Zhang et al. (2025) Quantifying the contributions of isolated and connected pores to soil permeability in alpine meadow soils

Identification

• Journal: Journal of Hydrology Regional Studies
• Year: 2025
• Date: 2025-11-20
• Authors: Yuhang Zhang, Baisha Weng, Denghua Yan, Yun Pan
• DOI: 10.1016/j.ejrh.2025.102925

Research Groups

• College of Resource Environment and Tourism, Capital Normal University, Beijing 100048, China
• State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China
• Yinshanbeilu Grassland Eco-hydrology National Observation and Research Station, China Institute of Water Resources and Hydropower Research, Beijing 100038, China

Short Summary

This study developed the DHC-FVAM model to quantify the distinct contributions of connected and isolated pores to soil permeability in alpine meadow soils during frozen soil thawing. It found that connected pores dominate water transport, with their contribution significantly increasing as thawing progresses due to enhanced connectivity and pore transformation.

Objective

• To obtain and quantitatively characterize the structural parameters of isolated and connected pores in alpine meadow soils during critical periods of frozen soil thawing.
• To analyze the evolution of pore structures in alpine meadow soils as they transition from solid ice to liquid water, and to investigate the mechanisms by which this evolution influences soil water migration, diffusion, and redistribution.
• To conduct numerical simulations of microscale pore structures using the Lattice Boltzmann Method (LBM) or Pore Network Modeling (PNM) to estimate the spatial distribution of soil permeability.
• To quantitatively calculate and compare the relative contributions of isolated and connected pores to the overall soil permeability at different stages of frozen soil thawing, and to simulate the three-dimensional distribution of water flow velocities.

Study Configuration

• Spatial Scale: Typical alpine meadow soils on the central Qinghai-Tibet Plateau, China. Sampling sites included Xiaotanggula Mountain (32°33′16″N, 91°49′26″E, elevation 5050 m) and Xiangmao Township (31°3′51″N, 91°41′33″E, elevation 4732 m). Soil samples were collected from 0 to 50 cm depth, with a central region of interest (ROI) of 2.5 cm × 2.5 cm × 5.0 cm extracted for analysis.
• Temporal Scale: Observations and simulations focused on the frozen soil thawing stage, specifically distinguishing between the initial thawing stage (soil temperature -0.5 °C < T ≤ 0 °C, ≥30% soil profile volume below 0 °C, ice content ≥50%) and the complete thawing stage (continuous soil temperature > 0 °C for ≥48 h, ice content ≤5%).

Methodology and Data

• Models used:
  • DHC-FVAM (Dual-Porosity Hydraulic Conductivity–Flow Velocity in Alpine Meadows) model, integrating X-ray CT imaging with numerical simulations.
  • Lattice Boltzmann Method (LBM) for simulating fluid flow in isolated pores and overall flow.
  • Pore Network Modeling (PNM) for constructing and simulating flow in connected pore networks.
  • Multiple Linear Regression (MLR) for analyzing the relationship between pore parameters and permeability.
• Data sources:
  • X-ray Computed Tomography (X-CT) (Phoenix/Nanotom, Germany) for 3D pore structure characterization (25 µm pixel resolution, 1500 slices, 1000 × 1000 pixels).
  • Field observations using EM50 sensors for soil temperature and TDR-315 sensors for liquid water content.
  • Laboratory analysis of soil properties: sandy loam texture (70–80% sand, 15–20% silt, 5–10% clay), 5–10% organic matter content, 10–15% gravel volume ratio, pH 6.5–7.5, and bulk density 1200–1400 kg/m³.
  • Validation data from in situ soil permeability measurements reported in previous studies from the Qinghai-Tibet Plateau.

Main Results

• Permeability Contributions: During the initial thawing stage, connected pores contributed 62.83 % more to total soil permeability than isolated pores, with values of (1.53 ± 1.13) × 10⁻¹⁰ m/s and (8.87 ± 0.30) × 10⁻¹¹ m/s, respectively. Upon complete thawing, this contribution rose to 83.74 % greater, with permeability values of (2.20 ± 1.17) × 10⁻¹⁰ m/s for connected pores and (8.67 ± 0.30) × 10⁻¹¹ m/s for isolated pores.
• Pore Structure Evolution: As frozen soil transitioned from initial to complete thawing, the volume fraction of connected pores increased by 10.49 %, and connectivity rose by 155 %, driving a nonlinear permeability surge. Concurrently, the permeability of connected pores increased by approximately 43.35 %, while the permeability of isolated pores decreased by approximately 1.61 %. The volume fraction of isolated pores decreased by approximately 59.19 %.
• Mechanism: The observed permeability surge is attributed to the freeze-thaw-induced coalescence of isolated pores into connected pores, where the increase in connectivity enhances flow path efficiency and reduces tortuosity, thereby amplifying soil water transport capacity.
• Model Accuracy: The DHC-FVAM model demonstrated high accuracy, with an R² value of 0.859 and an RMSE of 1.83 × 10⁻⁶ m/s when compared to in situ soil permeability data.

Contributions

• Developed and applied the DHC-FVAM model, a novel quantitative framework that integrates X-ray CT imaging with coupled Lattice Boltzmann Method (LBM) and Pore Network Modeling (PNM) to precisely separate and quantify the structural parameters and permeability contributions of isolated and connected pores in alpine meadow soils.
• Explicitly established the hydraulic response chain linking freeze-thaw-driven pore type transformation with enhanced structural connectivity, providing a microscale mechanistic explanation for the nonlinear permeability surge during thawing.
• Filled existing research gaps by offering a novel quantitative perspective for understanding hydrological processes in alpine ecosystems under climate change, particularly regarding pore type separation and dynamic response chain analysis.
• Provided critical microscale evidence and data for subsequent ecohydrological modeling and offered scientific guidance for local soil moisture management and ecological restoration strategies in alpine regions, especially in the context of extreme climate events.

Funding

• National Key R&D Program of China (No. 2022YFC3080300)
• Research Fund of the State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin (No. SKL2024YJTS03)
• IWHR Research & Development Support Program (No. MK0145B022021)
• Science and Technology Support Project for Ordos National Sustainable Development Agenda Innovation Demonstration Zone (No. KCX2024013)

Citation

@article{Zhang2025Quantifying,
  author = {Zhang, Yuhang and Weng, Baisha and Yan, Denghua and Pan, Yun},
  title = {Quantifying the contributions of isolated and connected pores to soil permeability in alpine meadow soils},
  journal = {Journal of Hydrology Regional Studies},
  year = {2025},
  doi = {10.1016/j.ejrh.2025.102925},
  url = {https://doi.org/10.1016/j.ejrh.2025.102925}
}