All three reviewers agree that this well written paper presents interesting new insights into the description of stationary transfer functions based on stable isotope data, even if "the use of time-invariant transfer functions can now almost be called old-fashioned" (reviewer 3). As reviewer 2 puts it "stationary response functions have progressively lost scientific relevance, (..), many simple models still perform discharge simulations through calibration of stationary response functions."

The reviewers recommend minor to moderate revisions and give detailed comments on how to further improve the manuscript. Accordingly, I invite the authors to submit a revised version addressing all the comments along the responses given in the public discussion.

The paper has been re-reviewed by one if the initial reviewers. There are a few technical suggestions left that could be addressed.