Round 1

Reviewer 1 Report

The paper lacks originality in its content and writing. In addition, I don't see any novelty in the work; similar works are widespread in the literature. Based on these comments, I feel that the publication of this work is unwarranted.

Author Response

We much appreciate your constructive and detail comments! The following has been revised according your advice.

1.The paper lacks originality in its content and writing. In addition, I don't see any novelty in the work; similar works are widespread in the literature. Based on these comments, I feel that the publication of this work is unwarranted.

Answer: Thank you very much for your constructive and detail comments! We have modified the paper according to your suggestion.

Current research suggests that trade-offs and synergies among ecosystem services also drive spatial and temporal variation in ecosystem services. However, few studies have explored the trade-offs and synergies between ESVs and their effects on ESVs. Based on the study of the spatial differentiation characteristics and influencing factors of ESV, this paper further investigates the trade-offs and synergies of ESV using correlation analysis methods and explores the influence of trade-offs and synergies on ESV using Geodetector.

Author Response File: Author Response.docx

Reviewer 2 Report

In the reviewer’s opinion, the paper could have been more interesting and better organised. In general, the overall contribution remains scientifically poor and technically questionable. In more detail, the paper’s title is quite clear, whilst its Abstract should have avoided the use of acronyms and technical details, which reduce its readability. The keyword list needs to be improved. Section 1 cites some references, but it does not provide a sufficiently exhaustive overview and critical discussion of the state of the art of the related literature. As further remark, the end of Section 1 should have summarised the general structure of the manuscript by briefly listing the contents of its sections. Section 2 should have addressed more details regarding the considered models and tools; in particular, it does not consider the robustness and reliability issues, due for example to uncertainty and disturbance effects, as well as the model-reality mismatch. This point is fundamental when the reliability and robustness features of the proposed solutions have to be verified and validated with respect to real engineering and safety critical systems. Therefore, the effectiveness of the methodology proposed in Sections 2 and 3 remains unclear and questionable. The authors should have helped the reader to understand the novelty issues of the developed scheme. Due to these flaws, the results considered in Sections 3 and 4 do not help the reader to understand the effectiveness and the efficacy of the proposed solutions. Moreover, more effective metrics and performance indices should be exploited to assess the advantages of the developed techniques. Finally, Section 5 does not suggest effective open problems and future issues that could require further investigations. On the other hand, the use of acronyms should have been avoided also here, as it should remain a stand-alone part of the manuscript.

Author Response

We much appreciate your constructive and detail comments! The following has been revised according your advice.

1. In the reviewer’s opinion, the paper could have been more interesting and better organised. In general, the overall contribution remains scientifically poor and technically questionable. In more detail, the paper’s title is quite clear, whilst its Abstract should have avoided the use of acronyms and technical details, which reduce its readability.

Answer: Thank you very much for your constructive and detail comments! We have modified the abstract according to your suggestion.

The full names to the abbreviations have been added when they appear for the first time.

2. The keyword list needs to be improved.

Answer: Thank you very much for your constructive and detail comments! We have modified the keywords according to your suggestion.

3. Section 1 cites some references, but it does not provide a sufficiently exhaustive overview and critical discussion of the state of the art of the related literature.

Answer: Thank you very much for your constructive and detail comments! We have modified the introduction according to your suggestion.

4. As further remark, the end of Section 1 should have summarised the general structure of the manuscript by briefly listing the contents of its sections.

Answer: Thank you very much for your constructive and detail comments! We have modified the introduction according to your suggestion.

Line: The following are the objectives of this paper: (1) to build a regional ESV estimation model and an index system of driving factors; (2) to measure the spatial and temporal dynamics of ESV, as well as the trade-offs and synergies relationships of each ecosystem service; and (3) to analyze the driving factors of the spatial variation pattern of ESV in the Nanjing metropolitan area using Geodetectors.

5.Section 2 should have addressed more details regarding the considered models and tools; in particular, it does not consider the robustness and reliability issues, due for example to uncertainty and disturbance effects, as well as the model-reality mismatch. This point is fundamental when the reliability and robustness features of the proposed solutions have to be verified and validated with respect to real engineering and safety critical systems. Therefore, the effectiveness of the methodology proposed in Sections 2 and 3 remains unclear and questionable. The authors should have helped the reader to understand the novelty issues of the developed scheme. Due to these flaws, the results considered in Sections 3 and 4 do not help the reader to understand the effectiveness and the efficacy of the proposed solutions. Moreover, more effective metrics and performance indices should be exploited to assess the advantages of the developed techniques.

Answer: Thank you very much for your constructive and detail comments!

So far, the method developed by Costanza et al. [17] based on unit area value equivalent factors has been widely employed to account for regional ESV. Xie et al. [18] revised the unit area value equivalent factor method and developed an equivalence factor table for the ESV of terrestrial ecosystems in China, which has been extensively utilized in China [9,12]. However, because ESV is estimated using unit area value coefficients, this method has a few disadvantages. Firstly, the determination of unit area value coefficients is to some extent subjective [19,20]. Secondly, whether the unit area value coefficients correspond to the current condition in the research area have a direct impact on ESV estimation accuracy. This paper revised the ESV factor table using the grain production and prices in the Nanjing Metropolitan Area during the period 2000-2020. The reliability of the revised ESV coefficients plays an important role in the accuracy of ESV assessment. Therefore, the sensitivity analysis on the revised ESV coefficients was carried out in this paper (see Table 4), and the results show that the sensitivity coefficients of the revised ESV coefficients for each land use type were less than 1. It means that the ESV of the Nanjing metropolitan area was stable, and the estimated ESV was reliable.

6.Finally, Section 5 does not suggest effective open problems and future issues that could require further investigations.

Answer: Thank you very much for your constructive and detail comments! We have modified the discussion according to your suggestion.

Line: Geography and ecology have devoted a lot of attention to the study of ESV since Costanza first introduced the concept of ESV [40]. And research on ESVs has gradually shifted from the early days of assessing their value to examining the distribution of ESVs in various ecosystem types and their driving variables. However, the exploration of spatio-temporal patterns of change and their driving mechanisms is a step-by-step task due to the complexity of ecosystems. Geodetector can better reveal the geographical scale driving mechanisms of regional ESV spatial divergence phenomenon, but the motivating factors still need to be further explored at the temporal scale. In the future, the existing index system can be expanded to examine the mechanisms underlying regional ESV evolution at multiple scales across time and space.

7.On the other hand, the use of acronyms should have been avoided also here, as it should remain a stand-alone part of the manuscript.

Answer: Thank you very much for your constructive and detail comments! We have modified the result according to your suggestion.

Author Response File: Author Response.docx

Reviewer 3 Report

L15: please describe the method in the abstract in at least one sentence.

L27: how did you arrive at this general conclusion? from a blue?

L40: indicate its full name first

L37: what are the reasons or study evidence to select these 7 factors?

Fig 2: we can see that in 2005, 2010, and 2015, construction land was very massive in the northern part of the study area. while it decreased in 2020. Is that correct construction replaced by cultivation or is it an error? This has an impact on ESV estimation from cultivated land or other land uses.

L167-68: I think, if the land is changed to construction, yes its ESV is decreased. And it should be indicated that the ESV of a vegetation area is decreased if it is changed to a construction area. If you didn't consider it, how do you estimate its decline in ESV?

Table 1: what is unused land? Is it bare land or what? please make it clear.

Table 2: we see that the total ESV of 2000 and 2020 are almost comparable (1527.9 & 1523.6), but in 2005 ESV was the highest and what was the reason for this? and what is then your conclusion?

Table 3: how these two classes had positive changes while others are negative ones? Because hydrological regulation is dependent on other land use changes and how it is positive while others have shown negative changes?

Section 4.2.: The contents of this section and figure 8 should go to the result in the section.

L413: what is the degree of excessive pop? And you didn't have statistical analysis in this study that shows an increasing population.

L435 in conclusion section: from where this conclusion is derived as you excluded it. I think you need to include construction land in your analysis.

Author Response

We much appreciate your constructive and detail comments! The following has been revised according your advice.

1. please describe the method in the abstract in at least one sentence.

Answer: Thank you very much for your constructive and detail comments! We have modified the abstract according to your suggestion.

Therefore, this paper used sensitivity analysis, correlation analysis, trade-offs and synergies analysis, and Geodetector to examine the changes in ESV over time and space and their influencing factors in the Nanjing metropolitan area.

2. L27: how did you arrive at this general conclusion? from a blue?

Answer: Thank you very much for your constructive and detail comments! We have modified the abstract according to your suggestion.

The main socio-economic factor influencing the spatial variations of the ESV was population density, while the main physical-geographical factors were digital elevation model (DEM), normalized difference vegetation index (NDVI), and precipitation. As a result, the Nanjing Metropolitan Area should tighten its grip on excessive population growth.

3. L40: indicate its full name first

Answer: Thank you very much for your constructive and detail comments! We have modified the introduction according to your suggestion.

The full names to the abbreviations have been added when they appear for the first time.

4. L37: what are the reasons or study evidence to select these 7 factors?

Answer: Thank you very much for your constructive and detail comments!

The seven drivers selected in this paper are five physical geographic factors and two socioeconomic factors, all of which were selected with reference to other literature for their high frequency of occurrence.

5. Fig 2: we can see that in 2005, 2010, and 2015, construction land was very massive in the northern part of the study area. while it decreased in 2020. Is that correct construction replaced by cultivation or is it an error? This has an impact on ESV estimation from cultivated land or other land uses.

Answer: Thank you very much for your constructive and detail comments!

The land use maps were downloaded from the Resource and Environmental Science and Data Center of the Chinese Academy of Sciences (http://www.resdc.cn/Default.aspx). Based on the Landsat TM and OLI images, the land cover maps were generated through manual visual interpretation, and the datasets were resampled to match a spatial resolution of 1km.

6. L167-68: I think, if the land is changed to construction, yes its ESV is decreased. And it should be indicated that the ESV of a vegetation area is decreased if it is changed to a construction area. If you didn't consider it, how do you estimate its decline in ESV?

Answer: Thank you very much for your constructive and detail comments! We have modified the section “2.3. ESV evaluation” according to your suggestion.

Previous studies have discovered that the ESV in construction land is extremely low [9], therefore the ESV in construction land was not considered and assigned to zero in this article.

Since the ESV of constructed land is 0, the conversion of other land use types to constructed land indicates a decrease in ESV.

7. Table 1: what is unused land? Is it bare land or what? please make it clear.

Answer: Thank you very much for your constructive and detail comments! We have modified the section “2.2. Data sources and processing” according to your suggestion.

The unused land indicates the saline land, marsh land, bare land, and bare rocky land.

8. Table 2: we see that the total ESV of 2000 and 2020 are almost comparable (1527.9 & 1523.6), but in 2005 ESV was the highest and what was the reason for this? and what is then your conclusion?

Answer: Thank you very much for your constructive and detail comments! We have modified the paper according to your suggestion.

High ESV ecosystems, such as forests, grasslands, wetlands, and water bodies, have an important influence in the increase and reduction of regional ESV. Although there was a considerable growth in construction land in the early stages of the study, with the backing of the strategy of returning farmland to forest and grassland, the area of cultivated land decreased significantly, resulting in an increase rather than a decrease in ESV. After 2005, with each region's rapid economic growth, land use types such as water body and grassland with high ESV coefficients were encroached upon by land use types such as construction land and cultivated land with low ESV coefficients, and forest and grassland degraded, and then the ecological quality of the region declined.

9. Table 3: how these two classes had positive changes while others are negative ones? Because hydrological regulation is dependent on other land use changes and how it is positive while others have shown negative changes?

Answer: Thank you very much for your constructive and detail comments! We have modified the paper according to your suggestion.

The slight increase in ESV of hydrological regulation function and environmental purification function in the research area was driven on by the expansion of water bodies' surface area during the research period, as the ESV of these two ecosystem service functions was mainly influenced by the area of water bodies. In contrast, other ecosystem service functions saw a decline in ESV, with the largest declines in the food production function and nutrient cycle maintenance function, which were caused by the decrease in the area of cultivated land and forest land during the research period because the area of either cultivated land or forestland had a significant impact on the ESV of various ecosystem service functions.

10. Section 4.2.: The contents of this section and figure 8 should go to the result in the section.

Answer: Thank you very much for your constructive and detail comments! We have modified the paper according to your suggestion.

11. L413: what is the degree of excessive pop? And you didn't have statistical analysis in this study that shows an increasing population.

Answer: Thank you very much for your constructive and detail comments! We have modified the paper according to your suggestion.

In addition, with the significant impact of population density on ESV, the massive pressure that population increase puts on the ecosystem must be relieved in order to better control excessive and rapid population growth.

12. L435 in conclusion section: from where this conclusion is derived as you excluded it. I think you need to include construction land in your analysis.

Answer: Thank you very much for your constructive and detail comments! We have modified the paper according to your suggestion.

Previous studies have discovered that the ESV in construction land is extremely low [9], therefore the ESV in construction land was not considered and assigned to zero in this article.

In this paper, the ESV of constructed land is assigned a value of 0 because it is small enough to be considered as having no ecosystem service value relative to other land use types.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Both the Introduction and Conclusion sections of the paper should avoid to use acronyms, which reduce their readability and should remain stand-alone parts of the manuscript.

Author Response

We much appreciate your constructive and detail comments! The following has been revised according your advice.

1. Both the Introduction and Conclusion sections of the paper should avoid to use acronyms, which reduce their readability and should remain stand-alone parts of the manuscript.

Answer: Thank you very much for your constructive and detail comments! We have modified the paper according to your suggestion.

The full names of the abbreviations have been added where they appear in the abstract and conclusion.

Author Response File: Author Response.docx