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| Titel |
Modeling soil gas dynamics in the context of noble gas tracer applications |
| VerfasserIn |
Florian Jenner, Simon Mayer, Werner Aeschbach, Bernhard Peregovich, Carlos Machado |
| 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 |
250137906
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| Publikation (Nr.) |
 EGU/EGU2017-777.pdf |
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| Zusammenfassung |
| Noble gas tracer applications show a particular relevance for the investigation of gas
dynamics in the unsaturated zone, but also for a treatment of soil contamination as well as
concerning exchange processes between soil and atmosphere. In this context, reliable
conclusions require a profound understanding of underlying biogeochemical processes. With
regard to noble gas tracer applications, the dynamics of reactive and inert gases in the
unsaturated zone is investigated. Based on long-term trends and varying climatic conditions,
this is the first study providing general insights concerning the role of unsaturated zone
processes. Modeling approaches are applied, in combination with an extensive set of
measured soil air composition data from appropriate sampling sites. On the one hand, a
simple modeling approach allows to identify processes which predominantly determine inert
gas mixing ratios in soil air. On the other hand, the well-proven and sophisticated
modeling routine Min3P is applied to describe the measured data by accounting for
the complex nature of subsurface gas dynamics. Both measured data and model
outcomes indicate a significant deviation of noble gas mixing ratios in soil air from the
respective atmospheric values, occurring on seasonal scale. Observed enhancements of
noble gas mixing ratios are mainly caused by an advective balancing of depleted
sum values of O2+CO2, resulting from microbial oxygen depletion in combination
with a preferential dissolution of CO2. A contrary effect, meaning an enhanced
sum value of O2+CO2, is shown to be induced at very dry conditions due to the
different diffusivities of O2 and CO2. Soil air composition data show a yearlong
mass-dependent fractionation, occurring as a relative enhancement of heavier gas species
with respect to lighter ones. The diffusive balancing of concentration gradients between
soil air and atmosphere is faster for lighter gas species compared to heavier ones.
The rather uniform fractionation is a consequence of the time scale of diffusive
transport which is decoupled from the typically stronger fluctuating advective impact. |
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