Dear Authors,

Thank you for providing detailed responses to the comments and suggestions offered by two reviewers.

Both reviewers recognized the scientific value and novelty of your manuscript, but the second reviewer also raised several critical issues. I agree that you need to pay more attention to uncertainties in estimating CO2 and CH4 fluxes when you evaluate the sink or source capacity of the studied reservoirs. I thought that the manuscript would require a substantial revision to address all the raised issues and a number of other comments, so I recommend ‘reconsider after major revisions’.

With regard to your assessment of net CO2 eq sink (19%), I would suggest that you consider uncertainties associated with CH4 loss via ebullition (as suggested by the second reviewer) and potential temporal (both diurnal and seasonal) variations in CO2 to provide ranges of estimates rather than one single estimate. You measured CO2 only in summer months, so you may have different (probably higher) values in other seasons due to changes in primary production. Please refer to other studies (or your own studies if you have) to estimate potential seasonal variations. You did not provide any detail about sampling frequency and time (Once per sampling, per season? Or repeated samplings to cover diurnal variation?). It would be quite misleading if you provide one single value out of uncertain estimates even though your sampling did not cover seasonal and diurnal variations.
Considering the critical role of phytoplankton in reservoir CO2 budgets, you might also need to provide more descriptions and discussion on the relationship between Chl a and CO2. It appears that your model (and also your discussion) does not consider this important relationship. Please check and discuss any lack or hidden relationship between Chl a and CO2 to assess the role of phytoplankton as a CO2 sink, particularly in relation to nutrient levels in the studied reservoirs (for instance, in lines 198-199 you can provide more information about how CO2 varies with Chl a and nutrient levels). Your discussion on nutrient control over phytoplankton and CO2 levels (lines 262-270) focuses on the positive relationship between N and CO2. Please refer to other studies reporting various relationships between nutrients (both N and P) and phytoplankton uptake and release of CO2 (and CH4) to provide a more in-depth discussion of the observed patterns (your succinct data presentation does not allow readers to find out detailed information on this topic).

I would like to ask you to make all the changes easily identifiable in a marked-up manuscript and a point-by-point reply to all the comments offered by the two reviewers and myself. I would also suggest that you specify the line numbers of the revised parts in your responses to the reviewers’ and my own comments (including minor comments below).

Sincerely,

Ji-Hyung Park
Associate Editor, Biogeosciences


- Line 22: It is not clear which optimal design and management can minimize GHG impact. Please elaborate on the implication of your findings in the context of GHG emission mitigation. You stated “evaluating the potential for reservoir design to minimize CO2-equivalent (CO2-e) emissions (line 71) as a primary goal of your study. However, as you mentioned in the following sentence (“By identifying the driving characteristics of farm dams that support reduced C emissions, our findings provide the first step to developing management strategies to help minimize farm carbon emissions.”), your results appear to provide some baseline information that could be useful in opting for emission mitigation strategies. Because this baseline information is not specific enough to suggest “the potential for reservoir design to minimize” GHG emissions, a more cautious wording would help readers grab some practical ramifications of your scientific findings.

- Line 73 (& 178-):. Is this (GAMs) a new approach proposed in this study? Please clarify whether you propose this approach here for the first time or simply follow other studies (then cite relevant references)

- Line 17 “address and manage their potential importance” – Please specify what specific importance you want to “address and manage” (?).

- Line 22 “eutrophication-driven CH4”: Do you mean “eutrophication-driven production of CH4”?

- Lines 28-54: These two paragraphs may be reversed in order.

- Line 172 “NOx”: Have you defined this earlier? Please note that NOx usually refers to nitrogen oxides in environmental science.

- Figs. 4-5: Can you make the data of the label “Farm reservoirs (this study)” stand out by using some special symbol or color?