Thank you for carefully considering each of the review comments. Would you please go ahead and submit a revised ms, with each of the modifications as per your responses here. Please submit this in track changes mode so that we can follow your revisions.

Please keep in mind that the concerns raised by the referees may also be those of future readers. It will be useful to transfer some of your very helpful response comments (in condensed form) to your revised manuscript.

For example, one point that seems a bit contradictory is in reponse to referee 2 who said:
"Could the authors thereby combine in situ spectral UV absorption and residence time (treated separately in much of the Discussion) into a single equation = cumulative UV exposure or absorption. In this way ‘light-limitation’ could occur through a) low surface irradiance and light limitation at all depths; b) complete absorption of irradiance in the surface waters
and light limitation at depth; or c) insufficient time (cumulative exposure) for complete photochemical breakdown."

You responded:
"This amount of “UV light exposure” and “DOC degradation” (from equation 3) is then multiplied by the residence time (which is what it seems the reviewer is requesting), and the results are presented in Fig. 9."

But then you say:
"Beyond what is presented in a figure, it might be convenient to have a single equation highlighting light exposure and residence time – this equation would multiply equation 3 by Rt, residence time. However, the situation as we present it in the manuscript is more complicated...."

This seems to contradict your previous statement. One way to handle this (but you may have a better way)would be to condense your comments into something in the Discussion like 'Equation 3 was multiplied by residence time (Rt) to generate the results in Fig. 9. However, a precise estimate of Rt is difficult to achieve in practice given that there are inputs of water and fresh CDOM as a parcel of water moves downstream.'