the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Nov 2025
Technical note: Water vapor sampling for the analysis of water stable isotopes in trees and soils – optimizing sampling protocols
Abstract. The study establishes an optimized, minimally invasive sampling protocol for water vapor – a semi-in situ method crucial to ecohydrology that addresses the limitations of destructive techniques. The key innovation is an integrated, multifactor assessment of how container type, flow rate, temperature, and storage time affect the isotopic stability of δ18O and δ2H. The optimal configuration uses 250 ml infusion glass bottles (ND 32), which provided the highest isotopic stability (±0.5 ‰ for δ18O and ±1‰ for δ2H over 24 hours), outperforming FlexFoil and aluminum-zip bags. The best results were obtained with flow rates of 100–125 ml/min and storage not exceeding 24 hours under ambient conditions (20–25 °C). δ18O was highly stable under nearly all conditions (<0.6 ‰), whereas δ2H was more sensitive (±0.3 ‰ to ±1.5 ‰); its variability increased markedly with storage beyond 24 hours or at extreme temperatures (4 °C or 40 °C), underscoring the need to minimize the time between sampling and measurement. This validated protocol provides an accessible and reliable methodology that expands the toolkit for high-temporal-resolution ecohydrological studies, particularly in remote areas or settings with limited infrastructure.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2025-5295', Ruth-Kristina Magh, 15 Jan 2026
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RC2: 'Comment on egusphere-2025-5295', Anonymous Referee #2, 11 Feb 2026
General comments:
In the manuscript by Iraheta et al. the authors present an optimized approach of obtaining water vapor samples for analysing the isotopic composition of water vapor. They performed systematic laboratory experiments initially for three different materials to test the effect of storage time, storage temperatures, and flow rates on tightness and isotopic stability of water vapor samples. To select the optimal container they defined ratings for each decision criterion, which resulted in a final score. With the identified optimal container further experiments were performed with three isotopically different waters, again testing and optimizing storage time, storage temperature and sampling flow rate.
The manuscript is well structured but it is far too long and contains largely redundant sections and figures, which makes it difficult to read. Also the discussion should be more focused, not repeating so many results. Manuscript lengths of Technical notes in other journals are sometimes limited to 7000 words - which is almost double for this manuscript.
My second concern is that the title is highly misleading. No water vapor sampling in trees and soils was conducted in this study. Water vapor was sampled from the headspace of 250 mL glass bottles, instead. Further, ‘optimizing sampling protocols’ promises somehow that several existing protocols which are used by the community could eventually be compared or optimized, which is not the case. The presented optimized method which the authors favor is more or less a follow up of two studies (Magh et al. (2022) and Havranek et al. (2021)) which also used glass bottles for vapor sampling. But in contrast to those studies, only data of water vapor sampling from glass bottles in lab experiments and no data of field applications were presented here.
I therefore recommend rephrasing the title and significantly shortening the manuscript.
Regarding the poor performance due to limited isotopic stability (L 549-551) of the 500 mL aluminum bags: I agree and I also guess there is a slight exchange at the zip-type seals (L 759-762) but this is probably the reason why the supplier recommends heat sealing! Maybe the results would have been significantly different with proper closed bags.
Specific Comments:
L 152 Figure 1: Blue and green lines are hard to distinguish, please change one of the colors.
L 205 Why ‘Summary’ here?
L 347 ‘bar’ is not the correct unit for flow rate. Please change appropriately.
L 349 What is ‘1/8 PPT tubing’? 1/8 inch? or 1/8”? PTFE tubing? Please check.
L 374-383 describes Fig. 4B, please add ‘(s. Fig 4B)’ somewhere.
L 384-393 describes Fig. 4A, please add ‘(s. Fig 4A)’ somewhere. Please swap these two sections so that it matches the order in the figure.
L 494-497 please delete – or does this information become relevant later?
L 525-527 This is already an interpretation of the results -> to discussion
L 595 How was ‘stable’ defined?
L 598 Can’t find Fig. S4, do you mean Fig. S1? And where do you refer to Fig. S2 in the text?
Figure S1 Small differences can’t be recognized due to the scaling of the y-axis for both isotopes. I suggest depicting d18-O from -5 to -25 and d2-H from -50 to -150‰.
Figure 9: Please add dashed lines at 0.0
Figure 10: Please add dashed lines at 0.0
Figure 10: Please change 2D to 2H
The data in Figure 11 are already shown in Fig. 9 and Fig. 10, correct? If so, please delete Fig. 11
Figure 12: Could you perhaps include the information about the MAE in Fig. 9 and Fig. 10? If so, you could delete Fig. 12.
L 965-971 Which parts of your approach are ‘semi-in-situ’? Where did you show that ‘it enables the capture of water vapor in equilibrium with soil and xylem’? Please rephrase.
Technical corrections:
L 54 ‘a need’ (blank is missing)
L 87 and throughout the manuscript: no blank between number and ‰
L 135 Please delete ‘Innovation.’
L 146 Please insert ‘Table’ before S1
L 203 ‘words,’ or ‘words:’ instead of ‘words.’
L 281 Change ‘Seven’ to ‘Six’
L 411 “…equation 1 (Craig (1961); Coplen (2011)):”
L 414 Two blanks are missing: ‘where Rsample’ ‘and RVSMOW’
L 414, 418, 428, 434: spacing between letters and superscripted numbers is too large
Figure 5, Figure 6: change ‘bag’ to ‘bags’, to be consistent with ‘bottles’
Figure 6: error bars are missing
L 611 IQR - define this acronym in the first instance
L 813 Please replace ‘one-liter’ by ‘1L’ to be consistent
L 822 Please insert ‘vapor’ before ‘concentration’
L 844 Please insert ‘adsorptive’ before ‘isotope exchange’
L 936 leorting?? …the feasibility
L 981 I suggest ‘hot glue’ instead of ‘adhesivo termofusible’
S1. List of materials: Refrigerator is probably ‘Samsung’ not ‘Sansung’
Citation: https://doi.org/10.5194/egusphere-2025-5295-RC2
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See my revision recommendation and specific comments in the pdf attached.