the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Jul 2026
Loess Soil Structural Changes Induced by Bio- and Synthetic Polymer Stabilizers: Geoelectrical Insights
Abstract. Traditional assessments of soil aggregate stability rely on destructive, ex situ protocols that fail to capture the continuous evolution of soil architecture. This study evaluates the divergent stabilization trajectories induced by chia seed mucilage (CSM) and anionic polyacrylamide (A-PAM) in loess soil over a 20-day incubation. By integrating Spectral Induced Polarization (SIP) with microbial respiration and tracer breakthrough experiments, we track the transition from initial aggregation to long-term structural outcomes. Results demonstrate that CSM-induced stabilization is strictly transient; rapid microbial degradation of the biopolymer results in progressive reversal of the induced structural modifications and a reversion to baseline hydraulic behaviour. In contrast, A-PAM provides persistent physicochemical reinforcement, establishing a dual-porosity regime characterized by immobile water domains and preferential flow pathways. SIP signatures effectively resolved these dynamics: high-frequency shifts in quadrature conductivity (σ'' ) provided geoelectrical evidence of micro-aggregate formation, while the development of a 'conductive reservoir' in in-phase conductivity (σ' ) identified hydraulically isolated ion accumulation. These findings establish SIP as a high-resolution, non-invasive proxy for monitoring the interplay between biochemical persistence and the mechanical stabilization of soil structure.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-3473', Anonymous Referee #1, 15 Aug 2026
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RC2: 'Comment on egusphere-2026-3473', Anonymous Referee #2, 25 Aug 2026
Review of "Loess Soil Structural Changes Induced by Bio- and Synthetic Polymer Stabilizers: Geoelectrical Insights" by Sonya Sara Altzitser, Yael Golda Mishael, Nimrod Schwartz
The present manuscript deals the geoelectrical monitoring of structural change induced by different treatments. It is intended for publication in SOIL. The study is of interest for the soil science community as soil structures influence many important processes. The manuscript is well written and, to the best of my knowledge, is using state-of-the-art experimental set-up and procedure. However, I do have some comments regarding the discussion and petrophysical interpretations that I develop in the detail list below.
Introduction : Given the topic of the paper, I think that the authors need to develop the literature of structural change monitoring using geophysical tools (e.g., Romero-Ruiz et al., 2018, 2022).
Section 2.2: Given the influence of partial saturation on SIP signals, could the author provide more detail their sample saturation degree in addition to the water content. My understanding is that it was fully water saturated but it would clearer by stating it (at the moment it is only implied in line 169).
Section 3.1: the physical limitations to microbial activity (i.e., soil respiration) and their relationship to aggregate (i.e., microstructural properties) through diffusive processes are discussed in the literature (e.g., Nuna, 2017, Fülöp et al., 2026).
Figure 5: I understand the use of fmax to plot the imaginary part of the conductivity, but I’m afraid that it hides potential information from the time series. What about the variation of f_max with time (since f_max could be related to aggregate size as discussed in lines 419-428) ? Given the heterogeneity in initial conductivities and the influence of the real part of the conductivity on the imaginary part, how is the phase evolving? Would it be possible to plot the pore water electrical conductivity as a function of time?
Lines 313-315: would the higher mucilage explain the higher respiration rate in figure 2?
Equation 4: Accounting for aggregate structures in the soil samples would required more refined petrophysical models (e.g., Day-Lewis et al., 2017; Romero-Ruiz et al., 2022). But then since equation 4 is not really used in the paper, I’m wondering if it should be removed and the conductivity variations only discuss in the text citing the literature.
References:
Day‐Lewis, F. D., Linde, N., Haggerty, R., Singha, K., & Briggs, M. A. (2017). Pore network modeling of the electrical signature of solute transport in dual‐domain media. Geophysical Research Letters, 44(10), 4908-4916.
Fülöp, O., Nunan, N., Gueye, M., & Jougnot, D. (2026). Electrical conductivity measurements as proxies for diffusion-limited microbial activity in soils under controlled laboratory conditions. Soil, 12(1), 703-714.
Nunan, N. (2017). The microbial habitat in soil: Scale, heterogeneity and functional consequences. Journal of Plant Nutrition and Soil Science, 180(4), 425-429.
Romero‐Ruiz, A., Linde, N., Keller, T., & Or, D. (2018). A review of geophysical methods for soil structure characterization. Reviews of Geophysics, 56(4), 672-697.
Romero‐Ruiz, A., Linde, N., Baron, L., Breitenstein, D., Keller, T., & Or, D. (2022). Lasting effects of soil compaction on soil water regime confirmed by geoelectrical monitoring. Water Resources Research, 58(2), e2021WR030696.Citation: https://doi.org/10.5194/egusphere-2026-3473-RC2 -
RC3: 'Comment on egusphere-2026-3473', Anonymous Referee #3, 30 Aug 2026
Altzitser et al. present a study investigating structural changes in loess following the addition of chia seed mucilage and polyacrylamide through measuring aggregate stability, CO2 respiration, tracer breakthroughs, and spectral induced polarization (SIP). The use of SIP is especially interesting as a non-destructive method for monitoring soil change. The manuscript is generally well-written and the experiment includes an interesting combination of methods. However, I generally share the concerns of the other two reviewers and also think that aspects of the experimental design, statistical analysis, and soil characterization require further clarification. Therefore, I believe major revisions are necessary before publication.
Major comments:
1. Interpretation of CO2 measurements
The authors primarily attribute the loss of mucilage-induced stabilization to microbial degradation of the mucilage. The higher CO2 production in the mucilage treatments could indicate increased microbial activity following labile carbon addition, but I do not think it directly demonstrates degradation of the mucilage itself. As the authors also acknowledge, it could be influenced by calcite dissolution. Additionally, the CO2 measurements were made in separate incubations under slightly different physical/hydrological conditions, which could influence microbial activity and degradation. As a result, I think the authors should be a bit more cautious using the respiration measurements to explain structural changes observed in the columns, unless there is additional evidence of degradation available.
2. Statistical analysis and replication
I could not find a description of the statistical analyses used in the manuscript. For example, in Fig 2, significant differences are shown among the treatments but it is not stated which test was used or how pairwise differences were determined. Replication is also unclear for some of the other measurements. Although replication is reported for the CO₂ and tracer experiments, the number of replicate columns used for the SIP measurements is also not clear. I think the manuscript would benefit from a statistical analysis section clearly describing tests used and the number of independent replicates for each part of the experiment.
3. Soil characterization
The description of the soil used seems quite limited considering how much of the discussion relies on mineralogy and chemistry. The soil is described mainly as a sandy clay loam collected from an uncultivated loess site, but later interpretations depend on calcite dissolution, surface conductivity, changes in pore-water chemistry, and mineral surface properties. I think more thorough characterization of the soil would add needed support to these interpretations. At minimum, it would be helpful to report pH, carbonate content, SOC, and particle-size distribution, and ideally CEC if available. If these properties were not measured, I think the authors should acknowledge this limitation and be more cautious in discussion of underlying mechanisms.
Minor comments:
1. Lines 124 and 206–207: There seems to be an inconsistency in the reported CO2 sampling dates. The methods state that samples were collected on days 1, 3, 4, 10, 14, 17, and 20, whereas the results refer to a significant difference on day 7. Please check and correct the sampling dates throughout the manuscript.
2. Lines 140–142: The sand fraction is estimated from the control based on the assumption that no highly stable aggregates are present and is then subtracted from all treatments. I think this assumption should be better justified, particularly since the highly stable fraction is important for the subsequent interpretation. It would also be useful to clarify why the sand fraction was not determined independently.
3. Lines 148–149 and 190–192: It is stated that A-PAMH was excluded from the tracer and SIP experiments because a stable flow could not be maintained due to excessive backpressure and leakage. I think this observation itself is potentially important and should be discussed when generalizing the A-PAML results to A-PAM more broadly.
Citation: https://doi.org/10.5194/egusphere-2026-3473-RC3
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The manuscript addresses an interesting topic and combines aggregate stability, microbial respiration, tracer transport, soil chemistry, and SIP measurements. In my opinion, the manuscript has potentially interesting observations, but the central mechanistic conclusions are insufficiently supported by the experimental evidence. The interpretation of SIP measurements, dual-porosity development, and the proposed conductive reservoir relies substantially on indirect inference. In addition, the limited tracer treatments, short experimental duration, and unresolved influence of soil solution chemistry substantially weaken the study. These are fundamental issues that cannot be adequately addressed through minor or moderate revision. I therefore recommend rejection in its present form.