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| Titel |
Depth-dependent molecular composition and photo-reactivity of dissolved organic matter in a boreal lake under winter and summer conditions |
| VerfasserIn |
M. Gonsior, P. Schmitt-Kopplin, D. Bastviken |
| 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 ; 10, no. 11 ; Nr. 10, no. 11 (2013-11-04), S.6945-6956 |
| Datensatznummer |
250085393
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| Publikation (Nr.) |
 copernicus.org/bg-10-6945-2013.pdf |
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| Zusammenfassung |
| Transformations of dissolved organic matter (DOM) in boreal lakes lead to
large greenhouse gas emissions as well as substantial carbon storage in
sediments. Using novel molecular characterization approaches and
photochemical degradation experiments we studied how seasonal patterns in
water column stratification affected the DOM in a Swedish lake under early
spring and summer conditions. Dissolved organic carbon (DOC) concentrations
were consistently higher above the sediment when compared to surface waters
throughout the sampling periods. Photobleaching alone could not explain
this difference in DOC because the lake was covered by 40 cm-thick ice
during late winter sampling and still showed the same DOC trend. The
differences in the molecular diversity between surface DOM in winter and
summer were consistent with ongoing photobleaching/decarboxylation and a
possible bacterial consumption of photo-products. Additional
photo-degradation experiments using simulated sunlight showed a production
of highly oxidized organic molecules and low molecular weight compounds in
all late winter samples and also in the deep water sample in summer. In the
surface summer DOM sample, few such molecules were produced during the
photo-degradation experiments, confirming that DOM was already photobleached
prior to the experiments. This study suggests that photobleaching, and
therefore also the ice cover during winter, plays a central role in surface
DOM transformation, with important differences in the molecular composition
of DOM between surface and deep boreal lake waters. The release of DOC from
boreal lake sediments also contribute to this pattern. Photochemical
degradation of DOM may be more extensive following ice-out and water column
turnover when non-light exposed and thereby photosensitive DOM is
photo-mineralized. Hence, the yearly DOM photo-mineralization may be greater
than inferred from studies of recently light-exposed DOM. |
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