 |
| Titel |
Origin and Distribution of Methane Entrapped in Calcareous Alpine Proglacial
Soil |
| VerfasserIn |
Biqing Zhu, Martin H. Schroth, Ruth Henneberger, Manuel Kübler, Josef Zeyer |
| Konferenz |
EGU General Assembly 2017
|
| Medientyp |
Artikel
|
| Sprache |
en
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250150591
|
| Publikation (Nr.) |
 EGU/EGU2017-15067.pdf |
|
|
|
|
|
| Zusammenfassung |
| Methane (CH4) is an important greenhouse gas. The atmospheric methane concentration has
been increasing in recent years, which is caused by imbalance between sources and sinks.
Methane has been recently discovered to be entrapped in calcareous Swiss Alpine proglacial
soil. This CH4 can be released upon mechanical impact and acidification. However, the
amount, distribution and environmental fate of this entrapped CH4 in proglacial environment
remain unknown.
The entrapped CH4 in proglacial soil may be of modern or ancient origin. Modern origin
includes ongoing or recent microbial CH4 production (methanogenesis) in subglacial or
proglacial environments. An ancient origin mainly refers to CH4 produced thermogenically.
This soil entrapped CH4 might be a common phenomenon along the entire glacial forefield,
or it might only be present at few locations and depth. We present results of studies from two
Swiss Alpine Glacier catchments, Wildstrubel Glacier (Canton Valais) and the Griessfirn
Glacier (Canton Uri). Our main goals were 1) to assess the origin of CH4 entrapped in
various glacial environments (subglacial, proglacial and supraglacial, soil and bedrocks)
using geochemical and microbiological evidence; 2) to assess the spatial distribution of
entrapped CH4.
We performed geochemical analysis (CH4 content, gas wetness ([C1]/[C2-C3] alkane
ratio), CH4 stable 13C- and 2H-isotopes, TOC) on subglacial, proglacial, and supraglacial soil
samples collected from well-aerated and water-logged locations. Geochemical analysis was
also selectively conducted on pore-water samples and on rock samples collected from
different geological formations along the catchments. We also performed batch
incubations on soil samples collected from subglacial, proglacial water-logged and
supraglacial zones. In addition, for the aforementioned three types of samples, we
also performed molecular analyses targeting the mcrA gene, which encodes the
α-subunit of the enzyme methyl-coenzyme M reductase, catalyzing the final step in
methanogenesis.
Substantial amounts of CH4 were found to be entrapped in all soil samples in both glacial
catchments. Results of the soil geochemical analyses provided strong evidence that the
entrapped CH4 is mainly of thermogenic origin. Meanwhile, batch incubations of samples
collected from proglacial water-logged zones and supraglacial zones indicated an active
microbial methane production. This is in line with the results from our molecular analysis.
Methane was found to be entrapped along the entire proglacial forefield with little difference
in soil-methane content at the Griessfirn Glacier forefield. We also found much
higher soil methane content at Wildstrubel Glacier compared with Griessfirn Glacier. |
|
|
|
|
|
|