Practical measurements of water stable isotopes in tree stems and soils using conservative water vapor storage
- 1Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden
- 2Hydrology, Albert Ludwigs University, Freiburg, Germany
- 3Ecosystem Physiology, Albert Ludwigs University, Freiburg, Germany
- 4Terrestrial Ecohydrology, Friedrich Schiller University, Jena, Germany (ruth.magh@posteo.net)
The interest of inferring plant water uptake depths/patterns and water movements through the soil matrix grew tremendously in recent years and, studies have shown the use of in-situ measurement systems based on laser absorption spectroscopy making e.g. plant or soil water stable isotope datasets available on-site and in real-time. However useful, in-situ systems are limited to sites with power supply and require constant care.
We tested, first in the lab and then in the field, a method for equilibrating, collecting, storing, and finally analysing water vapour for its isotopic composition. We used a vapour storage vial system (VSVS) that relies on in-situ sampling, using a pump and a flow meter powered through a small battery into crimp neck vials with a double coated lid, and measuring the samples in a laboratory. We tested the utility of the sampling method and the reliability of the VSVS to faithfully store the isotopic composition of its content by sampling a range of water vapour of known isotopic compositions (from -95 to 1700‰ for δ2H) and measuring the isotopic signature after the storage period. Samples for the field trial were taken in a tracer pulse chase experiment in a boreal forest in Northern Sweden.
We were able to prove the utility of the sampling method within defined uncertainties (0.6 to 4.4‰ for δ2H and 0.6 to 0.8‰ for δ18O) for natural abundance. For in 2H-enriched samples the range was adapted to higher uncertainty. We detected a small change in the isotopic composition of the sample after a longer storage period, which was consistently greater for oxygen but correctable by linear models.
Our method has the potential to combine the best of two worlds: sampling in-situ in high spatial or temporal resolution while measuring in the laboratory, could solve problems with location biases and give the community a tool that is not only cost-efficient but also easy to use while all components are commercially available.
How to cite: Magh, R., Gralher, B., Herbstritt, B., Kübert, A., Lim, H., Lundmark, T., and Marshall, J.: Practical measurements of water stable isotopes in tree stems and soils using conservative water vapor storage, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8800, https://doi.org/10.5194/egusphere-egu22-8800, 2022.
