the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Apr 2022
Seasonal δ2H and δ18O changes in river water from a high-altitude humid plain of the southern Alps (Cervières, France): tracking the transit time through a watershed
Abstract. The Alps Mountains play a major role in the water cycle at a regional scale in Europe. This mountain range acts as the ‘water tower’ of Europe by storing large volumes of ice and snow, and by regulating the runoff of the rivers constituting freshwater reservoirs of paramount importance for the biodiversity and human activity. Located in the French Southern Alps, the Cerveyrette valley and a high-altitude (≈ 2000 m) swampy plain constitute a watershed of about 100 km2. From August 2011 to July 2013, water samples were collected monthly from the Cerveyrette river upstream of the Cervières village (elevation = 1620 m) located in the Upper Durance catchment area. Apparent cyclicality in δ2H and δ18O of the river waters documented over these two years partly reflect seasonal variations in the isotopic compositions of precipitations that mainly occur as snow accumulating at altitudes ranging from ≈ 1700 m to 3300 m. The estimated time lag of three to four months between summer precipitations and their sampling in the Cerveyrette river at the discharge point of the watershed is interpreted to integrate both the mean transfer time of the water discharge and the rate of melting of the snow cover. Here, we show that the transfer time from mountain-accumulated snow toward the low-altitude cultivated areas (Provence) is a sensitive key variable responding to the current climate warming. Indeed, a lowering of the snow cover surface is expected to reduce the buffer effect of snow compared to rainfall, and to decrease the time period during which the discharge rate of the Durance river is large enough for constituting sizable water resources. Understanding and modeling water transit times in nival dominated watersheds are consequently critical to evaluate the impact of the ongoing climate warming on water circulation and resources in the Alps and downstream including the case of mitigation actions.
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RC1: 'Comment on hess-2022-132', Anonymous Referee #1, 18 May 2022
The authors present stream water isotope data from a catchment draining part of the French alps. The study considers seven sampling sites that have been sampled once and another site at which monthly samples were taken over a two year period. The water samples were analyzed for their stable isotopic composition (2H and 18O) and the authors show that there is a seasonal pattern in the 18O which they interpret to infer a rough transit time of snow to discharge at the sampling location “of about 3 to 4 months”. The analyses are very limited and also the data set is rather small. There is little novelty in the study over all. The manuscript is not well prepared, the structure is off with large parts of the methods and results showing up in the Discussion section. The introduction reads partly as a results and partly as a methods section, while no research question or hypothesis was posed. The conclusion refers to climate change, which was not discussed in the manuscript. The maps and photos contain very limited information to the reader, as one would have been interested in a map of the catchment extend and the elevation distribution.
Over all, the manuscript does not provide the necessary quality to grant a publication.
I believe that there are publications that show a why to address the research question that I believe the authors were targeting and I recommend the following work:
Kirchner, J. W. (2016a). Aggregation in environmental systems—Part 1: Seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments. Hydrology and Earth System Sciences, 20(1), 279–297. https://doi.org/10.5194/hess- 20-279-2016
Kirchner, J. W. (2016b). Aggregation in environmental systems—Part 2: Catchment mean transit times and young water fractions under hydro- logic nonstationarity. Hydrology and Earth System Sciences, 20(1), 299–328.
von Freyberg, J., Allen, S. T., Seeger, S., Weiler, M., & Kirchner, J. W. (2018). Sensitivity of young water fractions to hydro-climatic forcing and landscape properties across 22 Swiss catchments. Hydrology and Earth System Sciences, 22(7), 3841–3861. https://doi.org/10.5194/ hess-22-3841-2018
Campbell, É. M. S., Pavlovskii, I., & Ryan, M. C. (2020). Snowpack disrupts relationship between young water fraction and isotope amplitude ratio; approximately one fifth of mountain streamflow less than one year old. Hydrological Processes, 34, 4762-4775. doi: https://doi.org/10.1002/hyp.13914.
I provide some more technical and specific comments below:
L 30 – L37: The first paragraph of the introduction, in which you state what is being presented in this manuscript is in-conventional.
L 54-62: The number of references seems excessive.
Very detailed info (e.g., definition “orographic precipitation, alpine)
L86 – 90: This reads like something one would expect in the methods section
L 94: Why does this sentence start with “Why”?
L124: MAAT is not the correct expression when talking about months.
Figure 1: The map pf central Europe is unnecessary large and could instead be an insert in the lower satellite image.
Figure 2: The A) and B) of the caption should also be shown in the respective subplots. Instead of two satellite images, I would rather prefer a map showing the elevation and the area of the catchments.
Figure 3: These photos are not needed. I do not see any justification to show these photos.
L 133: “inhomogeneity” = heterogeneity?
L 134: Is that sampling spot as well shown in the Figure 2B that you refer to? I cannot see it labeled.
L 156 – 158: This would be part of the methods section
Figure 4: “binary plot”? That’s something else, because the presented data is not binary.
L 167: “pseudo cyclicity”? How is that defined? To me, it looks not pseudo at all, but like a very common seasonality pattern for such data.
L 181: I don’t see a relevance to compare your alpine data with “warm and dry areas such as Africa” (also Africa is too large to just have one defined climate).
L 188: Is there permafrost in the studied catchments? If so, please add info to site description.
Fig. 5 and 6: What do the error bars indicate?
L 199: MAAT? You had this defined earlier as mean annual air temperature. This needs to adjusted here.
L 198 – 201: This fits better in a methods section
L210: minor role
219: “pseudo-cyclicity”?
L213-224: This is all part of methods
L225-233: This is all part of results
L246: I think that you are suggesting to use the time lag between the estimated precipitation isotope data (derived from temperature observations) and the observed river water isotopes to infer the time it takes for snow to melt and rout to the outlet. However, it seems that this approach would neglect the time the snowpack accumulates and is present. This latter time would be also part of the time lag and not only the mentioned snowmelt and flow paths.
L 267: Why “if”?
L286: “equation of state of water predicts” definition and reference missing
L 313: It is unclear why it is referred to a “dampening effect of snow melting”. The opposite is the case. The relatively concentrated snowmelt allowing large amounts of precipitation to enter the catchment in short time period – compared to a no-snow climate in which the same precipitation amount enters the catchment over several months – is intensifying the changes in the isotope composition of the stream water.
L 317: It seems that this 3 to 4 months also includes the period of a present snowpack, because you do not present any consideration of lag between snowfall and snow melt.
L 320: The effects of climate warming have not been discussed in this manuscript.
Citation: https://doi.org/10.5194/hess-2022-132-RC1 -
AC1: 'Reply on RC1', Christophe Lecuyer, 05 Jul 2022
Dear reviewers, dear editor,
First of all, I would like to thank the three reviewers for the fair and elegant comments they made on our work. It is obvious that two of them, both with an academic background of physicists, provided negative recommendations for publication of our case study in HESS, while the third one, a geochemist was more enthusiastic.
Our basic idea was to consider a single and simple watershed to monitor the d18O and d2H of the Cerveyrette stream over two years. The isotopic record we obtained was interpreted as a seasonal record of ongoing precipitations delayed and buffered by the annual complete melting of the snowpack, keep in mind that there is no permafrost here with altitudes that remain below 2500 m in any case. Please, note also that the d18O and d2H variations are of very small magnitude and require very careful and optimal analytical conditions to be detected. Dephasing and flattening of the observed signal recorded in the stream is quantified relatively to the seasonal isotopic record of precipitations, itself inferred from the local meteorological data including monthly air temperatures combined to the equations relating the air temperature to the isotopic compositions of precipitations. Furthermore, it is well known since Rozanski et al. (1993) that the most negative d2H and d18O values of precipitation in Europe take place during the coldest months of the year. Our approach is indeed close to that used by Niinikoski, et al. (2016) who used stable isotopes to resolve transit times and travel routes of river water as exemplified by a case study from southern Finland.
We are aware that two reviewers recommended the rejection of our paper, so we consider to revise our manuscript taking into account all the comments, criticisms and suggestions we received from the reviewers before to submit it to a less-specialized journal.
With my best regards
On behalf of all co-authors
Prof. Dr. Christophe Lécuyer
Citation: https://doi.org/10.5194/hess-2022-132-AC1
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AC1: 'Reply on RC1', Christophe Lecuyer, 05 Jul 2022
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RC2: 'Comment on hess-2022-132', Anonymous Referee #2, 20 May 2022
General comments
This paper uses 2-years of monthly stable water isotope values in streamwater from a 100km2 French Alpine watershed to estimate the average time shift between snowfall and snowmelt being discharged at the catchment outlet. They further calculate d-excess values with the aim to identify moisture sources of precipitation, however, the small data set does not allow a conclusive analysis.
The paper lacks a clearly defined research question or an objective. The study results were not well placed into the wider context of Alpine (isotope) hydrology (e.g., is the result of a 3-4 month time shift exceptional or rather expected from the findings in other studies).
It is not clear as to why this study is relevant. Whereas the authors talk at length about the importance of Alpine water resources and the potential impacts of climate change on earlier snowmelt, they don’t conduct the necessary analyses to support their statements.
Given that the data set is rather small and many conclusions remain unspecific, I recommend a rejection of the manuscript.
Specific comments
Does the paper address relevant scientific questions within the scope of HESS?
- This paper does not address a specific research question. It rather presents and discusses two years of isotope data from a 100km2 catchment in the French Alps.
Does the paper present novel concepts, ideas, tools, or data?
- The data are presented for the first time, although stable water isotope data from Alpine streams have been published before.
- The first two sentences in the Introduction read (L30-34): “We investigated through a new methodological approach the complex relationship between the atmospheric water circulation, the local precipitations, the buffer effect of snow, swamps and soils and the resulting main water outlet of a watershed located in an alpine context. We show the importance of the transfer time from mountain-accumulated snow to the lower cultivated areas as a sensitive key variable responding to the current climate change, with a lowering of the snow cover surface and a reduced buffer effect of snow compared to rainfall.» However, nowhere in the paper, the authors explain why their method is «new», and they don’t show the importance of the transfer time! Thus, the novelty of the data/results/conclusions is not at all discussed in the paper.
Are substantial conclusions reached?
- The small data set does not allow for the conclusions to be substantial. The authors conclude that (L304)“(...) the river water mostly preserved the original isotopic compositions of precipitations. This observation means that the water did not suffer significant evaporation or mixing with other sources of water during its transit through the watershed.» This conclusion cannot be drawn without considering the hydrologic regime at the time of sampling. I would suspect that samples collected during baseflow will have a different isotopic composition/d-excess than those collected during high flow (i.e., during rain or snowmelt).
Are the scientific methods and assumptions valid and clearly outlined?
- The methods for data collection are valid. Some assumptions for data analysis are questionable and not well founded. E.g., the authors assume that the lightest isotopes in precipitation always occur during Dec-Feb (although L234 says “March”); is not clear whether this is true for both years of observation and why the authors decided to calculate long-term mean-monthly precipitation isotope values instead of the actual monthly isotope values for the specific study period. Furthermore, the authors interpret d-excess values without taking the climatic and hydrologic conditions into account.
Are the results sufficient to support the interpretations and conclusions?
- No, the results are insufficient to support the conclusions reached in this paper.
Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)?
- The authors provide the data in the manuscript.
Do the authors give proper credit to related work and clearly indicate their own new/original contribution?
- This could be improved, e.g. the authors relate to other work during paragraphs that are not relevant to this study (e.g. L47-62). They don’t relate their work to any isotope studies from other Alpine catchments, e.g. (Seeger and Weiler, 2014).
Does the title clearly reflect the contents of the paper?
- The tittle suggests a transit-time modelling study. This was clearly not done here.
Does the abstract provide a concise and complete summary?
- The abstract is not concise. It starts with mentioning that the Alps are an important water resource for Europe and ends with suggesting that water transit time modelling will help in evaluating the impact of climate change on Alpine water resources. This is not at all in line with the scope and the results of the presented study, which is based on 2-years of isotope data from one catchment. No transit-time model was used, no climate change impact assessment was conducted.
- A research question or objective is missing. Therefore, it is not clear, what the results of this study should be.
Is the overall presentation well structured and clear?
- The paper is not well structured. E.g., how can the authors conduct a study without a well-defined research question?
- The introduction starts with a repetition of the abstract (L30-37).
- Some Methods are part of the Discussion (Eq. 2 & 3). This is very confusing.
References:
Seeger, S. and Weiler, M.: Reevaluation of transit time distributions, mean transit times and their relation to catchment topography, Hydrol. Earth Syst. Sci., 18, 4751–4771, 2014.
Citation: https://doi.org/10.5194/hess-2022-132-RC2 -
AC2: 'Reply on RC2', Christophe Lecuyer, 05 Jul 2022
Dear reviewers, dear editor,
First of all, I would like to thank the three reviewers for the fair and elegant comments they made on our work. It is obvious that two of them, both with an academic background of physicists, provided negative recommendations for publication of our case study in HESS, while the third one, a geochemist was more enthusiastic.
Our basic idea was to consider a single and simple watershed to monitor the d18O and d2H of the Cerveyrette stream over two years. The isotopic record we obtained was interpreted as a seasonal record of ongoing precipitations delayed and buffered by the annual complete melting of the snowpack, keep in mind that there is no permafrost here with altitudes that remain below 2500 m in any case. Please, note also that the d18O and d2H variations are of very small magnitude and require very careful and optimal analytical conditions to be detected. Dephasing and flattening of the observed signal recorded in the stream is quantified relatively to the seasonal isotopic record of precipitations, itself inferred from the local meteorological data including monthly air temperatures combined to the equations relating the air temperature to the isotopic compositions of precipitations. Furthermore, it is well known since Rozanski et al. (1993) that the most negative d2H and d18O values of precipitation in Europe take place during the coldest months of the year. Our approach is indeed close to that used by Niinikoski, et al. (2016) who used stable isotopes to resolve transit times and travel routes of river water as exemplified by a case study from southern Finland.
We are aware that two reviewers recommended the rejection of our paper, so we consider to revise our manuscript taking into account all the comments, criticisms and suggestions we received from the reviewers before to submit it to a less-specialized journal.
With my best regards
On behalf of all co-authors
Prof. Dr. Christophe Lécuyer
Citation: https://doi.org/10.5194/hess-2022-132-AC2
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RC3: 'Comment on hess-2022-132', Anonymous Referee #3, 03 Jun 2022
The authors present novel isotope data from the Cerveyrette river and its catchment area located in the French Southern Alps. One site, situated river upstream of the Cervières village, was sampled for a period of two years, between 2011 and 2013, the other seven sites were sampled once. The aims of the paper are to estimate the average time between snowfall and melt discharged at the catchment situated at northern entry of the small town of Cervières, to give a best fit function to the measured data, to explore the meaning of the deuterium excess variations. The measured d18O values and local temperature distribution from a meteorological station are implemented in order to approximate a function f(t), where t is representing the independent variable in â. Than, the calculated isotopic compositions by using f(t) are compared with the measured ones, discussing differences.
The aims of investigation are well expressed; the amount of data sufficient in order to design the function and the presented novel method. The paragraphs are following in a logical manner and the text has also an educational value.
Minor changes should be done before the manuscript can be published. Some of the suggestions are included below, all comments being inserted with specific location on the attached PDF.
Page 3:
- On the maps the locations of the mentioned mountain peaks are not visible
- Relationship with the end of the Younger Dryas event?
Page 5:
- Tabor et al., 2020. Stable isotope geochemistry of the modern Shinfa River, northwestern Ethiopian lowlands: a potential model for interpreting ancient environments of the Middle Stone Age. GSL Special Publication 507, doi.org/10.1144/SP507-2020-219.
The slope is even 4 for this case.
Page 8:
- High d-excess values for the winter time were put in evidence at several circum Mediterranean sites. For discussion and references see Bojar, A.-V., Halas, S., Bojar, H.P. and Chmiel, S. 2017.
Stable isotope hydrology of precipitation and groundwater of a region with high continentality, South Carpathians, Romania. Carpathian Journal of Earth and Environmental Sciences, 12, 513–524.
A paragraph relating the potential of the method and study to monitor the effects of ongoing climatic changes would be of benefit.
Figures
Suggestions for Figures are given directly on the PDF.
A delimitation of the catchment area would be of help for the reader.
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AC3: 'Reply on RC3', Christophe Lecuyer, 05 Jul 2022
Dear reviewers, dear editor,
First of all, I would like to thank the three reviewers for the fair and elegant comments they made on our work. It is obvious that two of them, both with an academic background of physicists, provided negative recommendations for publication of our case study in HESS, while the third one, a geochemist was more enthusiastic.
Our basic idea was to consider a single and simple watershed to monitor the d18O and d2H of the Cerveyrette stream over two years. The isotopic record we obtained was interpreted as a seasonal record of ongoing precipitations delayed and buffered by the annual complete melting of the snowpack, keep in mind that there is no permafrost here with altitudes that remain below 2500 m in any case. Please, note also that the d18O and d2H variations are of very small magnitude and require very careful and optimal analytical conditions to be detected. Dephasing and flattening of the observed signal recorded in the stream is quantified relatively to the seasonal isotopic record of precipitations, itself inferred from the local meteorological data including monthly air temperatures combined to the equations relating the air temperature to the isotopic compositions of precipitations. Furthermore, it is well known since Rozanski et al. (1993) that the most negative d2H and d18O values of precipitation in Europe take place during the coldest months of the year. Our approach is indeed close to that used by Niinikoski, et al. (2016) who used stable isotopes to resolve transit times and travel routes of river water as exemplified by a case study from southern Finland.
We are aware that two reviewers recommended the rejection of our paper, so we consider to revise our manuscript taking into account all the comments, criticisms and suggestions we received from the reviewers before to submit it to a less-specialized journal.
With my best regards
On behalf of all co-authors
Prof. Dr. Christophe Lécuyer
Citation: https://doi.org/10.5194/hess-2022-132-AC3
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AC3: 'Reply on RC3', Christophe Lecuyer, 05 Jul 2022
Status: closed
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RC1: 'Comment on hess-2022-132', Anonymous Referee #1, 18 May 2022
The authors present stream water isotope data from a catchment draining part of the French alps. The study considers seven sampling sites that have been sampled once and another site at which monthly samples were taken over a two year period. The water samples were analyzed for their stable isotopic composition (2H and 18O) and the authors show that there is a seasonal pattern in the 18O which they interpret to infer a rough transit time of snow to discharge at the sampling location “of about 3 to 4 months”. The analyses are very limited and also the data set is rather small. There is little novelty in the study over all. The manuscript is not well prepared, the structure is off with large parts of the methods and results showing up in the Discussion section. The introduction reads partly as a results and partly as a methods section, while no research question or hypothesis was posed. The conclusion refers to climate change, which was not discussed in the manuscript. The maps and photos contain very limited information to the reader, as one would have been interested in a map of the catchment extend and the elevation distribution.
Over all, the manuscript does not provide the necessary quality to grant a publication.
I believe that there are publications that show a why to address the research question that I believe the authors were targeting and I recommend the following work:
Kirchner, J. W. (2016a). Aggregation in environmental systems—Part 1: Seasonal tracer cycles quantify young water fractions, but not mean transit times, in spatially heterogeneous catchments. Hydrology and Earth System Sciences, 20(1), 279–297. https://doi.org/10.5194/hess- 20-279-2016
Kirchner, J. W. (2016b). Aggregation in environmental systems—Part 2: Catchment mean transit times and young water fractions under hydro- logic nonstationarity. Hydrology and Earth System Sciences, 20(1), 299–328.
von Freyberg, J., Allen, S. T., Seeger, S., Weiler, M., & Kirchner, J. W. (2018). Sensitivity of young water fractions to hydro-climatic forcing and landscape properties across 22 Swiss catchments. Hydrology and Earth System Sciences, 22(7), 3841–3861. https://doi.org/10.5194/ hess-22-3841-2018
Campbell, É. M. S., Pavlovskii, I., & Ryan, M. C. (2020). Snowpack disrupts relationship between young water fraction and isotope amplitude ratio; approximately one fifth of mountain streamflow less than one year old. Hydrological Processes, 34, 4762-4775. doi: https://doi.org/10.1002/hyp.13914.
I provide some more technical and specific comments below:
L 30 – L37: The first paragraph of the introduction, in which you state what is being presented in this manuscript is in-conventional.
L 54-62: The number of references seems excessive.
Very detailed info (e.g., definition “orographic precipitation, alpine)
L86 – 90: This reads like something one would expect in the methods section
L 94: Why does this sentence start with “Why”?
L124: MAAT is not the correct expression when talking about months.
Figure 1: The map pf central Europe is unnecessary large and could instead be an insert in the lower satellite image.
Figure 2: The A) and B) of the caption should also be shown in the respective subplots. Instead of two satellite images, I would rather prefer a map showing the elevation and the area of the catchments.
Figure 3: These photos are not needed. I do not see any justification to show these photos.
L 133: “inhomogeneity” = heterogeneity?
L 134: Is that sampling spot as well shown in the Figure 2B that you refer to? I cannot see it labeled.
L 156 – 158: This would be part of the methods section
Figure 4: “binary plot”? That’s something else, because the presented data is not binary.
L 167: “pseudo cyclicity”? How is that defined? To me, it looks not pseudo at all, but like a very common seasonality pattern for such data.
L 181: I don’t see a relevance to compare your alpine data with “warm and dry areas such as Africa” (also Africa is too large to just have one defined climate).
L 188: Is there permafrost in the studied catchments? If so, please add info to site description.
Fig. 5 and 6: What do the error bars indicate?
L 199: MAAT? You had this defined earlier as mean annual air temperature. This needs to adjusted here.
L 198 – 201: This fits better in a methods section
L210: minor role
219: “pseudo-cyclicity”?
L213-224: This is all part of methods
L225-233: This is all part of results
L246: I think that you are suggesting to use the time lag between the estimated precipitation isotope data (derived from temperature observations) and the observed river water isotopes to infer the time it takes for snow to melt and rout to the outlet. However, it seems that this approach would neglect the time the snowpack accumulates and is present. This latter time would be also part of the time lag and not only the mentioned snowmelt and flow paths.
L 267: Why “if”?
L286: “equation of state of water predicts” definition and reference missing
L 313: It is unclear why it is referred to a “dampening effect of snow melting”. The opposite is the case. The relatively concentrated snowmelt allowing large amounts of precipitation to enter the catchment in short time period – compared to a no-snow climate in which the same precipitation amount enters the catchment over several months – is intensifying the changes in the isotope composition of the stream water.
L 317: It seems that this 3 to 4 months also includes the period of a present snowpack, because you do not present any consideration of lag between snowfall and snow melt.
L 320: The effects of climate warming have not been discussed in this manuscript.
Citation: https://doi.org/10.5194/hess-2022-132-RC1 -
AC1: 'Reply on RC1', Christophe Lecuyer, 05 Jul 2022
Dear reviewers, dear editor,
First of all, I would like to thank the three reviewers for the fair and elegant comments they made on our work. It is obvious that two of them, both with an academic background of physicists, provided negative recommendations for publication of our case study in HESS, while the third one, a geochemist was more enthusiastic.
Our basic idea was to consider a single and simple watershed to monitor the d18O and d2H of the Cerveyrette stream over two years. The isotopic record we obtained was interpreted as a seasonal record of ongoing precipitations delayed and buffered by the annual complete melting of the snowpack, keep in mind that there is no permafrost here with altitudes that remain below 2500 m in any case. Please, note also that the d18O and d2H variations are of very small magnitude and require very careful and optimal analytical conditions to be detected. Dephasing and flattening of the observed signal recorded in the stream is quantified relatively to the seasonal isotopic record of precipitations, itself inferred from the local meteorological data including monthly air temperatures combined to the equations relating the air temperature to the isotopic compositions of precipitations. Furthermore, it is well known since Rozanski et al. (1993) that the most negative d2H and d18O values of precipitation in Europe take place during the coldest months of the year. Our approach is indeed close to that used by Niinikoski, et al. (2016) who used stable isotopes to resolve transit times and travel routes of river water as exemplified by a case study from southern Finland.
We are aware that two reviewers recommended the rejection of our paper, so we consider to revise our manuscript taking into account all the comments, criticisms and suggestions we received from the reviewers before to submit it to a less-specialized journal.
With my best regards
On behalf of all co-authors
Prof. Dr. Christophe Lécuyer
Citation: https://doi.org/10.5194/hess-2022-132-AC1
-
AC1: 'Reply on RC1', Christophe Lecuyer, 05 Jul 2022
-
RC2: 'Comment on hess-2022-132', Anonymous Referee #2, 20 May 2022
General comments
This paper uses 2-years of monthly stable water isotope values in streamwater from a 100km2 French Alpine watershed to estimate the average time shift between snowfall and snowmelt being discharged at the catchment outlet. They further calculate d-excess values with the aim to identify moisture sources of precipitation, however, the small data set does not allow a conclusive analysis.
The paper lacks a clearly defined research question or an objective. The study results were not well placed into the wider context of Alpine (isotope) hydrology (e.g., is the result of a 3-4 month time shift exceptional or rather expected from the findings in other studies).
It is not clear as to why this study is relevant. Whereas the authors talk at length about the importance of Alpine water resources and the potential impacts of climate change on earlier snowmelt, they don’t conduct the necessary analyses to support their statements.
Given that the data set is rather small and many conclusions remain unspecific, I recommend a rejection of the manuscript.
Specific comments
Does the paper address relevant scientific questions within the scope of HESS?
- This paper does not address a specific research question. It rather presents and discusses two years of isotope data from a 100km2 catchment in the French Alps.
Does the paper present novel concepts, ideas, tools, or data?
- The data are presented for the first time, although stable water isotope data from Alpine streams have been published before.
- The first two sentences in the Introduction read (L30-34): “We investigated through a new methodological approach the complex relationship between the atmospheric water circulation, the local precipitations, the buffer effect of snow, swamps and soils and the resulting main water outlet of a watershed located in an alpine context. We show the importance of the transfer time from mountain-accumulated snow to the lower cultivated areas as a sensitive key variable responding to the current climate change, with a lowering of the snow cover surface and a reduced buffer effect of snow compared to rainfall.» However, nowhere in the paper, the authors explain why their method is «new», and they don’t show the importance of the transfer time! Thus, the novelty of the data/results/conclusions is not at all discussed in the paper.
Are substantial conclusions reached?
- The small data set does not allow for the conclusions to be substantial. The authors conclude that (L304)“(...) the river water mostly preserved the original isotopic compositions of precipitations. This observation means that the water did not suffer significant evaporation or mixing with other sources of water during its transit through the watershed.» This conclusion cannot be drawn without considering the hydrologic regime at the time of sampling. I would suspect that samples collected during baseflow will have a different isotopic composition/d-excess than those collected during high flow (i.e., during rain or snowmelt).
Are the scientific methods and assumptions valid and clearly outlined?
- The methods for data collection are valid. Some assumptions for data analysis are questionable and not well founded. E.g., the authors assume that the lightest isotopes in precipitation always occur during Dec-Feb (although L234 says “March”); is not clear whether this is true for both years of observation and why the authors decided to calculate long-term mean-monthly precipitation isotope values instead of the actual monthly isotope values for the specific study period. Furthermore, the authors interpret d-excess values without taking the climatic and hydrologic conditions into account.
Are the results sufficient to support the interpretations and conclusions?
- No, the results are insufficient to support the conclusions reached in this paper.
Is the description of experiments and calculations sufficiently complete and precise to allow their reproduction by fellow scientists (traceability of results)?
- The authors provide the data in the manuscript.
Do the authors give proper credit to related work and clearly indicate their own new/original contribution?
- This could be improved, e.g. the authors relate to other work during paragraphs that are not relevant to this study (e.g. L47-62). They don’t relate their work to any isotope studies from other Alpine catchments, e.g. (Seeger and Weiler, 2014).
Does the title clearly reflect the contents of the paper?
- The tittle suggests a transit-time modelling study. This was clearly not done here.
Does the abstract provide a concise and complete summary?
- The abstract is not concise. It starts with mentioning that the Alps are an important water resource for Europe and ends with suggesting that water transit time modelling will help in evaluating the impact of climate change on Alpine water resources. This is not at all in line with the scope and the results of the presented study, which is based on 2-years of isotope data from one catchment. No transit-time model was used, no climate change impact assessment was conducted.
- A research question or objective is missing. Therefore, it is not clear, what the results of this study should be.
Is the overall presentation well structured and clear?
- The paper is not well structured. E.g., how can the authors conduct a study without a well-defined research question?
- The introduction starts with a repetition of the abstract (L30-37).
- Some Methods are part of the Discussion (Eq. 2 & 3). This is very confusing.
References:
Seeger, S. and Weiler, M.: Reevaluation of transit time distributions, mean transit times and their relation to catchment topography, Hydrol. Earth Syst. Sci., 18, 4751–4771, 2014.
Citation: https://doi.org/10.5194/hess-2022-132-RC2 -
AC2: 'Reply on RC2', Christophe Lecuyer, 05 Jul 2022
Dear reviewers, dear editor,
First of all, I would like to thank the three reviewers for the fair and elegant comments they made on our work. It is obvious that two of them, both with an academic background of physicists, provided negative recommendations for publication of our case study in HESS, while the third one, a geochemist was more enthusiastic.
Our basic idea was to consider a single and simple watershed to monitor the d18O and d2H of the Cerveyrette stream over two years. The isotopic record we obtained was interpreted as a seasonal record of ongoing precipitations delayed and buffered by the annual complete melting of the snowpack, keep in mind that there is no permafrost here with altitudes that remain below 2500 m in any case. Please, note also that the d18O and d2H variations are of very small magnitude and require very careful and optimal analytical conditions to be detected. Dephasing and flattening of the observed signal recorded in the stream is quantified relatively to the seasonal isotopic record of precipitations, itself inferred from the local meteorological data including monthly air temperatures combined to the equations relating the air temperature to the isotopic compositions of precipitations. Furthermore, it is well known since Rozanski et al. (1993) that the most negative d2H and d18O values of precipitation in Europe take place during the coldest months of the year. Our approach is indeed close to that used by Niinikoski, et al. (2016) who used stable isotopes to resolve transit times and travel routes of river water as exemplified by a case study from southern Finland.
We are aware that two reviewers recommended the rejection of our paper, so we consider to revise our manuscript taking into account all the comments, criticisms and suggestions we received from the reviewers before to submit it to a less-specialized journal.
With my best regards
On behalf of all co-authors
Prof. Dr. Christophe Lécuyer
Citation: https://doi.org/10.5194/hess-2022-132-AC2
-
RC3: 'Comment on hess-2022-132', Anonymous Referee #3, 03 Jun 2022
The authors present novel isotope data from the Cerveyrette river and its catchment area located in the French Southern Alps. One site, situated river upstream of the Cervières village, was sampled for a period of two years, between 2011 and 2013, the other seven sites were sampled once. The aims of the paper are to estimate the average time between snowfall and melt discharged at the catchment situated at northern entry of the small town of Cervières, to give a best fit function to the measured data, to explore the meaning of the deuterium excess variations. The measured d18O values and local temperature distribution from a meteorological station are implemented in order to approximate a function f(t), where t is representing the independent variable in â. Than, the calculated isotopic compositions by using f(t) are compared with the measured ones, discussing differences.
The aims of investigation are well expressed; the amount of data sufficient in order to design the function and the presented novel method. The paragraphs are following in a logical manner and the text has also an educational value.
Minor changes should be done before the manuscript can be published. Some of the suggestions are included below, all comments being inserted with specific location on the attached PDF.
Page 3:
- On the maps the locations of the mentioned mountain peaks are not visible
- Relationship with the end of the Younger Dryas event?
Page 5:
- Tabor et al., 2020. Stable isotope geochemistry of the modern Shinfa River, northwestern Ethiopian lowlands: a potential model for interpreting ancient environments of the Middle Stone Age. GSL Special Publication 507, doi.org/10.1144/SP507-2020-219.
The slope is even 4 for this case.
Page 8:
- High d-excess values for the winter time were put in evidence at several circum Mediterranean sites. For discussion and references see Bojar, A.-V., Halas, S., Bojar, H.P. and Chmiel, S. 2017.
Stable isotope hydrology of precipitation and groundwater of a region with high continentality, South Carpathians, Romania. Carpathian Journal of Earth and Environmental Sciences, 12, 513–524.
A paragraph relating the potential of the method and study to monitor the effects of ongoing climatic changes would be of benefit.
Figures
Suggestions for Figures are given directly on the PDF.
A delimitation of the catchment area would be of help for the reader.
-
AC3: 'Reply on RC3', Christophe Lecuyer, 05 Jul 2022
Dear reviewers, dear editor,
First of all, I would like to thank the three reviewers for the fair and elegant comments they made on our work. It is obvious that two of them, both with an academic background of physicists, provided negative recommendations for publication of our case study in HESS, while the third one, a geochemist was more enthusiastic.
Our basic idea was to consider a single and simple watershed to monitor the d18O and d2H of the Cerveyrette stream over two years. The isotopic record we obtained was interpreted as a seasonal record of ongoing precipitations delayed and buffered by the annual complete melting of the snowpack, keep in mind that there is no permafrost here with altitudes that remain below 2500 m in any case. Please, note also that the d18O and d2H variations are of very small magnitude and require very careful and optimal analytical conditions to be detected. Dephasing and flattening of the observed signal recorded in the stream is quantified relatively to the seasonal isotopic record of precipitations, itself inferred from the local meteorological data including monthly air temperatures combined to the equations relating the air temperature to the isotopic compositions of precipitations. Furthermore, it is well known since Rozanski et al. (1993) that the most negative d2H and d18O values of precipitation in Europe take place during the coldest months of the year. Our approach is indeed close to that used by Niinikoski, et al. (2016) who used stable isotopes to resolve transit times and travel routes of river water as exemplified by a case study from southern Finland.
We are aware that two reviewers recommended the rejection of our paper, so we consider to revise our manuscript taking into account all the comments, criticisms and suggestions we received from the reviewers before to submit it to a less-specialized journal.
With my best regards
On behalf of all co-authors
Prof. Dr. Christophe Lécuyer
Citation: https://doi.org/10.5194/hess-2022-132-AC3
-
AC3: 'Reply on RC3', Christophe Lecuyer, 05 Jul 2022
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