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| Titel |
Determining the stable isotope composition of pore water from saturated and unsaturated zone core: improvements to the direct vapour equilibration laser spectrometry method |
| VerfasserIn |
M. J. Hendry, E. Schmeling, L. I. Wassenaar, S. L. Barbour, D. Pratt |
| 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 ; 19, no. 11 ; Nr. 19, no. 11 (2015-11-04), S.4427-4440 |
| Datensatznummer |
250120842
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| Publikation (Nr.) |
 copernicus.org/hess-19-4427-2015.pdf |
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| Zusammenfassung |
| A method to measure the δ2H and δ18O composition
of pore waters in saturated and unsaturated geologic core samples using
direct vapour equilibration and laser spectrometry (DVE–LS) was first
described in 2008, and has since been rapidly adopted. Here, we describe a
number of important methodological improvements and limitations encountered
in routine application of DVE–LS over several years. Generally, good
comparative agreement, as well as accuracy, is obtained between core pore water
isotopic data obtained using DVE–LS and that measured on water squeezed from
the same core. In complex hydrogeologic settings, high-resolution DVE–LS
depth profiles provide greater spatial resolution of isotopic profiles
compared to long-screened or nested piezometers. When fluid is used during
drilling and coring (e.g. water rotary or wet sonic drill methods), spiking
the drill fluid with 2H can be conducted to identify core
contamination. DVE–LS analyses yield accurate formational isotopic data for
fine-textured core (e.g. clay, shale) samples, but are less effective for
cores obtained from saturated permeable (e.g. sand, gravels) geologic media
or on chip samples that are easily contaminated by wet rotary drilling
fluid. Data obtained from DVE–LS analyses of core samples collected using
wet (contamination by drill water) and dry sonic (water loss by heating)
methods were also problematic. Accurate DVE–LS results can be obtained on
core samples with gravimetric water contents > 5 % by increasing
the sample size tested. Inexpensive Ziploc™ gas-sampling bags
were determined to be as good as, if not better than, other, more expensive
specialty bags. Sample storage in sample bags provides acceptable results
for up to 10 days of storage; however, measurable water loss, as well as evaporitic
isotopic enrichment, occurs for samples stored for up to 6 months. With
appropriate care taken during sample collection and storage, the DVE–LS
approach for obtaining high-resolution pore water isotopic data is a
promising alternative to study the hydrogeology of saturated and unsaturated
sediments. Eliminating analytical interferences from volatile organics
remains a challenge. |
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