐Fickian effect increases first and then decreases gradually with the increase of inlet flow velocityThe transformation mechanism process of advection and hydrodynamic diffusion is revealedThe relationship between the equilibrium concentration, corresponding time and flow velocity at different stages is quantified [ABSTRACT FROM AUTHOR]

Summary: Characteristic of all conifer needles, the transfusion tissue mediates the radial transport of water and sugar between the endodermis and axial vasculature. Physical constraints imposed by the needle's linear geometry introduce two potential extravascular bottlenecks where the opposition of sugar and water flows may frustrate sugar export: one at the vascular access point and the other at the endodermis.We developed a network model of the transfusion tissue to explore how its structure and composition affect the delivery of sugars to the axial phloem. To describe extravascular transport with cellular resolution, we construct networks from images of Pinus pinea needles obtained through tomographic microscopy, as well as fluorescence and electron microscopy.The transfusion tissue provides physically distinct pathways for sugar and water, reducing resistance between the vasculature and endodermis and mitigating flow constriction at the vascular flank. Dissipation of flow velocities through the transfusion tissue's branched structure allows for bidirectional transport of an inbound diffusive sugar flux against an outbound advective water flux across the endodermis.Our results clarify the structure–function relationships of the transfusion tissue under conditions free of physiological stress. The presented model framework is also applicable to different transfusion tissue morphologies in other gymnosperms. [ABSTRACT FROM AUTHOR]

Most previous investigations for consolidation-induced solute transport models have been limited to one-dimensional studies in unsaturated porous media and lack systematic parameter sensitivity analysis. This study addresses these gaps by analyzing the effects of hydraulic conductivity (K), shear modulus (G), saturation ( S r ), Poisson's ratio (ν), partitioning coefficient ( K d ), and anisotropy ratio ( K x K z and K y K z ) on pore water pressure, soil deformation, and solute transport. The findings reveal that higher K d values significantly hinder solute migration through enhanced adsorption and reduced vertical transport to deeper layers, while increasing anisotropy ratios primarily enhance horizontal migration, with their effects diminishing beyond a threshold. Additionally, a higher K accelerates pressure dissipation and solute movement, while a lower G increases soil deformation and speeds up solute migration. Saturation has a minor effect on solute concentration, with slight increases under higher S r . The Poisson ratio significantly impacts the transport of the solute, with smaller ν accelerating and larger ν slowing migration. These insights offer valuable theoretical support for optimizing models in unsaturated porous media. [ABSTRACT FROM AUTHOR]

[Objective] The aims of this study are to explicit the transport processes of heavy metals in soil under different addition amounts of iron-modified biochar, and to provide theoretical basis for soil heavy metals pollution control in loess area. [Methods] The mass ratios of iron-modified biochar to loessial soil were 0% (CK), 1% (A1), 2% (A2), 3% (A3), 4% (A4) and 5% (A5), respectively, and Pb2+was used as the tracer ion to simulate solute transport tests in indoor soil column. The effects of different amounts of iron-modified biochar on Pb2+transport in loessial soil were studied and simulated. [Results] (1) The saturated water conductivity (Ks) of A1, A2, A3, A4 and A5 treatments decreased by 6.90%, 20.70%, 27.60%, 31.03% and 37.93% compared with CK, respectively, which indicated that Ks gradually decreased with the increasing amount of iron-modified biochar application. (2) Compared with CK, the total duration of Pb2+concentration under different treatments was extended by 1.79, 13.00, 34.98, 35.34 and 40.81 hours, respectively. With the increasing of iron-modified biochar application, the initial and complete penetration time of heavy metals were significantly delayed. (3) The fitting curves of the two-zone model (TRM) and the convection-dispersion equation (CDE) agreed well with the measured curves, but the coefficient of determination (R²) of TRM was greater than that of CDE, and the root mean square error (RMSE) was less than that of CDE, so the simulation accuracy of TRM was better. [Conclusion] The application of iron-modified biochar in soil can effectively slow down the transport process of heavy metals, and provide theoretical reference for prevention of heavy metal pollution in loess area. [ABSTRACT FROM AUTHOR]

Adsorption characteristics play a crucial role in solute transport processes, serving as a fundamental factor for evaluating the performance of clay liners. Nonlinear adsorption isotherms are commonly found with metal ions and organic compounds, which introduce challenges in obtaining analytical solutions for solute transport models. In this study, analytical solutions are proposed for a fully coupled hydraulic‐mechanical‐chemical (HMC) model that accounts for both the Freundlich and Langmuir isotherms. To mitigate the difficulties arising from the variable coefficients, the system of second‐order partial differential equations involving three variables is linearized. The method of separation of variables, theory of integration, and Fourier series are utilized to derive analytical solutions. The analytical method presented can potentially be extended to a broad spectrum of nonlinear adsorption isotherms. The results reveal a 56.5% reduction in solute breakthrough time under the Freundlich isotherm and a remarkable 2.6‐fold extension under the Langmuir isotherm when compared to the linear isotherm. The adsorption constants of the Freundlich and Langmuir isotherms exhibit a positive correlation with breakthrough time, while the exponent of the Freundlich isotherm and the maximal adsorption capacity in the Langmuir isotherm demonstrate a negative association with breakthrough time. This study enhances the precision of solute transport prediction and provides a more scientific assessment of clay liner performance. [ABSTRACT FROM AUTHOR]

The capillary fringe (CF), a complex water–gas–solid interaction system, serves as a crucial pathway for solutes before they migrate below the water table. Sandbox experiments and numerical simulations have been employed to assess how tracer injection rates, boundary water levels, and evaporation intensities affect solute transport within the CF. The results showed that when the tracer injection rate was low, the tracer migrated laterally within the CF; however, as the injection rate increased, the tracer's migration velocity increased, and the contaminant plume expanded, eventually to below the water table. Furthermore, as the hydraulic head difference increased, the ratio of the lateral hydraulic gradient to the vertical hydraulic gradient became larger, resulting in the lateral migration of the tracer within the CF. Conversely, as the hydraulic head difference decreased, the CF became less of a barrier to vertical migration, allowing the tracer to migrate below the water table. Additionally, evaporation was found to significantly influence solute transport by reducing moisture content and unsaturated hydraulic conductivity, which in turn slowed lateral seepage and altered capillary rise dynamics, impacting the downward movement of the tracer. This research highlights the complex factors influencing solute transport in the CF, providing critical insights for accurate water resource evaluation in unsaturated and saturated zones. [ABSTRACT FROM AUTHOR]

An improved understanding of complex solute transport processes in a single fracture is the foundation for advancing fracture network research. This study addresses a radial reactive transport problem in a fractured rock matrix system, with an emphasis on the role of non-equilibrium sorption. A new model that integrates a two-site nonequilibrium sorption framework was developed in a single fracture under a radial flow condition. Semianalytical models were derived utilizing Laplace transform techniques. These solutions offer insights into the spatio-temporal concentration, back diffusion and diffusive mass flux issues. When benchmarked against prior solutions, the approach presented here demonstrates superior accuracy and robustness. Several significant results were obtained. First, nonequilibrium sorption leads to a more pronounced peak in the breakthrough curves (BTCs) and diminishes the tailing of BTCs in the system. Second, a higher degradation rate for nonequilibrium sorption reduces the concentration of BTCs in the later stage but has minimal impact in the early stage. Third, after clean water injection, the back diffusion from the rock matrices into the fracture was observed, predominantly near the wellbore, accounting for the tailing behavior. Meanwhile, the diffusive mass flux exhibits a sharp rise and then declines in the early stages. Finally, an increased proportion of equilibrium sorption in the fracture leads to a decrease in the diffusive mass flux, whereas it displays the inverse trend in the rock matrix. In general, these findings underscore the essential role of nonequilibrium sorption considerations for the accurate representation of solute transport processes in fractured rock matrix systems. [ABSTRACT FROM AUTHOR]

The movement of solutes in soil is crucial due to their potential to cause soil and groundwater pollution. In this study, a mathematical model based on the Advection Dispersion Equation (ADE) was developed to evaluate solutions for solute transport. This equation enabled us to attain a relationship for concentrations at different locations and times, also known as the breakthrough curve. Five columns (5 cm in diameter and 30 cm in height) of soil types were prepared to check the validity of the results. An evaluation of the calculated relations showed high accuracy in estimating the breakthrough curve and the saturated hydraulic conductivity of the soil. [ABSTRACT FROM AUTHOR]

Transport equations are widely used to describe the evolution of scalar quantities subject to advection, dispersion and, possibly, reactions. Numerical methods are required to solve these equations in applications, adopting either the advective or conservative formulations. Conservative formulations are usually preferred in practice because they conserve mass. Advective formulations do not, but have received more mathematical attention and are required for Lagrangian solution methods. To obtain an advective formulation that conserves mass, we subtract the discretized fluid flow equation, multiplied by concentration, from the conservative form of the transport equation. The resulting scheme not only conserves mass, but is also elegant in that it can be interpreted as averaging the advective term at cell interfaces, instead of approximating it at cell centers as in traditional centered schemes. The two schemes are identical when fluid velocity is constant, and both have second-order convergence, but the truncation errors are slightly different. We argue that the error terms appearing in the proposed scheme actually imply an improved representation of subgrid spreading/contraction and acceleration/deceleration caused by variable velocity. We compare the proposed and traditional schemes on several problems with variable velocity caused by recharge, discharge or evaporation, including two newly developed analytical solutions. The proposed method yields results that are slightly, but consistently, better than the traditional scheme, while always conserving mass (i.e., mass at the end equals mass at the beginning plus inputs minus outputs), which the traditional centered finite differences scheme does not. We conclude that this scheme should be preferred in finite difference solutions of transport. Article Highlights: Alternative scheme for finite difference solution of advective form of transport equations Proposed scheme averages advective term at interfaces instead of approximating it at cell centers Proposed scheme is second order, conserves mass, and yields slightly better concentrations than the traditional scheme [ABSTRACT FROM AUTHOR]

This study focuses on the Manimala River Basin (MMRB) situated in the Western Ghats region of Kerala, which has been significantly affected by landslides. The water quality in the MMRB is likely to be impacted by heavy rainfall and the resulting debris flows. A comprehensive analysis was conducted for 157 water samples collected from the MMRB, with an objective to evaluate the hydrogeological conditions and estimation of 23 physico-chemical parameters to determine the water quality. Pearson’s correlation matrix for geochemical data was performed to investigate the relationships among physical and chemical parameters, and various ions in the MMRB. The present study also aimed to identify the dominant geochemical facies present in the water samples and determine the geochemical processes responsible for modifying the hydrochemistry. The results revealed that elevated concentrations of Ca2+ and SO42- ions, which exert influence on the hydrochemistry of the region. Moreover, we utilized a fuzzy logic tool to categorize the water samples based on a water quality index, which indicated that approximately 92% of the MMRB samples are suitable for human consumption. This study offers valuable insights into the interplay of geochemical factors and water quality assessment, contributing to effective strategies for water resource management and conservation.

[Objective] To investigate the effects of different sand blending rates on the hydraulic properties and solute transport processes of moderately saline soils. [Methods] Four sand mixture ratios were established using an indoor soil column test: CK (0 sand mixing), B1 (10% sand mixing), B2 (15% sand mixing), and B3 (20% sand mixing), to investigate the solute transport characteristics of moderately saline soils under different sand mixing conditions and to perform model simulations. [Results] (1) In the range of 0~20%, sand mixing in moderately saline soil will obviously affect the change of soil moisture characteristic curve, and the larger the proportion of sand mixing, the closer the curve is to the Y-axis. Under any suction condition, the soil water content was ranked as CK>B1>B2>B3, and the larger the proportion of sand mixing, the more small pores in the soil, the reduction of small pores, and the weakening of soil water-holding properties. The saturated hydraulic conductivity of the soil increased with the increase of sand doping. (2) With the increase of sand doping, the solute penetration curve shifted significantly to the left, and the initial penetration time, complete penetration time, and total penetration time were reduced, and the total penetration time of B1, B2, and B3 treatments were reduced by 34.48%, 47.22%, and 69.71%, respectively, compared with that of CK. (3) Both the CED equation and the two-zone model can simulate the solute transport in soil under sand doping conditions well, but the fitting accuracy of the two-zone model is higher compared with the CDE equation. Analyses of the fitted parameters of the two-zone model showed that the soil pore flow rate, the water content ratio of the movable zone and the mass exchange coefficient gradually increased with the increase of sand doping, while the hydrodynamic dispersion coefficient and the dispersion degree showed a decreasing trend. [Conclusion] Therefore, sand blending in saline soils can effectively improve soil hydraulic properties, promote solute transport in the soil, and help alleviate the adverse effects of salinity on crop growth. The results of this study can provide reference for saline soil improvement and management work, and provide theoretical support and practical guidance for future research and practice.

Abstract In this study, the effects of surface roughness and Reynolds number (Re) on fluid flow and solute transport are investigated based on a double rough-walled fracture model that precisely represents the natural geometries of rock fractures. The double rough-walled fracture model is composed of two three-dimensional(3D) self-affine fracture surfaces generated using the improved successive random additions (SRA). Simulation of fluid flow and solute transport through the models were conducted by directly solving the Navier-Stokes equation and advection-diffusion equation (ADE), respectively. The results indicate that as the Re increases from 0.1 to 200, the flow regime changes from linear flow to nonlinear flow accompanied with the tortuous streamlines and significant eddies. Those eddies lead to the temporary stagnant zones that delay the solute migration. The increment of Re enhances the transport heterogeneity with the transport mode changing from the diffusion-dominated to the advection-dominated behavior, which is more significant in the fracture with a larger joint roughness coefficient (JRC). All breakthrough curves (BTCs) of rough-walled fractures exhibited typical non-Fickian transport characteristics with “early arrival” and “long tailing” of BTCs. Increasing the JRC and/or Re will enhances the non-Fickian transport characteristics. The ADE model is able to accurately fit the numerical BTCs and residence time distributions (RTDs) at a low Re, but fails to capture the non-Fickian transport characteristics at a large Re. In contrast, the continuous time random walk (CTRW) model provides a better fit to the numerical simulation results over the whole range of Re. Whereas, the fitting error gradually increases with increasing Re.

This research aims at studying the intrinsic vulnerability of groundwater to diffuse environmental pollutants in the Muravera coastal agricultural area of Sardinia, Italy. The area faces contamination risks arising from agricultural practices, especially the use of fertilizers, pesticides, and various chemicals that can seep into the groundwater. The study examined the interplay among hydrological elements, including soil characteristics, groundwater depth, climate conditions, land use, and aquifer properties. To do that, the outcomes of FLOWS 1D physically-based agrohydrological model were analyzed in parallel with those of the overlay-and-index model SINTACS, in a sort of reciprocal benchmarking. By using FLOWS, water movement and solute transport in the unsaturated zone were simulated by, respectively, solving the Richard Equation (RE) and the Advection-Dispersion equation (ADE). As such, this model allowed to account for the role of soil hydraulic and hydro-dispersive properties variability in determining the travel times of a conservative solute through the soil profile to the groundwater. For FLOWS simulations, a complete dataset was used as input, including soil horizons, soil physical and hydraulic properties of 36 soil profiles, average annual depth to groundwater table at each soil profile (ranging from 1 to 50 meters), and climatic temporal series data on rainfall and evapotranspiration. Detailed analyses of travel times for the movement of 25, 50, 75, and 100% of the solute mass to reach groundwater were conducted, revealing that the depth to groundwater predominantly influences vulnerability. This result was coherent with SINTACS vulnerability map due to the large impact of the depth to groundwater on SINTACS analysis. [ABSTRACT FROM AUTHOR]

As a promising alternative water source to alleviate irrigation water scarcity in red soil regions in southern China, low-quality water could enhance regional water resource utilization and promote sustainable agriculture. However, its soluble salt and ions could affect soil solute distribution and transport, potentially hindering crop growth. Undoubtedly, it is necessary to understand the mechanism of solute transport in red soil under low-quality water irrigation with different water salinity levels. Therefore, a one-dimensional vertical water infiltration experiment and a solute breakthrough experiment were conducted to evaluate the solute transport (soluble salt, Na+, and Cl−) in unsaturated and saturated homogenous red soil at different salinity levels [1 (S1), 2 (S2), 3 (S3), 5 (S5), and 10 (S10) g/L] when irrigated with simulated low-quality water using analytical-grade NaCl. Moreover, the potential factors affecting salt distribution in unsaturated red soil were determined. The findings indicate positive linear relationships between accumulations of three solutes and irrigation water salinity. Generally, the depth of maximum solute concentration increased with the increase in irrigation water salinity. Soluble salt, Na+, and Cl− exhibited early breakthrough and trailing in red soil, but higher irrigation water salinity could reduce PV and retardation. A mobile and immobile water model (MIM) showed that convection was dominant in solute transport in red soil under low-quality water irrigation. D decreased as a power function with increasing irrigation water salinity, while v and R decreased linearly. Furthermore, the red soil can adsorb Cl− resulting from its special charge characteristics under low-quality water irrigation, which may be the main source of salt adsorption. Additionally, v > soil pH > βsalt primarily influenced salt distribution in the 0–40 cm soil profile. This study can provide insights into solute transport in red soil under low-quality water irrigation, facilitating soil fertility and structure, as well as low-quality water irrigation strategy optimization. [ABSTRACT FROM AUTHOR]

Understanding solute transport in pipe flows is essential for ensuring consistent water quality throughout the entire drinking water supply network. This study used four planar laser-induced fluorescence (PLIF) units for the first time to quantify the cross-sectional concentration distribution resulting from a single pulse of tracer injected at an upstream location under both steady and accelerating flow conditions. Compared with conventional fluorometers, PLIF provides a better measure of the cross-sectional mean concentrations because it allows the cross-sectional distribution of the tracer to be quantified. Under steady turbulent flow conditions, the tracer was cross-sectionally well-mixed, and the concentration uniformity increased with increasing Reynolds number. In laminar flows, as a result of minimal radial mixing, the tracer exhibited a spatial distribution created by the longitudinal differential advection, transforming from a central core to an annulus, which expanded toward the pipe boundary. Under accelerating flows, the temporal concentration profiles displayed two peaks and the tracer close to the source was not cross-sectionally well-mixed. With increasing discharge, the tracer became cross-sectionally well-mixed while retaining the two peak profiles. These results have implications for water quality modeling in unsteady conditions, especially in domestic plumbing, when boundary and biofilm interactions control important processes. [ABSTRACT FROM AUTHOR]

To investigate the influence of flow rate increment on the solute transport parameter of immobile zones in a karst system, a dye tracer test was conducted in the Downtown Salado Spring Complex (DSSC) comprising three springs: Big Boiling, Anderson, and Doc Benedict springs. The Multiflow two-region nonequilibrium model (2RNE) was used to simulate the breakthrough curve (BTC) of the springs, and changes in the solute transport parameters in response to flow rate increment were observed. The simulation result showed that the 2RNE model was capable of reproducing the BTC of all the DSSC springs, with an R-squared value greater than 0.9 in all flow rate increment scenarios. The research demonstrates that a positive correlation will exist between the flow rate and solute transport parameter of the immobile zones if the tracer transport to the spring is truly influenced by immobile zones. In contrast, a negative correlation will exist between the flow rate and mass transfer coefficient if the immobile zone has less influence. Overall, the research provides insights into contaminant movement in karst by documenting how tracers are retained in the immobile fluid zone. [ABSTRACT FROM AUTHOR]

Most studies on solute transport in coastal aquifers affected by tides focus on the transport of instantaneous released solute, and there are few studies on continuously released solute affected by tides. In this study, the image monitoring method is used to establish the quantitative relationship between the concentration of the colored tracer and the hue value of the image, and the digital image is used to determine the tracer concentration distribution. Using image monitoring method laboratory experiments, quantitative analysis of the characteristics of continuously released solute transport in coastal unconfined aquifers under the tidal influence. Experiments show that the high tide inhibits the increase in the concentration of each point in the aquifer. Under the influence of tides, the solute plume retreats towards the land. During the low tide period, the solute plume migrates toward the sea again. And the solute plume will maintain a relatively stable shape after entering the aquifer for a long enough time. Ignoring the tidal effect seems to have little effect on the estimation of the position of the solute plume, but ignoring the tidal effect has a certain influence on the estimation of the dispersion range of the solute plume. No matter whether considering the tidal action, the final dispersion range of the solute plume is almost the same. But before the solute plume reaches a stable state, ignoring the tidal effect will lead to a smaller dispersion range of the solute plume. [ABSTRACT FROM AUTHOR]

Mining overburden bed separation grouting is an effective method for controlling coal mining subsidence. However, the slurry that is injected into the overburden bed separation space may impact the groundwater environment during the precipitation and consolidation process. To evaluate the impact of overburden bed separation grouting on the groundwater environment, coupled numerical simulations of groundwater flow and solute transport were carried out with the background of a grouting project in Northern China. In addition, the shallow groundwater quality at the site is monitored and evaluated. The results show that the groundwater level rises as a result of grouting and that the direction of groundwater flow changes in the vicinity of the grouting boreholes. After the end of the grouting project, the groundwater flow field gradually returned to its natural state. The characteristic solute aluminium in the slurry precipitation water slightly contaminates the aquifer above the grouted bed separation space, but the contamination remains within the working face. The contamination gradually disappears after the end of the grouting project. The evaluation results of the shallow groundwater samples collected before and after grouting showed little difference, suggesting that grouting did not significantly affect the quality of the shallow groundwater. The research results provide theoretical support for the protection of groundwater in mining overburden bed separation grouting areas. [ABSTRACT FROM AUTHOR]

This study investigated the efficacy of biochar as a soil amendment for enhancing soil physicochemical properties and solute transport dynamics, with implications for agricultural sustainability and environmental stewardship. Batch laboratory experiments and column studies were conducted to assess the effects of biochar application on soil parameters and solute transport under saturated conditions. The saturation soil extraction approach was employed in batch leaching tests, while column experiments replicated subsurface conditions. Transport modeling using CXTFIT 2.1 elucidated solute dispersion dynamics in biochar-amended soils. Batch experiments revealed significant alterations in soil pH, electrical conductivity, and nutrient release following biochar addition. Biochar exhibited adsorption capacity for fluoride ions and released dissolved organic carbon, highlighting its potential for soil carbon sequestration and microbial activity. Column studies demonstrated enhanced solute dispersion and increased microbial activity in biochar-amended soils, as evidenced by changes in breakthrough curves and degradation rates of nitrate. Indeed, nitrate first-order degradation coefficients were 9.08E-06 for the column with only sandy soil, 3.09E-05 and 1.47E-04 for the columns with minimum and maximum doses of biochar respectively. Biochar application significantly influenced soil physicochemical properties and solute transport dynamics, with potential implications for nutrient management and contaminant attenuation in agricultural systems. Despite limitations in laboratory-scale experiments, this research provides valuable insights into biochar-soil interactions. It underscores the need for further investigation under field conditions to validate findings and optimize biochar management practices for sustainable soil and environmental management. Highlights: The release of solutes following biochar application highlights the complex chemical biochar-soil interactions. Biochar application increased nitrate degradation coefficient in both minimum and maximum treatment. Biochar alters soil pore structure, leading to more extensive solute spreading. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Soil & Water Conservation (1009-2242) is the property of Institute of Soil & Water Conservation and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In this study, the effects of surface roughness and Reynolds number (Re) on fluid flow and solute transport are investigated based on a double rough-walled fracture model that precisely represents the natural geometries of rock fractures. The double rough-walled fracture model is composed of two three-dimensional(3D) self-affine fracture surfaces generated using the improved successive random additions (SRA). Simulation of fluid flow and solute transport through the models were conducted by directly solving the Navier-Stokes equation and advection-diffusion equation (ADE), respectively. The results indicate that as the Re increases from 0.1 to 200, the flow regime changes from linear flow to nonlinear flow accompanied with the tortuous streamlines and significant eddies. Those eddies lead to the temporary stagnant zones that delay the solute migration. The increment of Re enhances the transport heterogeneity with the transport mode changing from the diffusion-dominated to the advection-dominated behavior, which is more significant in the fracture with a larger joint roughness coefficient (JRC). All breakthrough curves (BTCs) of rough-walled fractures exhibited typical non-Fickian transport characteristics with "early arrival" and "long tailing" of BTCs. Increasing the JRC and/or Re will enhances the non-Fickian transport characteristics. The ADE model is able to accurately fit the numerical BTCs and residence time distributions (RTDs) at a low Re, but fails to capture the non-Fickian transport characteristics at a large Re. In contrast, the continuous time random walk (CTRW) model provides a better fit to the numerical simulation results over the whole range of Re. Whereas, the fitting error gradually increases with increasing Re. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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In this study, the spray characteristics of the cooling water flux of the traditional single nozzle and novel dual nozzle were innovatively and effectively incorporated into a 3D/2D flow-temperature-concentration segmented model. The model was used to investigate the effects of spray characteristics on the flow, heat distribution, solute transport, solidified shell, and mushy zone of steel in the continuous casting. The results showed that various flow patterns of liquid steel in the turbulent zone significantly affected the temperature and carbon concentration distribution. Until Zone 7, the cooling water fluxes in the six cases remained unchanged. The peak temperatures of cases 1 and 4 in Zone 7 were 1253.11 and 1273.51 K, respectively, indicating that the spray characteristic was the primary cause of the variations in slab surface temperatures. The cooling water fluxes in the six cases change from Zone 8 onward. The six cases had differences of −21.39, 17.87, 46.95, −22.08, 16.86, and 45.68 K between the initial and final temperatures in Zone 8, respectively, meeting the requirement of keeping the maximum temperature recovery rate of slab surface under 100 °C/m. However, the final temperatures for cases 2, 3, and 6 were 1225.62, 1196.50, and 1218.91 K, respectively. These temperatures fall within a realistic plastic temperature range, which must be higher than 1220 K. As a result, the plastic cracking in the slab was possible. The maximum temperature gradient differences of the six cases between feature lines at the end of Zone 8 were 0.793, 0.814, 0.829, 0.185, 0.179, and 0.179 K/mm. These results showed that the optimization effect on the temperature gradient difference was insignificant as the cooling intensity rose. However, the carbon concentration uniformity was marginally improved by increasing the cooling water flux. Finally, a state-owned steel company in China chose case 5 (dual nozzle with moderate cooling intensity at the slab solidified end) as the optimum option for the slab continuous casting caster. The dual nozzle enhanced and promoted the efficient and homogeneous production of the metallurgical process.

Abstract Groundwater is considered the most important natural resource to mankind. Groundwater constitutes an important part of the hydrological cycle and is more prone to pollution. Dumpsite located in close proximity to groundwater resources is highly susceptible to leachates pollution. Predicting the susceptibility of groundwater pollution is crucial to address industry-standard codes for groundwater flow, contaminant transport, local to regional-scale water quality, and source water protection issues. Therefore, predicting heavy metal transport in groundwater around Lemna dumpsite in Cross River State, Nigeria, was examined. Soil samples were purposively collected with a soil Auger, along a straight line at (5 m, 25 m and 50 m) in the dumpsite. Water samples were purposively collected from five (5) boreholes close to Lemna dumpsite. The study utilized pumping test method to obtain data for the analysis of heavy metal transport in groundwater. Data analysis of the laboratory results of soil and borehole water quality focuses on arsenic, lead, cadmium, chromium, nickel, and mercury. Paired sample t test was used to analyse the soil and borehole water quality. Visual Modflow was also used to analyse the solute transport of heavy metals in groundwater around Lemna dumpsite. The paired sample t test of the analysis of heavy metals in soil exhibited a significant difference (p

Groundwater is considered the most important natural resource to mankind. Groundwater constitutes an important part of the hydrological cycle and is more prone to pollution. Dumpsite located in close proximity to groundwater resources is highly susceptible to leachates pollution. Predicting the susceptibility of groundwater pollution is crucial to address industry-standard codes for groundwater flow, contaminant transport, local to regional-scale water quality, and source water protection issues. Therefore, predicting heavy metal transport in groundwater around Lemna dumpsite in Cross River State, Nigeria, was examined. Soil samples were purposively collected with a soil Auger, along a straight line at (5 m, 25 m and 50 m) in the dumpsite. Water samples were purposively collected from five (5) boreholes close to Lemna dumpsite. The study utilized pumping test method to obtain data for the analysis of heavy metal transport in groundwater. Data analysis of the laboratory results of soil and borehole water quality focuses on arsenic, lead, cadmium, chromium, nickel, and mercury. Paired sample t test was used to analyse the soil and borehole water quality. Visual Modflow was also used to analyse the solute transport of heavy metals in groundwater around Lemna dumpsite. The paired sample t test of the analysis of heavy metals in soil exhibited a significant difference (p < 0.05) compared to National Environmental Standard Regulation and Enforcement Agency limits. The paired sample t test of the analysis of heavy metals in borehole water exhibited a significant difference (p < 0.05) compared to World Health Organization limits. The significant level indicates contamination of the soil and borehole water. The findings revealed a spatial spread of 259.2000 m2/day, with the contaminant travelling up to 94,608 m2/year. The extent of heavy metals concentration exhibited a maximum of 0.991 mg/l to a minimum of (− 6.72 × 10–18 mg/l), with concentrations decreasing as the plume extend. The study recommends the need for remediation and stringent monitoring to mitigate heavy metal contamination of boreholes near Lemna dumpsite. [ABSTRACT FROM AUTHOR]

Hyporheic exchange flow, the movement of river water into streambed sediments and its subsequent return to the surface water after suffering biogeochemical transformations, impacts a stream's water quality and ecology. These processes, which are the basis for the self-purification capacity of river systems, depend on the quantity and travel time of the flow within the sediments. Different tracer-based approaches have been deployed for studying flow in saturated sediments, but few of these experimental methodologies are able to attain the high temporal resolutions that are needed to adequately capture the passage of a solute plume in a porous medium. To allow for a better description of such flows, we designed and fabricated an innovative, low-cost sensor system able to detect solute transport at multiple locations simultaneously at very high time resolutions. The sensors measure electrical conductivity as voltage drops at a frequency of up to 10 Hz, allowing for detailed solute breakthrough curves (BTCs). The fabricated sensors were tested in a laboratory experimental setup designed to examine solute transport under conditions that reproduce 1D flow in saturated sediments. The sensor system was able to successfully detect electrical conductivity (expressed as voltage drop) in real-time, at high temporal resolution, and at multiple locations. Solute BTCs collected with the system were consistent and highly repeatable under the same conditions. One-dimensional solute transport equations were modeled numerically using the finite differences technique, and the results showed good agreement between the measured and modeled BTCs for all materials. The proposed system is inexpensive compared to conventional EC probes, easy to operate, and sensitive to low solute concentrations. [ABSTRACT FROM AUTHOR]

Large‐scale seepage faces occur on tidal flats with gentle slope, which are widely distributed worldwide. Evaporation on these seepage faces, leading to salt retention and accumulation, may significantly impact the density‐dependent groundwater flow beneath the tidal flats. However, due to nonlinear complexities of the groundwater flow and solute transport on seepage faces, explicit boundary conditions and numerical models to quantify these processes are lacking. In this study, we present both mathematical and numerical models to quantify these processes. Compared to the results of our previous study, this paper shows that seepage‐face evaporation can (a) significantly increase the groundwater salinity in the upper intertidal zone, and form multiple groundwater circulation cells in the intertidal zone, (b) cause the disappearance of multiple seepage‐faces and reduce the spatial extent of seepage faces notably, (c) and intensify the groundwater and salt exchange as well as the seawater‐groundwater circulation through the intertidal zone. Plain Language Summary: Tidal flats with very gentle slopes are ubiquitously distributed around the world. Due to these minimal slopes, the intertidal zone can extend for several kilometers, leading to large‐scale seepage faces during ebb and low tides. Previous studies have shown that evaporation without seepage face causes salt retention and accumulation, which not only increases groundwater salinity significantly, but also alters the groundwater density and its subsurface pathways. However, explicit mathematical expression and associated numerical models to quantify the process of evaporation on seepage faces are lacking, due to the mathematically nonlinear complexities to deal with the density‐dependent groundwater flow and solute transport. Here, a new boundary condition considering evaporation on seepage faces as well as salt retention and accumulation was proposed. Compared with the seepage‐face boundary conditions of our previous study, we found that multiple seepage‐faces disappear and multiple groundwater circulation cells develop due to evaporation. Seepage‐face evaporation significantly increases the salinity in the upper intertidal zone, reduces the scale and existence of seepage faces, and promotes groundwater/salt exchange. This study systematically reveals the effects of seepage‐face with evaporation on the density‐dependent groundwater flows and salinity distributions in coastal aquifers, which have strong implications on biogeochemical processes within the intertidal zone. Key Points: A new evaporation boundary condition was proposed on seepage face with salt retained and accumulatedMultiple seepage‐faces disappear and multiple groundwater circulation cells develop due to evaporation in the intertidal zoneSeepage‐face evaporation significantly promotes groundwater and salt exchange within the intertidal zone [ABSTRACT FROM AUTHOR]

The migration of a groundwater contaminant plume consisting of light nonaqueous phase liquids (LNAPLs) along the Ionian coastline of Sicily, Italy, has been reported to follow a trajectory that is inconsistent with the regional hydraulic gradient. The influence of several faults affecting the fractured carbonate bedrock aquifer, and groundwater abstraction from a well, were hypothesized to be responsible for the anomalous trajectory of the contaminant plume. A conceptual hydrogeological model was developed for the study area that incorporated structural information derived from geophysical surveys and the mapping of fractures in bedrock outcrops. This conceptual model was incorporated into numerical groundwater flow and solute transport models to simulate the groundwater transport of the light nonaqueous phase liquids. Four model scenarios representing different levels of complexity were tested to assess the relative influence of geological heterogeneity and groundwater abstraction on the migration of the contaminant plume. Results show that underground major discontinuity systems, invoking the presence of the faults in the model domain accounted for the observed migration of the contaminant plume, act as conduits for groundwater flow. Conversely, groundwater abstraction from a well was found to result in relatively minor, localized impacts to the migration of the contamination plume. This study demonstrates the importance of incorporating geological heterogeneity into groundwater modelling and environmental risk assessments associated with the storage of LNAPLs. [ABSTRACT FROM AUTHOR]

Imidacloprid (IDP) products are applied via soil drenching in the citrus critical root zone (CCRZ) at 0–60 cm soil depth. This study aimed to determine the uptake and leaching of IDP in the CCRZ of a Florida Entisol. The treatments include: (1) a control with no IDP applied, (2) 1.6 g of active ingredient (a.i.) per tree (×2), and (3) 3.2 g a.i. per tree of IDP (×4). The treatments were applied to two trees within each experiment unit, replicated five times, and completely randomized. The IDP concentration in the Entisol was affected by the amount of water received within the sampling intervals. IDP movement in the Entisol was evident for the field trials in Fall 2021 and 2022, irrespective of the treatment. A total of 10 mm of daily irrigation was the major driver of IDP movement in Fall 2021 (September–December 2021), while 11.7 cm of cumulative rainfall plus 10 mm of daily irrigation were the major drivers for IDP in Fall 2022 (November–December 2022). The IDP uptake level by leaves was relatively low probably because of the relatively low temperature and humidity. More applications of IDP did not result in its higher uptake by citrus leaves in the Entisol. Given the persistence of IDP, there is a possibility of leaching, which could potentially contaminate the groundwater, surface water, and non-target organisms. Therefore, it is crucial to carefully manage the use of IDP in citrus production systems to mitigate the unintended environmental impacts.

Most previous investigations for consolidation-induced solute transport models have been limited to one-dimensional studies in unsaturated porous media and lack systematic parameter sensitivity analysis. This study addresses these gaps by analyzing the effects of hydraulic conductivity (K), shear modulus (G), saturation (Sr), Poisson’s ratio (ν), partitioning coefficient (Kd), and anisotropy ratio (KxKz and KyKz) on pore water pressure, soil deformation, and solute transport. The findings reveal that higher Kd values significantly hinder solute migration through enhanced adsorption and reduced vertical transport to deeper layers, while increasing anisotropy ratios primarily enhance horizontal migration, with their effects diminishing beyond a threshold. Additionally, a higher K accelerates pressure dissipation and solute movement, while a lower G increases soil deformation and speeds up solute migration. Saturation has a minor effect on solute concentration, with slight increases under higher Sr. The Poisson ratio significantly impacts the transport of the solute, with smaller ν accelerating and larger ν slowing migration. These insights offer valuable theoretical support for optimizing models in unsaturated porous media.

Microfluidic models are proving to be powerful systems to study fundamental processes in porous media, due to their ability to replicate topologically complex environments while allowing detailed, quantitative observations at the pore scale. Yet, while porous media such as living tissues, geological substrates, or industrial systems typically display a porosity that spans multiple scales, most microfluidic models to date are limited to a single porosity or a small range of pore sizes. Here, a novel microfluidic system with multiscale porosity is presented. By embedding polyacrylamide (PAAm) hydrogel structures through in‐situ photopolymerization in a landscape of microfabricated polydimethylsiloxane (PDMS) pillars with varying spacing, micromodels with porosity spanning several orders of magnitude, from nanometers to millimeters are created. Experiments conducted at different porosity patterns demonstrate the potential of this approach to characterize fundamental and ubiquitous biological and geochemical transport processes in porous media. Accounting for multiscale porosity allows studies of the resulting heterogeneous fluid flow and concentration fields of transported chemicals, as well as the biological behaviors associated with this heterogeneity, such as bacterial chemotaxis. This approach brings laboratory studies of transport in porous media a step closer to their natural counterparts in the environment, industry, and medicine. [ABSTRACT FROM AUTHOR]