On the Adsorption Mechanism of Humic Substances on Kaolinite and Their Microscopic Structure
Round 1
Reviewer 1 Report
The authors of the manuscript entitled "On the Adsorption Mechanism of Humic Substances on Kaolinite and Their Microscopic Structure" searched to understating soil organic matter (SOM)-clay interactions using classical molecular dynamics (MD) simulations on models of humic substances and kaolinite. The purpose of this paper is interesting and I was very excited when I start to read it. However, some points guide me to not recommend the paper for publication:
1) The paper is too theoretical: I understand that theoretical studies are also important, but in this paper more field studies still are need to support the results founded.
2) The concept of humic substances is not adequate: Here's a big concern, the concept of humic substances doesn’t represent the dynamic of the SOM in the soil, this was showed in this paper: https://www.nature.com/articles/nature16069
3) The paper need to fucus in new approaches of the SOM dynamic as is demonstrated in https://www.nature.com/articles/s41561-020-0612-3
This is not a big point, but I missed the main results founded by the study in the Abstract.
Author Response
Point 1: The paper is too theoretical: I understand that theoretical studies are also important, but in this paper more field studies still are need to support the results founded.
Response 1: We thank the reviewer for the comment and understand the concern. We are aware that our work is theoretical, however the results have been shown to be consistent with both experimental measurements and other simulations. References that support our work can be found in lines 52-62 and lines 379-392. We do not quite see how the need for more field studies invalidates theoretical work. Moreover, our theoretical findings on stabilization of SOM-mineral aggregates can be helpful for experimental studies both at lab and field scales.
Point 2: The concept of humic substances is not adequate: Here's a big concern, the concept of humic substances doesn’t represent the dynamic of the SOM in the soil, this was showed in this paper: https://www.nature.com/articles/nature16069
Response 2: We agree that the concept of humic substances is currently under great debate. However, we believe that its use is justified as a well-studied model. The thermodynamic properties of the LHA model used reconcile long-standing concepts with new hypotheses on SOM. See lines 371-374.
Point 3: The paper need to fucus in new approaches of the SOM dynamic as is demonstrated in https://www.nature.com/articles/s41561-020-0612-3
Response 3: We thank the reviewer for the comment. The lack of a generalized SOM sample to study the molecular interactions leads us to choose a model. The models generated by the VSOMM are in agreement with the molecular diversity concept defined in the paper suggested by the reviewer. Similarly, our results justify the persistence of organic carbon in soil in lines 374-378 and in lines 489-492.
This is not a big point, but I missed the main results founded by the study in the Abstract.
Response 4: The main results were added to the abstract in lines 23 and 26.
Reviewer 2 Report
I‘ve finished a review of the paper minerals-1402612 titled “On the adsorption mechanism of humic substances on kaolinite and their microscopic structure” and written by the authors: Edgar Galicia-Andrés, Chris Oostenbrink, Martin H. Gerzabek, Daniel Tunega.
In presented paper authors focuses on the interactions between humic substances (HSs) and kaolinite mineral as typical representants of SOM and soil minerals. By performing classical molecular dynamics (MD) simulations on models of HSs and kaolinite authors demonstrate how two dominant but chemically different kaolinite surfaces affect the stability of HSs microaggregates. The authors explain possible mechanisms of the formation of stable SOM-clay aggregates and show how a polarized environment affects the electrostatic interactions, stabilizing the microscopic structure of SOM-mineral aggregates.
In general, the paper is interesting for reading and well written. The authors made enough experiments and the results are well explained. The English is correct. The paper is fully in line with the topic of the journal. The aim of the study is very actual. I suggest the acceptance in the present form.
Only one suggestion to authors is to mark all Figures as a), b), c) not left, right, up, down.
Best regards
Author Response
In general, the paper is interesting for reading and well written. The authors made enough experiments and the results are well explained. The English is correct. The paper is fully in line with the topic of the journal. The aim of the study is very actual. I suggest the acceptance in the present form.
Response 1: We thank the reviewer for the time invested on the revision of our manuscript.
Only one suggestion to authors is to mark all Figures as a), b), c) not left, right, up, down.
Response 2: All figures were marked properly and captions modified as suggested by the reviewer.
Reviewer 3 Report
Dear Authors,
I think this manuscript from the scientific side is quite well written. The authors also undertake the description of an interesting topic. However, I believe that the authors should highlight some utilitarian features of their scientific activities in the manuscript. The methodology and the charts made also require a slight improvement.
Detailed comments below:
Line 105: A utilitarian description of your research is missing at this point. Write down why your research is so important. Who can use them? Will the results of your research be important e.g. for fertilizer producers? For the chemical industry? Or maybe for farmers? Only for scientists? Or maybe it is important information for people involved in the production of innovative materials? Try to answer the above questions. That's what's missing here.
Line 116: Software, test equipment, should be described as follows: name / model: manufacturer, country, city. Materials purchased for research are also described in a similar way. You will review the entire methodology in this regard.
Fig. 1. In the remaining figures add the notation c, d, e. Also adapt the description under the picture and in the text. I understand that these additional charts are an integral part of the charts, but the lack of markings is a bit vague. Adjust the rest of the charts as well.
Fig. 2: There are units on the axes but no description of the axis. This needs to be corrected.
Fig. 3. Same as above. Add the axis designations. As there are two separate charts in the figure, they should be marked with a, b. Also add an appropriate description under the figure and in the text.
Fig. 4. Add descriptions for the axes.
Fig. 5: Add a description on the x axis.
Fig. 6. No gray line marking. Other remarks as above.
Line 478: This conclusion seems good, but this information is missing in the introduction. This should be completed.
Author Response
Point 1: Line 105: A utilitarian description of your research is missing at this point. Write down why your research is so important. Who can use them? Will the results of your research be important e.g. for fertilizer producers? For the chemical industry? Or maybe for farmers? Only for scientists? Or maybe it is important information for people involved in the production of innovative materials? Try to answer the above questions. That's what's missing here.
Response 1: We thank the reviewer for the recommendation. We highlighted the target audience for our work as well as its relevance in lines 115-121.
Point 2: Line 116: Software, test equipment, should be described as follows: name / model: manufacturer, country, city. Materials purchased for research are also described in a similar way. You will review the entire methodology in this regard.
Response 2: in section “2.2 Simulation settings”, we cited the used software (GROMACS) in a standard way as it is done in many theoretical papers. We also describe all technical details of simulations to reproduce the simulations (timestep, temperature, pressure, …). It is not a common praxis to describe all technical details of used hardware; although it is referred in the acknowledgement as computer sources of university computer centers, as it is in our case where we acknowledge the Vienna Scientific Computer cluster vsc3.
Point 3: Fig. 1. In the remaining figures add the notation c, d, e. Also adapt the description under the picture and in the text. I understand that these additional charts are an integral part of the charts, but the lack of markings is a bit vague. Adjust the rest of the charts as well.
Response 3: We thank the reviewer for the suggestion. Figure 1 was marked properly and the caption modified as suggested by the reviewer.
Point 4: Fig. 2: There are units on the axes but no description of the axis. This needs to be corrected.
Response 4:The corresponding symbols of the axes were added in the caption.
Point 5: Fig. 3. Same as above. Add the axis designations. As there are two separate charts in the figure, they should be marked with a, b. Also add an appropriate description under the figure and in the text.
Response 5: Figure 3 was marked properly and the caption modified as suggested by the reviewer.
Point 6: Fig. 4. Add descriptions for the axes.
Response 6: The corresponding symbols of the axes were added in the caption.
Point 7: Fig. 5: Add a description on the x axis.
Response 7: The corresponding symbols of the axes were added in the caption.
Point 8: Fig. 6. No gray line marking. Other remarks as above.
Response 8: Figure 6 was marked properly and caption modified as suggested by the reviewer. The gray line was changed to red for clarity.
Point 9: Line 478: This conclusion seems good, but this information is missing in the introduction. This should be completed.
Response 9: We thank the reviewer for the advice. We added the missing information in lines 107-112.
Round 2
Reviewer 1 Report
The authors have carefully addresses the comments, therefore, the manuscript can now be accepted for publication.
