EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

How heterogenous distributions of hydrophobicity affects the capillary rise in soil

Jonas Bentz1, Eva Kroener1, Ravi Patel2, and Adrian Haupenthal
Jonas Bentz et al.
  • 1Universität Koblenz-Landau, Institut für Umweltwissenschaften, Group of Geophysics, Landau, Germany (
  • 2Paul Scherrer Institut

A central component of the rhizosphere is root mucilage, a hydrogel exuded by plants that dramatically alters chemical and physical properties of the soil. It is characterized by its large water holding capacity and is hydrophilic or hydrophobic depending on its hydration status: when swollen, mucilage is hydrophilic but becomes hydrophobic when dry, forming local hydrophobic spots on the surface of soil particles. The morphology of these hydrophobic regions formed by dried mucilage is affected by the type of mucilage and microorganisms and can vary from isolated local spots, to networks spanning across larger areas of the soil particle surface. However, until now the understanding on how this heterogeneous distribution and its morphology affect water retention and water repellency in soil is limited.

Therefore, the goal of this study is to investigate the impact of the spatially heterogeneous interfacial tension distributions on the capillary rise in soil. We utilize a two phase flow model based on the Lattice-Boltzmann to numerically simulate capillary rise between parallel slides having a heterogeneous distribution of interfacial tension during imbibition and drainage.

The simulations allow us to quantitatively evaluate how heterogeneous micro-scale distributions of interfacial tension affect the macro-scale water retention behavior. This we could approximately explain with three hypotheses: The equilibrium capillary rise volume (i) is a measure for the hydrophilicity of a field, (ii) capillary rise is affected by the standard deviation of the interfacial tension field, (iii) hysteresis is induced by the heterogeneous field and depends on the correlation length of the patterns.

In future, simulations will be extended also to the geometry of real soil.

How to cite: Bentz, J., Kroener, E., Patel, R., and Haupenthal, A.: How heterogenous distributions of hydrophobicity affects the capillary rise in soil , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13701,, 2020

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Presentation version 1 – uploaded on 28 Apr 2020
  • CC1: Comment on EGU2020-13701, Sarah Garré, 04 May 2020

    Dear Jonas, thanks for this nice presentation. It is indeed interesting to understand how these root exudates are changing larger scale processes. However, from what I read and heard before, I thought mucilage was degrading very fast. Would you have to change your way of modelling the impact of mucilage to take this into account or doesn't it affect your results.

    • AC1: Reply to CC1, Jonas Bentz, 05 May 2020

      Dear Sarah,
      thank you for your good question. We have the same open question. The simulations presented are intended as a first step to assess the influence of heterogeneous distribution of hydrophobicity on the capillary rise and to validate the program. After that, I could imagine to investigate temporally changeable distributions of the degradation of mucilage (however, I currently lack the information on how this happens and what effect it has on hydrophobicity).