Measurement on Diffusion Coefficients and Isotope Fractionation Factors by a Through-Diffusion Experiment

Hasegawa, Takuma; Nakata, Kotaro; Gwynne, Rhys

doi:10.3390/min11020208

Cited by 5 publications

(5 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…smallest pore in high-tension area). We do not distinguish between specific diffusion coefficients for δ 2 H and δ 18 O, as Hasegawa et al (2021) recently found generally equal diffusion properties of both isotopes in artificial and natural porous media.…”

Section: Simulation With the Dipmi Approachmentioning

confidence: 78%

See 1 more Smart Citation

A Lagrangian model framework for the simulation of fluid flow and solute transport in soils

Sternagel

Loritz

Zehe

2023

Preprint

View full text Add to dashboard Cite

We develop an integrated model framework for the simulation of a multitude of soil hydrological processes, such as (reactive) solute transport together with (preferential) water flow and diffusive mixing on the pore scale. This framework is called the Lagrangian Soil Water and Solute Transport (LAST) Model. It bases on a new theoretical concept and should serve as alternative to the common theories of the Darcy-Richards equation and the advection-dispersion-equation (ADE), which have limitations under more natural conditions. In the LAST-Model framework, soil water is represented by discrete water particles of constant mass. The model applies a Lagrangian perspective on the trajectories of particles through a partially saturated soil domain. Particle displacements along the trajectories are calculated by a non-linear, space domain random walk that combines physics and stochastic. We gradually extend the scope of the LAST-Model framework by additional routines. We implement routines for solute transport and preferential flow. Water particles are assigned by a solute mass and in this way, solutes are distributed together with the displacement of water particles. For preferential flow, a structural macropore domain is implemented as a second flow domain. Particles can infiltrate and travel purely by gravity in the macropore domain, independent from capillary-flow conditions in the soil matrix. As a result, they can bypass the bulk water fractions in the soil matrix before re-infiltrating the matrix and accumulating in greater depths. We modify the solute transport routine to allow for the simulation of the transport of reactive substances. Specific routines for sorption and degradation processes are implemented. Sorption is represented by an explicit solute mass transfer between water particles and the solid phase by means of non-linear Freundlich isotherms, and driven by a concentration gradient. Adsorbed solutes are then assumed to be microbially degraded following first-order decay kinetics. We introduce the diffusive pore mixing (DIPMI) approach as additional routine for the simulation of pore-size-dependent diffusive mixing of water and solutes over the pore space. This approach should produce more reliable descriptions of frequently observed (imperfect) mixing behaviours, in contrast to the common assumption of averaging concentrations over all pore sizes in a single time step. Each model extension is tested by simulations of field and laboratory experiments as well as sensitivity analyses. Simulation results are compared against observed data and results of a benchmark model that uses the Darcy-Richards theory and the ADE. The most important findings of the studies can be summarized as: <ul> <li>The structural macropore domain is key for a successful representation of preferential water flow and (reactive) solute transport. In heterogeneous soils, LAST simulations match better the observed redistribution and depth-accumulation of solutes compared to simulations with the Darcy-Richards + ADE model.</li> <li>Imperfect, diffusive mixing on the pore scale has a significant influence on macroscopic leaching behaviours and chemical/isotopic compositions of soil water fractions.</li> <li>The particle-based approach of the LAST-Model framework is a promising tool for further soil- and ecohydrological application fields.</li> </ul>

show abstract

Section: Simulation With the Dipmi Approachmentioning

confidence: 78%

“…The latter situation is the case when simulating the diffusive spreading of common solute tracers (e.g. bromide or chloride) in porous media, because diffusion coefficients of the dissolved solute molecules are usually smaller compared to those of pure water or stable water isotopes (Hasegawa et al, 2021).…”

Section: Analysis Of the Virtual Experimentsmentioning

confidence: 99%

A Lagrangian model framework for the simulation of fluid flow and solute transport in soils

Sternagel

Loritz

Zehe

2023

Preprint

View full text Add to dashboard Cite

show abstract

“…Pore-size-distributed D values thus range from ~ 1.9 • 10 -9 m² s -1 in bin 1 (= largest pore in low-tension area) to ~ 9.0 • 10 -12 m² s -1 in bin 200 (= smallest pore in high-tension area). We do not distinguish between specific diffusion coefficients for δ²H and δ 18 O, as Hasegawa et al (2021) recently found generally equal diffusion properties of both isotopes in artificial and natural porous media. 10…”

Section: Simulation With the Dipmi Approach 25mentioning

confidence: 85%

Stepping beyond perfectly mixed conditions in soil hydrological modelling using a Lagrangian approach

Sternagel

Loritz

Berkowitz

et al. 2021

Preprint

View full text Add to dashboard Cite

Abstract. A recent experiment of Bowers et al. (2020) revealed that diffusive mixing of water isotopes (δ2H, δ18O) over a fully saturated soil sample of a few centimetres in length required several days to equilibrate completely. In this study, we present an approach to simulate such time-delayed diffusive mixing processes on the pore scale beyond instantaneously and perfectly mixed conditions. The diffusive pore mixing (DIPMI) approach is based on a Lagrangian perspective on water particles moving by diffusion over the pore space of a soil volume and carrying concentrations of solutes or isotopes. The idea of DIPMI is to account for the self-diffusion of water particles across a characteristic length scale of the pore space using pore-size-dependent diffusion coefficients. The model parameters can be derived from the soil-specific water retention curve and no further calibration is needed. We test our DIPMI approach by simulating diffusive mixing of water isotopes over the pore space of a saturated soil volume using the experimental data of Bowers et al. (2020). Simulation results show the feasibility of the DIPMI approach to reproduce measured mixing times and concentrations of isotopes at different tensions over the pore space. This result corroborates the finding that diffusive mixing in soils depends on the pore size distribution and the specific soil water retention properties. Additionally, we perform a virtual experiment with the DIPMI approach by simulating mixing and leaching processes of a solute in a vertical, saturated soil column and comparing results against simulations with the common perfect-mixing assumption. Results of this virtual experiment reveal that the frequently observed steep rise and long tailing of breakthrough curves, which are typically associated with non-uniform transport in heterogeneous soils, may also occur in homogeneous media as a result of imperfect subscale mixing in a macroscopically homogeneous soil matrix.

show abstract

“…In the investigated Wakkanai formation, natural groundwater flow has been shown to be extremely slow, with a component of palaeo-seawater still preserved in the porewater 50 . In the matrix of the Wakkanai formation, the transport of solutes will be diffusion-dominated 51 . The distance over which Ca may be transported by diffusion can be estimated using the following equation 52 :…”

mentioning

confidence: 99%

“…In the matrix of the Wakkanai formation D = 10 −10 m 2 /s (based on through-diffusion experiments using non-sorbing tracers 51 ). Equation ( 1) then gives a maximum distance of Ca diffusion through the matrix of about 10 cm over 17 months.…”

mentioning

confidence: 99%

Post-earthquake rapid resealing of bedrock flow-paths by concretion-forming resin

Yoshida,

Yamamoto,

Asahara

et al. 2024

Commun Eng

View full text Add to dashboard Cite

Many underground activities may require reducing or preventing fluid flows through bedrock, e.g., sealing of site investigation boreholes, underground tunneling, hydrocarbon field abandonment, and nuclear waste disposal. Cementitious materials such as grout are commonly used for bedrock flow-path sealing, however conventionally used these materials unavoidably undergo physical and chemical degradation, therefore potentially decreasing seal durability. Here, we report a more durable sealing method for concretion-forming resin developed by learning from natural calcite, CaCO3, and spheroidal concretion formation. The method was tested by sealing flow paths next to a tunnel in an underground research laboratory at 350 m depth, in Hokkaido, Japan. The flow paths were initially sealed rapidly, then resealed after disturbance by repeated earthquakes with foci below the underground research laboratory at depths of 2–7 km and maximum magnitude Mw 5.4. The treated rock mass rapidly recovered its very low natural permeability, demonstrating robust self-sealing and healing.

show abstract

Measurement on Diffusion Coefficients and Isotope Fractionation Factors by a Through-Diffusion Experiment

Cited by 5 publications

References 20 publications

A Lagrangian model framework for the simulation of fluid flow and solute transport in soils

A Lagrangian model framework for the simulation of fluid flow and solute transport in soils

Stepping beyond perfectly mixed conditions in soil hydrological modelling using a Lagrangian approach

Post-earthquake rapid resealing of bedrock flow-paths by concretion-forming resin

Contact Info

Product

Resources

About