PONE-D-24-23965Distributary development in a 21st century river: The evolution of Neptune Pass and its delta, the largest new offshoot of the Mississippi RiverPLOS ONE

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Additional Editor Comments:

The study primarily relies on conventional methods for analyzing sediment transport and land formation, such as sediment core collections and remote sensing, which may not capture more complex aspects of distributary development and delta dynamics. Additionally, while it investigates sediment dynamics in Neptune Pass, it lacks a deeper exploration of the broader environmental or hydrological impacts, missing a nuanced understanding of how these processes affect local and regional ecosystems. The results are presented with varying levels of detail, which complicates full interpretation, as sediment volumes are reported with different levels of confidence and assumptions, potentially affecting the reliability of the conclusions. The discussion on potential management strategies is somewhat generic, lacking specific recommendations or actionable insights that could directly inform policy or management practices. Moreover, the paper does not adequately compare its findings with other studies or historical data, which would help contextualize the significance of Neptune Pass’s development within a broader framework of delta evolution and river management. The study reports a net deposition of sediment in Quarantine Bay but does not fully account for possible variations in sediment density or other factors influencing the sediment budget, which could strengthen the findings. The discussion of the "new land" versus "redistributed sediment" hypotheses may oversimplify the sediment dynamics, as both processes might contribute to land development, warranting a more detailed examination of sediment sources and pathways. Future predictions and management interventions are discussed without specific, data-driven scenarios; incorporating more detailed modeling and field studies could better predict the impacts of reduced flow or sediment retention measures on Neptune Pass. The generalizations about coastal management implications lack site-specific factors or challenges, and more precise recommendations tailored to the local context would be beneficial. Lastly, while the study highlights Neptune Pass as a net land-building system, it does not thoroughly explore the ecological consequences, such as impacts on local flora and fauna or changes in habitat conditions, which would provide a more comprehensive understanding of the delta's evolution.

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Reviewers' comments:

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Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

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

Reviewer #1: N/A

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). 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

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Reviewer #1: 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: Excellent paper that has left no ground unturned. Will be useful to both delta geoscientists and delta managers. Well done!

Minor points to rectify:

Line 118: potentially leading to ...

Lines 122ff and 126ff: Where do these hypotheses come from? If you are presenting them here for the first time then reword this as the presentation looks awkward and gives the impression that that these hypotheses are already extant.

Line 145: "to generate (rather than provide in order to avoid using "provide" twice in the same sentence).

Line 146ff: This information should also be useful to delta geoscientists, so although this is mentioned above, it can be reiterated following the management bit for delta geoscience management elsewhere.

Line 809: Fig. 14. Need to specify that this delta cycle refers to the Mississippi and reference Roberts as reference 18.

Line 584: "also consistent with ..."

Figures: Figure 1 is a bit disappointing. For an international readership, please show a regional USA map with the Mississippi delta in inset and add geographical coordinates to the figure.

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Reviewer #1: Yes:  Edward Anthony

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PONE-D-24-23965R1Distributary development in a 21st century river: The evolution of Neptune Pass and its delta, the largest new offshoot of the Mississippi RiverPLOS ONE

Dear Dr. Kolker,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’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 Mar 05 2025 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 plosone@plos.org . When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

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• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

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We look forward to receiving your revised manuscript.

Kind regards,

Venkatramanan S, Ph.D.

Academic Editor

PLOS ONE

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Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

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Reviewers' comments:

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: (No Response)

Reviewer #2: All comments have been addressed

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

**********

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

Reviewer #1: N/A

Reviewer #2: N/A

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). 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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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE 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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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: Review of PLOS ONE

“Distributary development in a 21st century river: The evolution of Neptune Pass and its delta, the largest new offshoot of the Mississippi River” by A. Kolker et al.

I reiterate my satisfaction with this manuscript which has monitored the potential inception factors, growth, and dynamics of a new delta pass with significantly rapid lobe sedimentation. I am sure it will be an impactful contribution to a better understanding of the Mississippi River delta and to delta science in general.

I SUGGEST MINOR EDITS THAT ARE LISTED BELOW:

Delta and delta lobe: The authors systematically refer to “delta” development with regards to the sediment accumulation associated with Neptune Pass. This is somewhat unfortunate as the background context is the Mississippi river and its DELTA. It may be less confusing to refer to delta LOBES (which all these other components of the Mississippi DELTA are), rather than individual DELTAS, e.g., lines 96-98, 121, 425-6. Sub-delta (line 699) is another new addition that does not clarify the picture.

• Lines 41-42: “observation, coincides with an era when rivers have been controlled by large engineering projects”. Delete comma after observation and be less sweeping regarding river modification: “many rivers have been controlled ...”.

• Lines 48-49: “it is building is comprised .. Awkward statement.

• Line 66: “..and often serve as a locus for human activities”. Use a more recent and more pertinent reference by some of the same authors:

- Anthony, E., Syvitski, J., Zăinescu, F., Nicholls, R.J., Cohen, K.M., Marriner, N., Saito, Y., Day, J., Minderhoud, P.S.J., Amorosi, A., Chen, Z., Morhange, C., Tamura, T., Vespremeanu-Stroe, A., Besset, M., Sabatier, F., Kaniewski, D., Maselli, V., 2024. Delta sustainability from the Holocene to the Anthropocene and envisioning the future. Nature Sustainability, 7,1235-1246. https://doi.org/10.1038/s41893-024-01426-3

• Line 69: and alter the biogeochemistry and ecology of coastal waters [7–9]. Consider also the recent paper on tipping points in delta channels:

- van de Vijsel, R.C., Scheffer, M., Hoitink, A.J.F., 2024. Tipping points in river deltas. Nature Reviews Earth & Environment, 5, 843–858. https://doi.org/10.1038/s43017-024-00610-5

• Line 131-2: “It should be noted that these hypotheses are not mutually exclusive and represent end-members on a spectrum of sediment input possibilities”. Remove parentheses as this is an important point.

• Line 173: “It is across the river ..”. Quaint or colloquial expression. Please rectify.

• Line 223: “by placing ‘a’ rock wall ..”

• Line 225: “to inform comments on such this proposal …” Rectify.

• Line 243: “and its potential impacts ‘on’… (on, in lieu of to).

• Lines 251-2: “data on discharge in the Mississippi River using data from multiple outside sources”. Awkward. Reword as “data on discharge in the Mississippi River and from multiple outside sources”

• Line 255: “data was compiled”. Use rather “data were compiled”. Check manuscript and homogenize, as, sometimes, “data” is/are referred to in the singular (in abstract for instance : “there is relatively little data …) or plural form (line 149: “data that provide..”; line 290: “survey data were integrated ..”) form.

• Line 1069: Syvitski J, Anthony E, F. SYZ,. Check author name SYZ….

Reviewer #2: I would like to commend the authors for their efforts in conducting this research to understand the role of new distributary systems in larger rivers in developing landforms through sedimentation processes. The methodology adopted for this study is clear and can be applied to other parts of the world where new distributary systems are being planned. This research also enhances our understanding of erosional and accretional processes along coastlines influenced by new river distributary systems. Additionally, the authors have significantly improved the article based on the constructive comments and suggestions provided by reviewers and editors during the previous review process. I recommend that this article be accepted for publication.

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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.

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Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy .

Reviewer #1: Yes:  Edward Anthony

Reviewer #2: No

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Distributary development in a 21st century river: The evolution of Neptune Pass and its delta, the largest new offshoot of the Mississippi River

PONE-D-24-23965R2

Dear Dr. Kolker,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Venkatramanan S, Ph.D.

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Based on the reviewer’s comments, the authors have revised the paper, and it is now ready for publication.

Reviewers' comments: