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| Titel |
Methane metabolism in a stratified boreal lake |
| VerfasserIn |
Hannu Nykänen, Sari Peura, Paula Kankaala, Roger Jones |
| 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 |
250075602
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| Zusammenfassung |
| Stratified lakes, typical of the boreal zone, are naturally anoxic from their bottoms. In these
lakes methanogenesis can account for up to half of organic matter degradation. However, a
major part of the methane (CH4) is oxidized in the water column before reaching the
atmosphere. Since methanotrophs use CH4 as their sole carbon and energy source, much
CH4-derived carbon is incorporated into their biomass. Microbially produced CH4 has
strongly negative δ13C compared to other carbon forms in ecosystems, making it possible to
follow its route in food webs. However, only a few studies have estimated the amount of this
microbial biomass or its carbon stable isotopic composition due to difficulties in separating it
from other biomass or from other carbon forms in the water column. We estimated
methanotrophic biomass from measured CH4 oxidation, and δ13C of the biomass from
measured δ13C values of CH4, DIC, POM and DOC. An estimate of the fraction of
methanotrophs in total microbial biomass is derived from bacterial community composition
measurements.
The study was made in, Alinen Mustajärvi, a small (area 0.75 ha, maximum depth 6.5 m,
mean depth 4.2 m,), oligotrophic, mesohumic headwater lake located in boreal coniferous
forest in southern Finland. CH4 and DIC concentrations and their δ13C were measured
over the deepest point of the lake at 1 m intervals. 13C of DOM and POM were
analyzed from composite samples from epi-, meta-, and hypolimnion. Evasion of CH4
and carbon dioxide from the lake surface to the atmosphere was estimated with
boundary layer diffusion equations. CH4oxidation was estimated by comparing
differences between observed concentrations and CH4potentially transported by
turbulent diffusion between different vertical layers in the lake and also by actual
methanotrophy measurements and from vertical differences in δ13C-CH4. The estimate of
CH4 production was based on the sum of oxidized and released CH4. Molecular
microbiology methods were used to evaluate which bacteria might be participating in these
processes.
A substantial part of the CH4 produced was oxidized in the anoxic water column. Our
results further show that production and oxidation of CH4 was important in microbial
biomass production and also affected the δ13C of biota in the water column. |
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