|I have received a revised version of the manuscript by Rodriguez-Blanco et al. The authors have made substantial changes to the Introduction of the manuscript, which is now much better structured. The novelty of combining the analysis of two different compounds is now also clearly stated in the Introduction. However, this novelty is not transmitted to the Discussion Section and it is not clear how the implications from this dual analysis deepen current understanding of nitrate dynamics. Arbitrary selection of event characteristics for explaining hysteresis patterns and simplistic statistical analysis further hampers interpretability of the results. Moreover, the authors did not add missing methodological details regarding event definition and identification that were requested in the initial review. Finally, although the clarity and the language of the manuscript was improved, the manuscript can definitely benefit from a thorough proofreading (there are many typos, tense inconsistencies and grammatical errors in the manuscript). Below I present my detailed comments.|
Event definition and identification: the provided definitions of events are very vague and imprecise. It is also not clear why the authors have opted for manual event identification. In the current state this study is not reproducible as it does not provide clear guidelines for event definition. I have already mentioned these concerns in the first round and they were not addressed. Please see my detailed comments.
No rationale for selecting event characteristics: There is no rationale provided on selecting the set of event characteristics as potential controls of hysteresis variability. The meaning of the characteristics is very poorly explained and are not always deductible from the terms used (e.g., water yield). It is not clear why only these characteristics were selected, why not others? More hypothesis-oriented selection of investigated characteristics might also help to provide a more insightful discussion that still fails to highlight new insights obtained from this study. See also my detailed comments.
Statistical analysis: the controls of hysteresis properties are identified by a simplistic bivariate correlation and redundancy analysis that expectedly provide very similar results as they are based on the same principle. The need of both analyses is not clear. The correlation between the examined event characteristics is not investigated and is likely to be quite high compromising the reliability of presented results. These limitations should be at least discussed.
Lack of novel insights in the Discussion: It is not clear which additional insights do we gain from the dual analysis performed in this study compared to the already existing findings. Perhaps a conceptual figure in the Discussion section that summarizes the role of different characteristics in the mobilization of NO3 and TKN during different events and corresponding activated processes will be helpful to clarify the advances made by this study.
Line 17: Not clear what is meant here by the overall dynamics of hysteresis. Please clarify.
Line 17, 198: The concept of dynamics of hysteresis (dR) is different from the hysteresis direction stated in the Method section. Please use only one term throughout the manuscript.
Line 18: Element is ambiguous, compound is a better term.
Lines 20-23: The meaning behind each of the mentioned characteristics (e.g., difference between peak discharge and event magnitude) and the direction of change produced by different event characteristics is not clear at this point. Please use more comprehensive terms.
Line 24: It is not clear what is meant by the magnitude of the event here. Is it the volume or the peak discharge. Please either explain the meaning of the characteristics used in the abstract directly in the abstract or use only unambiguous terms.
Figure 1: Please also label dilation and enrichment pattern. Consider highlighting the line showing the width by a different color. Please clarify in the caption if there is a difference between “rising slope” and “rising limb”. If not, use the same term.
Line 75, 204, 383: do not use the term “significant” if it is not associated with the significance testing.
Line 106: Please indicate how close the station is.
Line 110: It is not clear what is provided in the brackets? The range of elevation? Usually, the range is provided as min-max and not the other way around.
Figure 2. Please modify the colors of the land uses, it is difficult to distinguish. Consider simplifying the land use types. Please indicate the location of the three meteorological stations mentioned in the text,
Lines 133-134: How was the start of the rainfall event defined? To compute the increase relative to the start of the event, the start has to be defined first. Please clarify.
Lines 139-141: I do not think this information is used in the analysis. Please delete all unnecessary information or clarify how it was used.
Lines 149-150: This definition of rainfall start does not agree with autosampler operation mode described in Line 133-134. Please also clarify what does “usually exceeds 5 mm” mean? Is there no fixed threshold?
Line 153: What is a “perceptible increase”? Is there a clear threshold for that? Please clarify.
Line 154: It is not clear if events finish when they reach exactly the same initial baseflow conditions or not. Please clarify. Moreover, given an unclear definition for the event start it is also not clear how exactly the termination of the previous event is defined when it is followed immediately by the next event. Please clarify this too.
Line 162: term “water yield” is rather ambiguous, consider using “total runoff volume” instead.
Lines 164-166 Please clarify how rising and falling limbs are defined. Homogenize usage of Rd and RD.
Figure 3. Please also display how the slope of the falling limb is defined in this Figure. It would be helpful if all characteristics from Table 1 are displayed in this Figure. Please also make sure that the acronyms in the figure and in the table are identical.
Lines 174-175: It is not clear why the number of events has reduced from 156 to 102. Please clarify.
Line 178: Please clarify how close it has to be.
Table 1: All event characteristics have to be explained in the Table or in the text (e.g., how the initial phase of the falling limb identified?). Please use identical terms for event characteristics in the text and in the table (e.g., event magnitude relative to baseflow is listed here as magnitude of event and can be easily confused with peak discharge).
Line 215: previously the term “direction” was used instead of “rotation”. Please keep homogenous terminology throughout the manuscript.
Lines 217-218: What does it mean? Were these events treated differently? Please clarify.
Line 223: which examined characteristics can be considered biogeochemical? Please clarify.
Lines 225-227: From this description, it is not clear what is the additional value of the redundancy analysis compared to correlation. Please clarify.
Line 230-235: a boxplot figure displaying described variability among events will be useful here.
Figure 5: I think this figure is more comprehensive than figure 4 and they can be merged together. The date on the d panel is not clear. Please revise.
Line 246: Based on the units it should be volume instead of magnitude. It is not clear which data is not shown here. In general, all relevant data should be provided. Moreover, it is not clear what is the general length of recorded rainfall events (min and max).
Line 247: volume instead of magnitude?
Line 251-252: I do not really see it in figure 5. Autumn events are only displayed for NO3 and it is not really much different from winter in terms of concentrations. Moreover, be cautious in drawing such general conclusions from singular cherry-picked examples.
Section 3.2. Please add percentage instead of absolute number of events.
Figure 6: Please, add labels to the subplots. I see no horizontal dotted lines in this figure that are mentioned in the caption. Please clarify.t.
Section 3.3. Please use full names when referring to different event characteristics in the text to make it more readily understandable for the readers.
Line 305: it is not clear which variables exactly are meant here by “rainfall-runoff magnitude”. Please clarify.
Line 330-331: This conclusion is not straightforward. Please elaborate on that.
Line 337-338: This is not a part of the manuscript anymore, you cannot not reference the results that are not presented in the manuscript. Please revise.
Line 341-344: This reasoning is not convincing. The authors attribute the anticlockwise hysteresis patterns to different pathways (subsurface and groundwater), however low nitrate concentration in subsurface flow at the beginning of the runoff event could also be linked to the runoff generation zones that are closer to the stream, and therefore with the spatial distribution of sources. Please justify your reasoning on why this is not the case for the study area.
Line 356: event water contribution was not quantified in this study. Please revise.
Line 359: What is meant here by direct rainfall? Please clarify.
Line 376: the meaning of the information provided in the brackets is not clear. Please elaborate. Please also clarify how the distance of sources is related to event magnitude. Please notice that previously the term event magnitude was used in a different meaning (relative increase of streamflow compared to baseflow, while now it refers to precipitation volume). Please homogenize the terms throughout the manuscript.
Line 388: which rainfall characteristic is meant here? What is meant here by event magnitude? Please clarify.
Line 395: This statement needs a reference (e.g., Heathwayte and Bieroza 2021 might be suitable here) and a further explanation on how biogeochemical processes are influencing hysteresis patterns of nitrate.
Line 397: This statement also needs a reference. How does the buildup of nitrate affect the biogeochemical processes involved.
Line 402-403: This sentence has to be revised, it does not make sense.
Line 403-404: This is rather vague. What additional event-based studies can provide that was not observed here? Please clarify.
Line 412: Here I would expect a summary of main mechanisms that were identified by the dual analysis.
Line 18: dominated by enrichment
Line 33: freshwater bodies
Line 36: commonly at biweekly or monthly resolution
Line 43: nutrient concentration
Line 48: can be classified
Line 51: distant to the stream
Line 53: omit etc
Line 56: nitrogen species
Line 64: rainfall and runoff event characteristics
Line 78: through
Line 80: changes in the quality of freshwater resources
Line 87: C-Q relationships
Line 100: indicating relatively low nitrogen inputs in the Corbeira catchment compared to…
Line 161: determined according to Wischmeier and Smith (1958)
Line 180: evaluated visually
Figure 4: reduce white space
Line 233: selected events
Line 247: several events
Line 321: the Corbeira
Line 325: increased nitrogen concentration during individual events
Line 338: contribution from the subsurface flow
Line 348: that have recently received fertilizers
Line 383: on hysteresis patterns?
Line 393: particulate material
Heathwaite, A. L., & Bieroza, M. (2021). Fingerprinting hydrological and biogeochemical drivers of freshwater quality. Hydrological Processes, 35(1), e13973. https://doi.org/10.1002/hyp.13973