This title appears in the Scientific Report :
2014
High-frequency soil water isotope measurements in the laboratory
High-frequency soil water isotope measurements in the laboratory
In soils, the stable isotope compositions of water (δ2H and δ18O) provide qualitative information about whether water has only infiltrated or has already been re-evaporated since the last rainfall event, or about the location of the evaporation front. From water stable isotope profiles measured in s...
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Personal Name(s): | Rothfuss, Youri (Corresponding Author) |
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Gangi, Laura / Merz, Steffen / Pohlmeier, Andreas / Hermes, Normen / Weuthen, Ansgar / Vereecken, Harry / Brüggemann, Nicolas | |
Contributing Institute: |
Agrosphäre; IBG-3 |
Published in: | 2014 |
Imprint: |
2014
|
Conference: | IBG3 Internal Symposium, Jülich (Germany), 2014-04-21 - 2014-04-21 |
Document Type: |
Talk (non-conference) |
Research Program: |
Terrestrial Systems: From Observation to Prediction Modelling and Monitoring Terrestrial Systems: Methods and Technologies |
Publikationsportal JuSER |
In soils, the stable isotope compositions of water (δ2H and δ18O) provide qualitative information about whether water has only infiltrated or has already been re-evaporated since the last rainfall event, or about the location of the evaporation front. From water stable isotope profiles measured in soils, it is also possible, under certain assumptions, to derive quantitative information, such as soil evaporation flux and the identification of root water uptake depths. In addition, the fate and dynamics of water stable isotopologues have been well implemented into physically based Soil–Vegetation–Atmosphere Transfer (SVAT) models (e.g. Hydrus 1D, SiSPAT-Isotope, Soil–Litter iso, TOUGHREACT) and have demonstrated their potential.However, the main disadvantage of the use of stable isotopes in soil water studies is that, contrary to other state variables (e.g., water content and tension) that can be monitored over long periods (e.g., by time-domain reflectometry, capacitive sensing, tensiometry or micro-psychrometry), stable isotope compositions are analyzed following destructive sampling, and thus are available only at a given time. As a consequence, there are important discrepancies in time resolution between soil water and stable isotope information which greatly limit the insight potential of the latter. Recently, a novel technique based on infrared laser absorption spectroscopy was developed that allows simultaneous and direct measurements of δ2H and δ18O in water vapor, which constitutes a major breakthrough in stable isotope analysis. Many applications can be found in the literature for varying temporal and spatial scales. Here, we present a non-destructive method for monitoring soil liquid water δ2H and δ18O by sampling and measuring water vapor equilibrated with soil water using gas-permeable polypropylene tubing and a cavity ring-down laser absorption spectrometer. Three acrylic glass columns (diameter = 11 cm, height = 60 cm) were (i) equipped with temperature and soil water probes in addition to gas-permeable tubing sections at eight different depths (1, 3, 5, 7, 10, 20, 40, and 60 cm), (ii) filled with pure quartz sand (mean grain size 0.35 mm), and (iii) saturated from the bottom up to the surface. Finally, they were installed on balances and evaporated over a period of 300 days. One of the three columns, fully free of metal parts (thus not equipped with any sensors) was as well intended for Magnetic Resonance Imaging (MRI) additionally to the isotope measurements. |