A simple system for extracting water from soil and plant substrates –effects of substrate-derived exchangeable hydrogen on isotope ratios of extracted water–

ABSTRACT

Extraction of water from soil and plants for isotope analysis is a key step in hydrological and ecological studies. Current water extraction systems are either inefficient or complex and expensive, and depletion of heavy isotopes such as ²H (deuterium) in extracted water relative to spiked water is commonly observed. We constructed a simple water extraction system using commercially available parts and assessed its sample capacity and performance. We spiked 1% ¹H²HO aliquots into soil and plant substrates and analyzed water recovery and isotope exchange of deuterium in spiked water with exchangeable hydrogen in substrates. The water extraction system required 3 days to extract 100% of the spiked water volume when heated at 60°C for plant samples and 100°C for soil samples. Deuterium was depleted in extracted water relative to spiked water due to dilution by substrate-derived exchangeable hydrogen. The exchangeable hydrogen content varied among substrates, causing variation in the degree of deuterium depletion. The simple and low-cost system for water extraction from soil and plant samples decreases barriers to isotope analysis. Estimating substrate-derived exchangeable hydrogen is useful for accounting for deuterium depletion during water extraction.

KEYWORDS:

• Cryogenic vacuum distillation
• isotope analysis
• isotope fractionation effect
• exchangeable hydrogen
• soil hydrology

Acknowledgments

We thank Dr Y. Ishikawa (Institute for Environmental Sciences, Japan) and the analytical chemistry staff of ZAX Co., Ltd. (Japan) for help with isotope analysis. We also thank Dr Y. Takaku, Dr S. Hisamatsu (Institute for Environmental Sciences, Japan), and anonymous reviewers for helpful comments. This work was performed under contract with the Aomori Prefectural Government, Japan.

Disclosure statement

No potential conflict of interest was reported by the author(s).