Dear Authors,

Thank you for submitting your work for publication in Biogeosciences. Your manuscript has been reviewed by two referees. Both referees agreed that the manuscript represents a substantial contribution to scientific progress within the scope of this journal, and that the measurements discussed are novel and provide new insights on the chemical composition and photochemical reactivity of peatland DOM. At the same time, the reviewers recommended a number of improvements.

Both referees were concerned about the choice of irradiation source, how relevant this study's findings are to photochemical transformation processes in natural waters and how comparable the results are, in quantitative terms, with those of other studies. The implications of the choice of irradiation source would need to be discussed in detail in the revised manuscript, also in the context of previous studies discussing the dependence of absorption and fluorescence photobleaching on the spectral quality of exposure.

In addition, the reviewers recommended to show additional parameters to get more insights on the composition and transformation of DOM in the study region. Additional information, from ancillary measurements or existing literature, on downstream water composition and light attenuation/optical depth could also help address the question raised by the reviewers regarding downstream DOC processing/turnover rates.

As mentioned by Reviewer #2, filtration through 0.22 um does not completely remove bacteria from the sample. The authors should report in their revised manuscript whether during their experiments they observed any changes (with time) in CDOM or DOC in their "control" samples (0.22 um, not exposed to light). On line 286, the manuscript mentions that: "dark control samples showed a greater drop in absorbance upon irradiation than light exposed samples". More discussion is needed on these results.

Your responses to the referees’ comments will need to be incorporated in a revised version of the manuscript that will be reconsidered for publication in Biogeosciences. Please refer to the reviewers’ comments and your answers for the revisions.

I look forward to receiving your revised manuscript.

Sincerely,
Maria Tzortziou
Editor, Biogeosciences

Dear Authors,

Thank you for submitting your revised manuscript and response to the editor's and reviewers' comments. I have read your revised version and I am happy to inform you that your manuscript is now accepted for publication in Biogeosciences.

Best regards,
Maria Tzortziou, Associate Editor