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| Titel |
Lake size and water-column stability affect the importance of methane for pelagic food webs of boreal lakes |
| VerfasserIn |
Paula Kankaala, Jessica Lopez-Bellido, Anne Ojala, Tiina Tulonen, Roger I. 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 |
250073641
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| Zusammenfassung |
| Physical forcing, related to lake size and morphometry, plays an important role in
the landscape-scale biogeochemical processing and fluxes of terrestrial carbon in
lakes. Boreal lakes are typically dimictic, with mixing of the water column in spring
and autumn, but in small, sheltered, humic, forest lakes the spring mixing is often
incomplete. This leads to a steep summer stratification and oxygen depletion in
the hypolimnion of the lakes. As a result of anaerobic decomposition of organic
matter, high concentrations of CH4are typical in these lakes. At the oxic-anoxic
interface zone methanotrophic microbes oxidize CH4 to CO2 and partly incorporate
CH4-C into microbial biomass, and thus potentially provide a diet source for pelagic
consumers.
We studied production at the base of the pelagic food web by methane oxidising bacteria
(MOB), heterotrophic bacteria (HB) and phytoplankton (PP) in five boreal lakes with a
dissolved organic carbon (DOC) concentration varying between 7 and 25 mg C L-1 and an
area ranging from 0.004 to 13.4 km2. High MOB activity was detected in the water columns
of the three smallest lakes having anoxia in the hypolimnion during summer. The highest
MOB activities (ca. 2-12 μmol L-1 d-1) were observed when the CH4:O2 ratio varied
between ca. 0.5-12. Seasonally, the highest MOB activities were measured during
late-summer mixed layer deepening and autumnal mixing of the whole water column. The
proportion of MOB in the total basal production was highest in the two smallest lakes
(24-56 and 13-36%), having the steepest summertime stratification. The proportion
MOB in the basal production decreased with lake size being 70% of basal production was by PP. In all studied lakes HB contributed only
10-23% of the total basal production, suggesting that a transfer of allochthonous
DOC via HB plays only a modest role for the nutrition of the higher trophic levels. |
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