Measuring and Modeling Stable Isotopes of Mobile and Bulk Soil Water

Matthias Sprenger* (Corresponding Author), Doerthe Tetzlaff, Jim Buttle, Hjalmar Laudon, Hannes Leistert, Carl Mitchell, Jenna Snelgrove, Markus Weiler, Chris Soulsby

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

82 Citations (Scopus)
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Recent findings from stable isotope studies have opened up new questions about differences in the isotopic composition (δ2H and δ18O) of mobile (MW) and bulk water (BW) in soils. We sampled the isotopic compositions of MW using suction lysimeters and BW with the direct-equilibration method. The study was conducted at two landscape units in each of three catchments: the Bruntland Burn (Scotland), Dorset (Canada), and Krycklan (Sweden). We further used the numerical one-dimensional flow model SWIS (Soil Water Isotope Simulator) to simulate the hydrometric and isotopic dynamics. The model included evaporation fractionation, allowed differentiation between a fast and a slow flow domain, and included isotopic exchange via water vapor. Our measurements showed that MW plots along the local meteoric water lines, whereas BW plots below, which is indicative of evaporation fractionation. We suggest that the relative volume of MW to BW is relevant for explaining these isotopic differences because MW volumes are usually relatively low during periods of high evaporation. Under this condition, differences between MW and plant water isotopes are not paradoxical but rather related to the water that cannot be sampled with suction lysimeters but is still available for plant water uptake. The simulations accounting for fast and slow flow supported the conceptualization of the two soil pore domains with isotopic exchange via vapor exchange because this model setup resulted in the best model performance. Overall, these findings are of high relevance for current understanding related to the source and isotopic composition of water taken up by plants.
Original languageEnglish
Pages (from-to)1-18
Number of pages18
JournalVadose zone journal
Issue number1
Early online date12 Apr 2018
Publication statusPublished - Apr 2018

Bibliographical note

We thank Audrey Innes for support with the isotope analysis at University of Aberdeen for the Bruntland Burn and Krycklan sites, Johannes Tiwari (SLU) for the isotope sampling in Krycklan, Pernilla Löfvenius (SLU) for providing PET data for Krycklan, Pertti Ala-aho for providing snowmelt simulations for Krycklan, and Kimberely Janzen (University of Saskatoon) for soil water isotope analysis for the Dorset sites. The work at Krycklan was supported by KAW Branch-Points. We thank the European Research Council (ERC, project GA 335910 VeWa) for funding. We thank two anonymous reviewers and the associate editor for their suggestions and comments.


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