Numerical Simulation of Soil Water–Salt Dynamics and Agricultural Production in Reclaiming Coastal Areas Using Subsurface Pipe Drainage

Round 1

Reviewer 1 Report

Dear Authors,

This manuscript assessed the efficiency of subsurface pipe drainage to manage soil salinity from shallow groundwater in the coastal area of Eastern China using combined HYDRUS and AquaCrop models. Although this study is from a specific region of China, this research can be replicated or applied in other coastal areas to evaluate the efficiency of subsurface pipe drainage. Therefore, this research has practical implications for managing soil salinity in coastal areas and the effects of drainage on crop production under soil salinity conditions.

However, I have some major suggestions/comments on the abstract and conclusion section. Also, I have suggested a statistical test that can improve the quality of the presentation of this research. Moreover, some minor things need to be addressed before the publication of this manuscript. I have included my specific comments below and highlighted them in the attached pdf.

Best regards,

Specific comments/suggestions.

Lines 15-27: This highlighted portion (lines 15-27) of the abstract should include some of the highlighted and specified results (with data) obtained from this manuscript.

I suggest including some of the highlighted and critical results obtained in this study in the abstract. Please re-write the highlighted portion of the abstract to represent this research better. 

Lines 71-76: This is a very long sentence and difficult to understand. Re-write for clarity.

Lines 110-116: Some additional information about the overall soil types, physiography/surficial geology, including the topography of the landscapes, shallow groundwater, and land use, including vegetation of the area, is useful in this regard.

Line 129: Check for the chemical formula all over the manuscript and correct them.

Line 142: Check for the unit throughout the manuscript and correct them.

Line 145: How? Provide short details with reference.

Line 462: Provide an abbreviation of ND at the end of the table. All tables and figures should be stand-alone and self-descriptive.

Line 496-500: This figure contains very useful information regarding the efficiency of subsurface pipe drainage. Also, the authors analyzed the data and the efficiency in terms of a percent increased or decreased. However, my question and concern, re: is there any statistical analysis such as analysis of variance (ANOVA) or any other test of significance has been done for this?

In my opinion, the statistical analysis of this data can validate these results more effectively than presented. Therefore, I suggest a simple stat on this data and discussing it in this manuscript for more acceptability to the scientific community. Also, include the test statistics procedures followed in the materials and methods section.

Line 524-533: The conclusion section is bigger and includes some unnecessary sentences that could be avoided—for example, the highlighted text (lines 525-532).

I suggest avoiding these descriptive and repetitive sentences. Rather focus on the results obtained and the implication of those results with some future recommendations.

Re-write the conclusion section in a concise form.

Line 538: The highlighted text is not necessary

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

In this study, a two-dimensional field-scale flow domain with a series of seepage boundary open holes was established to simulate drainpipes using the soil hydraulic model, HYDRUS. The summary section serves its purpose as a thumbnail image of the article. The introductory section fulfills its purpose. The methodology section fulfills its purpose and is specific enough for replication. The results and discussion section is well elaborated and based on the statistical results obtained, there are only some minor problems and comments for some tables and figures. Comments and suggestions should be set out below:

- L71-76. Watch out for overly long sentences, revise throughout the text.

- L76-81. Idem.

- L142. There is a unit without formatting.

- Table 1. The terms used in the table should be defined as captions.

- Figure 5 and 6. Why not put the parameters used to evaluate the models in the figure?

- L439, 502. There was no acronym for this term subsurface pipe drainage?

- L525-537. This whole paragraph is superfluous, I recommend deleting it.

- L538-544. Same comment as above.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

The manuscript is well constructed, but it needs to be improved in several segments as well in English grammar and style intensively.

Abstract is not well constructed, it needs to include more specific, i.e. obtained results from the study. Also, please follow the next instructions:

Purpose: This should be a clear and concise statement of the research question or problem being addressed in the study.

Methods: This should provide a brief overview of the research design, participants, procedures, and data analysis methods used in the study.

Results: This should summarize the key findings of the study, including any statistical analyses and results.

Conclusions should present the main conclusions and implications of the study, and state how the results contribute to the field or suggest directions for future research.

Line 8 change hendle to manage.

Introduction

This section is need to be extended, and make it more clear and concise. You can follow the next instructions:

Background information: This should provide a general overview of the research topic and its significance, highlighting the key concepts and any relevant prior research.

Problem statement: This should clearly state the research question or problem being addressed in the study, and explain why it is important and relevant.

Research objectives or hypotheses: This should spell out the specific aims or objectives of the study, or the hypotheses being tested.

Significance: This should explain how the research contributes to the field and what new knowledge or insights it will provide.

Preview of the study: This should give a brief overview of the methods and design of the study, and what readers can expect to learn from the paper.

Finally, please explain the novelty of your study.

In Mat & Meth. this section should be shortened and some information about models description are not needed. In addition, more details are needed about pedological conditions, ie. classify the soil you tested by some of reference soil classification, please see below suggested reference. And statistical analyse that have been applied (there are some discrapancies in presented results and current methodology). In the abstract was wrongly presented that in the 30-year period plant production was monitored with underground salinity, which is not true and can only be seen in the description of the methodology lines 110-115. This part of the study is the most critical and needs to be adjusted and clarified. Why the authors did not include some other crop for modelling ?

In addition, the authors also state that the sampling plots were 2x2 m, and further state that they took only 5 wheat plants from them. This is too small a number of plants for such a large area. This needs to be clarified.

Lines 153-155 this need to be clarify, usually for enzymatic acitvities fresh plant materials are fastly preserved – shocked in some of organic solution or liquid N. Period of 30 min is not appropriate for this.

 Discussion is very poor and needs to be extended with some similar and recent studies, please see bellow some suggested references.

https://www.isric.org/explore/wrb#:~:text=The%20World%20Reference%20Base%20(WRB,Unesco%2C%201971%2D1981).

https://doi.org/10.1016/j.catena.2021.105987

https://doi.org/10.3390/agronomy12010033

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

The authors study the problem of coastal reclamation, where salinization due to groundwater is of particular concern. They develop a combination of two models to study the effects of various drainage distances, over several years, and under various climatic conditions and groundwater concentrations.

The problem studied in the paper is important and interesting. However, I have some concerns regarding the results.

1. From the most important figures of the paper (figure 8 and 10), it seems to me that the results for all drainage spacings look similar. Is there any statistical significance between different spacings? The greatest differences in scenarios were for different groundwater salinities and wet-dry years. In lines 459–462 you say that the advantage of small drain spacing would show only with “adequate precipitation or supplemental irrigation”. It seems to me that you have buried the lede here. One can rephrase this conclusion as follows: Drain spacing doesn’t matter if additional water is not supplied from above, either as rain or as irrigation. This would be interesting to read about. Can you simulate supplemental irrigation and see the effects for different spacings?

2. You claim that the water table yielded by Hydrus gives a better prediction of the AquaCrop model. How can we know this? Can you compare these predictions with a scenario where water table IS NOT according to Hydrus?

3. The exact nature of the integration between the two models is not made very clear. My understanding is that Hydrus’ results are inputs for AquaCrop, but not the other way around. The abstract promisses a “combined model”, but I found only two different models loosely connected. Furthermore, do you intend to publish the code and simulations together with the paper?

For these reasons, I would recommend a major revision to this paper.

I wrote below other points of concern.

• Abstract. You mention that the two models, Hydrus and AquaCrop, were “combined”. In reality, the water table from Hydrus is an input for AquaCrop. The abstract gives the reader the impression that a more substantial integration between the models took place.

• Line 32. The authors probably mean “this century”, the 21st century.

• Line 53. The meaning of “processed” is not clear in this sentence, please rephrase.

• Line 55. The meaning of “was leached” is not clear. Maybe “is leached”? How does that sentence connect to the one before? Rephrase please.

• Line 72. “Of” should probably be replaced with “like”.

• Line 196-197. It is not clear what “repetitive calculation” means. Rephrase please.

• Line 200. What does “such values” refer to? Values of what?

• Lines 220–228. These lines are identical to lines 193–201. Change text please.

• Section 3.1.1. What exactly was calibrated in the Hydrus model? Which parameters?

• Section 3.1.2. What exactly was calibrated in the AquaCrop model? Which parameters?

• Lines 432–435. The sentence is super long and confusing. Rephrase please.

• Line 441. Which soil solute concentration? Average over time?

• Lines 457–458. This difference, 10.9% and 12.62% seems quite small. Is this significant to how plants are grown? To soil health? In lines 454–455 you say that the discrepancies increase. With such a small difference, would that always be true? If you ran other 30-year simulations, would this result hold?

• Line 477. It is non linear, but it seems to be linear with one-over-the-distance: Increase distance by four, then solute mass is divided by four. And so on. Solute mass = C/distance, where C is constant. Seeing like this, this is hardly a “non-linear” surprise.

• Lines 477–481. This sentence is confusing and hard to understand. Please rephrase.

• Line 485. “for different” what?

• Lines 504–507. From the graph, the results claimed don’t seem statistically significant.

• Section 3.2.2. The box plots in Figure 10 don’t seem to show any statistical significance between different spacings. Can you quantify this, in order to support the claims in this subsection?

• Logically, the No-Drainage case should be placed to the right of the 40-m spacing, and not to the left of the 10-m spacing. No drainage is like taking spacing to infinity, so it makes sense if throughout the paper it was shown to the right of 40-m.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Dear Authors,

Thank you for carefully revising the manuscript as per the comments.

Best regards,

Author Response

Thanks very much for taking your time to review this manuscript. We really appreciate all your generous comments and suggestions!

Reviewer 3 Report

the authors have addresed most of the requested and suggested corrections

Author Response

Thanks very much for taking your time to review this manuscript. We really appreciate all your generous comments and suggestions! 

Reviewer 4 Report

In my opinion, the latest version of the manuscript has not been sufficiently improved.
The concern I raised in point 1 was not adequately addressed: the error bars in Fig. 10 almost overlap entirely, and one could not say that different spacings yield substantially different results, as suggested by the authors.
Furthermore, the authors say in lines 434--437 that there is a 2.43 g/L average difference between a 10 and 40-meter spacing under severe salinity. From the lowest panel in Fig. 8, I cannot see how this could possibly be the case, since the purple and yellow lines are never so far apart, certainly less than 2.4 according to the y-scale.
I have no further comments beyond what I wrote in the first round.

Author Response

Thanks very much for taking your time to review this manuscript. We really appreciate all your generous comments and suggestions.

Point 1: The error bars in Fig. 10 almost overlap entirely, and one could not say that different spacings yield substantially different results, as suggested by the authors.

Response 1: Thanks for your suggestion. We have rewritten the data descriptions for Fig 10 to clarify the response of GY, WP, and GS to the drain spacings under different groundwater salinity levels and precipitation years.

Point 2: The authors say in lines 434--437 that there is a 2.43 g/L average difference between a 10 and 40-meter spacing under severe salinity. From the lowest panel in Fig. 8, I cannot see how this could possibly be the case, since the purple and yellow lines are never so far apart, certainly less than 2.4 according to the y-scale.

Response 2: Thanks for your question. In Fig. 8, the difference between the 10-m and 40-m drain spacing scenarios under the condition of medium and high groundwater salinity were 0.50 and 0.67 g L^-1, respectively. Sorry about this mistake. For clearer presentation, we have divided Fig. 8 into three separate graphs.