07 Dec 2022
07 Dec 2022
Status: this preprint is currently under review for the journal HESS.

Technical note: Mobile, discrete in situ vapor sampling for measurements of matrix-bound water stable isotopes

Barbara Herbstritt1, Benjamin Gralher1,2, Stefan Seeger1, Michael Rinderer1,a, and Markus Weiler1 Barbara Herbstritt et al.
  • 1Hydrology, Faculty of Environment and Natural Resources, University of Freiburg, Germany
  • 2Groundwater Management, Technical University of Dresden, Germany
  • anow at: geo7 AG, Bern, Switzerland

Abstract. Methodological advancements have been made in in situ observations of water stable isotopes that have provided valuable insights in ecohydrological processes. The continuous measurement capabilities of laser-based analyzers allow for high temporal resolutions and non-destructive, minimally invasive study designs of such in situ approaches. However, isotope analyzers are expensive, heavy, and require shelter and access to electrical power which impedes many in situ assays. Therefore, we developed a new, inexpensive technique to collect discrete water vapor samples in the field via diffusion-tight inflatable bags that can later be analysed in the lab. In a series of structured experiments, we tested different procedural settings, bag materials, and closure types for diffusion-tightness during storage as well as for practical handling during filling and extraction. To facilitate re-usage of sampling bags, we present a conditioning procedure using ambient air as primer. In order to validate our method, direct measurements through hydrophobic in situ probes were compared to repeated measurements of vapor sampled with our bags from the same source. Performing pertinent calibration procedures, accuracy was better than 0.4 ‰ for δ18O and 1.9 ‰ for δ2H after one day of storage. Our technique is particularly suitable in combination with minimal invasive water vapor sampling in situ probes that have already been employed for soils and tree xylem. It is an important step towards monitoring stable isotope distributions and also time-series in soils and trees without the need to have field-access to an analyzer and therefore a promising tool for many applications in eco-hydrology and meteorology.

Barbara Herbstritt et al.

Status: open (extended)

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  • RC1: 'Comment on hess-2022-393', Anonymous Referee #1, 05 Jan 2023 reply

Barbara Herbstritt et al.

Barbara Herbstritt et al.


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Short summary
We present a new method to collect discrete water vapor samples in the field without an in-field analyser, followed by isotope analysis in the lab. It resolves even fine-scaled natural isotope variations. It combines low-cost and light-weight components for maximum spatial and temporal flexibility regarding environmental setups. Hence, it allows for sampling even in terrains that are rather difficult to access, enabling future extended isotope datasets in soil sciences and ecohydrology.