| 1. |
- Ask, Jenny, 1976-, et al.
(författare)
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Terrestrial organic matter and light penetration : Effects on bacterial and primary production in lakes
- 2009
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Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography, Inc.. - 0024-3590 .- 1939-5590. ; 54:6, s. 2034-2040
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 2. |
- Ask, Jenny, 1976-, et al.
(författare)
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Whole-lake estimates of carbon flux through algae and bacteria in benthic and pelagic habitats of clear-water lakes
- 2009
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Ingår i: Ecology. - Washington, DC, USA : Ecological Society of America. - 0012-9658 .- 1939-9170. ; 90:7, s. 1923-1932
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Tidskriftsartikel (refereegranskat)abstract
- This study quantified new biomass production of algae and bacteria in both benthic and pelagic habitats of clear-water lakes to contrast how carbon from the atmosphere and terrestrial sources regulates whole-lake metabolism. We studied four small unproductive lakes in subarctic northern Sweden during one summer season. The production of new biomass in both benthic and pelagic habitats was calculated as the sum of autotrophic production by algae and heterotrophic production by bacteria using allochthonous organic carbon (OC). Whole-lake production of new biomass was dominated by the benthic habitat (86% +/- 4% [mean +/- SD]) and by primary production (77% +/- 9%). Still, heterotrophic bacteria fueled by allochthonous OC constituted a significant portion of the new biomass production in both benthic (19% +/- 11%) and pelagic habitats (51% +/- 24%). In addition, overall net production (primary production minus respiration) was close to zero in the benthic habitats but highly negative (-163 +/- 81 mg C.m(-2).d(-1)) in pelagic regions of all lakes. We conclude (1) that allochthonous OC supported a significant part of total production of new biomass in both pelagic and benthic habitats, (2) that benthic habitats dominated the whole-lake production of new biomass, and (3) that respiration and net CO2 production dominated the carbon flux of the pelagic habitats and biomass production dominated the benthic carbon flux. Taken together, these findings suggest that previous investigations have greatly underestimated the productivity of clear-water lakes when benthic autotrophic production and metabolism of allochthonous OC have not been measured.
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| 3. |
- Byström, Pär, et al.
(författare)
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Substitution of top predators : effects of pike invasion in a subarctic lake
- 2007
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Ingår i: Freshwater Biology. - : John Wiley & Sons, Inc. - 0046-5070 .- 1365-2427. ; 52:7, s. 1271–1280-
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Tidskriftsartikel (refereegranskat)abstract
- 1. Invasions of top predators may have strong cascading effects in ecosystems affecting both prey species abundance and lower trophic levels. A recently discussed factor that may enhance species invasion is climate change and in this context, we studied the effects of an invasion of northern pike into a subarctic lake ecosystem formerly inhabited by the native top predator Arctic char and its prey fish, ninespined stickleback. 2. Our study demonstrated a strong change in fish community composition from a system with Arctic char as top predator and high densities of sticklebacks to a system with northern pike as top predator and very low densities of sticklebacks. A combination of both predation and competition from pike is the likely cause of the extinction of char. 3. The change in top predator species also cascaded down to primary consumers as both zooplankton and predator-sensitive macroinvertebrates increased in abundance. 4. Although the pike invasion coincided with increasing summer temperatures in the study area we have no conclusive evidence that the temperature increase is the causal mechanism behind the pike invasion. But still, our study provides possible effects of future pike invasions in mountain lakes related to climate change. We suggest that future pike invasions will have strong effects in lake ecosystems, both by replacing native top consumers and through cascading effects on lower trophic levels.
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| 4. |
- Karlsson, Jan, 1969-, et al.
(författare)
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Winter respiration of allochthonous and autochthonous organic carbon in a subarctic clear-water lake
- 2008
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Ingår i: Limnology and Oceanography. - : American Society of Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 53:3, s. 948-954
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Tidskriftsartikel (refereegranskat)abstract
- We studied a small subarctic lake to assess the magnitude of winter respiration and the organic carbon (OC) source for this respiration. The concentration and stable isotopic composition (d13C) of dissolved inorganic carbon (DIC) accumulating in the lake water under ice was analyzed over one winter (7 months). The DIC concentration increased and the d13C of DIC decreased over time, with the greatest changes at the lake bottom. Winter respiration was 26% of annual respiration in the lake. Keeling plot analysis demonstrated that the d13C of respired DIC varied spatially, high d13C values occurring at shallow (2.5 m, 21.7‰) compared with intermediate (4 m, 25.1‰) and deep (6 m, 27.8‰) locations in the lake. The variation in the d13C of respired DIC was related to the variation in the d13C of the sediments between locations, suggesting that sediment OC supported much of the winter respiration and that the dominant OC source for respiration was OC from benthic algae at shallow locations and settled OC, of predominately terrestrial origin, at deep locations. The respiration of OC from benthic algae constituted 55% of the winter respiration, equaling 54% of the primary production by benthic algae the previous summer. The study indicates the importance of temporal and spatial variation in respiration for the metabolism and net DIC production in unproductive high-latitude lakes; both allochthonous and autochthonous carbon can contribute to winter DIC accumulation and, consequently, to spring CO2 emissions from lakes.
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