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| Titel |
A novel in-situ method for real-time monitoring of gas transport in soil |
| VerfasserIn |
Thomas Laemmel, Martin Maier, Helmer Schack-Kirchner, Friederike Lang |
| 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 |
250149728
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| Publikation (Nr.) |
 EGU/EGU2017-14107.pdf |
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| Zusammenfassung |
| Gas exchange between soil and atmosphere is important for the biogeochemistry of soils. Gas
transport in soil is commonly assumed to be governed by molecular diffusion and is usually
described by the soil gas diffusion coefficient DS characterizing the ability of the soil to
“transport passively“ gas through the soil. One way to determine DS is sampling
soil cores in the field and measuring DS in the lab. Unfortunately this method is
destructive and laborious. Moreover, a few previous field studies identified other
gas transport processes in soil to significantly enhance the diffusive gas transport.
However, until now, no method is available to measure gas transport in situ in the
soil.
We developed a novel method to monitor gas transport in soil in situ. The method
includes a custom made gas sampling device, the continuous injection of an inert tracer gas
and inverse gas transport modelling in the soil. The gas sampling device has several sampling
depths and can be easily installed into a vertical hole drilled by an auger, which allows for
fast installation of the system. Helium (He) as inert tracer gas was injected continuously
at the lower end of the device. The resulting steady state distribution of He was
used to deduce the depth profile of DS. Gas transport in the soil surrounding the
gas-sampling-device/soil system was modeled using the Finite Element Modeling program
COMSOL .
We tested our new method both in the lab and during two short field studies and
compared the results with a reference method using soil cores. DS profiles obtained
by our in-situ method were consistent with DS profiles determined based on soil
core analyses. During a longer monitoring field campaign, typical soil-moisture
effects upon gas diffusivity such as an increase during a drying period or a decrease
after rain could be observed consistently. Under windy conditions we additionally
measured for the first time the direct enhancement of gas transport in soil due to
wind-induced pressure-pumping which could increase the effective DS up to 30% in the
topsoil.
Our novel monitoring method can be quickly and easily installed and allows for
monitoring continuously soil gas transport over a long time. It allows monitoring physical
modifications of soil gas diffusivity due to rain events or evaporation but it also allows
studying non-diffusive gas transport processes in the soil. |
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