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Titel |
Subsurface dynamics of reactive and inert gases in the context of noble gases as environmental tracers in groundwater hydrology |
VerfasserIn |
Simon Mayer, Florian Jenner, Werner Aeschbach |
Konferenz |
EGU General Assembly 2017
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 19 (2017) |
Datensatznummer |
250137888
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Publikation (Nr.) |
EGU/EGU2017-754.pdf |
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Zusammenfassung |
Applications of inert gases in groundwater hydrology require a profound understanding of
underlying biogeochemical processes. Some of these processes are, however, not well
understood and therefore require further investigation. This is the first study simultaneously
investigating soil air and groundwater in the context of noble gas tracer applications,
accounting for seasonal effects in different climate regions. The sampled data confirm a
general reliability of common assumptions proposed in the literature. In particular, a
solubility-controlled description of excess air formation and of groundwater degassing can be
confirmed. This study identifies certain effects which need to be taken into account to
reliably evaluate noble gas patterns. First, long-term samplings suggest a permanent
temperature-driven equilibration of shallow groundwater with entrapped air bubbles, even
some years after recharge. Second, minor groundwater degassing is found to challenge
existing excess air model approaches, depending on the amount and the fractionation of
excess air. Third, soil air composition data of this study imply a potential bias of
noble gas temperatures by up to about 2℃ due to microbial oxygen depletion and a
reduced sum value of O2+CO2. This effect causes systematically lower noble gas
temperatures in tropical groundwater samples and in shallow mid-latitude groundwater
samples after strong recharge during the warm season. However, a general bias of
noble gas temperatures in mid-latitudes is probably prevented by a predominant
recharge during the cold season, accompanied by nearly atmospheric noble gas mixing
ratios in the soil air. Findings of this study provide a remarkable contribution to the
reliability of noble gas tracer applications in hydrology, in particular with regard to
paleoclimate reconstructions and an understanding of subsurface gas dynamics. |
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