Comment on hess-2020-648

The “Technical note: Evaporating water is different from bulk soil water in d2H and d18O” describes an experiment to elucidate hysteresis of water isotopic signals during evaporation. The process described is known, but the experiment nicely shows the concept and the implication for deriving evaporative loss from isotopic signals. It is, however, a pity that the difference in d18O was not high enough to result in significant differences in evaporative loss. In this context, it would be beneficial to add more hypothetical calculations under which conditions (difference pre-event/event water) and soils this process might be important. The latter would strengthen the conclusions. It general, it would have been beneficial to have information on soil texture and eventually matric potential.

The "Technical note: Evaporating water is different from bulk soil water in d2H and d18O" describes an experiment to elucidate hysteresis of water isotopic signals during evaporation. The process described is known, but the experiment nicely shows the concept and the implication for deriving evaporative loss from isotopic signals. It is, however, a pity that the difference in d18O was not high enough to result in significant differences in evaporative loss. In this context, it would be beneficial to add more hypothetical calculations under which conditions (difference pre-event/event water) and soils this process might be important. The latter would strengthen the conclusions. It general, it would have been beneficial to have information on soil texture and eventually matric potential.
Another point that is not addressed yet is that evaporation of heavier water than bulk water evaporation loss cannot be calculated. The authors should comment on whether such replacement of heavier isotope occurs under natural conditions and which effect it could have to calculate evaporative loss for natural isotope abundances. Another main point concerns the description of the calculations. The equation and variables used should be introduced sequentially. The Figures are appropriate and relevant literature cited. However, the manuscript should be corrected by a native speaker (particularly the first part until Discussion). Finally, the title should be adapted since evaporating water is per se different from bulk soil water, and as such, the title does not reflect the process you seek to investigate.
L26 Please make clear that this is not a general statement but specific to the conditions of your experiment.
L28 Which important implications? L41 "occupied" seems not the right term in this context. L45 Please rephrase the sentence.
L54 Large pores instead of pore.

L37-59 This section should be moved to the methods.
L82-84 This should be moved to the method section.
L84 Rephrase: This study may help to ….
L98 Add values or signature in the sentence.
L107 "secondary" evaporation L129-130 It is not clear whether the authors refer in this sentence to there own findings (in this case I would move the sentence to the results) or if there refer to other studies (in this case they should be cited). Moreover, the structure of the sentence is not clear and should be corrected. L131: When are higher temperature needed? In case of higher clay content. This is not clear from the sentence. Could you provide soil texture information? L147: "sub samples" L159 Use the present tense for referring to Tables and Figures. L167-: Why did you change the soil of the lysimeters. The reason is not apparent.
L222-228: Here, the introduction of the variables an equations is mixed up and difficult to follow. Please introduce each equation with its variables from top to bottom since this is an important aspect of your study.
L240: Is the variable n introduced?
L277: What is meant by newly added water? The irrigation water? Please use the same terminology as before.
L300-306: style: delete some "therefore" L414: Could you explain how you estimated the value of 3.52 to result in significant differences.
L418: Do you mean matric potential? L436: Please make clear that this statement refers only to small differences in isotopic signals.