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| Titel |
Continual in situ monitoring of pore water stable isotopes in the subsurface |
| VerfasserIn |
T. H. M. Volkmann, M. Weiler |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 18, no. 5 ; Nr. 18, no. 5 (2014-05-20), S.1819-1833 |
| Datensatznummer |
250120360
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| Publikation (Nr.) |
 copernicus.org/hess-18-1819-2014.pdf |
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| Zusammenfassung |
| Stable isotope signatures provide an integral fingerprint of origin, flow
paths, transport processes, and residence times of water in the environment.
However, the full potential of stable isotopes to quantitatively
characterize subsurface water dynamics is yet unfolded due to the difficulty
in obtaining extensive, detailed, and repeated measurements of pore water in
the unsaturated and saturated zone. This paper presents a functional and
cost-efficient system for non-destructive continual in situ monitoring of
pore water stable isotope signatures with high resolution. Automatic
controllable valve arrays are used to continuously extract diluted water
vapor in soil air via a branching network of small microporous probes into a
commercial laser-based isotope analyzer. Normalized liquid-phase isotope
signatures are then obtained based on a specific on-site calibration approach
along with basic corrections for instrument bias and temperature dependent
isotopic fractionation. The system was applied to sample depth profiles on
three experimental plots with varied vegetation cover in southwest Germany.
Two methods (i.e., based on advective versus diffusive vapor extraction) and
two modes of sampling (i.e., using multiple permanently installed probes
versus a single repeatedly inserted probe) were tested and compared. The
results show that the isotope distribution along natural profiles could be
resolved with sufficiently high accuracy and precision at sampling intervals
of less than four minutes. The presented in situ approaches may thereby be
used interchangeably with each other and with concurrent laboratory-based
direct equilibration measurements of destructively collected samples. It is
thus found that the introduced sampling techniques provide powerful tools
towards a detailed quantitative understanding of dynamic and heterogeneous
shallow subsurface and vadose zone processes. |
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