PWAT-D-21-00022

Solar circulator to restore dissolved oxygen in a hypoxic ice-covered lake

PLOS Water

Dear Dr. Flynn,

Thank you for submitting your manuscript to PLOS Water. Two referees have reviewed your paper, one reviewers accepts and another have minor comments. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. The reviewer comments are included with this letter. Please make necessary revisions and resubmit the manuscript.

Please submit your revised manuscript by Nov 28 2021 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 water@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pwat/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

• A rebuttal letter that responds to each point raised by the editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.
• A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.
• An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

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,

Sher Muhammad, PhD

Academic Editor

PLOS Water

Journal Requirements:

1. In your Methods section, please provide additional information regarding any permits you obtained for the work. Please ensure you have included the full name of the authority that approved your field site access and, if no permits were required, a brief statement explaining why.

2. Please provide separate figure files in .tif or .eps format only, and remove any figures embedded in your manuscript file.  If you are using LaTeX, you do not need to remove embedded figures.

For more information about figure files please see our guidelines: 

https://journals.plos.org/water/s/figures

3. We noticed that you used “data not shown”/"unpublished data" in the manuscript. We do not allow these references, as the PLOS data access policy requires that all data be either published with the manuscript or made available in a publicly accessible database. Please either remove these references, or amend the supplementary material to include the referenced data.

4. We do not publish any copyright or trademark symbols that usually accompany proprietary names, eg (R), (C), or TM  (e.g. next to drug or reagent names). Therefore please remove all instances of trademark/copyright symbols throughout the text.

5. We notice that your supplementary figures/tables are included in the manuscript file.  Please remove them and upload them  with the file type 'Supporting Information'  . Please ensure that all Supporting Information files are included correctly and that each one has a legend listed in the manuscript after the references list. 

6. In the online submission form, you indicated that your data will be submitted to the Dryad database upon acceptance. Should your submission be accepted, we will require the following information in your Data Availability Statement: 

1. The DOI provided by Dryad

2. The citation for your data package in the reference section of your manuscript

3. The citation for your data package in the methods section

If you are unable to adhere to our open data policy, please kindly revise your statement to explain your reasoning and we will seek the editor's input on an exemption. Please be assured that, once you have provided your new statement, the assessment of your exemption will not hold up the peer review process.

7. Please amend your detailed Financial Disclosure statement. This is published with the article, therefore should be completed in full sentences and contain the exact wording you wish to be published.

State what role the funders took in the study. If the funders had no role in your study, please state: “The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.”

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.

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Does this manuscript meet PLOS Water’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

**********

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

Reviewer #1: Yes

Reviewer #2: Yes

**********

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: No

Reviewer #2: Yes

**********

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

PLOS Water 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

**********

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: This is an interesting paper about efforts to induce improve dissolved oxygen in a shallow ice covered lake by having an impeller forcing a polynya to stay open. I made notes in the PDF as I was reading paper, and attach that to review. I’ll summarize my key questions below.

It would be very helpful and informative to include a sketch of what the authors think the circulation is near the impeller and in the far field. I was not clear how wide the polynya was, but presumable this is closely related to the near field circulation? You mention it is is pumping 0.5 m^3/s up, but how far out does this water go due to just impeller, if buoyancy gradients were not important? Does this set size of polynya? It looks like it might be 50 m wide from photo?

Related to this is question about what sets the circulation in far field. The authors acknowledge that the polynya does two things, it increases DO fluxes at same time as it cools the water. A crucial detail that isn’t really discussed in paper is the inverse thermal stratification present under ice. Water is densest at 4oC, so you always see this warmest water at bottom of lakes. Cooling surface water makes it lighter, until it freezes. So the polynya is acting as a source of “light” water that would flow away from source at a speed roughly similar to the internal wave speed U = sqrt(g’ H) where g’ is reduced gravity between 4 and 0 C water, and H the depth of outflowing layer. These speeds are slow and many authors describe how in winter lakes = that Coriolis forces become important on scales of 1-2 km (the Rossby radius), possibly trapping effects of polynya (see recent work by Bernard Laval at UBc and Alex Forrest at UC Davis). In particular these Coriolis driven gyre circulate water which might explain why more oxygen at 1000S rather than 1000E

It is isn’t clear where the temperature plotted at Fig 4c is. This matters for discussing water circulation, as you need to know where it is in inverse stratification. Main feature is it stays near 4oC for whole record. At the moment this is only record shown of water temperature, so I can’t speculate about circulation.

The MiniDOT sensors also record water temperature, and I encourage authors to include data related to Figure 5, where only a time series of DO is plotted at the top and bottom of water column. You should see a cooling effect due to impeler, and bee able to say something about spatial gradients of T. For instance you could make a contour plot of T as a function of death and distance going south and east for times before and after the impeller stopped. The differences in stratification should indicate what the circulation was. This would then look similar to the contour plots in Figure 7 for DO.

I feel if the authors could speculate on the circulation based on temperature records, they would be better able to explain far field movements of DO, which would help them predict how useful impellers are in wide lakes, and how many you might need.

This is interesting data and I hope changes I am suggesting are easy to implement!

Mathew Wells

Reviewer #2: The manuscript is well written and for the most part easily comprehendible. By use of the monitoring equipment, a large amount of data were collected about water quality and weather condition over time. The manuscript contains an organized presentation of the data showing what occurred as the lake surface progressed from open water, to ice cover, to thaw. The paper is useful for this reason alone.

The result obtained with the water circulation device is what I would have expected - failure. However, the positive aspect of the effort was to describe exactly what was occurring with the water of the lake in response to weather conditions. These findings should be valuable to those trying to develop and market devices for preventing winterkill in lakes. The data allow insight as to why the device failed that should be useful in improving it.

The study was practical and directed at testing the effectiveness of a water circulator. But, the water quality findings should be of interest even for theoretical limnologists.

**********

6. 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: Yes: Claude E. Boyd

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

Attachments

Attachment

Submitted filename: PWAT-D-21-00022_MGW.pdf

Solar circulator to restore dissolved oxygen in a hypoxic ice-covered lake

PWAT-D-21-00022R1

Dear Dr. Flynn,

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. 

Within one week, you'll receive an e-mail detailing the required amendments. When these have been addressed, you'll receive a formal acceptance letter and your manuscript will be scheduled for publication. The journal will begin publishing content in early 2022.

An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at https://www.editorialmanager.com/pwat/ click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org.

If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they'll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact water@plos.org.

Kind regards,

Sher Muhammad, PhD

Academic Editor

PLOS Water

Additional Editor Comments (optional):

The authors are advised to revise Figure S2.

Journal requirements:

- Please ensure that all potentially competing interests are disclosed per PLOS Water policy: https://journals.plos.org/water/s/competing-interests. Specifically, it seems that authors' affiliations to KF2 consulting and CDM Smith, Inc should be disclosed under this policy.

- In the Methods, please include whether permission was needed (and if so, whether it was obtained) to access URRL for the purposes of this study.

- In the legend to figure 1A, please include the source of the map base layer and ensure that the map can be published under a CC BY license that PLOS Water applies to all published work.

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: All comments have been addressed

**********

2. Does this manuscript meet PLOS Water’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

**********

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

Reviewer #1: 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

**********

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

PLOS Water 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

**********

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: The authors have addressed all my comments.

I still think there is room to improve on the Figure S2 though. I agree that plotting the mean of top and bottom temperature doesn't tell you much about circulation. It would be better to also plot the difference between the top and bottom logger, as this would then link in with your new S1 and Fig 2b. For example, S1 clearly shows there is 1-3 degrees of vertical stratification in much of pond, which controls all the internal mixing. I assume that near the impeller, that the vertical stratification was weak when the impeller was running, but further away it was stronger? I would encourage authors to add a figure S3 that shows these vertical differences, rather than just means as in S2. In winter all temperatures are in range 0-4 C so the subtle vertical and horizontal gradient drive all the slow circulation patterns.

**********

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

**********