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Terrestrial organic matter and light penetration: Effects on bacterial and primary production in lakes
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Climate Impacts Research Centre (CIRC), Abisko, Sweden)
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
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2009 (English)In: Limnology and Oceanography, ISSN 0024-3590, Vol. 54, no 6, 2034-2040 p.Article in journal (Refereed) Published
Abstract [en]

We investigated productivity at the basal trophic level in 15 unproductive lakes in a gradient ranging from clear-water to brown-water (humic) lakes in northern Sweden. Primary production and bacterial production in benthic and pelagic habitats were measured to estimate the variation in energy mobilization from external energy sources (primary production plus bacterial production on allochthonous organic carbon) along the gradient. Clear-water lakes were dominated by autotrophic energy mobilization in the benthic habitat, whereas humic lakes were dominated by heterotrophic energy mobilization in the pelagic habitat. Whole-lake (benthic + pelagic) energy mobilization was negatively correlated to the light-extinction coefficient, which was determined by colored terrestrial organic matter in the lake water. Thus, variation in the concentration of terrestrial organic matter and its light-absorbing characteristics exerts strong control on the magnitude, as well as on the processes and pathways, of energy mobilization in unproductive lakes. We suggest that unproductive lakes in general are sensitive to input of terrestrial organic matter because of its effects on basal energy mobilization in both benthic and pelagic habitats.

Place, publisher, year, edition, pages
American Society of Limnology and Oceanography, Inc. , 2009. Vol. 54, no 6, 2034-2040 p.
URN: urn:nbn:se:umu:diva-26800OAI: diva2:274206
Available from: 2009-10-27 Created: 2009-10-27 Last updated: 2012-10-11Bibliographically approved
In thesis
1. Carbon metabolism in clear-water and brown-water lakes
Open this publication in new window or tab >>Carbon metabolism in clear-water and brown-water lakes
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The trophic state of lakes is commonly defined by the concentration of nutrients in the water column. High nutrient concentrations generate high phytoplankton production, and lakes with low nutrient concentrations are considered low-productive. This simplified view of lake productivity ignores the fact that benthic primary producers and heterotrophic bacteria can be important basal producers in lake ecosystems.

In this thesis I have studied clear-water and brown-water lakes with respect to primary production, respiration and bacterial production based on allochthonous organic carbon. These processes were quantified in pelagic and benthic habitats on temporal and spatial scales. I also calculated the net ecosystem production of the lakes, defined as the difference between gross primary production (GPP) and respiration (R). The net ecosystem production indicates whether a lake is net heterotrophic (GPP < R), net autotrophic (GPP > R) or in metabolic balance (GPP = R). Net heterotrophic lakes are sources of carbon dioxide (CO2) to the atmosphere since respiration in these lakes, by definition, is subsidized by an external organic carbon source. External organic carbon is transported to lakes from the terrestrial environment via inlets, and can serve as a carbon source for bacteria but it also limits light availability for primary producers by absorbing light.

On a seasonal scale, four of the clear-water lakes studied in this thesis were dominated by primary production in the soft-bottom benthic habitat and by respiration in the pelagic habitat. Concentrations of dissolved organic carbon (DOC) were low in the lakes, but still high enough to cause the lakes to be net heterotrophic. However, the lakes were not low-productive due to the high production in the benthic habitat. One of the clear-water lakes was studied also during the winter and much of the respiration under ice was supported by the benthic primary production from the previous summer. This is in contrast to brown-water lakes where winter respiration is suggested to be supported by allochthonous organic carbon.

By studying lakes in a DOC gradient (i.e. from clear-water to brown-water lakes) I could draw two major conclusions. The lakes became less productive since benthic primary production decreased with increasing light extinction, and the lakes became larger sources of CO2 to the atmosphere since pelagic respiration was subsidized by allochthonous organic carbon. Thus, lake carbon metabolism can have an important role in the global carbon cycle due to their processing of terrestrial organic carbon and to their possible feedback effects on the climate system.

Place, publisher, year, edition, pages
Umeå: Institutionen för ekologi, miljö och geovetenskap, Department of Ecology and Environmental Sciences, 2010. 31 p.
clear-water lakes, brown-water lakes, primary production, bacterial production, benthic, pelagic, net ecosystem production, allochthonous organic carbon, CO2, DOC
National Category
Physical Geography Ecology
Research subject
Limnology; Physical Geography
urn:nbn:se:umu:diva-33488 (URN)978-91-7264-954-5 (ISBN)
Public defence
2010-05-21, KBC, Stora Hörsalen (KB3B1), Umeå Universitet, Umeå, 10:00 (English)
Available from: 2010-04-29 Created: 2010-04-26 Last updated: 2016-10-14Bibliographically approved

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Ask, JennyKarlsson, JanPersson, LennartAsk, PerByström, PärJansson, Mats
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