Optimizing Sampling Strategies for Estimating Riverine Nutrient Loads in the Yiluo River Watershed, China

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Dear Authors,

The research article entitled ‘Optimizing Sampling Strategies for Estimating Riverine Nutrient Loads: Influence of Sampling Frequency and Calculation Methods in the Yiluo River Watershed, China’ is written in a very interesting way. This study assessed sampling frequencies and calculation methods for estimating TN and TP loads in the Yiluo River watershed, China. Extreme weather events, especially during summer, significantly affected nutrient export, emphasizing the need for effective monitoring and management strategies in agricultural watersheds. This study holds significance because accurate estimation of nutrient loads is crucial for effectively managing and monitoring aquatic ecosystems. By evaluating different sampling frequencies and calculation methods, the research provides insights into optimizing water quality monitoring schemes and management strategies, particularly in medium and small agricultural watersheds like the Yiluo River watershed in China. From this point of view, this article should be published with the current contents. However, for being accepted, some improvements should be made.

Some minor comments are detailed below:

‘Introduction’ section

What I miss in the introduction section is a brief overview of the existing gaps or limitations in current research on nutrient load estimation. This could involve mentioning any specific challenges or shortcomings in previous studies, such as limited consideration of seasonal variability, inadequate assessment of high-flow seasons and extreme precipitation events, or a lack of focus on agricultural watersheds characterized by non-point source pollution. Additionally, you might want to emphasize the significance of addressing these gaps in understanding the uncertainty of nutrient load estimates. Highlighting the importance of accurately assessing nutrient loads under various hydrological and seasonal conditions can underscore the relevance and necessity of your study. Furthermore, it could be beneficial to provide a clearer statement of the research objectives or hypotheses guiding your study.

‘Results’ section

It should be considered to discuss any methodological considerations or limitations that may have influenced your results. This could include factors such as data quality, measurement error, or assumptions underlying the estimation methods used. Addressing these considerations can help interpret the findings accurately and highlight areas for future research improvement. Moreover, all the figures are intriguing, but unfortunately, they lack clarity and readability. For instance, in figures 8 and 9 or others, neither the axis descriptions nor the numbers are discernible, making it challenging to interpret the data. It is crucial to improve the visual presentation of the figures to ensure that all relevant information, such as axis labels, titles, and numerical values, is clearly visible and understandable. This improvement will enhance the overall quality of the figures and facilitate better comprehension of the data they represent.

‘Discussion’ section

To enrich this section, consider incorporating the following additions:

• Provide a comparison with previous studies that have evaluated nutrient load estimation methods and sampling strategies. Highlight any consistencies or discrepancies between your findings and those reported in the literature. Discuss how your study builds upon or adds to the existing knowledge base in this field.
• Discuss the importance of considering watershed-specific characteristics, such as land use patterns, hydrological regimes, and nutrient sources, when selecting optimal sampling strategies and estimation methods. Emphasize the need for tailored approaches that account for the unique conditions of each watershed.
• Address the cost-effectiveness of different sampling strategies and estimation methods. Discuss how the trade-offs between data resolution, accuracy, and monitoring costs influence decision-making in watershed management. Consider exploring potential avenues for optimizing monitoring programs to achieve the desired balance between accuracy and cost-efficiency.

‘Conclusions’ section

Please provide recommendations for future research directions based on the identified limitations and gaps in the current study. Suggest exploring more advanced estimation techniques, investigating the effects of environmental changes on nutrient export dynamics, and developing adaptive monitoring strategies to account for the non-stationary nature of nutrient dynamics.

Comments on the Quality of English Language

Minor editing of English language required

Author Response

We sincerely thank the reviewer for their evaluation of our manuscript. Your professional and in-depth comments have been insightful and made us realize that certain aspects of the article require further refinement and clarification. Following your suggestions, we have thoroughly revised and supplemented the paper. Detailed explanations of the changes and responses can be found below, with the revised content marked in red/track changes mode in the revised manuscript. We believe that after this revision, the quality and readability of the paper have been greatly enhanced. We genuinely appreciate the time and effort you have invested. If there are any further questions or suggestions, we welcome your feedback at any time. Please see the attachment.

My best,

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Please see my review in the attached file.

Comments for author File: Comments.pdf

Author Response

Dear reviewer,

We sincerely thank the reviewer for their evaluation and valuable comments on our manuscript. Through your remarks, we have reconsidered certain weaknesses in the article and have accordingly made comprehensive revisions and improvements. We have responded to the issues you raised point by point in the text below, and the corresponding changes have been marked in red/track changes mode in the resubmitted manuscript. Your comments have been very helpful, making this article more rigorous, clear, and complete. We are truly grateful for your efforts in helping us improve this paper. If you have any other suggestions, we welcome and will seriously consider them.Please see the attachment.

my best.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is devoted to the analysis of the uncertainties in the calculation of TN and TP riverine loads from the medium size Yiluo R. watershed (about 20 000 km2) with significant share of farmlands. Taking into account the key role of nutrients for the water quality and elevated concentration of TP and TN in the Yiluo R. waters, it is obviously that evaluation of the nutrient fluxes from the watershed is important. Authors have analyzed nine equations for the calculation of nutrient fluxes at the different inputting data, and recommend some of them having less uncertainty.  One can agree that this study adds scientific background for the optimization of water quality monitoring chemes in medium and small agricultural watersheds, and will help to manage water use in the region studied. At the same time, there are some questions and comments not allowing recommending manuscript for publication as it is.

1.       Manuscript is overloaded by the results of fluxes calculation, and Tables 2 and 3 are duplicated by Fig. 2 and Fig.3. The Tables 2 and 3 should be omitted (transferred  to the Supplementary Materials);

2.       The data on the seasonal changes in precipitation, runoff, TP and TN concentrations (Fig. 9) ask more detailed explanation and discussion. What are the possible reasons of such notable increase in TN concentration at the end 2019 and beginning of 2020?  What are the possible reasons of the sustained decrease trend in nutrients concentration during almost all 2019? At least it should be discussed somehow. Moreover, it would be useful to let know readers is such level of nutrients in Yiluo R. typical compare with previous years or not. Readers need such explanation, because variability of concentration plays a key role in the variability of the fluxes;

3.       Figures 3-6 are very difficult to read due to small size scripts (written characters) on the axises. Inscriptions to Fig. 3-6 are unreadable in present form. Might be authors will decrease the amount of the subfigures, because some of them are rather similar, but will increase scripts size. Additionally, the text explanation of the Figures 3-6 could be more detailed. The information should be added to the title of the Fig. 3-6 also: what means the boxes, outliers, middle line insight the boxes - ?.

4.       Figures 7, 8 are not clear enough and seems excessive, because these figures do not used in the discussion.

5.       The acronyms should be explained at the first appearance in the text (e.g. standard deviation of the percentage errors (STD) or Mean relative error (MRE). The term “Method 3”  in the Abstract is also should be described, as it done at L.19 for Method 7 (flow-weighted concentration).

Author Response

Dear Editor and Reviewers,

Thank you very much for taking the time and effort to review this manuscript. We greatly appreciate your constructive comments and suggestions, which have significantly contributed to improving the quality of the article. We have carefully considered each point and made corresponding revisions and additions. The revised content has been highlighted in red/track changes mode in the resubmitted files. Once again, thank you for your contribution. We hope that the revised manuscript will meet the publication requirements of the journal. If there are any questions or need for further clarification, please do not hesitate to let us know. Please see the attachment.

my best.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

1. Please simplify the title.

2. provide the full name of an abbreviation or acronym the first time it is mentioned in the text, including in the abstract section.

3. Fig. 2, it is recommended to label each graph with ABCD.

4. Figure caption should be below the figures. In addition, the resolution of Figs. 3, 4,5,6 is too low, making it difficult to obtain useful data.

5. The discussion should elaborate on the implications of the findings, specifically how they could inform monitoring programs and management strategies in agricultural watersheds. The conclusion should sum up the study’s main findings, clearly state the cause-and-effect relationships, and be brief and focused, emphasizing the study’s importance and its impact on the field.

Author Response

Dear Editors and Reviewers,

We would like to express our sincere gratitude to the reviewer for their thorough review and unbiased opinions. Your comments have led us to re-examine the article and identify areas that needed improvement and clarification. We have responded to your comments point by point and made corresponding revisions and additions in the revised manuscript, as detailed below. The modified parts have been marked in red/track changes mode in the text. Your comments and suggestions have greatly helped us enhance the quality of the paper, making it more rigorous and complete. Thank you once again for reviewing our manuscript despite your busy schedule. If there are any further questions, please let us know. Please see the attchment.

my best.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I accept the author's feedback with a significant notice on the limitation of old techniques for TN and TP load estimation. 

But again, the authors need to carefully correct the following minor points: 

ID: water-2994062

1. Line 17: “scale . For monthly”” Please check all typo

2. Line 20: typo “ <10% ”

Line 52 - 57: you mentioned about “ systematic research on the 53

influence of sampling frequency and estimation methods on the uncertainty of nutrient load estimates under different seasonal and hydrological conditions,”: Actually, this systematic research/ review need to be designed with a wider geographical regions with a higher number of monitoring station. Due to the limitations of sampling station and only 1 watershed in this study, I suggest to narrow down your argument to fit the local conditions and the study site.

3. Line 58 - 65 should be merged with lines 52 - 57

4. Line 113: typo “load[12-15]”

5. Line 112 - 114: unclear sentence. Should revise.

6. Line 125 - 126: empty space error

7. Line 128 - 131: empty space and redundant text

8. Line 133 - 134: need to present in the form of an equation with cited reference

9. Line 145: Python code should be sourced to a reference or library

10. Line 171: 60day or 60-day?

11. Line 195: typo “(down).Note”

12. Line 205: typo “limitations[31].”

13. Line 211: typo “conditions[32]”

14. Line 285: Figure 7 need to carefully revised with the following works: (1) increase font size of the axis title, still too small; (2) Set the similar font size among the titles/ captions; (3) Fig. 7d, redundant text below the X title; (4) Fig. 7f, I don’t the Y axis title; Fig. 7g, please check both Y and Z titles, e.g., Runoff, concentration(mg/L) and an overlapping

15. Line 298: typo “fluxes[33, 34].”

16. Line 320, typo “watersheds[12, 13, 19]”

17. Line 327:watersheds[12, 13, 19]ypo “catchments[21].”

18. Line 350, typo “constraints[13, 23].”

19. Line 413: typo “ runoff[31, 35, 36]”

20.  Line 494 - 499: please revise redundant words in line 494 and wrong statement in line 497

to make your manuscript cleaner. 

Author Response

Dear reviewer,

  Thank you for your thorough review and valuable comments on our manuscript. We have carefully considered each of your suggestions and made the necessary revisions to improve the clarity and quality of our paper. Below, we address each of your comments point by point. Please see the attachment.

my best,

 

Author Response File: Author Response.pdf