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| Titel |
Technical Note: Disturbance of soil structure can lead to release of entrapped methane in glacier forefield soils |
| VerfasserIn |
P. A. Nauer, E. Chiri, J. Zeyer, M. H. Schroth |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 3 ; Nr. 11, no. 3 (2014-02-04), S.613-620 |
| Datensatznummer |
250117186
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| Publikation (Nr.) |
 copernicus.org/bg-11-613-2014.pdf |
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| Zusammenfassung |
Investigations of sources and sinks of atmospheric CH4 are needed to
understand the global CH4 cycle and climate-change mitigation options.
Glaciated environments might play a critical role due to potential feedbacks
with global glacial meltdown. In an emerging glacier forefield, an
ecological shift occurs from an anoxic, potentially methanogenic subglacial
sediment to an oxic proglacial soil, in which soil-microbial consumption of
atmospheric CH4 is initiated. The development of this change in
CH4 turnover can be quantified by soil-gas profile analysis.
We found evidence for CH4 entrapped in glacier forefield soils when
comparing two methods for the collection of soil-gas samples: a modified
steel rod (SR) designed for one-time sampling and rapid screening (samples
collected ∼1 min after hammering the SR into the soil), and a
novel multilevel sampler (MLS) for repetitive sampling through a previously
installed access tube (samples collected weeks after access-tube
installation). In glacier forefields on siliceous bedrock, sub-atmospheric
CH4 concentrations were observed with both methods. Conversely,
elevated soil-CH4 concentrations were observed in calcareous glacier
forefields, but only in samples collected with the SR, while MLS samples all
showed sub-atmospheric CH4 concentrations. Time-series of SR soil-gas
sampling (additional samples collected 2, 3, 5, and 7 min after hammering)
confirmed the transient nature of the elevated soil-CH4 concentrations,
which were decreasing from ∼100 μL L−1 towards
background levels within minutes. This hints towards the existence of
entrapped CH4 in calcareous glacier forefield soil that can be released
when sampling soil-gas with the SR.
Laboratory experiments with miniature soil cores collected from two glacier
forefields confirmed CH4 entrapment in these soils. Treatment by
sonication and acidification resulted in a massive release of CH4 from
calcareous cores (on average 0.3–1.8 μg CH4 (g d.w.)−1) (d.w. – dry weight);
release from siliceous cores was 1–2 orders of magnitude lower (0.02–0.03 μg CH4
(g d.w.)−1). Clearly, some form of CH4 entrapment
exists in calcareous glacier forefield soils, and to a much lesser extent in
siliceous glacier forefield soils. Its nature and origin remain unclear and
will be subject of future investigations. |
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