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| Titel |
Reassessing the stable isotope composition assigned to methane flux from natural wetlands in isotope-constrained budgets |
| VerfasserIn |
Edward Hornibrook, Peter Maxfield, Vincent Gauci, Andrew Stott |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083924
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| Zusammenfassung |
| Stable isotope ratios in CH4 preserve information about its origin and history, and are
commonly used to constrain global CH4 budgets. Wetlands are key contributors to the
atmospheric burden of CH4 and typically are assigned a stable carbon isotope composition of
~-60 permil in isotope-weighted stable isotope models despite the considerable range of
δ13C(CH4) values (~ -100 to -40 permil) known to occur in these diverse ecosystems.
Kinetic isotope effects (KIEs) associated with the metabolism of CH4-producing
microorganisms generate much of the natural variation but highly negative and positive
δ13C(CH4) values generally result from secondary processes (e.g., diffusive transport or
oxidation by soil methanotrophs). Despite these complexities, consistent patterns exist in the
isotope composition of wetland CH4 that can be linked conclusively to trophic status
and consequently, natural succession or human perturbations that impact nutrient
levels.
Another challenge for accurate representation of wetlands in carbon cycle models is
parameterisation of sporadic CH4 emission events. Abrupt release of large volumes of
CH4-rich bubbles in short periods of time can account for a significant proportion of
the annual CH4 flux from a wetland but such events are difficult to detect using
conventional methods. New infrared spectroscopy techniques capable of high temporal
resolution measurements of CH4 concentration and stable isotope composition can
readily quantify short-lived CH4 pulses. Moreover, the isotope data can be used
conclusively to determine shifts in the mode of CH4 transport and provide the potential to
link initiation of abrupt emission events to forcing by internal or external factors. |
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