Dear Dr. Reichwaldt,

I very much agree with both reviewers that the method you proposed is interesting and has quite some innovation potential for assessment of pollutant concentration in estuaries. As such the paper is well within the scope of HESS and will optionally be published.
I also agree with both reviewers that the manuscript would greatly benefit from a) a clearer structure, b) being more to the point with respect to terms like “pollution” and from c) providing references to more recent similar studies dealing with the potential of muscles as sentinel organisms for N-pollution. Both reviewers also pointed out several substantial points that need to be clarified within the revised manuscript for fully explaining your findings and for evaluating to which extent they may be generalized. This is for instance the joint effect of particulate organic matter and NO3, or whether different species were included into the sampling protocol and whether their metabolism might react in a different manner to inherent dynamic changes of environmental conditions in an estuary.
Please attach a detailed explanation how you addressed these points and the many technical recommendations to your revised manuscript.

I wish you good success and remain with best regards,

Erwin Zehe

I have assessed the manuscript on the basis of the reviews stemming from the revision process. I do agree with the assessment of the reviewer involved in the second round of reviews. As a consequence, I see no reason to further delay acceptance of the study.