Dear Authors

Thank you for the responses to the reviewer comments. I have taken some time to read thoroughly through the comments and responses, but please note I have highlighted several instances where I am unclear how you plan to revise the manuscript to address the criticisms or suggestions that have been made (listed separately below).

Overall, the reviewers have found merit in the study and highlight the paper is potentially of interest to the scientific community, and is technically sound aside from some minor issues. However, the main concerns raised by Reviewer2 and Reviewer3 is the quality of discussion of the results and the significance of the findings. In particular the most significant issue in my view is aligning the scope and the general discussion linking the hydrology and land-use of the system to the DOM character – strengthening the results to better link the hydrological and land-use conditions with the DOM is needed here and this could be achieved through some simple additions to the analysis whereby you compute indicative lake/river retention times, evapo-concentration factors etc, and comment on how land-use change may impact DOM character and regional DOM cycling.

In summary, if these major revisions are undertaken adequately then I do believe the paper will be suitable for publication. When you resubmit please make sure you reply to the substantive issues raised here (by myself and by the reviewers) outlining specifically how the paper has been updated, or why the manuscript hasn't been edited to address the concern.

Best regards and I look forward to seeing the revised version of the manuscript.
Matt Hipsey



Response to Reviewer2 General Comments:
The summary of the proposed changes to the reviewers comment about focus is lacking here, and specifically the question about the scope not adequately considering the hydrological context is not addressed.

Response to Reviewer3 Query A:
The response to this suggestion seems misguided. Changing the term from terminal to saline waters is not the appropriate change in my view since it is not the fact it is saline that is of interest, but the fact that it is a lake. Indeed one could have a saline river. If you are referring to a lake without an outflow (as I think you are), then you should use the term “terminal lake”, or alternatively the “saline lakes”

Response to Reviewer3 Query B:
Ideally for the lakes you should also indicate an indicative retention time (ie: volume/inflow rate). This is relevant for the time scale of carbon reactivity, and you mention this as an important factor in the discussion but only ever in a qualitative way. I also highlight that HESS is a hydrology journal rather than biogeochemistry journal and exploring the link between hydrology and biogeochemistry is important (note also Reviewer 2 made this comment).

Why does Table 3 only show freshwater lakes? aren't there also saline lakes to be summarised?

Response to Reviewer3 Query C:
Your answer to (C) on C3116 does not respond to the question that the reviewer suggested. I agree with the reviewer that the geomorphological context of the region should be outlined (briefly). This is different from meteorological and hydrological information. Instead issues around erosion and the age of the landscape are relevant.

Response to Reviewer3 Query D:
You can’t have it both ways – on one hand you argue the carbon storage is significant, but in the review you argue the data is too little. In your own words the “DOM … is the largest reservoir of organic carbon on Earth”. Can you expand on this in the discussion to highlight the significance of the shift in DOM characteristics across the region for carbon cycling.

Response to Reviewer3 Query E:
Your answer to (E) is just general literature review and not properly addressing the comment. As per the reviewer comment, and my comment above, it is necessary to synthesize your results in the context of this literature to provide clear insights as to why your DOM reactivity information is relevant. Ie how would DOC recycling to CO2 shift geographically across the domain based on your data? Would this vary seasonally.

Response to Reviewer3 Query F:
It is unclear from your answer how you intend to improve the manuscript to address this concern, however, I do agree with the reviewer that this sort of discussion is needed to help add value to the data presented in the paper.

Dear Authors,
Thank you for the revision. Your revised manuscript has been reviewed again and please find listed below some minor revisions that have been suggested.
Please can you upload a revised manuscript that addresses these comments, and in your cover letter please outline how you have responded to each item.
Regards
Matt Hipsey



Reviewer#3:
The authors have responded in much detail to the concerns from previous reviewers. Some paragraphs could still profit from a grammar check. I do indicate some of the respective sections in my detailed comments below. However, I consider the scientific content to be accessible to the reader and do find the presentation of the work clear and concise. Also, and as indicated earlier, I consider the presentation of the detailed optical measurements on surface waters from this region to be valuable. As stressed by the authors, the variability patterns presented do contrast variability patterns from other regions.

Detailed comments:
p.2 l.4-7 The last sentence of your abstract is very vague. Consider to revise and to replace the word "might": the word's connotation reminds of a hopeful guess.
p.2 l.19 replace “has” with “is”
p.4 l 22-24 Check entire sentence for English, I suggest “.. altered CDOM properties, when compared to ..”
p.4 l25 “storage levels” not “storages levels”
p. 5 l28 Point (1), you probably mean “within” not “with the plain”.
p.4 l28 – p.5 l4 Check entire paragraph for English grammar, and I would replace “propose the following issues” with “addressed the following issues”.
p.5 29 I do not think that many readers are used to the unit “hours sunshine per year”. Alternatively, you could state how many days per year there were hours (one or more) with direct sunlight (blue sky). That would be XX days of sun per year. – It is rough (like your 3,000 h probably are too), but more assessable to the reader.

P 5-12 Methods and Results: concise and well written.

p. 11 l22-25 I do not follow your calculations: “fg C”, do you really mean “femto gram”? That would be 10 to the power of minus 15? This does not make any sense to me. Do you mean “pg C”, but that would be too high. – Please check carefully and revise. Also, instead of absolute numbers, consider to use a % of the global transport (as you do on line 23 for the area). I would consider such more assessable to the reader than the gigantic numbers.

P. 21 l22-23 The first sentence of the conclusions is hard to understand that is again due to the language. Do you want to stress that the CDOM properties of the plateau lakes were not well studied prior to your work? – Please consider to revise this sentence.

Fig 1 The plots are blurry: please see that they will be submitted as line graphs and sharp. Also, the different landcover types listed in the legend of Fig 1a are by far not all visible on the map. If applicable, please reduce legend to what is truly visible on the map.
Fig. 1b write “cities” not “cyties”
Fig 4 Nice figure! - It is very informative.

Dear Authors
Thank you for your revised version. There are still a few "minor" issues to deal with to improve the readability of the paper, and so I have undertaken a editor review, and provided some edits in the attached pdf to help you finalise the paper. Could you please make the required changes and resubmit?

Please don't hesitate to contact me should you wish to discuss any of these suggestions.

Many Thanks
Matt Hipsey

Dear authors - thank you for the further effort for your revision. I am now satisfied the issues have been dealt with and I think the manuscript is a useful contribution.