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Aging of allochthonous organic carbon regulates bacterial production in unproductive boreal lakes
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2009 (English)In: Limnology and Oceanography, ISSN 0024-3590, Vol. 54, no 4, 1333-1342 p.Article in journal (Refereed) Published
Abstract [en]

We calculated average aquatic dissolved organic carbon (DOC) age (the time span from soil discharge to observation) in water from the inlets and outlets of two unproductive Swedish lakes at different times during an annual cycle. Bacterial production (BP) and bacterial growth efficiency (BGE) determined during 7-d bioassays decreased with increasing average aquatic DOC age. Parallel to the declines in BP and BGE there was a rise in specific ultraviolet absorbance at the wavelength of 254 nm (SUVA254), which indicates that decreasing BP and BGE were connected to a shift to a more aromatic and recalcitrant DOC pool. The relationships between bacterial metabolism and DOC age were stronger after a Q10 correction of the DOC age, showing that temperature affected rates of DOC quality changes over time and should be taken into account when relating lake bacterial growth to substrate aging in natural environments. We propose that hydrological variability in combination with lake size (water renewal time) have a large influence on pelagic BP in lakes with high input of terrigenous DOC.

Place, publisher, year, edition, pages
2009. Vol. 54, no 4, 1333-1342 p.
URN: urn:nbn:se:umu:diva-23250OAI: diva2:222368
Available from: 2009-06-08 Created: 2009-06-08 Last updated: 2009-12-02
In thesis
1. Bacterial use of allochthonous organic carbon for respiration and growth in boreal freshwater systems
Open this publication in new window or tab >>Bacterial use of allochthonous organic carbon for respiration and growth in boreal freshwater systems
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Aquatic systems worldwide receive large amounts of organic carbon from terrestrial sources. This ‘allochthonous’ organic carbon (AlloOC) affects critical physical and chemical properties of freshwater ecosystems, with consequences for food web structures and exchange of greenhouse gases with the atmosphere. In the boreal region, loadings of AlloOC are particularly high due to leaching from huge organic deposits in boreal forest, mire and tundra soils.

A main process of AlloOC turnover in aquatic systems is its use by heterotrophic bacteria. Applying a bioassay approach, I measured the respiration and growth (production) of bacteria in northern Sweden, in streams and lakes almost totally dominated by AlloOC. The objective was to elucidate how variations in AlloOC source, age, composition and concentration impact on its use by aquatic bacteria, and how AlloOC properties, in turn, are regulated by landscape composition and by hydrology.

The bacterial respiration (30-309 µg C L-1 d-1) was roughly proportional to the concentration of AlloOC (7-47 mg C L-1), but not significantly related to AlloOC source or character. Bacterial production (4-94 µg C L-1 d-1), on the other hand, was coupled to the AlloOC character, rather than concentration. A strong coupling to AlloOC character was also found for bacterial growth efficiency (0.06-0.51), i.e. production per unit of assimilated carbon. Bacterial production and growth efficiency increased with rising concentrations of low molecular weight AlloOC (carboxylic acids, free amino acids and simple carbohydrates). While the total AlloOC concentrations generally were the highest in mire-dominated catchments, low molecular weight AlloOC concentrations were much higher in forested catchments, compared to mire-dominated. These patterns were reflected in a strong landscape control of aquatic bacterial metabolism. Moreover, high flow episodes increased the export of organic carbon from forests, in relation to the export from mires, stimulating the bacterial production and growth efficiency in streams with mixed (forest and mire) catchments. The potential of AlloOC to support efficient bacterial growth decreased on time-scales of weeks to months, as the AlloOC was aged in laboratory or lake in situ conditions.

To conclude, landscape, hydrology and conditions which determine AlloOC age have large influence on bacterial metabolism in boreal aquatic systems. Considering the role of bacteria in heterotrophic food chains, these factors can have spin-off effects on the structure and function of boreal aquatic ecosystems.

Place, publisher, year, edition, pages
Umeå: Umeå universitet, Institutionen för ekologi, miljö och geovetenskap, 2009. 17 + 4 papers p.
lakes, streams, boreal, bacterial respiration, bacterial production, bacterial growth efficiency, allochthonous organic carbon, low molecular weight compounds
Research subject
Physical Geography
urn:nbn:se:umu:diva-30051 (URN)978-91-7264-870-8 (ISBN)
Public defence
2010-01-15, Stora hörsalen, KBC, Linnaeus väg 6, Universitetsområdet, Umeå, 10:00 (English)
Available from: 2009-12-04 Created: 2009-12-01 Last updated: 2009-12-04Bibliographically approved

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