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| Titel |
Ancient dissolved methane in inland waters at low concentrations revealed by
a new collection method for radiocarbon (14C) analysis |
| VerfasserIn |
Joshua F. Dean, Michael F. Billett, Callum Murray, Mark H. Garnett |
| 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 |
250144837
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| Publikation (Nr.) |
 EGU/EGU2017-8710.pdf |
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| Zusammenfassung |
| Methane (CH4) is a powerful greenhouse gas and is released to the atmosphere from
freshwater systems in numerous biomes globally. Radiocarbon (14C) analysis of methane can
provide unique information about its age, source and rate of cycling in natural environments.
Methane is often released from aquatic sediments in bubbles (ebullition), but dissolved
methane is also present in lakes and streams at lower concentrations, and may not be of the
same age or source. Obtaining sufficient non-ebullitive aquatic methane for 14C analysis
remains a major technical challenge. Previous studies have shown that freshwater methane, in
both dissolved and ebullitive form, can be significantly older than other forms of aquatic
carbon (C), and it is therefore important to characterise this part of the terrestrial C
balance.
We present a novel method to capture sufficient amounts of dissolved methane from
freshwater environments for 14C analysis by circulating water across a hydrophobic,
gas-permeable membrane and collecting the methane in a large collapsible vessel. The results
of laboratory and field tests show that reliable dissolved δ13CH4 and 14CH4 samples can be
readily collected over short time periods (∼4 to 24 hours), at relatively low cost and from a
variety of surface water types.
The initial results further support previous findings that dissolved methane can be
significantly older than other forms of aquatic C, especially in organic-rich catchments, and is
currently unaccounted for in many terrestrial C balances and models. This method is suitable
for use in remote locations, and could potentially be used to detect the leakage of unique
14CH4 signatures from point sources into waterways, e.g. coal seam gas and landfill gas. |
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