Technical note: Unresolved aspects of the direct vapor equilibration method for stable isotope analysis (<i>δ</i><sup>18</sup>O, <i>δ</i><sup>2</sup>H) of matrix-bound water: unifying protocols through empirical and mathematical scrutiny
-
Published:2021-09-27
Issue:9
Volume:25
Page:5219-5235
-
ISSN:1607-7938
-
Container-title:Hydrology and Earth System Sciences
-
language:en
-
Short-container-title:Hydrol. Earth Syst. Sci.
Author:
Gralher Benjamin, Herbstritt BarbaraORCID, Weiler MarkusORCID
Abstract
Abstract. The direct vapor equilibration laser spectrometry (DVE-LS) method has been developed for obtaining matrix-bound water stable isotope data in soils, the critical zone, and bedrock, deriving therefrom subsurface water flow and transport processes and, ultimately, characterizing, for example, groundwater recharge and vulnerability. Recently, DVE-LS has been increasingly adopted due to its possible high sample throughput, relative simplicity, and cost-efficiency. However, this has come at the cost of a non-unified standard operation protocol (SOP), and several contradictory suggestions regarding protocol details do exist which have not been resolved to date. Particularly, sample container material and equilibration times have not yet been agreed upon. Beside practical constraints, this often limits DVE-LS applicability to interpreting relative isotope dynamics instead of absolute values. It also prevents data comparability among studies or laboratories, and several previous comparisons of DVE-LS with other, more traditional approaches of water extraction and subsequent stable isotope analysis yielded significant discrepancies for various sample matrices and physical states. In a series of empirical tests, we scrutinized the controversial DVE-LS protocol details. Specifically, we tested 10 different easily available and cost-efficient inflatable bags previously employed or potentially suitable for DVE-LS sample collection and equilibration. In storage tests similar to the DVE-LS equilibration process but lasting several weeks, we quickly found heat-sealed bags made of laminated aluminum (Al) sheets to be superior by several orders of magnitude over more frequently used freezer bags in terms of evaporation safety and accompanying adverse isotope effects. For the first time, Al-laminated bags allow the applied equilibration time to be adapted exclusively to sample requirements instead of accepting reduced data quality in a trade-off with material shortcomings. Based on detailed physical considerations, we further describe how to calculate the minimum available container headspace and sample-contained liquid water volume and how their ratio affects analytical precision and accuracy. We are confident that these guidelines will expand DVE-LS applicability and improve data quality and comparability among studies and laboratories by contributing to a more unified, physically well-founded SOP based on more appropriate components.
Funder
Bundesministerium für Bildung und Forschung
Publisher
Copernicus GmbH
Subject
General Earth and Planetary Sciences,General Engineering,General Environmental Science
Reference57 articles.
1. Araguás-Araguás, L., Rozanski, K., Gonfiantini, R., and Louvat, D.: Isotope effects accompanying vacuum extraction of soil water for stable isotope analyses, J. Hydrol., 168, 159–171, https://doi.org/10.1016/0022-1694(94)02636-P, 1995. 2. Bachmat, Y. and Bear, J.: On the Concept and Size of a Representative Elementary Volume (Rev), in: Advances in Transport Phenomena in Porous Media, edited by: Bear, J. and Corapcioglu, M. Y., NATO ASI Series (Series E: Applied Sciences), 128, Springer, Dordrecht, https://doi.org/10.1007/978-94-009-3625-6_1, 1987. 3. Bertrand, G., Masini, J., Goldscheider, N., Meeks, J., Lavastre, V., Celle-Jeanton, H., Gobat, J.-M., and Hunkeler, D.: Determination of spatiotemporal variability of tree water uptake using stable isotopes (δ18O, δ2H) in an alluvial system supplied by a high-altitude watershed, Pfyn forest, Switzerland, Ecohydrology, 7, 319–333, https://doi.org/10.1002/eco.1347, 2014. 4. Boumaiza, L., Chesnaux, R., Walter, J., and Stumpp, C.: Assessing groundwater recharge and transpiration in a humid northern region dominated by snowmelt using vadose-zone depth profiles, Hydrogeol. J., 28, 2315–2329, https://doi.org/10.1007/s10040-020-02204-z, 2020. 5. Brand, W. A., Geilmann, H., Crosson, E. R., and Rella, C. W.: Cavity ring-down spectroscopy versus high-temperature conversion isotope ratio mass spectrometry; a case study on δ2H and δ18O of pure water samples and alcohol/water mixtures, Rapid Commun. Mass Sp., 23, 1879–1884, https://doi.org/10.1002/rcm.4083, 2009.
Cited by
11 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献
|
|