Preprints
https://doi.org/10.5194/hess-2021-582
https://doi.org/10.5194/hess-2021-582

  03 Dec 2021

03 Dec 2021

Review status: this preprint is currently under review for the journal HESS.

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

Alexander Sternagel1, Ralf Loritz1, Brian Berkowitz2, and Erwin Zehe1 Alexander Sternagel et al.
  • 1Karlsruhe Institute of Technology (KIT), Institute of Water Resources and River Basin Management, Hydrology, Germany
  • 2Department of Earth and Planetary Sciences, Weizmann Institute of Science, Israel

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.

Alexander Sternagel et al.

Status: open (until 24 Feb 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on hess-2021-582', Anonymous Referee #1, 20 Jan 2022 reply

Alexander Sternagel et al.

Alexander Sternagel et al.

Viewed

Total article views: 368 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
298 67 3 368 0 6
  • HTML: 298
  • PDF: 67
  • XML: 3
  • Total: 368
  • BibTeX: 0
  • EndNote: 6
Views and downloads (calculated since 03 Dec 2021)
Cumulative views and downloads (calculated since 03 Dec 2021)

Viewed (geographical distribution)

Total article views: 361 (including HTML, PDF, and XML) Thereof 361 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 20 Jan 2022
Download
Short summary
We present a (physically-based) Lagrangian approach to simulate diffusive mixing processes on the pore scale beyond perfectly mixed conditions. Results show the feasibility of the approach to reproduce measured mixing times and concentrations of isotopes over pore sizes, and that typical shapes of breakthrough curves (normally associated with non-uniform transport in heterogeneous soils) may also occur as a result of imperfect subscale mixing in a macroscopically homogeneous soil matrix.