Dear Authors

Thank you for your replies to the reviewers and my apolgies for the wait in assessment of the paper. Both reviewers acknowledge that the paper is a novel assessment and suitable for publication. I agree with Reviewer 2 that the abstract could be sharpened, in particular make the clear the novel methodological approach adopted here and highlight the broader significance of the research (bearing in mind the general nature of HESS and broad readership). I think it is a bit confusing at the moment for some non-experts in this field.

I would also ask that in the revision you review the headings and sub-headings to ensure the logical progression is clear (for example methodology is used for Section 3 heading, but plenty of methodology is described also in Section 2).
Similarly, the first sentence of the discussion is a results statement – it would be beneficial in my view to open the paragraphs with a clear statement on finding or opinion, that is then developed within the paragraph, in order to ensure readers clear follow the “story” of the research work. I also like the discussion you had with reviewer 2 to link to the work to geochemical modelling prior results, and in particular in the latter part of the discussion it would be ideal if some lines are added to make clear the broader implications of this study (beyond Waldsee) – for example can this be a cost-saving method others could use in other lakes? also, are our current lake mixing models that focus on surface heating adequate, and/or does this approach open a new opportunity for exploring new numerical model approaches?

A final suggestion – since the overall paper is not very long and given the discussion in particular is relatively short, it seems possible to potentially merge the discussion and “summary”(/conclusions), and then introduce 2 or 3 sub-headings to help guide the reader. This may help address the issues I raised above since the clear statements of your findings in the discussion can help put the technical discussion in context, helping the overall readability.

I look forward to seeing your revised submission.

Regards
Matt Hipsey

Dear authors,

The revised manuscript has many improvements in response to the reviewers, but it remains filled with numerous frustrating errors and editorial issues and needs further polishing before publication. I have made my own review of the paper (see below) to help guide you on necessary revisions. Please can you ensure that the revised submission is carefully proof-read and you also refer to specifics in the HESS formatting guidelines to ensure consistency.

Regards
Matt Hipsey



Page 1 – Overall the front of the abstract is better but some recommended changes to the abstract are required as I was still left with some confusion after reading this version.
Lines 9-11 – needs rewording
Line 12 – changing … the … chemocline height
Line 15+ - The sentence “ In addition, we constructed a lab experiment …” I think could be better worded to improve the flow:
“A lab experiment was undertaken to further demonstrate that …

Page 2 – lines 1-5. This ending I find confusing. The lab experiment is described without a purpose and instead a statement of result (ln 17, “iron was removed”, see above comment), and then that result is repeated “precipitates were observed” – this is referring to the same thing and could be more concisely described. Also, organic material is introduced here, but it is not clear the relevance. Finally, the final abstract statement it is not clear. It should be better worded to link the field and lab observations and the significance. This sentence describes a finding about the sources of water and introduces the concept of iron rich groundwater for the first time. If understanding the importance of Fe rich groundwater is the purpose then should it not be an aim / knowledge gap identified at the beginning of the abstract?


Line 10 – with … the … atmosphere
Line 20 – replace loads with release . ?
Line 21 - which … are likely to … be exploited …
Line 25 - Meromictic lakes … have been … identified

Page 3 , line 1 - where stratification … limits
Line 4 - stratification … has even been …
Line 11 – replace e.g. with “, for example by”
Line 17 – needs a reference or to be stated more clearly as an unknown.
Line 19-20 - One prominent reactant is iron, which … precipitates within … the oxygenated mixolimnetic waters and dissolves in the anoxic (reducing) … conditions of the monimolimnion
Line 21 – Exemplarily is not a good word. Also – is this sentence stated as fact or as a hypothesis?
Line 24-25 – It seems this question is answering the “proposed” question and bringing into question the need for this paper. Some rewording needed here

Page 4 – Line 4-7, this paragraph seems to summarise the above paragraph, so I think they would be better together (not separated)
Line 11-13 – the use of summed is not clear (what is nbeing summed?) – I think you need to point out the sum is over the vertical profile
Line 12 - replace “give a rough” with “give an approximate”

Page 5 – The section 2.2 is a mix of prior results and lit review on the lake. lines 16-19 is written more like results than “site description”, and should be more clear this is historical data, not data collected as in Section 3.2 where the vertical profiles are described. Needs rewording like: “Prior monitoring has indicated …”

Methods – litres should be capital L (throughout)

Eq (5) – maybe worth putting the full integral form before the summation as well?

Results
Page 12 – line 1 – “attributed to … the … expected”
Line 4 : change to : “The precipitation of iron hydroxide flocks was visible.”
Update the Figure 5 caption to be more useful
Lines 16-23 – this paragraph is crossing into discussion. Don't use the word “obviously”. Don't open a sentence with “In conclusion…” as you should not be making a conclusion in the results, just presenting the data and helping the reader with the interpretation. Please improve the wording of this paragraph.

Page 13 – line 2: replace lab with laboratory
Line 3 – replace drastically with significantly
Line 7 – word needed before DOC

Note: DFe DOC and TIC are being defined in the results – they need to be defined in the methods where the chemical analysis is described!

Line 25-26 – is a discussion statement, not results.

Discussion
Page 15 Line 6 : doesn't make sense: “…of a closed system Lake Waldsee.”
Line 12 – what graph?? Are you referring to lab or field? This para could be more specific than generically referring to graphs and curves.
Line 22 – subsequent rise … of the … chemocline

Page 16 Line 5 – comma after However
Line 14 Reword: “of the biochemically iron hydroxide reduction “

Line 19: replace re-covering with recovery
Line 22: replace “temporarily” with temporary

Page 17 – fix up: “This is where our investigation our findings …”

Line 18 : “…for the parameterization”

Page 18 line 2: remove “in a 5 m high PVC pipe”

Figure 4. Remove the “in” in the X-axis labek so it is Time [h]. Also put EC in brackets in the caption so it links to the Y-axis label (same in Fig 5)

Dear Authors
Thanks for your further revisions and technical corrections.
I think the paper is significantly improved and an interesting piece of research, so happy to accept the paper for publication. I do ask that you carefully check the proofs in due course for any final editorial errors.
Kind Regards
Matt Hipsey