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Volume 22, issue 7 | Copyright
Hydrol. Earth Syst. Sci., 22, 3619-3637, 2018
https://doi.org/10.5194/hess-22-3619-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 06 Jul 2018

Research article | 06 Jul 2018

Inter-laboratory comparison of cryogenic water extraction systems for stable isotope analysis of soil water

Natalie Orlowski1,2,12, Lutz Breuer2,3, Nicolas Angeli4, Pascal Boeckx5, Christophe Brumbt6, Craig S. Cook7, Maren Dubbert8,22, Jens Dyckmans9, Barbora Gallagher10, Benjamin Gralher11, Barbara Herbstritt12, Pedro Hervé-Fernández5,6,13, Christophe Hissler14, Paul Koeniger15, Arnaud Legout16, Chandelle Joan Macdonald7, Carlos Oyarzún6, Regine Redelstein17, Christof Seidler18, Rolf Siegwolf19, Christine Stumpp11,20, Simon Thomsen21, Markus Weiler12, Christiane Werner8,22, and Jeffrey J. McDonnell1 Natalie Orlowski et al.
  • 1Global Institute for Water Security, School of Environment and Sustainability, University of Saskatchewan, Saskatoon, Canada
  • 2Institute for Landscape Ecology and Resources Management (ILR), Research Centre for BioSystems, Land Use and Nutrition (IFZ), Justus Liebig University Giessen, Giessen, Germany
  • 3Centre for International Development and Environmental Research, Justus Liebig University Giessen, Giessen, Germany
  • 4INRA-UHP Ecologie et Ecophysiologie Forestières, INRA Centre de Nancy, Champenoux, France
  • 5Isotope Bioscience Laboratory (ISOFYS), Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium
  • 6Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile
  • 7Department of Ecosystem Science and Management, Stable Isotope Facility, University of Wyoming, Laramie, Wyoming, USA
  • 8BayCEER, University of Bayreuth, Bayreuth, Germany
  • 9Institute of Soil Science and Forest Nutrition, Centre for Stable Isotope Research and Analysis (KOSI), University of Göttingen, Göttingen, Germany
  • 10Institute for Environmental Research, Australia Nuclear Science and Technology Organization, Sydney, Australia
  • 11Institute of Groundwater Ecology, German Research Center for Environmental Health, Helmholtz Zentrum München, Neuherberg, Germany
  • 12Hydrology, Faculty of Environment and Natural Resources, University of Freiburg, Freiburg, Germany
  • 13Laboratory of Hydrology and Water Management, Faculty of Bioscience Engineering, Ghent University, Ghent, Belgium
  • 14Luxembourg Institute of Science and Technology (LIST), Department of Environmental Research and Innovation (ERIN), Esch-sur-Alzette, Luxembourg, Luxembourg
  • 15German Federal Institute for Geosciences and Natural Resources (BGR), Hanover, Germany
  • 16INRA UR1138 Biogéochimie des Ecosystèmes Forestiers, INRA Centre de Nancy, Champenoux, France
  • 17Plant Ecology and Ecosystems Research, University of Göttingen, Göttingen, Germany
  • 18Ecophysiology of Plants, Technical University of Munich, Munich, Germany
  • 19Stable Isotope Research Facility, Paul Scherrer Institute (PSI), Villigen, Switzerland
  • 20Institute of Hydraulics and Rural Water Management (IHLW), University of Natural and Life Sciences (BOKU), Vienna, Austria
  • 21Institute of Soil Science, University of Hamburg, Hamburg, Germany
  • 22Ecosystem Physiology, University of Freiburg, Freiburg, Germany

Abstract. For more than two decades, research groups in hydrology, ecology, soil science, and biogeochemistry have performed cryogenic water extractions (CWEs) for the analysis of δ2H and δ18O of soil water. Recent studies have shown that extraction conditions (time, temperature, and vacuum) along with physicochemical soil properties may affect extracted soil water isotope composition. Here we present results from the first worldwide round robin laboratory intercomparison. We test the null hypothesis that, with identical soils, standards, extraction protocols, and isotope analyses, cryogenic extractions across all laboratories are identical. Two standard soils with different physicochemical characteristics along with deionized (DI) reference water of known isotopic composition were shipped to 16 participating laboratories. Participants oven-dried and rewetted the soils to 8 and 20% gravimetric water content (WC), using the deionized reference water. One batch of soil samples was extracted via predefined extraction conditions (time, temperature, and vacuum) identical to all laboratories; the second batch was extracted via conditions considered routine in the respective laboratory. All extracted water samples were analyzed for δ18O and δ2H by the lead laboratory (Global Institute for Water Security, GIWS, Saskatoon, Canada) using both a laser and an isotope ratio mass spectrometer (OA-ICOS and IRMS, respectively). We rejected the null hypothesis. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to soil type and soil water content with mean differences compared to the reference water ranging from +18.1 to −108.4‰ for δ2H and +11.8 to −14.9‰ for δ18O across all laboratories. In addition, differences were observed between OA-ICOS and IRMS isotope data. These were related to spectral interferences during OA-ICOS analysis that are especially problematic for the clayey loam soils used. While the types of cryogenic extraction lab construction varied from manifold systems to single chambers, no clear trends between system construction, applied extraction conditions, and extraction results were found. Rather, observed differences in the isotope data were influenced by interactions between multiple factors (soil type and properties, soil water content, system setup, extraction efficiency, extraction system leaks, and each lab's internal accuracy). Our results question the usefulness of cryogenic extraction as a standard for water extraction since results are not comparable across laboratories. This suggests that defining any sort of standard extraction procedure applicable across laboratories is challenging. Laboratories might have to establish calibration functions for their specific extraction system for each natural soil type, individually.

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To extract water from soils for isotopic analysis, cryogenic water extraction is the most widely used removal technique. This work presents results from a worldwide laboratory intercomparison test of cryogenic extraction systems. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to interactions between soil type and properties, system setup, extraction efficiency, extraction system leaks, and each lab’s internal accuracy.
To extract water from soils for isotopic analysis, cryogenic water extraction is the most widely...
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