the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Mar 2024
First comprehensive stable isotope dataset of diverse water units in a permafrost-dominated catchment on the Qinghai–Xizang Plateau
Abstract. Considered as the Asian water tower, the Qinghai–Xizang Plateau (QXP) processes substantial permafrost, where its hydrological environments are spatially differed and can be easily disturbed by changing permafrost and melting ground ice. Permafrost degradation compels melting permafrost to become an important source of surface runoff, changes the storage of groundwater, and greatly influences the hydrological processes in permafrost regions. However, the evidences linking permafrost degradation and hydrological processes on the QXP are lacking, which increase the uncertainties of the evaluation results of changing permafrost on the water resources. Stable isotopes offer valuable information on the connections between changing permafrost (ground ice) and water components. It is therefore particularly important to observe the changes in the stable isotopes of different waterbodies, which can vary over hourly to annual timescales and truly capture the thawing signals and reflect the influence of permafrost (ground ice) on the regional hydrological processes. The Beiluhe Basin (BLH) in the hinterland of QXP were selected, which well integrates all the water components related to hydrological cycles, and is an ideal site to study hydrological effect of permafrost change. This paper presents the temporal data of stable isotopes (δ18O, δD, and d-excess) in different water bodies (precipitation, stream water, thermokarst lake, and groundwater) in the BLH produced between 2017 and 2022. In special, the first detailed stable isotope data of ground ice at 17 boreholes and 2 thaw slumps are presented. A detailed description of the sampling processes, sample pretreating processes, and isotopic data quality control is given. The data firstly described the full seasonal isotope amplitude in the precipitation, stream, and thermokarst lakes, and delineated the depth isotopic variability in ground ice. Totally, 554 precipitation samples, 2402 lakes/ponds samples, 675 stream water samples, 102 supra-permafrost water samples, and 19 sub-permafrost water samples were collected during six years’ continuous sampling work. Importantly, 359 ground ice samples at different depths from 17 boreholes and 2 profiles were collected. This first data set provides a new basis for understanding the hydrological effects of permafrost degradation on the QXP. It also provides supports on the cryospheric study on the Northern Hemisphere.
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Status: final response (author comments only)
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RC1: 'Comment on essd-2024-54', Anonymous Referee #1, 15 Apr 2024
In this manuscript, Yang et al. present an extensive isotope data set (d18O, dD, d-excess) of samples taken over 6 years from different compartments associated to a permafrost environment (e.g. precipitation, thermokast ponds, ground ice, etc).
These raw data are available via a link to a data repository. The data are distributed to five different Excel-sheets, clustered by compartments. On the one hand this is legit due to the high number of samples and necessity to include information about sampling sites. On the other hand it complicates the handling of the data.
The study concept is sound and sampling, sample preparation and analysis have been conducted according to state-of-the-art methods. Specific care has been taken to prevent evaporative isotopic enrichment of the samples.
The manuscipt includes a basic description of time-series and borehole data. Further, intercorrelations between different isotopes are shown, which is fundamental in isotope hydrology and justifiable to be presented in a data-description paper.
While there is a growing database of isotopes in precipitation and surface waters, data from permafrost environments are still scarce and limited to some study sites, mainly from Alaska and Siberia, plus a minor scale pilot study from the same study area as in this manuscript (all cited in the text). However, permafrost associated data are important to fully assess the potential of isotope applications within the hydrological cycle, specifically when this is influenced by melting of permafrost archives in course of global warming.
Therefore, I recommend the publication of this manuscript in ESSD after the completion of minor revisions.
Comments:
Data: I miss a clear statement about analytical error / uncertainty of isotope data. There are no uncertainty values reported in the data files. Line 226ff gives values for analytical accuracy but it is not explained how this values have been calculated. Were samples measured in replicates? Clear and transparent information about analytical uncertainty and how it has been evaluated is essential for a data description paper.
Thermokast lake data: these are „mixed data“ so it is not possible to associate data from different seasons/sampling days to specific ponds. Probably those change a lot due to melting? If this is the case, add a sentence or two to the methods part, explaining this issue.
Data organisation: the distribution of the whole data set to five Excel files is legit. Nevertheless, I suggest to evaluate alternative versions of data management, with a more condensed organisation in less or – in best case- only one single excel-spreadsheets.
l.17: not everybody is familiar with „Xizang“. Please note in brackets that it is Qingai-Tibet-Plateau at least once in the beginning, which is a term better known to most researchers outside of China.
l.87: what precisely is „scarce“? The compartments (thermokast lakes, ponds, etc) or the data from those? Please rephrase for clarification
l.99/100: reference to Fig. 1 is needed here
l.110-120: short description/explanation of permafrost associated terms, such as thermokast active layer, etc, would be beneficient (lateron the same accounts for „pore ice, „segregated ice“, etc). The latter here it is written as „active-layer“ while in other parts of the manuscript without dash „active layer“. Please correct.
l.134: explain how the rain gauge in combination with the steel plate works. Which efforts were undertaken to prevent isotopic enrichment of the sampled water
l.142: how was this identified?
l.145: again, provide more details, i.e. from which depths does the water of wells/springs come from, to classify them as sub or supra permafrost
l.179: clarify for which years the Covid-rules did apply
Figure 2 caption: put the labels of panels before the respective phrase, i.e: (a) General conditions… …, (b) typical feature … …, etc.
Table 2 and 3: better write „number of samples“. Sampling size is a bit confusing.
l.224: why actually not melting the permafrost samples directly in the field and further treat and process them the same way as liquid samples?
l.255: describe which lab standards were used
Figure 4: the greyish and turquoise y-axes and labels are not good to read. Explain abbreviations GSHQ and GSYTQ in figure caption or refer to Fig. 2.
Figure 4: similar scales of y-axes would make data better comparable. I would also change order of the sub plots in a more logical way: move the most negative d18O precipitation down (closer/above PP [mm]), then maybe streams and lakes above.
l.315ff / section 5.1.3: I assume there is no information / data about different ages of ground ice formation at this point?
Figure 5: I suggest to decrease dot-size a bit
Figure 6: again, explain all abbreviations (LEL, FL, AP, SP, WP, etc) in the figure caption, even if they are explained in the text.
l.395: there is something wrong with this sentence, please check
l.421: isotopic values, not contents
Supplement: while the main manuscript shows d18O values, the supplemantary figs shows time series also for dD and d-excess of precipitation, streams, ponds, etc. (complementary to Fig. 4). To do it in a consistent way, similar figures for the boreholes could be included (complementary to Fig. 5).
Citation: https://doi.org/10.5194/essd-2024-54-RC1 -
RC2: 'Comment on essd-2024-54', Anonymous Referee #2, 17 Apr 2024
This paper deals with an extensive dataset of stable isotope composition of water (precipitation, thermokarst ponds, ground ice, stream) in samples collected on a permafrost dominated area.
The raw data is available at https://doi.org/10.5281/zenodo.10684110 in five Excel files organised in a logical way.
The concept of the study is good and ambitious, the applied sampling and analytical methods are adequate, although the description of the stable isotope measurements is not totally clear for me. How was the drift corrected and how were the raw data normalized to the SMOW-SLAP scale? Were all the five laboratory standards used in every measurement sequence? Please, make this part of the manuscript clear.
The terms related to ground ice are not widely known, e.g. pore ice, pure ice layer, segregated ice, excess ice. Please, define these terms.
The dataset is very important and the manuscript is well written, therefore I recommend its publication after minor revision (see above and below).
Detailed comments
In the title I recommend to use Qinghai–Tibetan Plateau, because in the English literature it is much more known?
Page 3
Lines 49-50: You use the phrases “permafrost degradation” and “ground ice melting” side by side as two different ideas, but for me they are not so different. What is the difference between them?
Line 58: “Immerzeel et al., 2010” is missing from the list of references.
Line 68: “Liu et al., 2022)” – In the References there is Liu et al., 2022a and Liu et al., 2022b. Please, specify which one is intended here.
Page 5
Line 106: “between 2017 to 2020” – I recommend to write “between 2017 and 2020”.
Lines 107-108: “393.71 mm”, “555.99 mm”. – There is no reason to give decimals here. Write 394 mm and 556 mm.
Line 111: “Lin et al., 2010” – In the list of references I could find Lin et al., 2020! Probably wrong year.
Line 116: “melting water from permafrost and ground ice” – For me “melt water from permafrost” or “melt water from ground ice” are the same. Am I wrong? If I am wrong then please, make the difference clear in the manuscript!
Page 7
Line 134: “to collected daily rain” – please, replace with “to collect daily rain”
Line 135: “we select a typical” – better would be “we selected a typical”
Line 144: “one drinking spring (CSQ)” – CSQ is not indicated on Figure 1. I think it is the “Sub-permafrost water” on the second map of Figure 1, but it is not indicated. If my supposition is true, then the legend should be modified as “Sub-permafrost water (CSQ)”. Anyway, I have never met with the phrase “drinking spring”. Why drinking? I think that in this case the word “drinking” should be omitted.
Page 11
Line 195: “QXH” – What it stands for?
Page 13
Lines 213-214: “All the treated raw frozen soil samples were immediately preserved in HDPE bottles.” – How could you put the frozen soil samples into the bottles?
Lines 226-227: “The analyzing accuracy was less than 0.02 ‰ for the δ18О value measurements and 0.05 ‰ for the δD value measurements” – I recommend to provide one standard deviation instead of accuracy, and please describe how you calculated the standard deviation.
Lines 228-229: “IAEA standard Vienna Standard Ocean Water (VSMOW) standard” – The first “standard” should be deleted.
Line 230: “δ=(Rsa/Rst-VSMOW-1) × 1000 ‰” – I recommend to write “δ=(Rsa/Rst-1) × 1000 ‰”.
Page 14
Line 234: “events were occurred” – correctly “events occurred”.
Line 236: “were mixed”. – In which ratio? In amount-weighted ratio?
Line 255: “Five laboratory standards for each group of 10 samples”. – Do you mean 10 unknown samples, or the 10 samples included the five lab-standards?
Page 15
Line 277: “lakes/ponds more positive” – correctly “lakes/ponds are more positive”.
Page 16
Line 284: “the isotopic contents of lakes/ponds are lower in” – The phrase “isotopic content” has no meaning. I recommend the following: “the heavy isotope contents of lakes/ponds are lower in”.
Lines 287-288: “isotopes of lakes/ponds are positive in May, June, July, and October (Fig. 4; Fig. S3) due to evaporation and isotopic-positive precipitation”. – Bad wording. The isotopes of lakes cannot be positive, only the delta values can be positive. And there is no “isotopic-positive precipitation”. But even the delta values of lakes are not always positive in May, June, July and October! Please, describe clearly what you mean.
Line 291: “The mean values are equivalent to the average levels of precipitation”. – I recommend to change the word “levels” for “values”.
Line 311: “isotopic-negative water” – I recommend to use “isotopically light water”.
Page 17
Figure 4. The legend and the figure caption do not explain every symbols used on the figure. E.g. δ18Oprecipitation diagram: I think that the grey dots denote event values, while the red dots denote the monthly average values, but this is not stated. It is interesting that the number of red dots of one year varies between 7 and 10. Wintertime there are months without red dots, but zooming into the precipitation amount diagram (PP at the bottom of the figure), we can see very low bars indicating small amount of precipitation (I think that event precipitation), but there is no data (grey dot) on the δ18O diagram. Why? Was the amount insufficient for performing analysis?
In few cases the red dots on the δ18O diagram stand without grey dots. E.g. the very first red dot. Why? Was there only one precipitation event in that month?
Lines 319-320: “isotopic points of ground ice are located in the left sides of the mean level of precipitation (Fig. 5), i.e., the ground ice represented more negative isotopes” – Bad wording again. “mean level”: please replace it with “mean value”; and provide this mean value in brackets (‑10.94‰). “negative isotope” – an isotope is not negative; it can be light or heavy. I recommend the following wording: “δ18O points of ground ice are located in the left sides of the mean value of precipitation (‑10.94‰) on Figure 5, i.e., the ground ice is isotopically lighter than the precipitation”.
Page 18
Line 328: “past precipitation; et al)” – Please, delete “et al”.
Line 331: “(Fig. 4)” – correctly (Fig. 5).
Line 334: “more negative isotopes” – isotopically lighter.
“(Fig. 4; Table 4)” – correctly (Fig. 5; Table 4).
Line 337: “isotopic-positive pore ice” – the delta value can be positive.
Page 19
I recommend to give the δD data with one decimal only.
Page 20
Figure 5: There is a blue vertical line on every diagram. I suppose it indicates the mean δ18O value of precipitation. If this is true, then please, write it down in the figure caption.
It would be interesting to check the relation between the δ18O values and the type of ice (segregated ice, pore ice, …). May be it gives some clue for the interpretation of the wide variation.
Lines 362-363: “The local meteoric water line (LMWL), determined by ordinary least square regression using the daily isotopic data during six years (2017-2022),” – This is only one way of determining the LMWL and not the most wide-spread one. It is widely accepted that the LMWL is calculated using monthly data. The LMWL based on daily data may differ significantly from that based on monthly data, see e.g. Barešić et al. 2006. Therefore, I recommend to determine the LMWL using monthly data. The most sophisticated way to determine the LMWL is using the amount-weighted multi-monthly mean isotopic values. See, e.g., Kern et al. 2016. I recommend to calculate the LMWL by all three ways.
Page 21
Line 384: “Yang et al., 2017a” – Only Yang et al. 2017 exists in the list of references. If “Yang et al., 2017a” is intended to denote another paper than it is missing from the list.
Page 22
Figure 6: Please, insert to the figure caption what “Wt. avg. AP”, “Wt. avg. SP” and “Wt. avg. WP” stand for.
Lines 396-397: “the d-excess values of ground ice are more negative than those of river water and more positive than the amount-weighted average value of annual/summer precipitation” – The mean d-excess values of ground ice are positive numbers except one (BLH-L-6), see Table 4. I recommend the following sentence: “the d-excess values of ground ice are lower than those of river water and the amount-weighted average value of annual/summer precipitation”.
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Lines 406-407: “All the stable isotope data that support the findings of this study The dataset provided in this paper can be obtained at https://doi.org/10.5281/zenodo.10684110” – Please, delete the text “The dataset provided in this paper”.
Page 24
The cited texts below are characterised by bad wording, see my comments above.
Lines 420-421: “lower isotopic contents” – isotopically lighter.
Line 422: “isotopic-positive precipitation”
Lines 423-424: “The slopes of the three LELs are all lower than those of LMWL, indicating strong evaporation.” – The first part of the sentence is evident, otherwise we would not call it “evaporation line”. The meaning of “strong evaporation” is not clear. Actually the slope of the evaporation line is related to the relative air humidity, there is a positive correlation between them. See Figure 2-8 in the Clark & Fritz 1997. So, lower slope means lower relative humidity.
Line 426: “isotopic-negative water”.
Pages 26-30
The journal names should be written with capital initials, but is many cases it is not so. E.g. in reference [4] “Nature communications is written instead of “Nature Communications”. The same is true for references [25], [34], [52], [56], [59] and [67].
What is reference [5]? A book? Who is the publisher? It is an incomplete bibliography.
Reference [42] is also incomplete, volume and page numbers are missing.
References
Clark, I., Fritz, P. (1997) Environmental Isotopes in Hydrogeology. Lewis Publishers, Boca Raton – New York
Barešić J, Horvatinčić N., Krajcar Bronić I., Obelić B., Vreča P. (2006) Stable isotope composition of daily and monthly precipitation in Zagreb. Isotopes in Environmental and Health Studies 42(3):239-249
Kern Z., R. S. Harmon, I. Fórizs (2016) Stable Isotope Signatures of Seasonal Precipitation on the Pacific Coast of Central Panama. Isotopes in Environmental and Health Studies 52(1-2):128-140
Citation: https://doi.org/10.5194/essd-2024-54-RC2 -
RC3: 'Comment on essd-2024-54', Anonymous Referee #3, 21 Apr 2024
Yang et al. offer to the benefit of the wider scientific community a dataset of stable isotope measurements in several components of the hydrological cycle in a typical permafrost area located in the Tibetan (Qinghai–Xizang) Plateau. The data is well-presented and the sampling strategy was designed to maximize the results. Except for a few minor technical comments, the manuscript is well organized and written and I recommend its publication in the journal, ESSD. One note, though: while the data is good, some of the interpretations are simplistic, they should either be improved, or left out entirely.
Technical comments
- Although the authors call the sampling area a “watershed” it is not clear which is its extent. It would help adding the outlines of the watershed on the map in Fig. 1b. If several watersheds are present (as I suspect), all should be mapped in Fig. 1b. Also, it would help adding the surface streams and all lakes, whether they were mapped or not. This would put the results in a better hydrological context.
- It is not clear what is the source of water in the springs (lines 142-145) and which are the differences between these As the authors only offer data and no interpretation (as per journal regulations), potential users of the data need this kind of information.
- Lines 167-168: am not sure what contamination the authors refer to. Please clarify.
- L168-169: it is not clear whether the water was collected at 20.00 every day or at the end of precipitation, regardless of time, as implied in line 169. I suspect the former, but please clarify.
- L170-171 (and also line 134 above): how was sampling done during periods of freezing? Was ice scrapped from the plate, was the plate put at room temperature? And how was the plate constructed in order to minimize water loss during melting? A photo of the sampling device would help.
- L 171-172: I understand from here that rain water was collected on a plate? Is this correct? How was evaporation/exchange with moisture prevented? This is crucial for the integrity of the data.
- L173: which bottles? Was rainwater collected separately for washing? This entire section (4.1.1.) is unclear, at least to me and needs to be clarified.
- L177-180: while the implication is that lake water was collected for six months per year for six years, in line 180 it is said that water was sampled in 2 months, only. Please clarify. (Table 1 shows more than 2 months).
- L183: how was sub-permafrost and supra-permafrost water collected?
- L201: please clarify the number of sample – perhaps[s separate the sentence in “boreholes” and “profiles”.
- L233-245: this should go under “methods” rather QC
- L241: I don’t see how this could be. Please clarify
- L244-245: not sure this sentence applies here.
- L249: 12 injections of each of the 14 samples?
- L250-255: please specify the time of this analysis to better understand the drift.
- L255-257: please detail the “calibration of the instrument (?)”
- L260-262: so, analysis was restarted every time the ppm dropped below 19000 or increased above 20000?? Or you just used the good/bad info from Picarro’s GUI?
- L268: “seasonal variability” is better than “trend”
- L273-274: on one hand, it is more complex than that, but on the other hand, the seasonal variability could be simply explained by temperature variability. “Transitions of moisture sources” means “changes in moisture sources”?
- L282: again, “transitions of source waters and evaporation differences (?)” means nothing, either detail, or delete.
- L288: “isotopic-positive precipitation” is meaningless. Perhaps “2H and 18O-enriched precipitation water”? Generally, check the manuscripts for stable isotope jargon and correct. Sharp (2017), available here for free (https://digitalrepository.unm.edu/unm_oer/1/) offers good advice on stable isotope nomenclature (for instance, “isotope values” is ambiguous)
- L292: no contribution of winter precipitation (snow)? Also, “stable isotopes of streams” is incorrect/ambiguous
- L293: please clarify how the short residence time results in less variability
- L296-298: this contradicts the statement in L 293-295
- L299: please explain the differences between the two
- L311: why during cold periods? I would expect sub-permafrost water to be release from the melting permafrost.
- L316: please (!) rephrase. Also rephrase the line below with the position of values left or right of the pp line. Describe the data variability, not the chart itself.
- L320: more negative isotopes. No such thing exists; see my comment above on nomenclature.
- L324-338: slightly speculative, not sure it fits the scope of the journal, perhaps it should be simplified.
- L388: stream water exhibit a clear evaporative effect, they do not lie on the LMWL (and similar for the lake waters). Ground ice exhibits a clear freezing slope (Jouzel and Souchez, 1982, Souchez and Jouzel, 1984, Lacelle et al., 2011, Persoiu et al., 2011 etc).
- Conclusions> please see the comments above on data interpretation and adjust the conclusions accordingly.
Fig. 1. Show the outlines of the watershed and the hydrological connectivity. What is the base map in fig. 1b?
Citation: https://doi.org/10.5194/essd-2024-54-RC3
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