Influence of Dissolved Oxygen and Temperature on Nitrogen Transport and Reaction in Point Bars of River

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

I suggest to improve the description of the results and the discussion. The goal of word is not clear, so  it is difficult to understand the focus of the discussion of results.

Reduce the references, too many!

Comments for author File: Comments.pdf

Author Response

Response to comments of Reviewer:

Comment 1: I suggest to improve the description of the results and the discussion. The goal of word is not clear, so it is difficult to understand the focus of the discussion of results. Reduce the references, too many!

Response: Thanks for your valuable comment. We have improved the description of the results and discussion in the new manuscript and removed some redundant and unnecessary references

Comment 2: I advise the authors to expand on the concepts introduced in the introduction, in particular when discussing the factors influencing denitrification. Moreover, the authors used a model to simulate the water flow movement, but it is not introduced into the aim of study, but the concept appeared only in M&M. I suggest to introduce or indicate in the Introduction whether or not there are any studies that have applied a similar approach.

Response: Thank you for your suggestions. We have made the corresponding expansion and additions in the introduction. Please see *Line 57, *Line 68-75, and *Line 122-131. 

Comment 3: Lines 58-61: contaminants as? I suggest to add examples and more references.

Response: Thank you for your careful check. We have added the examples and references in the new manuscript. Please see *Line 61-68.

Comment 4: Lines 60-62: improve the concept. What causes nitrite accumulation? Is it by incomplete nitrification or denitrification? Under what conditions does it accumulate?

Response: Thank you for your advice. We have provided corresponding explanations and additions in the text. Please see *Line 63-67.

Comment 5: Lines 65-66: What happened when water pH is acid and/or basic?

Response: After thoroughly reviewing the references. We have made corresponding additions to the new manuscript. Please refer to *Line 78-80.

Comment 6: Lines 74-76: added examples of “exogenous loads”.

Response: We have added examples of  “exogenous loads”. (*Line 88).

Comment 7: Lines 87-89: I suggest to explain as the temperature influence the oxygen diffusion or the nutrients distribution.

Response: Thank you for your professional comment. We have made corresponding changes in the text. Please see *Line 101-102.

Comment 8: Lines 102: also the oxygen concentration was influenced by temperature. fact, the high temperature reduced the oxygen dissolution. Moreover, the high temperature simulated the organic compounds mineralization, thus reduced the oxygen concentrations in systems. Consequently, I suggest to authors to add also this information, according to different studies, as follows:

Veraart, A. J., De Klein, J. J., & Scheffer, M. (2011). Warming can boost denitrification disproportionately due to altered oxygen dynamics. PLoS One, 6(3), e18508. https://doi.org/10.1371/journal.pone.0018508.

de Klein, J. J., Overbeek, C. C., Juncher Jørgensen, C., & Veraart, A. J. (2017). Effect of temperature on oxygen profiles and denitrificaƟon rates in freshwater sediments. Wetlands, 37, 975-983. https://doi.org/10.1007/s13157-017-0933-1

Rajesh, M., & Rehana, S. (2022). Impact of climate change on river water temperature and dissolved oxygen: Indian riverine thermal regimes. Scientific Reports, 12(1), 9222. https://doi.org/10.1038/s41598-022-12996-7.

Response: Thanks for your professional comments, according to the above studies, we have added this information to the discussion. Please see *Line 491-496.

Comment 9: Lines 115-117: I suggest to add other information on software (annual certificate, ect)

Response: We have added the relevant information on the software. Please see *Line 142.

Comment 10: Lines 169-171: Why? I suggest to justify this choice.

Response: We have explained this choice. Please see *Line 195-197.

Comment 12: Line 190: “changes” during the time? Specify it.

Response: Thank you so much for your careful check. We have specified it in the new manuscript. Please see *Line 214.

Comment 13: Eq.11 and 12: I suggest to use the term “t” to indicate the time and not “T”, It is usually use to indicate the temperature, and may be create confusion.

Response: We were really sorry for our carelessness. In our new manuscript, this error has been corrected. Please see Eq.11,12, 13 and *Line 254.

Comment 14: Lines 263-266: I suggest to add more details to explain the cause of this trend

Response: Thank you for your careful review. We have added some details to explain the cause of this trend. Please see *Line 299-304.

Comment 15: Line 450-452, Lines 471-476: I suggest to moved these sentences in conclusion paragraph.
  Response: Thank you for your suggestions. We have moved these sentences into conclusion paragraphs.

 

 

 

Thanks again for your comments. We hope that we have addressed all the comments. Should you have any further queries, please do not hesitate to contact with us.

Yours sincerely

Ying Liu

On behalf of all the co-authors

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The article titled “Influence of DO and Temperature on Nitrogen Transport and Reaction in Point Bars of River” demonstrates the impact of dissolved oxygen (DO) concentration and temperature on nitrogen transport and reaction in point bars of the river. This step was performed using two-dimensional coupled surface water-groundwater model:

1-    The authors should mention why they have selected point bars in their study

2-    Also, why they have selected two-dimensional model; why not using CFD tool

33 -    What is the sensitivity analysis for the data given in “Table 2. Key parameters of a multi-component solute reactive transport model”

44 -    What is the accuracy of the proposed model in predicting other parameters than DO and temperature

55 -    The suggested mechanism for the transfer of pollutants should be supported by conducting a mass balance model (influent, effluent, and accumulation)

66 -    What about the real application of the proposed model

7-    The expected drawbacks and limitations in section “4.3. Limitations of This Study” should be supported by a figure or a table

8-    What will happen for the presence of toxic compounds in the river

Comments on the Quality of English Language

Moderate editing of English language required

Author Response

Response to comments of Reviewer:

Comment 1: The authors should mention why they have selected point bars in their study

Response: Thank you for your suggestions, we have provided the corresponding explanation in the text; please refer to *Line 36-45, *Line 116-121.

Comment 2: Also, why they have selected two-dimensional model; why not using CFD tool

Response: Thank you for your professional comments, The two-dimensional model exhibits high convergence and has the advantage of quick and convenient computation. You give us great advice, the three-dimensional model may provide more accurate predictions, and we will focus on the construction and computation of the three-dimensional model in future research. We used COMSOL's CFD tools to simulate surface water flow. Our previous research has analyzed the hydrodynamic characteristics of surface water, and in this study, we only applied the results data (pressure) of the surface water model from the previous study (Song et al. 2024).

Song, X.; Liu, Y.; Liu, D.; Feng, J.; Li, L.; Guo, Y.; Luo, J.; Jiang, W., Influence of point bars on nitrogen transport and reaction in riparian zones. Journal of Hydrology 2024, 637, 131388.

Comment 3: What is the sensitivity analysis for the data given in “Table 2. Key parameters of a multi-component solute reactive transport model

Response: Thank you for your careful review. The data in Table 2, such as the permeability coefficient and porosity, are measured values, while reference values are provided for parameters like the diffusion coefficient and the concentrations of nitrate, ammonia nitrogen, and dissolved organic carbon in the river. These data are fixed, and the study variables in this paper are twofold—temperature and dissolved oxygen. Therefore, we conducted a sensitivity analysis only on temperature and dissolved oxygen. Please see *Line 411-412.

Comment 4: What is the accuracy of the proposed model in predicting other parameters than DO and temperature

Response: In addition to dissolved oxygen and temperature, such models are also commonly used to predict the source-sink functions of nitrate, demonstrating considerable accuracy.

Ping, X.; Jin, M.; Xian, Y., Effect of biologging on the nitrate source and sink function of a hyporheic zone. Journal of Hydrology 2020, 590, 125425.

Lin, Y.; Lu, C.; Wu, C.; Liu, B.; Shu, L., Hyporheic exchange and nitrogen cycle processes under the dual effects of flooding and heterogeneous streambed. Journal of Hydrology 2023, 626, 130188.

Comment 5: The suggested mechanism for the transfer of pollutants should be supported by conducting a mass balance model (influent, effluent, and accumulation)

Response: Your comments are very professional and insightful. We add the mass balance analysis method in section 2.4, and mass balance data in tables 3 and 4.

Comment 6: What about the real application of the proposed model

Response: These models provide a theoretical basis and scientific guidance for river ecological restoration projects (the in-stream structures, point bars, floodplain, etc.), and it is believed that there will be more specific applications in the future.

Comment 7: The expected drawbacks and limitations in section “4.3. Limitations of This Study” should be supported by a figure or a table

Response: Thank you for your advice. Unfortunately, we are uncertain about how to present these limitations in tabular or graphical form. If you think this is very important and necessary, we look forward to having more consultations and exchanges with you.

Comment 8: What will happen for the presence of toxic compounds in the river

Response: We have provided a possible answer to this issue. Please refer to *Line 64-68.

Comment 9: Moderate editing of English language required

Response: Thank you for your suggestions. We have edited and improved the language of the paper.

 

Thanks again for your comments. We hope that we have addressed all the comments. Should you have any further queries, please do not hesitate to contact with us.

Yours sincerely

Ying Liu

On behalf of all the co-authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

 

2. Materials and Methods

• Doesn't the assumption of uniform and stable temperatures in the point bar affect the results obtained? (Line 127-128)
• What was the total mesh size used in this simulation?

 

• Don't sediments have an effect on DO and temperature on nitrogen transport? (Line 214). In this table, there are no sediment parameters (density, permeability coefficient, longitudinal and lateral diffusion coefficient

 

3. Results

 

• The choice of maximum DO concentrations of 0.1, 0.2 and 0.4 mol/m³ at the interface was not justified.  What are the scientific arguments for choosing such maximum concentrations? (Lines 251-313)

 

• The choice of temperatures of 5°C, 15°C and 25°C to assess the effect of temperature on the transport and reaction of nitrogen was not justified in the text.( lines 374 -379)

Comments for author File: Comments.pdf

Author Response

Response to comments of Reviewer:

Comment 1: Doesn't the assumption of uniform and stable temperatures in the point bar affect the results obtained? (Line 127-128)

Response: Thank you for your professional comments. To facilitate our study, we assumed that the temperature of the riverbank is uniform and stable, and used this uniform and stable temperature as an independent variable to explore its impact on the nitrogen cycle. We reference the methods that were applied in the study by Zheng et al. (2016). Your advice is helpful, we will continue to delve into the nitrogen cycling process under complex temperature conditions (variable or non-uniform temperature).

Zheng, L.; Cardenas, M. B.; Wang, L., Temperature effects on nitrogen cycling and nitrate removal‐production efficiency in bed form‐induced hyporheic zones. Journal of Geophysical Research: Biogeosciences 2016, 121, (4), 1086-1103.

Comment 2: What was the total mesh size used in this simulation?

Response: To enhance the accuracy of the simulation results, we employed a highly refined free triangular mesh, dividing the model domain into 113,616 mesh elements. See *Line 203-204.

Comment 3: Don't sediments have an effect on DO and temperature on nitrogen transport? (Line 214). In this table, there are no sediment parameters (density, permeability coefficient, longitudinal and lateral diffusion coefficient

Response: Thank you for your careful review. In this study, the nitrogen migration simulated in sediments was modeled using the porous media mass transfer equation. This process is related to the sediment's porosity, permeability, and diffusion coefficient (Table 2, *Line 238), but is independent of sediment density. The fluid diffusion coefficient model used in this study follows the Milling-Quirk model, employing uniform values (1E-9 m²/s).

Comment 4: The choice of maximum DO concentrations of 0.1, 0.2 and 0.4 mol/m³ at the interface was not justified. What are the scientific arguments for choosing such maximum concentrations? (Lines 251-313)

Response: Thank you so much for your careful review. Regarding the selection of dissolved oxygen concentration, we referred to relevant surface water environmental quality standards and related literature.

SEPA, 2002. Environmental Quality Standard for Surface Water (GB3838-2002). State Environmental Protection Administration of China, Beijing of Regula.

Ping, X.; Jin, M.; Xian, Y., Effect of biologging on the nitrate source and sink function of a hyporheic zone. Journal of Hydrology 2020, 590, 125425.

Comment 5: The choice of temperatures of 5°C, 15°C, and 25°C to assess the effect of temperature on the transport and reaction of nitrogen was not justified in the text.( lines 374 -379).

Response: We would like to thank you for your valuable reviews. From our temperature monitoring of the hyporheic zone of the test river (0-30 cm depth of river bed), the average winter temperature is about 8 ℃, and the average summer temperature is 26℃. Therefore, we selected 5, 15, and 25°C as the study temperatures. Your advice is helpful. The results presented cannot fully characterize the effect of temperature on nitrogen transformation, nor could a linear relationship between temperature and nitrogen removal be concluded. The effect of temperature on the transport and reaction of nitrogen needs more justified research in the future.

 

Thanks again for your comments. We hope that we have addressed all the comments. Should you have any further queries, please do not hesitate to contact with us.

Yours sincerely

Ying Liu

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Lines 136-137: It is usefull, maybe the authors should be to move this sentence in M&M paragraph.

Lines 63-67: I suggest to improve and simplify the sentences in the brackets.

 

 

Author Response

Response to comments of Reviewer:

Comment 1: Lines 136-137: It is usefull, maybe the authors should be to move this sentence in M&M paragraph.

Response: Thank you for pointing this out. We have moved this sentence to the M&M paragraph. Please see *Line 125-129.

Comment 2: Lines 63-67: I suggest to improve and simplify the sentences in the brackets.

Response: Thank you for your careful reading. We have improved and simplified the sentences in the brackets. Please see *Line 61-63.

Thanks again for your attention and time. Your valuable comments have significantly improved the manuscript. Should you have any further queries, please do not hesitate to contact us.

Kind regards,

Ying Liu

On behalf of all the co-authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The authors responses are satisfactory

Comments on the Quality of English Language

Minor editing of English language required.

Author Response

Comment 1: The authors responses are satisfactory.

Response: Thank you very much. We are deeply honored by your recognition of our work.

Comment 2: Minor editing of English language required.

Response: Thank you for your suggestions. We have polished our manuscript carefully and corrected the grammatical, styling, and typos found in our manuscript.

 

Thanks again for your attention and time. Your valuable comments have significantly improved the manuscript. Should you have any further queries, please do not hesitate to contact us.

Kind regards,

Ying Liu

On behalf of all the co-authors

Author Response File: Author Response.pdf