Dear first reviewer, 

We are very thankful for the time and feedback you gave us. 

Please find below a point by point response (following double carrots >>) to your specific comments. In addition to general clarifications, we have 1) proposed a first conceptual figure; 2) performed an analysis of moving average effects; 3) explored how the streamflow periods B, E, and M relate to the stream flow percentiles.  The clarifications could be transferred to the manuscript in a more condensed manner, which we would be happy to implement.  We will carefully revise the manuscript and incorporate your minor comments and technical corrections once we receive the editor’s response.

Sincerely, 

The Authors

===============================================

- The abstract is too generic and vague. I suggest rewriting it and make it more process-oriented so the reader can better appreciate what are the main findings and contribution of this work in terms of understanding the hydrological functioning of this catchment.

>> We will be happy to rework the abstract to focus on the process oriented process and highlight the main findings.  

- Introduction:

1) The first part of the Introduction works well but what is missing is a clear statement about the main gaps in the current literature and the main research gaps that this work aims at addressing. Reporting that “this work attempts to quantify dominant drivers…” is ok for a general objective but this is not clearly link to a current lack of knowledge that this work could contribute to fill in. Please, rewrite lines 51-63.

>> We will rewrite lines 51-63 with a more clear statement, such as: 

To fill the gaps in existing studies, namely the elevational and the seasonal gaps, this work quantifies drivers of the hydrologic response of a high elevation catchment throughout all streamflow periods, ranging from winter low flow, to different stages of the melt season and the autumn recession by compiling and complementing observational data from the intensively studied Vallon de Nant catchment in the Swiss Alps (Benoit et al., 2018; Giaccone et al., 2019; Ceperley et al., 2020; Mächler et al., 2021; Michelon et al., 2021a; Thornton et al., 2021a; Beria et al., In revision; Antoniazza et al., Submitted). 

This work brings together four different tracers in a unique fashion. First,  stable isotope composition of water, a natural tracer that has been extensively used to characterize hydrological processes related to snow (e.g. Beria et al., 2018), which is particularly useful to examine the interplay of different water compartments (rainfall, snowpack, springs, groundwater), recharge and evaporation processes (e.g. Sprenger et al., 2016). Second, electrical conductivity measurements that provide additional information on subsurface flow paths and relative water residence times in the subsurface (Cano-Paoli et al., 2019). Third temperature measurements of water which trace connectivity between water sources and the atmosphere (Constantz, 2008).  And fourth, soil temperature measurements which inform identification of periods of thermal insulation from the seasonal snowcover (Trask et al., 2020). 

2) Similar, the specific objectives (64-70) are all lumped together, and this does not make justice to the worked carried out. I strongly suggest restating them as specific questions that can be measurable and are clearly linked to the different sub-sections of the results.  

>> We will rewrite lines 64-70 with a more specific questions, such as: 

The specific objective of this work is to examine the dominant hydrological processes that explain the catchment-scale hydrological response during different periods of the year through the lenses of four different tracers: soil temperature, water temperature, electrical conductivity, and stable isotopes of water. Using these four tracers, we shed light on 6 questions. 1) What is the origin of winter streamflow (from subsurface storage versus from localized snow melting) (Floriancic et al., 2018; Hayashi, 2020); What are the dominant runoff processes that 2) drive streamflow generation during early spring snow melt (Brauchli et al., 2017)?,3) later on in the snowmelt season?, and 4) during the season recession?  5) What is the role of shallow groundwater in the hillslopes and of alluvial or talus groundwater systems (Hayashi, 2020) in the streamflow generation throughout the year. Finally, what transferable insights into the value of these four tracers for hydrologic process investigation are relevant for comparable catchments?

3) The weakest part of this manuscript is the Discussion:

A) it’s highly fragmented in small subsections that, instead of making the structure clearer, produce a confusing picture.

>> The discussion actually mirrors our specific questions exactly, but to make that more clear, we will redefine the structure according to the following outline, which the 3 sections of dominant runoff processes grouped together as subsections: 

• 5.1  origin of winter streamflow
• 5. 2  dominant runoff processes 
  • 5.2.1 during early spring snow melt
  • 5.2.2 during melt periods
  • 5.2.3 during the seasonal recession
• 5.3 interplay of shallow groundwater in talus systems
• 5.4   Instead of presenting the last section, “lessons learned from our four tracers” (previously: Transferable insights into the value of the observed variables for hydrologic process investigations in comparable catchments), as a single section with subsections, we will break it into a final paragraph at the end of each other section of the discussion and a summary paragraph that will go in the conclusion.   

B) The results are discussed “internally” and there are almost no references to other works. This make it confusing to the readers to understand what is different and new compared to previous knowledge, and what is the contribution of this research.

>> Thank you for your point of view and pointers of key references, we will happily develop the discussion further along these lines. 

C) As a results, the novelty and the original contribution of this paper (which, in my opinion, exists) is hidden and not stressed at all, making it, unfairly, a general case study.

>> As we revise this manuscript, we will emphasize the unique contribution of this study to hopefully move it out of the general case study category.  

D) As a results of the confusing structure of this Section (point 1), the most important finding of this work is not very clear to the reader as it could be, ie, how this catchment responds to precipitation and snowmelt inputs! Time series and reported ranges of values are of course important but I suggest adding a sort of conceptual graph showing the main runoff generation processes and the general behaviour of this catchment (a sort of graphical conceptual model of catchment response). I think this will make the paper of more impact.

>>In the attached supplement is the beginning of a conceptual figure (Fig. 1) that we plan to integrate in the final manuscript. We will continue to improve, discuss, and integrate it as we prepare the final manuscript.  

4) Finally, the language is overall good but sometimes there are not accurate terms, vague descriptions, and awkward sentences. Since there is at least one native speaker (I assume) in the authorship and other well-known and highly-experienced researchers, I believe that the language issues could be easily fixed.

>> We will happily work through the whole manuscript with this in mind.  

5) At line 248 a 7-day moving average is mentioned and applied. In my experience, moving averages of such a long period produce i) a slight temporal shift of streamflow peaks; ii) a reduction of streamflow peaks. Please, comment this issue and its possible effect on the results, or adopt another smoothing method.

>> This is a good point.  In this case we are just using the moving average to have a better image of what is going on and help determined the stream flow periods.  

i) There will not be a temporal shift since the seven day window extends 3.5 days forward and 3.5 days backward.  Please see the attached figure (Fig. 2 in the attached supplement).  ii) There is a reduction of the peaks, which helps us to interpret the processes.  This information is used along side the actual data not instead of it.   We will make our method and purpose more clear in the text. 

6) At line 249 the Authors introduce the three streamflow periods B, E and M. Although I overall agree with them I’m afraid that this is an arbitrary selection not based on an objective criterion (eg, the use of a streamflow percentile threshold). Please, comment this issue and its possible effect on the results, or adopt another more objective selection method.

>> We have compared our periods, and come up with some more quantitive guides, visitible in a table (Table 1, attached supplement).  A condensed form of this table and points could be added to the manuscript or the supplementary material.  The divisions were identified as follows: 

• The transition from M to R is always the peak of the 7 day moving average. 
• Flow is increasing in E and M and decreasing in R and B.
• E is the first “wave of discharge”, where the flow increases but the daily range doesn’t yet jump up. 
• During M, there is a much higher diel variation in flow. 
• Similarly form R to B, the daily variation drops off. 
• B has median of daily flow quantiles < 30, E around 50, M > 80, and R around 70 or 75
• The change in flow of B per day (using 7-day average data to override event effects) in m³/s/d is around 0, E around 0.1, M >0.1 up to 0.3 and for R is <0 around -0.1
• The median peak time of discharge is not as consistent, but it is late at night for E and closer to mid day or late afternoon for M.  During R, it might be early afternoon or morning.  B is not at all fixed
• The range of daily values is low, around 0.02 in m³/s for B, 0.1 for E or R, and high 0.3 for M. 

7) 523-551. I suggest combining subsections 5.2, 5.3 and 5.4. I also suggest combining 5.6.3 with 5.1.

>> Thank you for this suggestion, it fits with our plan to restructure the discussion in point 3A. 

8) Why can it be a calibration issue? What is this statement based on? Please, explain.

>> Their divergence is unexpected.  However at the end of base flow, it is very likely that there was not adequate water in the piezometers for accurate measurement.  We were referring to this phenomenon.  We will change our wording in the manuscript. 

Dear second reviewer, 

We are very thankful for the time and feedback you gave us. 

Please find below a point by point response (following double carrots >>) to your specific comments. In addition to general clarifications, we have 1) proposed a first conceptual figure; 2) made the specific improvements to figures that you recommend; and 3) clarified the technical details around lapse rates and spring locations and counts.  The clarifications could be transferred to the manuscript in a more condensed manner, which we would be happy to implement.  We will carefully revise the manuscript and incorporate your minor comments and technical corrections once we receive the editor’s response.

Sincerely, 

The Authors

=============================================================================

Title: Studying the dynamics of a high alpine catchment based on multiple natural tracers

Michelon et al., 2022 HESS

General comment:

The paper makes an important contribution to increasing the understanding on flow dynamics in alpine catchments. This is done by combining different datasets, including stable water isotope tracers, EC and Temperature. Sampling of stable water isotopes in different storage compartments in the catchment (including vegetation) helps disentangle different hydrological processes (i.e. how does the catchment function). The figures are well prepared and the fact that the data is available will surely aid further research in alpine areas. The methods are clear and sound. Having said that and despite the interesting topic and relevance of the study I have concerns with the presentation and structure of the manuscript.   In general;

• The Methods section would benefit from being more brief.

>> We will work to condense it, relying more on the referenced papers. 

• The results section should be revised and the sentences which discuss results moved to the discussion section.

>> Thank you for identifying our organizational mistake.  We will make this rearrangement. 

• Interpretation of results from the multi-tracer approach would benefit from the addition of a conceptual diagram (see specific comments in E).

>> Thank you for recommending a conceptual diagram. We include here a first idea (also benefitting form the suggestion of the first reviewer). It is visible as the first figure in the supplement to the reply to the reviewer.  

• More references to international literature is needed in discussion and careful selection of figures to be referenced.

>> Thank you for recommending this.  We will develop our connections to literature, as also suggested by the first reviewer.  

• Conclusions section needs strengthening.

>> Thank you for suggesting this.  We will do this in part by including a concluding paragraph with our lessons learned from our simultaneous examination of 4 tracers that is currently in the 5.6 section of the discussion.  

Below I leave section by section comments which include both specific and technical comments.

1. Introduction:

Line 51 -  70: It seems that you repeat in a way the study aim (see technical comments below). I suggest to restructure that part starting with a clear overarching aim and then

>> We’ve rephrased this section as follows: 

To fill the gaps in existing studies, that is the elevational and the seasonal gaps, this work quantifies drivers of the hydrologic response of a high elevation catchment through continuous measurements of natural tracers covering a period of two years for the streamflow. Hence this includes periods of winter low flow, to different stages of the melt season and the autumn recession, all for the intensively studied Vallon de Nant catchment in the Swiss Alps (Benoit et al., 2018; Giaccone et al., 2019; Ceperley et al., 2020; Mächler et al., 2021; Michelon et al., 2021a; Thornton et al., 2021a; Beria et al., In revision; Antoniazza et al., Submitted). 

Four different tracers are combined in a unique fashion. First, hydrogen and oxygen stable isotope compositions of water, a natural tracer that has been extensively used to characterize hydrological processes related to snow (e.g. Beria et al., 2018), which is particularly useful to examine the interplay of different sources of water (rainfall, snowpack, springs, groundwater), as well as recharge and evaporation processes (e.g. Sprenger et al., 2016). Second, electrical conductivity measurements that provide additional information on subsurface flow paths and relative water residence times in the subsurface (Cano-Paoli et al., 2019). Third, temperature measurements of water that trace connectivity between water sources and the atmosphere (Constantz, 2008).  And fourth, soil temperature measurements that identify periods of thermal insulation from the seasonal snowcover (Trask et al., 2020). 

The specific objective of this work is to examine the dominant hydrological processes that explain the catchment-scale hydrological response during different periods of the year through a combined use of the four different tracers. Using these tracers, we principally address 6 questions: 1) What is the origin of winter streamflow (from subsurface storage versus from localized snow melting) (Floriancic et al., 2018; Hayashi, 2020)? 2) What are the dominant runoff processes that drive streamflow generation during early spring snow melt (Brauchli et al., 2017)? 3) What drives streamflow later on during the snowmelt season?, and 4) during the season of recession?  5) What is the role of shallow groundwater in the hillslopes and of alluvial or talus groundwater systems (Hayashi, 2020) in the streamflow generation throughout the year. Finally, what transferable insights into the value of these four tracers for hydrologic process investigation are relevant for comparable catchments?

1. (Section 2.1.) Study area: this section is unnecessary long. Is all the provided information then related to the study results? If not, you can reference previous papers for details on e.g. geology, and save space here.

>> Thank you for this suggestion, we will proceed as recommended as you also suggested for the entire methods section.  

Lines 98-102: as written currently this paragraph reads like a discussion and it is not (e.g. “this topographic particularity might seem enough”). Please rewrite or move to discussion (e.g. to section 4.3.2.)

>> We have rewritten this as follows: 

The location of springs correlates with low slopes (see Figure S6 in Supplementary material), a topographic particularity explaining the location of springs along the right bank of the main stream and within the grassy slopes in the west area of the catchment, where the slopes are low. In the same way, the absence of tributaries over the north-western parts of the catchment are related to steep slopes, explained by the large hydraulic conductivity and locally well-developed soils.

Figure 1: There is no “A” on the Figure 1, as indicated in the caption, please add. In caption “where the spring is picked up” – what do you mean by this? Also, can you make the legend of the B map, at present it is difficult to read.

>>A is missing indeed, it will be corrected. The note in the figure legend has been rephrased as :”Note that the AUBG spring location shows where the water is sourced from, even though it is sampled from a pipe at the Auberge weather station point, 800 m further north.“ and will be moved to the main text.  The two legends will be placed together to make a single more comprehensive legend. 

1. (Section 2.2.)

Line 130 – 135: This seems like results (i.e. you analysed the data to derive the annual average streamflow, for example). I would somehow include it in Results section.

>> section 2.2 will be split into results and methods with a similar section starting the results section. 

Line 139 – 143 refers to the meteorology. Given the title of section 2.1. starts with meteorology, I suggest you present this first to follow a logical order.

>> This is a good point, we will reorganize it as you suggest. 

1. Method: This section is very long. While the methods described are worth mentioning the descriptions are too wordy and make the reading monotonous. Here a few examples/suggestions on how to change that along with some minor technical notes.

>> We will rearrange this section to first be instrumentation (meteorological then hydrological), then tracers with subsections of 1) stable H- and O-isotopes of water, 2. water temperature, 3. conductivity, and 4. soil temperature, followed by additional data. 

Line 153: Change “Water” (first word) with “Streamflow”. Water is too generic, you sample water from various places.

>> Thank you for the reminder to be precise. We prefer to use a parenthesis for specificity as not all the water that we sample is streamflow: (from streams, springs, and piezometers) 

Line 167: “ The same borosilicate glass vials were also used for…” – this sentence is long and redundant.  Define the type of vials and their volume once at the beginning of the subsection 3.1.1. and then only refer to them as “vials”. It will save a lot of reading time.

>> thank you for the suggestion. 

Line 179: remove “sampled”, as it is redundant

>> thank you for the suggestion. 

Line 219: I can count 5 springs on Fig.1 but T was measured in four. Can you spell out in which one you did not measure temperature?

>>  We will clarify that we didn’t measure temperature in the auberge spring (AUBG).   We did not have access to the spring directly, only to a fountain where it was delivered by pipe.  The information will be moved from the figure legend to the corresponding method section. 

Subsection 3.1.2. Is extremely long and too much detail is given. These are standard methods, just give references and keep it tight. Only if you did something different or unique in the calculations then spell out which part that is to guide the reader.

>> Thank you for this recommendation.  Unnecessary details will be moved to a supplementary file. 

Line 225: Reference “Figure 1” in “(At Auberge station).

>> Thank you for catching this omission 

Line 227: see previous comment on excessive description of the vials

>> thank you for suggesting this. 

236: change “particularly useful for us” to “particularly useful for this study”

>> thank you for this suggestion. 

244: you mention that the gridded data was useful for gap filling but you do not say when did you have do gap fill and what % of your data that is. Please spell out.

>> Thank you, we will include this calculation. 

1. Results

Specific comment: The results section contains parts of discussion which should be moved to the discussion section (some examples below).

The interpretation of results and to connect findings via different methods I suggest that you include a new figure, a conceptual model/diagram, which can also serve as a graphical abstract. This figure can be composed of 4 panels (A to D) and each one of them can describe graphically what have you learned with the multitracer method in A) The baseflow period, early melt period, melt period and seasonal recession period (as described in lines 248-249). This will aid the reader and will align with the aim “to provide transferable insights into the value of observed variables for hydrological process investigations in comparable catchments” (see lines 68-70).

>> Thank you for this suggestion.  We’ve included our first attempt at a conceptual figure as Fig. 1 in the supplement. 

Other comments:

Lines 257-259: This is discussion. Move it there.

>> Thank you, we will. 

Figure 3: Add to the legend what B, E, M R mean. This saves the reader having to go back to the text and search for definitions. What is the faint blue line in the bottom panel? It looks as faint as the streamflow. At present this bottom panel is a bit confusing. Refer to Figure 1 for the abbreviations of e.g. soils, piezometer, spring IDs.

>>B, E, M, R will be added in the figure caption. The faint blue line in the bottom panel is the temperature at the outlet (HyS1), we will pick a better color to be more distinctive from the streamflow, and also another color for streamflow to be more distinctive from PZ1 and PZ3. We propose to add a title and subtitles to the legend on the figure to help the reader to understand, i.e:

WATER TEMPERATURE

Outlet

 - HyS1

Springs

 - GRAS

 - ROCK

 - SPRING

 - ICEC

Piezometers

 - PZ1

 - PZ3

Line 317: sentence is too long. Change to “Sampled spring and ground water sources show varying correlations…” and add…”;having PZ1 the strongest correlatios…”

>> thank you for this recommendation. 

Lines 334 – 344: example paragraph where the conceptual diagram will help the reader understand the description.

>> indeed, good idea. Please note the illustration as figure 1 in the supplement. 

Lines 353 – 359: this seems to belong to methods.

>> we will move it there. 

Lines 364- 368: Move this to the beginning of subsection 4.3.3. as this presents a more general finding. Then discuss the rest but please rewrite and remove the details that may belong to the methods.

>> good idea. 

(Section 4.1.) 

374 – 379: This is more of a discussion, not a result.

>> We will move it to the discussion. 

379-381: Sentence is too long. Rewrite or split in two.

>> According to your previous suggestion, part of this sentence will be moved to the discussion, thus we will break it in two.  In the results, only a sentence staying that we observe an event-scale lag in both streamflow and EC. 

Figure 4: You do not make use of the subplot annotations A,B,C, etc. in the caption. Please edit your caption and organise by subplots. Also, when you reference this figure in the text you start with Figure 4F (Line 370). Please organise your subplots so they match the story line (e.g. if you first talk about EC then present the EC plot as Figure 4A). Same comment on the order applies to subsection 4.5.1.

>>We will add the annotations, A, B, C, and rearrange the text and subplots to correspond to each other.   

Line 406: this is the first time  you use lapse rate. Please define it very briefly earlier (e.g. in methods).

>> We will add a sentence regarding how we calculated lapse rate in the methods.  

Subsection 4.5.1. is structured poorly. You mention a lot of Figures but make little use of them.

>> We will develop and organize the section further. 

Figure 5- 7: Similarly to Figure 4 you make subplot annotations A,B,C,..but do not use them in the caption. Also, is there a way to skip one or two of the subplots (and move them to supplementary materials) and consequently make the plots larger and horizontally oriented. At present it is very difficult to read them if you don’t print the manuscript.

>>We will add the annotations, A, B, C, and rearrange the text and subplots to correspond to each other.   We will consider moving some of them into the supplementary materials so that they can be horizontal. This is a good suggestion.

Subsection 4.5.2.

Line 427-428: if the variations are similar between the different stable water isotopes and you will comment only on δ¹⁸O then why don’t you save space and present those in supplementary material?

>> The is a good idea, thank you. 

Line 439: remove “it’s”

>> Thank you. 

Subsection 4.5.3., 4.5.4.

Make more reference to your Figures in the text. And similarly to Subsection 4.5.2. – move to supplementary meterials the figures you do not reference.

>> Thank you for this advice.  We will.  

Subsection 4.5.5.

Line 480: The first sentence is not a good start of a subsection. Remove is and simply reference the figure in brackets in a rewritten first sentence. In the first sentence present the general idea/finding from lc-excess. Second sentence at present is too difficult to follow as it is too long– split in two.

>> Thank you for this advice.  They now read as: 

The range of values of LC-excess for the rainfall samples are related to the spread around the evaporation line (Figure 4F). We see that the median value of the snowpack samples is close to the reference for rainfall (0 ‰). Our observations validate Beria et al. (2020)’s review of snowpack data for entire snow seasons and does often not show a significant deviation from median values from the reference precipitation value. 

1. Discussion;

You discuss the results in terms of interpretation of the data but do not make a reference to other literature. In this regard the discussion needs more work and strengthening.

>> Thank you for this feedback.  The first reviewer also said something along these lines.  We look forward to the opportunity to develop our discussion particularly in terms of comparison and discussion of international literature. 

Also, the terminology used in this section sounds a bit awkward. Examples below:

>> We will carefully edit and revise all the text with attention to this critique. 

Line 515: “enrichment in light isotopes during winter” – which are the light isotopes of hydrogen and oxygen? Do you mean “stable water isotope signal becomes more depleted during winter”?

>> We’ve revised it to read: 

 However, we measured diverging isotopic ratios in two springs, one demonstrating an enrichment in the heavy H- and O-isotope composition (AUBG) and the other a depletion in these isotopes (BRDG) during winter (Figure 5). 

Lines 516, 534: “light isotopes” – same comment. Revise the terminology

>> We’ve revised it to read: 

 Winter melt processes contributing to the groundwater system throughout the winter would lead to such a depletion in the heavy H- and O-isotopes. 

Section 5.2. would benefit from reference to the conceptual diagram I suggest above.

>> Thank you, we look forward to adding it, built on the basis of figure 1 in the supplement. 

Lines 555 – 558: this sentence is too long and difficult to follow. Rewrite.

>> We’ve rewritten it as: 

During M2, both BRDG and PZ3 temperature is correlated with streamflow variations although one is a positive anomaly (BRDG) and the other negative (PZ3).  The positive anomaly measured at BRDG suggests a snowmelt input that is heated up before infiltration, which is understandable because BRDG collects snowmelt from the nearby riparian area and steep slopes facing west in direct sun exposure. In contrast, the negative anomaly at PZ3 suggests the melted snow is directly infiltrating as it begins with  the melt period and ends when the area is free of snow (200 m from soil temperature sensor at 1,530 masl), suggesting that the infiltration of snowmelt is local. 

Line 578: “streamflow isotopes” would sound better as “isotope signal in streamflow”

>> We’ve change this to “isotope composition of the water in the streamflow”. Further more we will correct the language imprecision or colloquialism throughout the manuscript.  We will use observe for what we see and measure for what we measure in our revision. 

Line 611: “which locations become more enriched in heavy isotopes” – the location do not become more enriched, it is rather the water in those locations shows a more enriched isotope signal. Please rewrite.

>> We’ve rewritten this to read: 

However, this requires year-round time series to measure where and when water becomes enriched or depleted. 

1. Conclusions

The conclusions section needs strengthening. Mention what are the implications of your findings and how is this study important in terms of better understanding the water dynamics of Apline catchments.

>> Thank you for this feedback.  We will rewrite the conclusions.  

Lines 650 – 655: This is not a strong ending of a conclusion section and it does not reflect the efforts employed in developing and executing the field study. I suggest a small subsection is dedicated on δ¹⁷O somewhere earlier in the manuscript and all the findings are concentrated there.

>> This will be moved to a section of the discussion following “the added value of EC”: “The added value of δ¹⁷O and ¹⁷O-excess”.  

Dear third reviewer, 

We are very thankful for the time and feedback you gave us. 

Please find below a point by point response (in italics) to your specific comments. We are pursuing deeper analyses similar to those that you recommend for subsequent publication.  This paper is really meant to focus on the added value of this set of observations fairly directly from the field.  We will however develop our discussion and conclusion to address the imbalance you describe.   We also will refine our conclusion to be concrete rather the the vague claim that you perceived of “more must be done”. 

We will carefully revise the manuscript and incorporate your minor comments and technical corrections once we receive the editor’s response.

Sincerely, 

The Authors

=============================================================================

I am reviewing MS HESS-2022-48 by Michelon et al. on “Studying the dynamic of a high alpine catchment based on multiple natural tracers”. The authors report on a quite comprehensive (3 years long) dataset of temperatures, water electrical conductivity (EC) and stable isotopic compositions in a range of (eco)hydrological compartments (stream, springs and vegetation) of the Swiss “Vallon de Nant” high-altitude headwater catchment for the investigation of “dominant hydrological processes”.

The MS is well written, easy to follow and of appropriate size, and the figures are well crafted (despite incomplete legends). Finally, the MS obviously fits the scope of HESS well.

The main outcome of the study seems to be that “more must be done”, possibly using the same types of observations (using a multi-tracer framework by coupling EC, temperature, and isotopic analyses) but at higher temporal resolution to achieve the aforementioned goal. There is a general imbalance between the amount and quality of data collected and the quite superficial analysis presented. For a deeper analysis, the authors could, for instance test a simple two-end member approach as per the seasonal origin index, with rain vs snow as end-members to investigate tree water uptake seasonal use?? Also, some of the co-authors have extensive knowledge of catchment hydrology process-based modeling; the data may also call for such an application to calculate e.g. transit time distribution etc.

>> Thank you for this feedback and suggestions. 

My specific comments follow below.

TITLE

The dynamic in what?

>> This is a good point.  As you know, Alpine catchments are considered particularly dynamic (see the introduction of the Mächler 2021 paper about the same catchment for a more complete explanation) and we would like to emphasize that in the title.  With the support and recommendation of the editor, we are planning to change the title to: 

• Hydrodynamics of a high alpine catchment as characterized by four natural tracers.

ABSTRACT

L16. This goes for pretty much all environments displaying dynamics in water δ, right?

>> This is true, but is especially apparent and relevant in this environment with clear seasonal cycles influencing these tracers.  In any case, the abstract has been completely reworked according to suggestions of other reviewers and this sentence no longer appears.  In the one location still using the phrase “such environments”, we have added “dynamic” to clarify the characteristic of the environment that necessitates year-round water sampling.  

INTRODUCTION

L55. I would not refer to unpublished works, also because you have quite a few papers to cite from, some of which are only 1 year old.

>> the reference list will be updated upon resubmission and any still unpublished works will be removed. 

L64. It is your “overall” objective, not (one of) your specific one(s).

>> indeed, we will change the wording. 

L65-66. Or a mix of the two? Or is it implied here?

>> indeed, we have clarified this by changing the wording to: “the alteration and mixing of subsurface storage and from localized snow melting” 

METHOD

L186. It comes as a surprise at this point of the MS that you would sample from the vegetation. What is the purpose? This should be introduced somewhere earlier.

>> Indeed, we will remove this and save it for a subsequent analysis (and manuscript) focused on hydrological interactions with vegetation. 

L190. There is just one delta notation, used for different elements and their stable isotopes. Please rephrase.

>> this has been rephrased 

L196-197. “and data from the last 6 injections were kept”

>> thank you

L209-210. To be “less temperature sensitive” and “convey additional information on evaporation processes and on climatic conditions” seems to be contradicting… please rephrase/elaborate

>> We have reworded this: 

Both d-excess and ¹⁷O-excess are known to respond to relative humidity during evaporative processes but ¹⁷O-excess may be less temperature sensitive (Surma et al., 2021; Bershaw et al., 2020) than d-excess and thus changes in its composition may be more sensitive to net evaporation, including secondary evaporation, as well as the meteorological conditions even when they would be invisible with d-excess (Risi et al., 2010). 

L219. Why “GRAS” and “ROCK” are in capital letters?

>> We are using four letter capital abbreviations for names of sampling locations. We will make this more clear in the site description.  

L241. “long”?

>> We have replaced with the length of series. 

L242. “influenced by the low”

>> We have replaced “influenced” with “limited”

Figure 3. It is a nice picture, but could use more info: e.g., name each of the three different panels. It is difficult to understand what “bottom” refers to (i.e., is it the bottom part of the top panel, or the actual bottom graphics?). The caption should be as self-explanatory as possible, therefore define also here what “B”, “E”, “M”, and “R” mean. Bottom graphics: it is difficult to differentiate between streamflow data and the water temperatures in gray colors. Maybe move the 2nd y-axis legend (“Streamflow [mm/day]”) a bit down so that it faces lower values, e.g. [0-20 mm/day] in each panel?

>> Thank you for your feedback.  We will incorporate as many of your suggestions as possible as we rework the figure. 

RESULTS

Usually, (campaign) results are related in past tense to differentiate with literature findings and general statements (made in present tense). Also avoid using “shows this and that…”. Use a more direct formulation, e.g., in L251: “The baseflow period extends from the end of September to early spring (mid-March to beginning of April) and shows a streamflow of around 1 mm/d only” vs. “The baseflow period extends from the end of September to early spring (mid-March to beginning of April) with streamflow values of approx. 1 mm/d only…”

>> Thank you for this feedback.  We will take it into account as we edit and restructure the results section. 

L257-259. Could be a nice discussion and moved there.

>> Thank you, we will. 

L260. “due to an important water input from snowmelt.” Do we need this piece of info again?

>> You are right, this is redundant.  We will delete it. 

L260-262. But isn’t it because there was no early melt period that the melt period started sooner in 2018?

>> Perhaps, we will reword this to make this clear. 

L317-319. Avoid such formulation and just start with the actual results, e.g., “Correlation between spring and air temperature at the Auberge station was source-specific…”.

>> Indeed, this sentence has been modified as to recommendations from a previous reviewer. 

Also: BRDG and ICEC acronyms are not defined

>> Thank you for pointing this out, we will define all point names in the site description section. 

L320. I am not a specialist, but does a spring have a “volume”, strictly speaking?

>> You are right, we have clarified this to refer to the magnitude of flow out of the spring.  

L325. “temperature [curve]”

>> We have changed this to: “The shape of the curve of temperature fluctuations of the …”

Table 1. Why it the maximum stream temperature not reported?

>> This is an oversight on our part, we will add it. 

L353-354. The Lag “L” should have its own equation reported in section 3.2. It is difficult, at least to me, to understand what was done here…

>> As noted, we reported this in Appendix 2, but will happily move it back to the methods section so that it is clearer for the readers. 

L401-402. Such an intro within the result section is not needed. Instead give the results and point to the figure/table for substantiation.

>> Thank you for this reminder.  We plan to vigorously edit the results sections so that it is more to the point. 

L403. Please define “lapse rate”.

>> Indeed, we have added a sentence regarding lapse rate definition and determination in the methods as per a recommendation from another reviewer. 

Fig. 5 vs Fig 6 & 7. Why are you connecting the dots for springs, therefore implying linear interpolation, when you do not do this for e.g., streamflow or rainfall? 

>> We are sorry that you felt like we are misleading you.  We felt that this depiction made it easier to distinguish and compare the fluctuations at the different springs.  We will reconsider the lines and be more clear about their purpose in the text, regardless.

Also replace “δD” by “δ²H” throughout, please. I would remove all unnecessary material, that is all variables that are not described in the text. This would also make the figures more reader friendly.

>> Thank you for this advice, indeed, we only use δ²H in the text. We will change the notation in the figures.  Additionally, we are planning to move some material from the figures to the supplementary files. 

L427-428. What is shown in Fig. 5 should be discussed, so why showing both δ²H and δ¹⁸O when only δ¹⁸O is discussed?

>> indeed, we are planning to move the other subplots to the supplementary information as per suggestions from other reviewers. 

L431. “with [lower] isotopic values”

>> thank you 

L455. “and a significant decrease in the [isotopic composition]”. 

>> thank you

What about the rest of the variables this time (δ¹⁸O & δ¹⁷O)?

>> indeed, we said we focus on δ¹⁸O, we will correct this or clarify. 

L475. “local scale process information”. Name some examples.

>> Here we are referring to the interplay of mixing verses fractionation in the immediate vicinity of sampling.   In order to interpret these results, we must consider the storage and release processes on a catchment scale.  

L481. What evaporation line? Here you are looking at the deviation from the LMWL...

>> true, this is a typo on our part

L484-485. I do not understand. Please rephrase. Do you mean to say that larch trees xylem water have low Lc-Excess values, meaning they sample from water departing isotopically from meteoritic water sources (i.e., evaporatively-enriched soil water)?

>> You are correct, this is an oversimplification on our part.  We will remove discussion of vegetation for the purposes of this paper and focus on it in a subsequent paper. 

L486. “negative median [lc-excess] value”

>> Thank you

L492-496. 17-Excess measurements are very tricky, and I ask myself if differences to other studies have to do with the analysis technique used, i.e., mass vs. laser spectrometer?

>> We do not believe that this is the case, as for both mass and laser spectrometers, the calibrations are done with standards that are calibrated with the MS-analytical approach.  However memory effects can influence the 17-O measurements.   We will add more discussion regarding the risk of this in the respective methods and discussion sections as appropriate.   

L508-509. This is not needed.

>> Indeed, we will reword this to actually be a topic sentence. 

DISCUSSION

L514-515. This I never read 😊: please change to e.g., “an enrichment (depletion) in heavier stable isotopes at AUBG (BRDG)…”

“Such a depletion by heavier isotopes”

>> We’ve revised it to read: 

 However, we measured diverging isotopic ratios in two springs, one demonstrating an enrichment (AUBG) and the other a depletion (BRDG) in the heavy H- and O-isotopes during winter (Figure 5). 

L534-535. “Although the δ²H, δ¹⁷O and δ¹⁸O annual medians of AUBG, ROCK, BRDG and ICEC decrease with elevation”

>> Thank you

L622. Again, I doubt that the δ¹⁷O and ¹⁷O-Excess add value to the already measured δ²H and δ¹⁸O time series…

>> This discovery would already be an added value as not that many δ¹⁷O and ¹⁷O-Excess have been made so far.  We will emphasize this. 

CONCLUSION

L650. The reader still does not know what you mean by “local-scale snow hydrological processes”

 >> We will move this conclusion into a discussion section and elaborate more extensively and explain what we are referring to here.