Kenji Tsuruta, Hiroyuki Yamamoto, Masanori Katsuyama, Yoshiko Kosugi, Motonori Okumura, Naoko Matsuo
Received 2018/10/22, Accepted 2018/12/26, Published 2019/02/02

Kenji Tsuruta1), Hiroyuki Yamamoto2), Masanori Katsuyama2), Yoshiko Kosugi2), Motonori Okumura3), Naoko Matsuo4)

1) Department of Forest Soils, Forestry and Forest Products Research Institute, Japan
2) Graduate School of Agriculture, Kyoto University, Japan
3) Research Institute of Environment, Agriculture, and Fisheries, Osaka Prefecture, Japan
4) Graduate School of Bioresources, Mie University, Japan

Cryogenic vacuum distillation (CVD) methods have been widely used to extract water from unsaturated soil materials. However, recent studies have reported that extraction conditions (e.g. extraction time) and soil type can influence the stable isotope ratios of soil water extracted by CVD. We examined (i) the effects of extraction time on the stable isotope ratios of soil water extracted by CVD, and (ii) how the stable isotope ratios differed from those of soil water extracted by other methods. We first examined extraction times of 1–6 h, and observed no significant differences in the δ2H or δ18O values of extracted soil water for extraction times >2 h. However, extraction for 1 h collected only 48% of soil water, and the δ2H and δ18O values were significantly lower than those for extraction times >2 h. We then compared the stable isotope ratios of soil water extracted by CVD and centrifugation. Although the stable isotope ratios for both extraction methods were within the range of that of rainwater, the stable isotope ratios for water extracted by CVD were lower than those for water extracted by centrifugation. Our results highlight questions surrounding the use of CVD for stable isotope analysis of soil water.

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