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Dynamics and Stable Isotope Composition of Gaseous and Dissolved Oxygen
Author(s) -
Wassenaar L. I.,
Hendry M. J.
Publication year - 2007
Publication title -
groundwater
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.84
H-Index - 94
eISSN - 1745-6584
pISSN - 0017-467X
DOI - 10.1111/j.1745-6584.2007.00328.x
Subject(s) - vadose zone , aquifer , isotope fractionation , groundwater , environmental chemistry , sink (geography) , fractionation , isotopes of oxygen , isotope analysis , chemistry , geology , geochemistry , oceanography , geotechnical engineering , cartography , organic chemistry , geography
The vadose zone and ground water environments are a sink for atmospheric O 2 . The pathways and rates of O 2 consumption are primarily related to the availability and rate of oxidation of key reductants (e.g., organics, sulfides), through a combination of biological or abiotic reactions. The range in δ 18 O of O 2 in the subsurface is large, from +20‰ to +39‰ (Vienna Standard Mean Ocean Water) in the vadose zone and from +12‰ to +46‰ in ground water. The aggregated O 2 isotope fractionation by consumption ( α k ) was found to range from 0.970 to 1.300 and 0.980 to 1.030 in vadose zones and aquifers, respectively. These data suggest the δ 18 O patterns in both unsaturated zones and aquifers can be attributed to microbially mediated reactions ( α k = range from 0.975 to 1.000), but there are apparently other inverse isotope fractionating processes ( α k > 1.000). Circumstantial evidence suggested O 2 processed during the sulfide oxidation and precipitation of Fe‐oxyhydroxides process (or other unidentified processes) could be the cause of the significant 18 O depletions. Overall, δ 18 O data from vadose zones and ground water revealed that isotope fractionation by consumption of gaseous and dissolved O 2 in the subsurface and ground water environments is more complicated than what has classically been attributed solely to geomicrobial respiration. Given the questions and inexplicable data arising from this study, further detailed research on O 2 consuming processes in the Earth’s subsurface and ground water is warranted.