A Long-Term Perspective of Seasonal Shifts in Nutrient Dynamics and Eutrophication in the Romanian Black Sea Coast

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study presented by the authors examines the long-term impacts of climate change on nutrient dynamics, dissolved oxygen levels, and eutrophication in the Romanian Black Sea coastal waters using long-term datasets (1960/1976/1980-2023). Their study highlights significant trends, including rising sea surface temperatures, declining oxygen levels, and nutrient imbalances (e.g., increasing nitrogen-to-phosphorus ratios). These trends are linked to ecological disruptions, such as harmful algal blooms. Hence, the study provides actionable strategies for sustainable marine ecosystem management in the context of climate change that aligns with global Sustainable Development Goals (SDGs). The study is relevant to the field of study and is publishable after addressing some of the few concerns raised.

1.     Improve the qualities of some of the Figures (e.g. Figs. 1 and 12).

2.   There are two labels for Fig. 1. Check the figure numbering again and readjust them.

3. Provide more explanation on the societal and economic implications of eutrophication and ecosystem changes.

4. Besides factors like temperature and nutrient ratios, what are the roles of riverine nutrient inputs, agricultural runoff, and industrial discharges in nutrient dynamics?

Author Response

Dear Reviewers and Academic Editors,

We sincerely appreciate your valuable feedback and insightful comments on our manuscript, formerly titled "Time Scales Shift by Climate Change on Nutrient and Eutrophication Dynamics: Insights from the Romanian Black Sea Coast." Your constructive suggestions have greatly contributed to enhancing the quality and clarity of our work.

In response to your comments, we have carefully revised the manuscript, implementing substantial improvements to better address your concerns.

All changes and corresponding responses to the reviewer comments have been documented in the tables below for easy reference.

Below is a summary of the key modifications:

Title Revision

The manuscript title has been updated to "A Long-Term Perspective of Seasonal Shifts in Nutrient Dynamics and Eutrophication in the Romanian Black Sea Coast", ensuring better alignment with the study's scope and findings.

Abstract Enhancement

Minor revisions have been made to the abstract to reflect the updated title and improve clarity.

Material and Methods

Several sections have been revised to provide more comprehensive details.

Results and Discussion

We have completed the results to provide a clearer presentation and deeper insights into the key findings. Additional discussion has been included to address the societal and economic implications of eutrophication, as well as the influence of riverine inputs and anthropogenic factors on nutrient dynamics.

Figures and Tables

Improvements have been made to the figures' quality and numbering consistency, ensuring better visualization and readability.

We firmly believe that these revisions have significantly strengthened our manuscript and have addressed all the comments provided by the reviewers. Detailed responses to each comment, along with the corresponding revisions, can be found in the response tables below for easy reference.

Once again, we express our heartfelt gratitude for your time, effort, and valuable contributions to our work. We are committed to maintaining the highest standards of academic rigor and welcome any further feedback you may have.

Thank you for your continued support and consideration.

Kind regards,

The Authors

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors

In their research, the authors try to determine the role of climate change on the dynamics of nutrients and eutrophication in the Romanian Black Sea coast. In my opinion, the title does not fully reflect the scope of the research conducted. Climate change is a very broad concept. In their study, the authors focused only on the temperature of surface waters, and this is just one of many elements describing the climate. Atmospheric precipitation is very important in this type of research, as the authors themselves write about - lines 34-35. Also changing, among others, is the amount of evaporation, the frequency of extreme phenomena: storms at sea, etc., which affect the dynamics of surface sea waters. The manuscript seems interesting, but requires several important additions:

In the introduction section, what is the aim of the research? It is not clearly defined, whether it is about:

1. The need for comprehensive research that takes into account both anthropogenic and climatic factors – line 98-100

2. Conducting research on eutrophication and nutrient dynamics in the Black Sea – line 101-102

3. Investigating the impact of long-term warming and nutrient dynamics on RBSC – line 104-105

4. Or finally defining the United Nations Sustainable Development Goals (SDGs), specifically SDG 13 (Climate Action), SDG 14 (Life Below Water) and SDG 3 (Good Health and Well-being).

In Fig. 1. the scale is incorrect, according to the authors the distance between Bulgaria and Georgia is about 12 km.

The numbering of figures in the entire article should be corrected, on page 5 the figure no. 1 appears again.

Why are the data in tables 1, 2 and partly 3 in red and in the supplementary materials?

The Materials and Methods section requires supplementation.

1. The authors write that the data come from 1960, 1976 and the period 1980-2023, while the graphs include annual data from 1960? It is necessary to clearly specify which data refer to specific research periods.

2. There is no information whether the research was carried out directly in the field by the authors? or is this data from an institution?

3. Were the concentrations of dissolved nutrients measured throughout the research period 1960-2023 on the aforementioned spectrophotometer? What device was used?

4. In the case of Noctiluca scintillans, the authors should state which period the historical data refer to and how the research material was collected during that time, as well as the period when they conducted the research themselves.

5. How was dissolved oxygen measured? There is no information on this subject.

The conclusions section is very weak. Apart from the first paragraph (lines 634-642), the remaining paragraphs are of a discussion nature and do not result from any research.

Author Response

Dear Reviewers and Academic Editors,

We sincerely appreciate your valuable feedback and insightful comments on our manuscript, formerly titled "Time Scales Shift by Climate Change on Nutrient and Eutrophication Dynamics: Insights from the Romanian Black Sea Coast." Your constructive suggestions have greatly contributed to enhancing the quality and clarity of our work.

In response to your comments, we have carefully revised the manuscript, implementing substantial improvements to better address your concerns.

All changes and corresponding responses to the reviewer comments have been documented in the tables below for easy reference.

Below is a summary of the key modifications:

Title Revision

The manuscript title has been updated to "A Long-Term Perspective of Seasonal Shifts in Nutrient Dynamics and Eutrophication in the Romanian Black Sea Coast", ensuring better alignment with the study's scope and findings.

Abstract Enhancement

Minor revisions have been made to the abstract to reflect the updated title and improve clarity.

Material and Methods

Several sections have been revised to provide more comprehensive details.

Results and Discussion

We have completed the results to provide a clearer presentation and deeper insights into the key findings. Additional discussion has been included to address the societal and economic implications of eutrophication, as well as the influence of riverine inputs and anthropogenic factors on nutrient dynamics.

Figures and Tables

Improvements have been made to the figures' quality and numbering consistency, ensuring better visualization and readability.

 

We firmly believe that these revisions have significantly strengthened our manuscript and have addressed all the comments provided by the reviewers. Detailed responses to each comment, along with the corresponding revisions, can be found in the response tables below for easy reference.

Once again, we express our heartfelt gratitude for your time, effort, and valuable contributions to our work. We are committed to maintaining the highest standards of academic rigor and welcome any further feedback you may have.

Thank you for your continued support and consideration.

Kind regards,

The Authors

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

In general, the manuscript is at a satisfactory stage for submission to “Sustainability”. The study is well-designed, based on a reliable statistical dataset and supported by adequate documentation. It addresses a contemporary environmental challenge -the relationship between climate change, nutrient dynamics and eutrophication in the Black Sea, a region subject to significant environmental pressures. With a few enhancements, the study's reliability and scientific rigor could be further strengthened. The terms "Time Scales Shift" in the title require strong quantitative analysis and place significant emphasis on points 4 and 8 (see below), which require robust documentation of temporal changes to justify their inclusion.

 

Some points:

1.       [minor] In line 5, there is an initial "space" that should be removed.

2.       [minor] Two different figures in the text are labeled as 'Figure 1,' referenced in lines 151 and 194, respectively. Each figure should have a unique label to ensure that the references to them are unambiguous.

3.       [major] The phrase “The study utilizes a long-term dataset (1960/1976/1980–2023) from the Black Sea coastal region …” in line 116 suggests that the data were collected during different periods and from multiple sources, as further explained below. However, as currently written, it might cause confusion. It would be beneficial to clarify explicitly which parameters correspond to which time periods. A table summarizing the data collection years for each parameter would enhance understanding. For example, a table with three columns (Parameter - Collection Method - Time Period) could provide a clearer overview of the data's origin and temporal coverage, which is currently lacking. It could be included in the main text of the paper or even in the supplementary material.

4.       [major] Lines 120–142 reveal significant heterogeneity in data collection methods. Combined with the previous note (3) regarding temporal coverage, it becomes necessary to conduct  preparations on the data before applying any regression models. This will ensure the consistency of the measurements (e.g., with standardization of the data, where all variables will have equal influence on the principal components and most importantly, there will be no large differences in their variability). This step is very important to guarantee that the trend analysis results presented in Chapter 3 are reliable and that discrepancies due to heterogeneity are minimized. It is also crucial to document this procedures in the study, given the high degree of heterogeneity in the data (collected with different instruments and methods over different time periods). It could also be included in the main text of the paper or even in the supplementary material.

5.       [major] It is important to verify the assumptions of the linear regressions in the study to ensure the accuracy and reliability of the results presented in Tables 1, 2, and 3. The regressions involve different variables, and their validity depends on meeting the basic regression assumptions. A clear description of the checks performed and how potential issues were addressed should be included in the "Materials and Methods" section, and the results of these checks should be added to the supplementary material. Specifically, for the regression described in Table 3 (Noctiluca scintillans and environmental parameters), multicollinearity among the variables must also be assessed due to the strong correlations observed in Tables S1–S5.

6.       [major] The relationships between seasonal variations and environmental parameters described in Chapter “3.4.2. Seasonal variation” are presented descriptively, with no statistical tests to confirm the significance of the observed seasonal differences. As a result, it is unclear whether the seasonal patterns significantly change over time (e.g., due to climate change). Even a basic ANOVA test would suffice to demonstrate whether the values of a parameter, such as the density or biomass of Noctiluca scintillans or the concentrations of phosphates (PO₄³⁻) or silicates (SiO₄), exhibit statistically significant differences across seasons.

7.       [minor] Between lines 473 and 479, it would be helpful to state the percentage of total variance explained by Factor 1 and Factor 2 in the PCA analysis. This would clarify how well the two principal components represent the data.

8.       [major] Although the PCA indicates correlations between variables (e.g., N:P ratio and Noctiluca scintillans abundance), no analysis was conducted to confirm whether these relationships vary over time (a similar issue to observation 6). Given the study’s goals and conclusions, quantitative confirmation of any temporal variation is essential. A simple, practical approach would be to split the data into time periods (e.g., decades), perform PCA separately for each period, and compare the loadings of the components across periods. Quantitatively documenting the “dynamics” of changes over time is essential to validate the study’s objectives.

9.       [minor] In Chapter "5. Conclusions," a brief note is missing on the impact of data heterogeneity, which can introduce methodological limitations and remains a factor that must be considered to improve the accuracy of future research.

10.   [minor] Line 698 should end with a "." instead of a ",".

Comments for author File: Comments.pdf

Author Response

Dear Reviewers and Academic Editors,

We sincerely appreciate your valuable feedback and insightful comments on our manuscript, formerly titled "Time Scales Shift by Climate Change on Nutrient and Eutrophication Dynamics: Insights from the Romanian Black Sea Coast." Your constructive suggestions have greatly contributed to enhancing the quality and clarity of our work.

In response to your comments, we have carefully revised the manuscript, implementing substantial improvements to better address your concerns.

All changes and corresponding responses to the reviewer comments have been documented in the tables below for easy reference.

Below is a summary of the key modifications:

Title Revision

The manuscript title has been updated to "A Long-Term Perspective of Seasonal Shifts in Nutrient Dynamics and Eutrophication in the Romanian Black Sea Coast", ensuring better alignment with the study's scope and findings.

Abstract Enhancement

Minor revisions have been made to the abstract to reflect the updated title and improve clarity.

Material and Methods

Several sections have been revised to provide more comprehensive details.

Results and Discussion

We have completed the results to provide a clearer presentation and deeper insights into the key findings. Additional discussion has been included to address the societal and economic implications of eutrophication, as well as the influence of riverine inputs and anthropogenic factors on nutrient dynamics.

Figures and Tables

Improvements have been made to the figures' quality and numbering consistency, ensuring better visualization and readability.

 

We firmly believe that these revisions have significantly strengthened our manuscript and have addressed all the comments provided by the reviewers. Detailed responses to each comment, along with the corresponding revisions, can be found in the response tables below for easy reference.

Once again, we express our heartfelt gratitude for your time, effort, and valuable contributions to our work. We are committed to maintaining the highest standards of academic rigor and welcome any further feedback you may have.

Thank you for your continued support and consideration.

Kind regards,

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have addressed the concerns raised. It can now be accepted for publication in its current form.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors

Thank you for the opportunity to review the manuscript again. In the revised version, the authors have included the recommended additions. I have no major comments, the article can be published in the proposed version. I leave the final decision to the Editors.

Reviewer 3 Report

Comments and Suggestions for Authors

The revisions made are sufficient and significant, contributing to the improvement of the overall quality and clarity of the work. In its revised form, the proposed improvements have been successfully incorporated, and the work is now ready to proceed to publication.