Recurringly Hypoxic: Bottom Water Oxygen Depletion Is Linked to Temperature and Precipitation in a Great Lakes Estuary

Round 1

Reviewer 1 Report

The manuscript deals with a very interesting issue that many lakes around the world are facing due to both eutrophication and climate changes. Hypoxic conditions in lakes during the stratification period may be more severe in the future with greater impact on both aquatic biota and ecosystem services. The authors investigated the temporal trend of hypoxia and related parameters in the 2011-2021 decade in a Great Lakes estuary and developed a new hypoxia severity index accounting for both duration and severity of hypoxia.

The manuscript is well written, and the data properly analysed and discussed. I think it is a valuable work which can be accepted for publication in its current form. I found only few typos.

Line 36: remove comma “because sensitive”

Line 63: specify Representative Concentration Pathway (RCP)

Line 156: Missing data occur

Line 165: were visualized

Line 210: hypoxia. A sensitivity

Line 251: remove dot

Line 272: occurs

Line 359: drive

Line 360: add dot after 0.899

Line 430: River

Line 448: heavy precipitation years

Line 484: leading to

Lines 504-505: add commas

Line 513: generate

Check figures numeration in the text (Figure 6)

Be consistent in the use of subchapter numeration (see results versus other sections)

Author Response

Please see the attachment. 

Author Response File: Author Response.docx

Reviewer 2 Report

Hypolimnetic hypoxia, which poses vital adverse effects on aquatic ecosystems, is expanding globally due to anthropogenic eutrophication and climate warming. The authors investigated the spatial and temporal distribution of the hypoxia and stratification characteristics in Muskegon Lake based on time-series monitoring data during 2011-2021. The results clarified the various patterns and their determining factors including temperatures (both air and surface water), precipitation, and wind mixing. Although the authors tried to establish a reasonable correlation between recurring hypoxia and precipitation and temperature, I would rather like to know how can we predict the occurrence and duration of hypoxia based on the environmental conditions. If we can do it would be meaningful for the management implications. It would be helpful to carry out more in-depth statistical analysis of the existing data, rather than simply descriptive treatment in the current paper.

Some specific comments:

1.      Page7, lines 3-5, the conclusion of “More precipitation and higher…” can hardly be indicated from the current results of temperatures of both air and water in Fig 4 and S2, mainly because of the time intermit based on a year other than a month. Moreover, obviously lower precipitations occurred in 2021 which was considered a severe hypoxic year.

2.      Page 9, line 267, in this paper, lack of wind data and its effects on the mixing of the water column, it would be wondering how can it influence the water mixing in depth below 11m.

3.      Page 9, line 272, water intrusions should not be a qualitative description but should be supported by more data, including, at least, water volume, frequency, and duration. This can help readers to evaluate the extent of water mixing resulting from the bottom water inflowed from Lake Michigan wedges.

4.      Page 11, line298, Schmidt stability values shown in the Figures are all below 500J/m².

5.      Page 14, line 392, lacks data for nutrients and OM inputs in the current paper to support the authors’ conclusion.

For the reasons above mentioned, I cannot recommend this manuscript to be published with the current edition, and also I suggest authors to further improve the writing quality and complement the necessary data.

Overall, the English language is well.

Author Response

Please see the attachment. 

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

After the author's modifications to the manuscript, I consider this work suitable for publication.

Author Response

Thank you for reviewing our responses to the your valuable comments, and approving the revised manuscript.