Solute Movement Research Articles

The permeability contrast influence on the plume propagation with variable physical properties

ABSTRACT This paper deals with the modelling of variable-density flow and solute transport in saturated porous media. The mathematical formulation for such problems is solved by a combination of the mixed hybrid finite element method and discontinuous finite element method. The specific point of interest in this study is the investigation of dense plume behaviour in presence of heterogeneity. The model under consideration called FRIPE is used: (i) to study the behaviour of a dense solution locally injected into a stratified porous medium without groundwater flow field and (ii) to simulate the movement of radioactive salt solutions in Lake Karachai (Russia).

The physiological plasticity of salinity tolerance in Fundulus species

Despite their renowned euryhaline lifestyle, considerable variation in salinity tolerance appears to exist amongst different species of Fundulus, and amongst different populations of a single Fundulus species. This presentation will describe the physiological plasticity and the genomic underpinnings of abrupt salinity transfers in different populations of F. heteroclitus, F. majalis, F. diaphanus, and F. grandis collected along the Atlantic or Gulf of Mexico coasts of the U.S. Gills have been archived for transcriptomic profiling, and many other tissues have been analyzed for comprehensive physiological profiling. Physiology data processed so far (plasma osmolality and gill epithelial structure) indicate significant differences in plasticity between populations and species of Fundulus. Current work is also investigating the adaptive role of claudins, a constitutive component of epithelial tight junctions, in regulating the paracellular movement of solutes during osmotic stress. We have recently cloned several claudin genes from the gills of Fundulus, and are assessing their regulation during abrupt salinity transfers. This work was funded by an NSF grant to FG and AW (Award no. 0723771).

TESTING SOME PEDO-TRANSFER FUNCTIONS (PTFS) IN APULIA REGION

The knowledge of soil water retention vs. soil water matric potential is used to study irrigation and drainage schedules, soil water storage capacity (plant available water), solute movement, plant growth and water stress. The hydraulic soil properties measuring is expensive, laborious and takes too long time, so, frequently, matemathic models, called pedo-transfer functions (PTFs) are utilized to estimate hydraulic soil properties through soil chimical and phisical characteristics. Six pedo-transfer functions have been evaluated (Gupta & Larson, 1979; Rawls et al., 1982; De Jong et al., 1983; Rawls & Brakensiek, 1985; Saxton et al., 1986; Vereecken et al., 1989) by comparing estimated with measured soil moisture values at soil water matric potential of –33 and –1500 kPa of 361 soil samples collected from 185 pedons of Apulia Region (South Italy), having various combinations of particle-size distribution, soil organic matter content and bulk density. Accuracy of the soil moisture predictions have been evaluated by statistic indexes such as Weighted stantard error (WSEE), Mean Deviation (MD), Root Mean Squared Deviation (RMSD) and the determination coefficient (R2) between estimated and measured water retention values. The Rawls PTF model demostrated to have the lowest values of WSEE, MD and RMSD indexes (0.044, -0.007 and 0.059 m3 H2O m-3 soil, respectively) at –33 Kpa soil water matric potential (Field Capacity), while for estimating soil moisture at the Wilting Point (-1500 kPa) Rawls & Brakensiek model is adequate (WSEE, MD and RMSD of 0.034, -0.016 and 0.046 m3 H2O m-3 soil). De Jong, Saxton and Rawls & Brakensiek models, at –33 kPa soil water matric potential and Gupta & Larson and De Jong models at –1500 kPa soil water matric potential, showed the highest statistic errors.

Analytical Solution for Multi-Species Contaminant Transport Subject to Sequential First-Order Decay Reactions in Finite Media

Transport equations governing the movement of multiple solutes undergoing sequential first-order decay reactions have relevance in analyzing a variety of subsurface contaminant transport problems. In this study, a one-dimensional analytical solution for multi-species transport is obtained for finite porous media and constant boundary conditions. The solution permits different retardation factors for the various species. The solution procedure involves a classic algebraic substitution that transforms the advection-dispersion partial differential equation for each species into an equation that is purely diffusive. The new system of partial differential equations is solved analytically using the Classic Integral Transform Technique (CITT). Results for a classic test case involving a three-species nitrification chain are shown to agree with previously reported literature values. Because the new solution was obtained for a finite domain, it should be especially useful for testing numerical solution procedures.

Independent two-photon measurements of albumin GSC give low values

Independent two-photon measurements of albumin GSC give low values

Evidence for unidirectional flow through plasmodesmata.

The leaf trichome of tobacco (Nicotiana tabacum) represents a unique secretory structure in which the basal trichome cell is connected to the epidermis by numerous plasmodesmata (PD). Small fluorescent probes microinjected into the basal trichome cell moved apically into distal trichome cells but not into the subtending epidermal cell. In marked contrast, the same probes moved apically into trichome cells when injected into the epidermal cell. Noninvasive methods of dye loading, including ester loading into the apical secretory cell by trichome "capping" and by infiltration of caged fluorescein, produced the same result. In transgenic tobacco plants constitutively expressing photoactivatable green fluorescent protein (PAGFP), activation of PAGFP above the epidermal/trichome (e/t) boundary resulted in movement of protein apically into the distal trichome cells but not across the e/t boundary, while PAGFP activated in the epidermal cell moved apically across the e/t boundary. Experiments with apoplastic tracers also revealed the presence of a distinct apoplastic barrier to solute movement at the e/t interface. These data point to unidirectional transport of solutes through PD. PAGFP activated in individual cells equidistant between the basal cell and the apical cell moved bidirectionally from these cells, suggesting that mass flow was not the driving force for unidirectional transport. We found that unidirectional transport across the e/t boundary was not affected by virus infection or by addition of the actin inhibitor latrunculin but could be dissipated completely by addition of sodium azide. Collectively, our data suggest that active, unidirectional transport of molecules may occur through PD located at unique interfaces in the plant.

Adjoint-Based Sensitivity Analysis and Error Correction Methods Applied to Solid Oxide Fuel Cells

Sensitivity analysis and design optimization of solid oxide fuel cells are presented. Multispecies diffusion, low speed convection, and chemical kinetics are included in a two-dimensional numerical model, and sensitivity derivatives are computed using both discrete adjoint method and direct differentiation. The implementation of the discrete adjoint method is validated by comparing sensitivity derivatives obtained using the adjoint with results obtained using direct differentiation and finite-difference methods. For optimization, cost functions describing hydrogen concentration along the anode-electrolyte interface, hydrogen concentration at the channel outlet, and standard deviation of temperature inside the anode are considered. Material properties of the anode, operating conditions, and a shape parameter are selected as design variables. The development of an initial design environment to automate the flowfield solution, sensitivity computation, optimization, and mesh movement is also described. Finally, an adjoint-based error correction method is implemented and demonstrated to provide accurate estimations for a desired objective function on a fine mesh by combining information obtained from analysis and adjoint solutions on a coarser one.

Modelling solute transport in soil columns using advective–dispersive equations with fractional spatial derivatives

Solute transport in soils is commonly simulated with the advective-dispersive equation, or ADE. It has been reported that this model cannot take into account several important features of solute movement through soil. Recently, a new model has been suggested that results in a solute transport equation with fractional spatial derivatives, or FADE. We have assembled a database on published solute transport experiments in soil columns to test the new model. The FADE appears to be a useful generalization of the ADE. The order of the fractional differentiation reflects differences in physical conditions of the solute transport in soil.

Phloem loading strategies in three plant species that transport sugar alcohols.

Many plants translocate sugar alcohols in the phloem. However, the mechanism(s) of sugar alcohol loading in the minor veins of leaves are debated. We characterized the loading strategies of two species that transport sorbitol (Plantago major and apple [Malus domestica]), and one that transports mannitol (Asarina scandens). Plasmodesmata are abundant at all interfaces in the minor vein phloem of apple, and in one of two types of phloem in the minor veins of A. scandens. Few plasmodesmata are present in the minor veins of P. major. Apple differs from the other two species in that sugar alcohol and sucrose (Suc) are present in much higher concentrations in leaves. Apple leaf tissue exposed to exogenous [(14)C]sorbitol, [(14)C]Suc, or (14)CO(2) did not accumulate radiolabel in the minor veins, as determined by macroautoradiography. P. major minor veins accumulated radiolabel from [(14)C]Suc, [(14)C]sorbitol, and (14)CO(2). A. scandens minor veins accumulated (14)C from [(14)C]Suc and (14)CO(2), but not from [(14)C]mannitol. We conclude that the movement of sugar alcohol from the mesophyll into the phloem in apple and A. scandens is symplastic and passive, but in P. major it involves an apoplastic step and is energized. We also suggest that apple leaves transport sorbitol in high concentrations to avoid the feedback limitation of photosynthesis that would result from driving passive movement of solute into the phloem with high levels of Suc alone. The loading pathways and the mechanisms by which hydrostatic pressure is maintained in the minor vein phloem of these species are discussed.

Modeling of Flow and Advection Dominant Solute Transport in Variably Saturated Porous Media

In this paper we are presenting a numerical model to simulate transient flow and solute transport through a variably saturated zone. The mixed form of the Richards equation is used for the solution of the flow component as it is mass conserving, and the advection dispersion equation (ADE) is used for the solute transport. The Richards equation is solved numerically by finite difference and modified Picards iteration is used to deal with its inherent nonlinearity, and the resulting matrix is solved by a strongly implicit procedure. The numerical solution of ADE poses oscillations when there is a sharp front due to discontinuity in the solution. In this paper, we are presenting a numerical scheme to address the problems faced by the advective dominant front. The ADE is solved by the operator split method in which advection is solved by explicit finite volume and dispersion by the fully implicit finite difference method. A new numerical scheme is presented for the solution of the advection part of the equation. The advection flux is solved by using a locally one-dimensional approach, with the predictor-corrector method for the time step. Each step is made total variation diminishing to avoid oscillations. Performance of the model is tested for a few cases, like flow and transport into very dry soils, transient unconfined recharge and drainage through seepage face, and transient infiltration into randomly heterogeneous soils. The model is also used to study the effect of water table boundary and seepage face on the movement of solute.

Fluid and Solute Transport in Bone: Flow-Induced Mechanotransduction.

Much recent evidence suggests that bone cells sense their mechanical environment via interstitial fluid flow. In this review, we summarize theoretical and experimental approaches to quantify fluid and solute transport in bone, starting with the early investigations of fluid shear stress applied to bone cells. The pathways of bone interstitial fluid and solute movement are high-lighted based on recent theoretical models, as well as a new generation of tracer experiments that have clarified and refined the structure and function of the osteocyte pericellular matrix. Then we trace how the fluid-flow models for mechanotransduction have evolved as new ultrastructural features of the osteocyte lacunar-canalicular porosity have been identified and how more recent in vitro fluid-flow and cell-stretch experiments have helped elucidate at the molecular level the possible pathways for cellular excitation in bone.

Aquaporin-6 is expressed along the rat gastrointestinal tract and upregulated by feeding in the small intestine

BackgroundSeveral aquaporins (a family of integral membrane proteins) have been recently identified in the mammalian gastrointestinal tract, and their involvement in the movement of fluid and small solutes has been suggested. In this direction we investigated, in some regions of the rat gastrointestinal tract, the presence and localization of aquaporin-6, given its peculiar function as an ion selective channel.ResultsRT-PCR and immunoblotting experiments showed that aquaporin-6 was expressed in all the investigated portions of the rat gastrointestinal tract. The RT-PCR experiments showed that aquaporin-6 transcript was highly expressed in small intestine and rectum, and less in stomach, caecum and colon. In addition, jejunal mRNA expression was specifically stimulated by feeding.Immunoblotting analysis showed a major band with a molecular weight of about 55 kDa corresponding to the aquaporin-6 protein dimer; this band was stronger in the stomach and large intestine than in the small intestine. Immunoblotting analysis of brush border membrane vesicle preparations showed an intense signal for aquaporin-6 protein.The results of in situ hybridization experiments demonstrate that aquaporin-6 transcript is present in the isthmus, neck and basal regions of the stomach lining, and throughout the crypt-villus axis in both small and large intestine. In the latter regions, immunohistochemistry revealed strong aquaporin-6 labelling in the apical membrane of the surface epithelial cells, while weak or no labelling was observed in the crypt cells. In the stomach, an intense staining was observed in mucous neck cells and lower signal in principal cells and some parietal cells.ConclusionThe results indicate that aquaporin-6 is distributed throughout the gastrointestinal tract. Aquaporin-6 localization at the apical pole of the superficial epithelial cells and its upregulation by feeding suggest that it may be involved in movements of water and anions through the epithelium of the villi.

The Effect of Different Flow Patterns on Anode Fluid Behaviors of Micro Direct Methanol Fuel Cells

Based on the visualization technology, we investigated experimentally the effect of different flow patterns on anode fluid behaviors of the μDMFC (Micro Direct Methanol Fuel Cell) with a transparent material under the same condition. Stainless steel mesh was utilized as the current collector which was distinct from the carbon cloth or carbon paper. Four dissimilar flow patterns were developed and tested. The observation of the effect of different flow patterns revealed that movements of dilute methanol solutions and CO2 gas bubbles in the dot and parallel flow fields represented more difficult, which could result in a decline of the μDMFC performance. The study also showed that a channel blocking in the single-serpentine flow field would be extremely terrible which could lead to a fuels leaking of the μDMFC, meanwhile the liquid-gas flow was more fluent and stable in a double-serpentine flow field. Therefore, due to its advantages, a double-serpentine flow pattern is more suitable for the μDMFC application compared with the other flow patterns.

Chapter 2 Biological and Biophysical Properties of Vascular Connexin Channels

Intercellular channels formed by connexin proteins play a pivotal role in the direct movement of ions and larger cytoplasmic solutes between vascular endothelial cells, between vascular smooth muscle cells, and between endothelial and smooth muscle cells. Multiple genetic and epigenetic factors modulate connexin expression levels and/or channel function, including cell-type-independent and cell-type-specific transcription factors, posttranslational modifications, and localized membrane targeting. Additionally, differences in protein-protein interactions, including those between connexins, significantly contribute to both vascular homeostasis and disease progression. The biophysical properties of the connexin channels identified in the vasculature, those formed by Cx37, Cx40, Cx43 and/or Cx45 proteins, are discussed in this chapter in the physiological and pathophysiological context of vessel function.

A field experiment with variable-suction multi-compartment samplers to measure the spatio-temporal distribution of solute leaching in an agricultural soil

Solutes spread out in time and space as they move downwards from the soil surface with infiltrating water. Solute monitoring in the field is often limited to observations of resident concentrations, while flux concentrations govern the movement of solutes in soils. A recently developed multi-compartment sampler is capable of measuring fluxes at a high spatial resolution with minimal disturbance of the local pressure head field. The objective of this paper is to use this sampler to quantify the spatial and temporal variation of solute leaching below the root zone in an agricultural field under natural rainfall in winter and spring. We placed two samplers at 31 and 25 cm depth in an agricultural field, leaving the soil above undisturbed. Each sampler contained 100 separate cells of 31 × 31 mm. Water fluxes were measured every 5 min for each cell. We monitored leaching of a chloride pulse under natural rainfall by frequently extracting the collected leachate while leaving the samplers buried in situ. This experiment was followed by a dye tracer experiment. This setting yielded information that widely surpassed the information that can be provided by separate anionic and dye tracer trials, and solute transport monitoring by coring or suction cups. The detailed information provided by the samplers showed that percolation at the sampling depth started much faster (approximately 3 h after the start of rainfall) in initially wet soil (pressure head above − 65 cm) than in drier soil (more than 14 h at pressure heads below − 80 cm). At any time, 25% of the drainage passed through 5–6% of the sampled area, reflecting the effect of heterogeneity on the flow paths. The amount of solute carried by individual cells varied over four orders of magnitude. The lateral concentration differences were limited though. This suggests a convective–dispersive regime despite the short vertical travel distance. On the other hand, the dilution index indicates a slight tendency towards stochastic–convective transport at this depth. There was no evidence in the observed drainage patterns and dye stained profiles of significant disturbance of the flow field by the samplers.

AtTIP1;3 and AtTIP5;1, the only highly expressed Arabidopsis pollen-specific aquaporins, transport water and urea

Pollination includes processes where water and/or solute movements must be finely regulated, suggesting participation of aquaporins. Using information available from different transcriptional profilings of Arabidopsis thaliana mature pollen, we showed that the only aquaporins that are selectively and highly expressed in mature pollen are two TIPs: AtTIP1;3 and AtTIP5;1. Pollen exhibited a lower number and more exclusive type of aquaporin expressed genes when compared to other single cell transcriptional profilings. When characterized using Xenopus oocyte swelling assays, AtTIP1;3 and AtTIP5;1 showed intermediate water permeabilities. Although they displayed neither glycerol nor boric acid permeability they both transported urea. In conclusion, these results suggest a function for AtTIP1;3 and AtTIP5;1 as specific water and urea channels in Arabidopsis pollen.

Leaching surfaces to characterize transport in a heterogeneous aquifer: Comparison between flux concentrations, resident concentrations, and flux concentrations estimated from temporal moment analysis

For subsurface solute transport, flux concentrations are key, while usually resident concentrations are measured. Flux concentrations are frequently estimated from resident concentrations by temporal moment analysis. We tested this approach by simulating transport of an injected tracer during steady flow in an aquifer with a heterogeneous saturated hydraulic conductivity. We constructed grid cell–scale breakthrough curves (BTCs) from flux concentrations and approximated BTCs from resident concentrations and estimated flux concentrations. We assembled these BTCs into spatiotemporal leaching surfaces at various aquifer cross sections for subsequent analysis. Resident concentrations were unsuitable to assess solute movement in the aquifer. Temporal moment analysis worked well when the entire aquifer cross section was considered but performed poorer at the grid cell scale because it approximates the local velocity by the trajectory average. The leaching surfaces served as valuable tools to demonstrate and quantify the limitations of temporal moment analysis.

Analysis of the source of heterogeneity in the osmotic response of plant membrane vesicles

Plasma membrane vesicles have been widely employed to understand the biophysics of water movements, especially when active aquaporins are present. In general, water permeability coefficients in these preparations outcome from the analysis of the osmotic response of the vesicles by means of light scattering. As from now, this is possible by following a theoretical approach that assumes that scattered light follows a single exponential function and that this behavior is the consequence of vesicle volume changes due to an osmotic challenge. However, some experimental data do not necessarily fit to single exponentials but to double ones. It is argued that the observed double exponential behavior has two possible causes: different vesicle population in terms of permeability or in terms of size distribution. As classical models cannot identify this source of heterogeneity, a mathematical modeling approach was developed based on phenomenological equations of water transport. In the three comparative models presented here, it was assumed that water moves according to an osmotic mechanism across the vesicles, and there is no solute movement across them. Interestingly, when tested in a well described plasma membrane vesicle preparation, the application of these models indicates that the source of heterogeneity in the osmotic response is vesicles having different permeability, clearly discarding the variable size effect. In conclusion, the mathematical approach presented here allows to identify the source of heterogeneity; this information being of particular interest, especially when studying gating mechanisms triggered in water channel activity.

Hydrogeological Relationships of Sandy Deposits: Modeling of Two‐Dimensional Unsaturated Water and Pesticide Transport

Prediction of the movement of water and solutes in the vadose zone requires information on the distribution of spatial trends and heterogeneities in porous media. The present study describes different lithofacies origination mainly from glaciofluvial deposits. Among different lithofacies, hydrological relationships were investigated. By means of a two-dimensional hydrological model it was evaluated how the flow of water and leaching of metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one) was affected. Two selected large outcrop sections consisting of glacial outwash deposits were used in the modeling study. Eleven different lithofacies were distinguished and described in terms of texture distribution, sorting, bedding style, and external boundaries based on excavated soil profiles from 27 locations representing seven predominantly sandy landforms in Denmark. Undisturbed soil columns were sampled from each of the lithofacies and brought to the laboratory to be analyzed. With respect to their soil hydraulic properties, the different lithofacies formed four different hydrofacies having relatively homogeneous, hydrogeological properties. Two large outcrop sections from one of the locations (a gravel pit) located near the terminal moraine of the former Weichsel glacier were used for the HYDRUS-2D modeling. Modeling results revealed that the spatial distribution of sedimentary bodies affected water flow and the leaching of metribuzin.

Simulating nonequilibrium movement of water, solutes and particles using hydrus - a review of recent applications

Water and contaminants moving through the vadose zone are often subject to a large number of simultaneous physical and chemical nonequilibrium processes. Traditional modeling tools for describing flow and transport in soils either do not consider nonequilibrium processes at all, or consider them only separately. By contrast, a wide range of nonequilibrium flow and transport modeling approaches are currently available in the latest versions of the HYDRUS software packages. The formulations range from classical models simulating uniform flow and transport, to relatively traditional mobile-immobile water physical and two-site chemical nonequilibrium models, to more complex dual-permeability models that consider both physical and chemical nonequilibrium. In this paper we briefly review recent applications of the HYDRUS models that used these nonequilibrium features to simulate nonequilibrium water flow (water storage in immobile domains and/or preferential water flow in structured soils with macropores and other preferential flow pathways), and transport of solutes (pesticides and other organic compounds) and particles (colloids, bacteria and viruses) in the vadose zone.