|
Titel |
Direct monitoring of wind-induced pressure-pumping on gas transport in soil |
VerfasserIn |
Thomas Laemmel, Manuel Mohr, Dirk Schindler, Helmer Schack-Kirchner, Martin Maier |
Konferenz |
EGU General Assembly 2017
|
Medientyp |
Artikel
|
Sprache |
en
|
Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 19 (2017) |
Datensatznummer |
250149978
|
Publikation (Nr.) |
EGU/EGU2017-14393.pdf |
|
|
|
Zusammenfassung |
Gas exchange between soil and atmosphere is important for the biogeochemistry of soils and
is commonly assumed to be governed by molecular diffusion. Yet a few previous field studies
identified other gas transport processes such as wind-induced pressure-pumping to enhance
soil-atmosphere fluxes significantly. However, since these wind-induced non-diffusive gas
transport processes in soil often occur intermittently, the quantification of their contribution to
soil gas emissions is challenging.
To quantify the effects of wind-induced pressure-pumping on soil gas transport, we
developed a method for in situ monitoring of soil gas transport. The method includes the use
of Helium (He) as a tracer gas which was continuously injected into the soil. The resulting He
steady-state concentration profile was monitored. Gas transport parameters of the soil were
inversely modelled.
We used our method during a field campaign in a well-aerated forest soil over three
months. During periods of low wind speed, soil gas transport was modelled assuming
diffusion as transport process. During periods of high wind speed, the previously steady
diffusive He concentration profile showed temporary concentration decreases in the topsoil,
indicating an increase of the effective gas transport rate in the topsoil up to 30%. The
enhancement of effective topsoil soil gas diffusivity resulted from wind-induced air pressure
fluctuations which are referred to as pressure-pumping. These air pressure fluctuations had
frequencies between 0.1 and 0.01 Hz and amplitudes up to 10 Pa and occurred at
above-canopy wind speeds greater than 5 m s−1. We could show the importance of the
enhancement of the gas transport rate in relation with the wind intensity and corresponding
air pressure fluctuations characteristics.
We directly detected and quantified the pressure-pumping effect on gas transport in soil in
a field study for the first time, and could thus validate and underpin the importance of this
non-diffusive gas transport process. Our method can also be used to study other non-diffusive
gas transport processes occurring in soil and snow, and their possible feedbacks or
interactions with biogeochemical processes. |
|
|
|
|
|