Spatial–Temporal Evolution Monitoring and Ecological Risk Assessment of Coastal Wetlands on Hainan Island, China

Round 1

Reviewer 1 Report

Thanks for your inviting me to review the manuscript “Spatial-temporal evolution monitoring and ecological risk assessment of coastal wetlands on Hainan Island, China ”. The author uses remote sensing to study about the spatial and temporal evolutionary characteristics, stability and ecological risks of coastal wetlands on Hainan Island. I read the manuscript carefully, I think the manuscript still needs a lot of improvement before it can be published.

1. I suggest that authors refine the expression abstract, and highlight the innovation and necessity of research. Please add a sentence which shows the necessity of this study.

2. In the introduction, the length is too short and the description of the research background is too simplistic, which makes it difficult to understand the core logic that the author is trying to express and the hierarchy is not clear.

3. I do not think the authors make it very clear of their contributes to this field. Please follow the literature review by a clear and concise state of the art analysis. Clearly discuss what the previous studies that you are referring to. In addition, in the introduction, what are the Research Gaps/Contributions? Please note that the paper could be clearly research gap and novelty of the study.

4. The author needs to further explain the uniqueness of in the coastal wetlands and the necessity of studying the Spatial-temporal evolution monitoring and ecological risk assessment in this area. Your research methods are not clear enough.

5. In the results section, you should focus on the main points of your research rather than putting in all your images. In addition, I recommend authors to present your results in a different way, thus enhancing the manuscript.

6. Another obvious problem with this paper is lack of sufficient explanation of the simulation results. You need to explain your simulation results in detail and why you got such results.

7. In the discussion section, I recommend author adding several reasoning and comparison of the study finding with other similar published work through available in the literature. In addition, please link your empirical results with a broader and deeper literature review.

8. The conclusions should be expanded as it doesn’t refer to the finding. The conclusion needs to add some specific values. In the conclusions, except to summarizing the actions, please strengthen the explanation of their significance, especially those stemming from previous work to make the findings and contributions of the paper clearer.

Author Response

Dear editors and reviewers,

On behalf of my co-authors, we thank you very much for giving suggestions to our manuscript, we appreciate the editors and reviewers very much for your positive and constructive comments and suggestions on our manuscript entitled “Spatial–temporal evolution monitoring and ecological risk assessment of coastal wetlands on Hainan Island, China” (ID: remotesensing-2179469).

We have studied the comments carefully and have made revision highlighted. We have tried our best to revise our manuscript according to the comments. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

Responses to Reviewer #1’s Comments

Thanks for your inviting me to review the manuscript “Spatial-temporal evolution monitoring and ecological risk assessment of coastal wetlands on Hainan Island, China”. The author uses remote sensing to study about the spatial and temporal evolutionary characteristics, stability and ecological risks of coastal wetlands on Hainan Island. I read the manuscript carefully, I think the manuscript still needs a lot of improvement before it can be published.

[1] I suggest that authors refine the expression abstract, and highlight the innovation and necessity of research. Please add a sentence which shows the necessity of this study.

Answers: Thank you for your suggestion. We have added a sentence which shows the necessity of this study in line 15-19.

Line 78-80: The coastal wetlands of Hainan Island, China, are coastal wetlands typical of tropical islands and are extremely sensitive to climate change. In the context of global sea level rise, studying the characteristics of spatial and temporal distribution of coastal wetlands on Hainan Island, as well as changes in their vulnerability, could provide scientific and technological support to address the adverse effects of climate change.

[2] In the introduction, the length is too short and the description of the research background is too simplistic, which makes it difficult to understand the core logic that the author is trying to express and the hierarchy is not clear.

Answers: Thank you for your reminding. We have expanded the introduction section to make it easier to understand the logic we are trying to express and to make the hierarchy more clear. More information can be seen in the “introduction” section with blue font.

[3] I do not think the authors make it very clear of their contributes to this field. Please follow the literature review by a clear and concise state of the art analysis. Clearly discuss what the previous studies that you are referring to. In addition, in the introduction, what are the Research Gaps/Contributions? Please note that the paper could be clearly research gap and novelty of the study.

Answers: Thank you for your reminding. To make it more clear of our contributes to this field. We have followed the literature review by a clear and concise state of the art analysis in line 84-88, line 108-112.

Line 84-88: However, these studies mainly focus on the spatial–temporal variation in coastal wet-lands along the mainland and typical harbor wetlands. Up to now, we have poor knowledge of the spatial–temporal evolutionary characteristics of coastal wetlands on a typical tropical mountain island, which are extremely sensitive and vulnerable to climate change.

Line 108-112: However, only a few scholars have attempted to assess the historical evolution of coastal wetland stability or ecological vulnerability [35, 36]. Inadequate knowledge of the history of changes in the vulnerability of coastal wetlands will be an obstacle to accurately predicting their future changes.

[4] The author needs to further explain the uniqueness of in the coastal wetlands and the necessity of studying the Spatial-temporal evolution monitoring and ecological risk assessment in this area. Your research methods are not clear enough.

Answers: Thank you for your suggestion. We have tried our best to further explain the uniqueness of the coastal wetlands and the necessity of studying the spatial-temporal evolution monitoring and ecological risk assessment in this area by adding more information about our study area both in the last paragraph of “introduction” section and in the “study area” section. More information can be seen in the last paragraph of the “introduction” section (line 113-114, line 116-117) the “study area” section (line 131-134) with blue front.

For the methods section, we also tried to make it more clear. More information can be seen in the “methods” section (line 154-159) with blue front.

Line 113-114: Hainan Island is a typical mountainous tropical island, influenced by both the mainland and the ocean.

Line 116-117: Understanding the past is the basis for predicting the future.

Line 131-134: The topography of Hainan Island is characterized by mountains in the middle, sur-rounded by coastal plains, with elevation decreasing from the middle to the surroundings. There are many rivers and harbors in the developed mountainous water system.

Line 154-159: Since the dry season has more sunny days and less clouds than the rainy season, most of the rainy season data are not up to standard; thus, to ensure the consistency of the data, all the remote sensing data are from the dry season. Data pre-processing, such as atmospheric calibration, Landsat-7 ETM+ image strip repair, and the export of the cropped data to TIFF format, were conducted on the Google Earth Engine (GEE) platform.

[5] In the results section, you should focus on the main points of your research rather than putting in all your images. In addition, I recommend authors to present your results in a different way, thus enhancing the manuscript.

Answers: Thank you for your suggestion. We have tried our best to make the result section more clear to enhance our manuscript. More information can be seen in the “result” section (line 280-283, line 306-311, line 313-314, line 322-323, line 329-332, line 347-349) with blue front.

Line 280-283: The artificial wetlands in all harbors showed a clear and continuous increasing trend, in-dicating that the intensity of human activities on Hainan Island continued to intensify during the study period. The total area of mangrove wetlands and natural wetlands in DZG exhibited a consistent increase, but fluctuating changes were shown in other areas.

Line 306-311: This ratio showed an increasing trend (from 15.12% in 1990 to 21.89% in 2020). This in-creasing trend has been especially significant since 2015. It shows that the earlier the pro-tection, the better the development of natural coastal wetlands. In contrast, the mangrove area ratio of BMG decreased significantly, from 15.77% to 8.72%, indicating that human activities are an important cause of the degradation of natural coastal wetlands such as mangroves.

Line 313-314: Among them, the highest artificial wetland area ratios were found in CQH (from 2.13% in 1990 to 32.50% in 2020) and BMG (from 6.06% in 1990 to 25.98% in 2020).

Line 322-323: It shows that the ecological risk of Hainan Island is increasing in general.

Line 329-332: The average WRI was below 0.15 for all harbors, indicating that the ecological risk of coastal wetlands on Hainan Island is low. The CQH (0.15), WKH (0.14), BMG (0.12), and MLG (0.12) are of medium risk level. The average WRI for other harbors ranged from 0.05 to 0.06. DZG had the lowest mean WRI (0.03), followed by CHG (0.04) and DZW (0.05).

Line 347-349: The higher the degree of protection of coastal wetlands, the lower the WRI. The stronger the human activity and the more intense the development, the higher the WRI.

[6] Another obvious problem with this paper is lack of sufficient explanation of the simulation results. You need to explain your simulation results in detail and why you got such results.

Answers: Thank you for your suggestion. We have tried our best to explain our simulation results in detail and why we got such results in both “result” section and “discussion” section. More information can be seen in the “result” section (line 280-283, line 306-311, line 313-314, line 322-323, line 347-349) and “discussion” section (line 411-421, line 431-449) with blue front.

Line 280-283: The artificial wetlands in all harbors showed a clear and continuous increasing trend, in-dicating that the intensity of human activities on Hainan Island continued to intensify during the study period. The total area of mangrove wetlands and natural wetlands in DZG exhibited a consistent increase, but fluctuating changes were shown in other areas.

Line 306-311: This ratio showed an increasing trend (from 15.12% in 1990 to 21.89% in 2020). This in-creasing trend has been especially significant since 2015. It shows that the earlier the pro-tection, the better the development of natural coastal wetlands. In contrast, the mangrove area ratio of BMG decreased significantly, from 15.77% to 8.72%, indicating that human activities are an important cause of the degradation of natural coastal wetlands such as mangroves.

Line 313-314: Among them, the highest artificial wetland area ratios were found in CQH (from 2.13% in 1990 to 32.50% in 2020) and BMG (from 6.06% in 1990 to 25.98% in 2020).

Line 322-323: It shows that the ecological risk of Hainan Island is increasing in general.

Line 347-349: The higher the degree of protection of coastal wetlands, the lower the WRI. The stronger the human activity and the more intense the development, the higher the WRI.

Line 411-421: Many factors that would influence the results of ecological risk assessment were not in-cluded, for example, natural factors such as sea level changes, typhoons, extreme climate events, wetland elevation changes, etc., and human factors such as the total value of na-tional economic output related to wetland, changes in population near wetlands, changes in artificial construction area and hardened area in and around wetlands, changes in total road miles and levels in and near wetlands, artificial seawall miles, etc. If all these factors were considered, the ecological risk to wetlands on Hainan Island could be even higher. However, datasets relevant to these factors are difficult to obtain. We therefore did not take them into consideration in this study, which inevitably reduces the comprehensiveness of the assessment results [31, 36, 46].

Line 431-449: In Hainan Island, thanks to two important policies, up to now, no significant reduc-tion in coastal natural wetlands on Hainan Island has occurred. First, mangrove protec-tion in Hainan Island started earlier than in other areas. Wetland reserves or wetland parks have been established in large, typical coastal wetlands on Hainan Island, such as the DZG national nature reserves, the BMG provincial nature reserve, the DZW Haiwei wetland park, etc [23, 37, 53, 54]. Take the DZG as an example: natural wetlands have been effectively protected there since 1986 when the DZG Mangrove National Nature Re-serve was established. Therefore, the mangrove wetlands in DZG can maintain an in-creasing trend even though the area of aquaculture ponds continues to increase [23, 37]. Although the area of aquaculture ponds has also increased significantly, this has been achieved mainly by outward expansion, and the outward expansion of artificial wetlands has to some extent provided the conditions for the expansion of natural wetlands. Second, Hainan Island has insisted on the strategy of regional economic development driven by tourism development for a long time. Therefore industrial development is slow, and the damage to coastal wetlands is very low [63]. Meanwhile, the coastal wetlands on Hainan Island are facing serious threats. On the one hand, with the growth of the population and socio-economic development, a large area of coastal lowland was developed into aqua-culture ponds or artificial land surface (such as hotels, tourist ports, roads, other tourist support facilities, etc) [49, 53, 63].

[7] In the discussion section, I recommend author adding several reasoning and comparison of the study finding with other similar published work through available in the literature. In addition, please link your empirical results with a broader and deeper literature review.

Answers: Thank you for your suggestion. We have added several reasoning and comparison of the study finding with other similar published work through available literature. More information can be seen in the “discussion” section (line 362-365, line 367-368, line 370-379, line 401-402) with blue front. But for “risk assessment”, as there are few relevant studies, we have added very little relevant content.

Line 362-365: In general, areas of natural coastal wetlands, such as the mangroves on Hainan Island, did not undergo a significant decrease during the study period, while the area of artificial wetlands such as aquaculture ponds exhibited a continuous process of increase.

Line 367-368: Similar findings were reported by Wang et al. [47], Fu et al. [37], Li et al. [48], and Liao et al. [49].

Line 370-379: Spatially, aquaculture ponds are mainly located in Wenchang in the northeastern part of Hainan Island [52]. However, regionally, the changes in coastal wetlands on Hainan Is-land have obvious regional differences, which is also similar to the results of previous studies. Cai et al. found that no further decrease in mangrove area occurred in DZG after 1990 [23]. In contrast, Jia et al. [53] and Zhu et al. [54] showed that, between 1987 and 2020, the mangrove forests in BMG successively underwent a process of degradation followed by fluctuating recovery, but the overall mangrove area was significantly reduced, with most of the lost mangrove forests being converted into aquaculture ponds, buildings and agricultural land.

Line 401-402: Although the various risk indices of the major harbor wetlands in the Hainan Island are low, the variability varies across different harbors.

[8] The conclusions should be expanded as it doesn’t refer to the finding. The conclusion needs to add some specific values. In the conclusions, except to summarizing the actions, please strengthen the explanation of their significance, especially those stemming from previous work to make the findings and contributions of the paper clearer.

Answers: Thank you for your suggestion. We have expanded our conclusion. More information can be seen in the “conclusion” section (line 494-501, line 504-510) with blue front.

Line 401-402: Mangrove wetland areas with a high degree of protection such as DZG have increased (increased from 15.12% in 1990 to 21.89% in 2020). The mangrove wetlands in areas with strong human activities such as BMG were largely taken over by artificial wetlands (de-creased from 15.77% in 1990 to 8.72% in 2020). (2) Overall, the coastal wetland ecosystem of Hainan Island is relatively stable and has a low ecological risk index (WRI is less than 0.15). The WRI was negatively correlated with the degree of protection and positively cor-related with the intensity of human activities, with a correlation coefficient of -0.703.

Line 401-402: Sea level rise due to climate warming and increasing intensity of human activities will be the challenge for future coastal wetlands on Hainan Island to achieve their ecosystem ser-vice functions. The understanding of coastal wetland change and its drivers in Hainan Island and the key data obtained from the results of this study is a complement to the cur-rent knowledge gap in the region. These data will provide scientific guidance for regional environmental assessment and government decision making.

Reviewer 2 Report

Comments for author File: Comments.pdf

Author Response

Dear editors and reviewers,

On behalf of my co-authors, we thank you very much for giving suggestions to our manuscript, we appreciate the editors and reviewers very much for your positive and constructive comments and suggestions on our manuscript entitled “Spatial–temporal evolution monitoring and ecological risk assessment of coastal wetlands on Hainan Island, China” (ID: remotesensing-2179469).

We have studied the comments carefully and have made revision highlighted. We have tried our best to revise our manuscript according to the comments. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

Responses to Reviewer #2’s Comments

[1] A native speaker should help with the English language, grammar and syntax are not up to par.

Answers: Thank you for your suggestion. The manuscript has undergone English language editing by MDPI. The text has been checked for correct use of grammar and common technical terms, and edited to a level suitable for reporting research in a scholarly journal. MDPI uses experienced, native English speaking editors.

[2] Lines 62-64: The sentence does not make sense.

Answers: Thank you for your reminding. We have rewritten the paragraph to make it more clear. More information can be found in line 89-112.

Line 89-112: In coastal wetland vulnerability studies, a large number of scholars have studied the ef-fects of different magnitudes of sea level rise on the stability and ecological functions of coastal wetlands under different emission scenarios in the future [23, 29-34]. Schuerch et al. predict that the total area of global coastal wetlands can be increased by up to 60% if enough space for coastal wetlands to retreat is available; otherwise, it may be reduced by 30% [29]. Saintilan et al. predicted that mangroves are likely (>90% probability) to fail to grow sustainably when the relative sea level rise rate exceeds 6.1 mm per year. Moreover, in the high emissions scenario, the tropical coastline is likely to exceed this threshold within 30 years [30]. Estrela-Segrelles et al. evaluated the risk of coastal wetlands in the Mediterranean under different emission scenarios [31]. Cai et al. predicted that under RCP 4.5 and RCP 8.5, sea level rise is expected to result in the loss of 26% of the mangroves in Dongzhai Harbor by 2100, and under RCP 2.6, 17% of the mangroves may be lost [23]. Chatting et al. predicted the changes in mangrove carbon stocks under future climate change and deforestation [32]. By integrating data from 166 estuaries around the United States, Osland et al. predict that the migration of coastal wetlands to land will alter coast-lines, but not offset the loss to the ocean. Two-thirds of the potential wetland migration is expected to be at the expense of coastal freshwater wetlands, while the remaining one-third is expected to be at the expense of valuable uplands, including agricultural lands, forests, pastures, and grasslands [33]. Van der Stocken et al. predicted that global changes in seawater density would disrupt the spread of mangroves [34]. However, only a few scholars have attempted to assess the historical evolution of coastal wetland stability or ecological vulnerability [35, 36]. Inadequate knowledge of the history of changes in the vulnerability of coastal wetlands will be an obstacle to accurately predicting their future changes.

[3] “Since the dry season has more sunny days and less clouds, the remote sensing data are mainly from dry season”. Does that mean that some of them are not taken during dry season? And if some of them are not, does that not affect the validity of the comparison? Please specify or rephrase, otherwise the validity of your results could be questionable.

Answers: Thank you for your reminding. Yes, all the images we used are from dry season. We have rewrite related content in line 154-157.

Line 154-157: Since the dry season has more sunny days and less clouds than the rainy season, most of the rainy season data are not up to standard; thus, to ensure the consistency of the data, all the remote sensing data are from the dry season.

[4] Line 508: The doi:10.1177/002076409904500102 of [38] belongs to another article (Application and results of the Manchester Short Assessment of Quality of Life (MANSA) - PubMed (nih.gov)) and not to the cited conference proceedings.

Answers: Thank you for your reminding. We have revised it and checked all the reference.

Reviewer 3 Report

I have reviewed the manuscript titled " Spatial-temporal evolution monitoring and ecological risk assessment of coastal wetlands on Hainan Island, China". This manuscript discusses the coastal wetlands in Hainan Island.

The manuscript describes work that is a very important component to ecological work associated with the coastal area. Educating and optimizing the implementation of multi-purpose wetlands or any other ecological systems is paramount of stakeholder acceptance and long-term success.

The abstract of the paper is mostly textual and introduces the approach used in research well enough. However, fails to provide insights on the findings or shortcomings of the findings or anything more that can be useful. I strongly believe that writing the abstract to reflect the paper in its entirety will be a good addition.

The keywords are plain, it will be interesting if the authors can come up with a set of more pertinent keywords that can allow a further insight into the work done here.  

1.           The MS does contribute scientifically or new in terms of methodology - a set of well-known methods are applied and used in this study to evaluate the

2.           I see a fruitful discussion on the generated datasets and scientific problem is analyzed and solved.

3.           The introduction is strong, the method section is written well and Discussion is existing. Most of the literature cited is about wetlands, however, there are more recent literature is required.

4.           I don't feel qualified to judge about the English language and style but the English language needs improvement.

Overall authors have applied useful statistics to extract useful results towards environmental significance.  

Recommendation.

Summarize my comments, I would recommend to Authors to address the revision and this manuscript can be published.

 

 

Author Response

Dear editors and reviewers,

On behalf of my co-authors, we thank you very much for giving suggestions to our manuscript, we appreciate the editors and reviewers very much for your positive and constructive comments and suggestions on our manuscript entitled “Spatial–temporal evolution monitoring and ecological risk assessment of coastal wetlands on Hainan Island, China” (ID: remotesensing-2179469).

We have studied the comments carefully and have made revision highlighted. We have tried our best to revise our manuscript according to the comments. The main corrections in the paper and the responds to the reviewer’s comments are as flowing:

Responses to Reviewer #3’s Comments

I have reviewed the manuscript titled " Spatial-temporal evolution monitoring and ecological risk assessment of coastal wetlands on Hainan Island, China". This manuscript discusses the coastal wetlands in Hainan Island.

The manuscript describes work that is a very important component to ecological work associated with the coastal area. Educating and optimizing the implementation of multi-purpose wetlands or any other ecological systems is paramount of stakeholder acceptance and long-term success.

The abstract of the paper is mostly textual and introduces the approach used in research well enough. However, fails to provide insights on the findings or shortcomings of the findings or anything more that can be useful. I strongly believe that writing the abstract to reflect the paper in its entirety will be a good addition.

The keywords are plain, it will be interesting if the authors can come up with a set of more pertinent keywords that can allow a further insight into the work done here. 

1. The MS does contribute scientifically or new in terms of methodology - a set of well-known methods are applied and used in this study to evaluate the
2. I see a fruitful discussion on the generated datasets and scientific problem is analyzed and solved.
3. The introduction is strong, the method section is written well and Discussion is existing. Most of the literature cited is about wetlands, however, there are more recent literature is required.
4. I don't feel qualified to judge about the English language and style but the English language needs improvement.

Overall authors have applied useful statistics to extract useful results towards environmental significance. 

Recommendation.

Summarize my comments, I would recommend to Authors to address the revision and this manuscript can be published.

Answers: Thank you very much for your affirmation and you suggestion. We have added some information in the abstract to make it more clear in line 15-19.

For the keywords, we have tried to changed some keywords to make it more pertinent in line 33-34.

Line 15-19: The coastal wetlands of Hainan Island, China, are coastal wetlands typical of tropical islands and are extremely sensitive to climate change. In the context of global sea level rise, studying the characteristics of spatial and temporal distribution of coastal wetlands on Hainan Island, as well as changes in their vulnerability, could provide scientific and technological support to address the adverse effects of climate change.

Line 15-19: Coastal Wetland; Hainan Island; Spatial–temporal Evolution ; Risk Assessment; Sea Level Rise; Human Activity

Round 2

Reviewer 1 Report

Please refer to editor's comments.