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Monitoring water stable isotopic composition in soils using gas‐permeable tubing and infrared laser absorption spectroscopy
Author(s) -
Rothfuss Youri,
Vereecken Harry,
Brüggemann Nicolas
Publication year - 2013
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1002/wrcr.20311
Subject(s) - soil water , δ18o , water vapor , evaporation , sampling (signal processing) , environmental science , analytical chemistry (journal) , environmental chemistry , stable isotope ratio , soil science , chemistry , meteorology , physics , organic chemistry , quantum mechanics , filter (signal processing) , computer science , computer vision
In soils, the isotopic composition of water ( δ 2 H and δ 18 O) provides qualitative (e.g., location of the evaporation front) and quantitative (e.g., evaporation flux and root water uptake depths) information. However, the main disadvantage of the isotope methodology is that contrary to other soil state variables that can be monitored over long time periods, δ 2 H and δ 18 O are typically analyzed following destructive sampling. Here we present a nondestructive method for monitoring soil liquid water δ 2 H and δ 18 O over a wide range of water availability conditions and temperatures by sampling water vapor equilibrated with soil water using gas‐permeable polypropylene tubing and a cavity ring‐down laser absorption spectrometer. By analyzing water vapor δ 2 H and δ 18 O sampled with the tubing from a fine sand for temperatures ranging between 8°C and 24°C, we demonstrate that our new method is capable of monitoring δ 2 H and δ 18 O in soils online with high precision and after calibration, also with high accuracy. Our sampling protocol enabled detecting changes of δ 2 H and δ 18 O following nonfractionating addition and removal of liquid water and water vapor of different isotopic compositions. Finally, the time needed for the tubing to monitor these changes is compatible with the observed variations of δ 2 H and δ 18 O in soils under natural conditions.