PCLM-D-23-00220

Fantastic Wetlands and Why to Monitor Them: Demonstrating the Social and Financial Benefit Potential of Methane Abatement through Salt Marsh Restoration

PLOS Climate

Dear Dr. Reilly,

Thank you for submitting your manuscript to PLOS Climate. After careful consideration, we feel that it has merit but does not fully meet PLOS Climate’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by May 04 2024 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at climate@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pclm/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

We look forward to receiving your revised manuscript.

Kind regards,

Yangyang Xu

Academic Editor

PLOS Climate

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Additional Editor Comments (if provided):

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does this manuscript meet PLOS Climate’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS Climate does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The paper demonstrates a timely and valuable calculation of the methane mitigation potential of restoring salt marsh salinity and the potential carbon credits and social benefits associated. The paper offers a sound rationale for the importance of wetland monitoring and an avenue for restoration cost offsetting through carbon crediting. What this paper does particularly well is call attention to the potential for directed scientific monitoring to make a real impact on mitigating climate change. The topic is a good fit for the audience of PLOS Climate.

My major concerns are surrounding the salinity-methane emission relationship which does not include any estimation of spatial or temporal variance and assumes a threshold rather than a linear, or other continuous relationship. A true meta-analysis of this relationship to develop more nuanced emissions factors, would be extremely valuable to the field and go a long way in improving the credibility of the present work. Further, adding an estimation of uncertainty to your emissions factors and propagating that error throughout your results is necessary. Overall writing and grammar could be improved to fix some typos and awkward phrasing.

Other suggestions for improving the manuscript:

Abstract

You state that you conducted a meta-analysis of the salt marsh salinity-methane relationship but you do not describe this in your methods or results. Did you use a systematic search of the literature? How many papers were returned? It appears to me only two papers were used to source the CH4 emissions factors; if this is the case, I would not describe it as a ‘meta-analysis’.

Introduction

Cite Holmquist, J. R. et al. Mapping methane reduction potential of tidal wetland restoration in the United States. Communications Earth & Environment 4, 1–11 (2023) to describe an estimate of candidate sites for this kind of restoration.

Methods

Table 2 and the paragraph on GWP is probably unnecessary. Sufficient to state the value applied in your analysis and that other conversions exist, but no need to go into detail.

You use the acronyms SCM and SCC without properly defining them first.

Results

You cite McGarigal’s estimate of how much tidal restriction there is in Massachusetts. Could you explain in a little more detail how this is estimated and what 50% restriction means (is that by area? by volume?).

Since you calculate an upper bound of statewide restoration outcomes, could you calculate a lower bound, or more conservative estimate. One way you could do this is to assume only ⅓ of all restorable sites have sufficiently reduced salinity, as seen in the Audubon monitoring data, and go from there?

Discussion

The caveats around temporal and spatial variability in salinity are addressed well in your discussion. Since you have fairly good temporal resolution in the data, it would improve the quality of your analysis to include this in your estimation of CH4 emissions.

Can you add a discussion of the caveats surrounding your assumed rates of CH4 production. What if you assumed a linear relationship between salinity and CH4 production instead of a threshold?

Your discussion of an amended approach to blue carbon crediting is a bit speculative. For example, a remote sensing approach for detecting salinity based on flora is unlikely to be feasible given that Spartina grows over such a large salinity range. Try to avoid speculation in general – why don’t you mention low cost methane sensors?

Your discussion of decentralized wastewater technologies is a bit unrelated and could probably be omitted.

Provide the full URL for data links (not just the hyperlinked text).

Reviewer #2: This study aimed to determine whether methane emissions resulting from salt marsh freshening, post-restoration, are mitigated by curbing salinity-reducing factors. This was considered using a case study of six salt marsh restoration sites, a meta-analysis of the relationship between methane emissions and salinity levels, which showed only two of these sites were successful in improving salinity levels. This was paired with a closer look into using salinity levels for estimating methane emissions (and carbon sequestration rates in the appendix) and applying the verified carbon standard for estimating the social cost of these emissions. The authors make sound choices to create meaningful findings despite the lack of data and do a sufficient job of acknowledging the limitations of these choices and how they may be addressed going forward. Many of these limitations have larger implications for the field’s understanding of methane emissions resulting from salt marsh restoration and how they may impact environmental policy such as the use of carbon credits. Ultimately, they called for attention towards the lack of coordination and consistency when accounting for emissions, considering mitigation strategies, and carbon credit project monitoring. This work is valuable because it sheds light on manageable ways to improve salt marsh restoration projects, a well-established climate intervention, and emphasized the short-term climate impacts as well as the potential impacts on carbon credit programming.

Minor Revisions:

The abstract could benefit from 1-2 sentences on your results on avoided annual methane emissions as well as the social cost of these methane emissions. At the end of your introduction, quantifying these estimates appears to be central to your paper’s listed purpose, and I agree that it is.

The section in the introduction on culvert widening was effective in illustrating what you are referring to when you call for practices that help reduce the freshening of salt marshes; however, it is the only time an example of what strategies we would want to further monitor.

Despite mentioning the short-term impacts of methane, even including methane’s GWP-100 and GWP-20, when you present the methane emissions estimates, you only use the GWP-100 results. Although this choice makes sense for the analysis going forward, as the verified carbon standard appears to utilize CO2e based on GWP-100, it feels as if the presentation of methane emissions rates is incomplete without representing them in CO2e using GWP-20, as well. This is a simple addition to your study and would allow you to drive home how important it is to begin to better address these methane emissions with urgency.

It is mentioned briefly that the cost of avoided methane emissions could potentially help offset the costs of salt marsh restoration and I think it would be helpful for the reader to understand how these numbers compare. This could look like just simply comparing your estimates to the typical cost of salt marsh restoration.

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Reviewer #1: No

Reviewer #2: Yes: Stephane Sartzetakis

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Fantastic Wetlands and Why to Monitor Them: Demonstrating the Social and Financial Benefit Potential of Methane Abatement through Salt Marsh Restoration

PCLM-D-23-00220R1

Dear Mr. Reilly,

We are pleased to inform you that your manuscript 'Fantastic Wetlands and Why to Monitor Them: Demonstrating the Social and Financial Benefit Potential of Methane Abatement through Salt Marsh Restoration' has been provisionally accepted for publication in PLOS Climate.

Before your manuscript can be formally accepted you will need to complete some formatting changes, which you will receive in a follow-up email from a member of our team. 

Please note that your manuscript will not be scheduled for publication until you have made the required changes, so a swift response is appreciated.

IMPORTANT: The editorial review process is now complete. PLOS will only permit corrections to spelling, formatting or significant scientific errors from this point onwards. Requests for major changes, or any which affect the scientific understanding of your work, will cause delays to the publication date of your manuscript.

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Thank you again for supporting Open Access publishing; we are looking forward to publishing your work in PLOS Climate.

Best regards,

Yangyang Xu

Academic Editor

PLOS Climate

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Reviewer Comments (if any, and for reference):

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

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2. Does this manuscript meet PLOS Climate’s publication criteria? Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe methodologically and ethically rigorous research with conclusions that are appropriately drawn based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available (please refer to the Data Availability Statement at the start of the manuscript PDF file)?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception. The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS Climate does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: I am satisfied with the authors revisions of the text. They have addressed all of my concerns.

Reviewer #2: The amended submission was thoughtful in the feedback it incorporated, particularly in refining the discussion of the analysis. The edits appropriately tackle the major feedback on analytical and stylistic issues. I recommend the acceptance of the manuscript.

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7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

Do you want your identity to be public for this peer review? If you choose “no”, your identity will remain anonymous but your review may still be made public.

For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

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