Research Progress on Nitrogen and Phosphorus Loss in Small Watersheds: A Regional Review

Round 1

Reviewer 1 Report

The manuscript is focused on N and P loss in small watershed and it´s a review paper.The review of research progress in mentioned items summarizes the results from the China experimental works, only 1 watershed is from Canada, and 1 from Japan. From that point of view, it is not a review, it is a regional review.

The review of the N, P loss is focused on several parameters: rainfall amount, rainfall intensity, rainfall duration, and lan use types (agriculture, wetland, grassland, forest, urban). The review analyzed 6 watersheds (tab.1) and 6 waterseds in tab.2.

My findings/comments/recommendations:

1. This is not a review, it is a regional review

2. 6+6 watersheds are too low for the generalized analysis

3. There are no basic hydrological information to presented watersheds such as area, average slope, geology, annual rainfall/runoff information

4. There are no information about the input/output and transformation processes of N and P in watersheds (general description about pathways and processes)

5. The important part of N,P loss are sources (inputs), there are no information related to e.g. N deposition, N sources e.g. from agriculture etc. This was not reviewed.

I strongly recommend to change the title as a regional review and to make a major revision of the manuscript with respect mainly the points 3-5.

Author Response

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Reviewer 2 Report

1.     In Introduction, the authors could clarify their research objective more explicitly. The aim seems to be a comprehensive review of small watershed research, but it is not clearly stated until the very end of the introduction. I suggest repositioning this statement to earlier in the text, and perhaps framing it as a specific research question or goal.

2.     The introduction provides an extensive overview of the historical development of small watershed research, both globally and in China. While this offers valuable context, it may be too detailed for the introduction of a paper focused on N and P loss due to rainfall in small watersheds. If the historical information doesn't directly contribute to understanding the specific problem at hand, it might be condensed or moved to a different section of the paper.

3.     The authors discuss the use of models like the SWAT and SWMM for studying N and P loss in small watersheds. They argue that while these studies have achieved phased results, the findings are fragmented and lack summary. It would be beneficial for the authors to more explicitly connect these previous studies to their own work. Are they addressing gaps left by previous research, building upon the models used in the past, or using a different approach altogether? This could strengthen the argument for the relevance of their own study.

4.     Section 2, In many parts of the text, the results are simply described as increases or decreases, without providing the exact values or percentages to reflect the changes. For instance, in the line "...runoff generated under high rainfall intensities is more susceptible to sediment loss compared to runoff generated under medium and low rainfall intensities," the text could benefit from quantifiable data to support the claim and provide a clear comparison.

5.     Section 2, While there are plenty of examples of different function correlations between rainfall and N and P output, there is no clear analysis on what these differing correlations imply about the overall effect of rainfall on N and P output. For example, the article could discuss why there might be different relationships (exponential, power, logarithmic, etc.) and what implications these different relationships might have.

6.     Section 3, While it provides detailed information on the effects of each type of land use on nitrogen and phosphorus loss, it fails to offer a comparative analysis across these types. Understanding which type of land use results in the highest or lowest loss of nitrogen and phosphorus can provide practical insights for decision-making in land use planning.

7.     Section 4, it states that "the use of mixed fertilizers can aid in reducing nitrate N leaching," but does not provide any specific examples of such fertilizers or data demonstrating their efficacy. Similarly, it states that "constructed wetland technology... offers advantages such as low operating costs, efficient pollutant purification, and notable ecological and environmental benefits," but does not offer any specific case studies or data to substantiate these benefits. Providing specific examples and data can help the reader better understand and evaluate the effectiveness of these proposed measures.

8.     Section 4, Discussing the potential challenges or limitations associated with these measures could provide a more balanced and nuanced perspective on their potential use and effectiveness.

9.     Section 5, it doesn't provide specific research questions or objectives that should be pursued. For instance, what specific questions should this extensive research on rainfall processes aim to answer? What specific aspects of N and P concentrations should be monitored, and how can these monitoring results be applied to improve prevention and control measures? By providing more specific directions for future research, the paper can more effectively guide subsequent studies in this field.

Minor editing of English language required

Author Response

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Reviewer 3 Report

The manuscript "Research progress on nitrogen and phosphorus loss in small watershed: A Review" it very interesting. I think that the manuscript can be accepted. I advise the authors to improve the table presentations and improve the quality of figure 1, the writings inside the figure 1 are not legible.

Author Response

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Author Response File: Author Response.docx

Reviewer 4 Report

Dear Authors,

 

Authors submitted a review paper for nitrogen and phosphorus losses.

It looks like your abstract as below;

Currently, non-point source pollution in small watersheds is more severe and eutrophication problems in watershed waters are more pronounced.

Efficient fertilizer application, adjustment of planting structures, use of artificial wetland technology, and slope protection construction of forests and grasslands were found to be effective to reduce nitrogen and phosphorus losses.

A future topic as below;

It is important to investigate and predictively model surface and underground pathway of nitrogen and phosphorus. Then, the processes of leaching, sorption, conversion, and volatilization should be necessary.

 

I was wondering if you could consider adding more information as below;

・Pages 3, Line on 129

Is it possible to add more details of "the underlying processes"?

 

・Pages 5, Lines on 202-204

What do you mean that "but it was clearly seen that the output load of N and P during 202 rainfall in small watershed was lower than that in medium and large watersheds, which 203 was related to the watershed area."

Please could you clarify and add the sentences to help readers understanding?

 

・Pages 7, Lines on 273-274

"part of N is volatilized to the atmosphere in the form of ammonia"

For volatilized nitrogen shifting to the gas phase, what will happen after that?

 

Sincerely,

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Thank you to respect my recommendations/comments.

Reviewer 2 Report

The authors addressed reviewers' comments accordingly.

English is fine.