| 1. |
- Algesten, Grete, et al.
(author)
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Contribution of sediment respiration to summer CO2 emission from boreal and subarctic lakes
- 2005
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In: Microbial Ecology. - : Springer Science and Business Media LLC. - 0095-3628 .- 1432-184X. ; 50:4, s. 529-535
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Journal article (peer-reviewed)abstract
- We measured sediment production of carbon dioxide (CO(2)) and methane (CH(4)) and the net flux of CO(2) across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were made in situ under ambient light conditions. The flux of CO(2) between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m(-2) day(-1) from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated to dissolved organic carbon (DOC) concentration in the water (r(2) = 0.61). The net flux of CO(2) across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed layer (r(2) = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration. Lakes with DOC concentrations <5.6 mg L(-1) had net consumption of CO(2) in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic (<2.6 mg L(-1)) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources.
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| 2. |
- Algesten, Grete, et al.
(author)
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Contribution of sediment respiration to summer CO2 emission from low productive boreal and subarctic lakes
- 2005
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In: Microbial Ecology. - : Springer Science and Business Media LLC. - 0095-3628 .- 1432-184X. ; 50:4, s. 529-535
-
Journal article (peer-reviewed)abstract
- We measured sediment production of carbon dioxide (CO2) and methane (CH4) and the net flux of CO2 across the surfaces of 15 boreal and subarctic lakes of different humic contents. Sediment respiration measurements were made in situ under ambient light conditions. The flux of CO2 between sediment and water varied between an uptake of 53 and an efflux of 182 mg C m−2 day−1 from the sediments. The mean respiration rate for sediments in contact with the upper mixed layer (SedR) was positively correlated to dissolved organic carbon (DOC) concentration in the water (r 2 = 0.61). The net flux of CO2 across the lake surface [net ecosystem exchange (NEE)] was also closely correlated to DOC concentration in the upper mixed layer (r 2 = 0.73). The respiration in the water column was generally 10-fold higher per unit lake area compared to sediment respiration. Lakes with DOC concentrations <5.6 mg L−1 had net consumption of CO2 in the sediments, which we ascribe to benthic primary production. Only lakes with very low DOC concentrations were net autotrophic (<2.6 mg L−1) due to the dominance of dissolved allochthonous organic carbon in the water as an energy source for aquatic organisms. In addition to previous findings of allochthonous organic matter as an important driver of heterotrophic metabolism in the water column of lakes, this study suggests that sediment metabolism is also highly dependent on allochthonous carbon sources.
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| 3. |
- Berggren, Martin, et al.
(author)
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Lake secondary production fueled by rapid transfer of low molecular weight organic carbon from terrestrial sources to aquatic consumers
- 2010
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In: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 13:7, s. 870-880
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Journal article (peer-reviewed)abstract
- P>Carbon of terrestrial origin often makes up a significant share of consumer biomass in unproductive lake ecosystems. However, the mechanisms for terrestrial support of lake secondary production are largely unclear. By using a modelling approach, we show that terrestrial export of dissolved labile low molecular weight carbon (LMWC) compounds supported 80% (34-95%), 54% (19-90%) and 23% (7-45%) of the secondary production by bacteria, protozoa and metazoa, respectively, in a 7-km2 boreal lake (conservative to liberal estimates in brackets). Bacterial growth on LMWC was of similar magnitude as that of primary production (PP), and grazing on bacteria effectively channelled the LMWC carbon to higher trophic levels. We suggest that rapid turnover of forest LMWC pools enables continuous export of fresh photosynthates and other labile metabolites to aquatic systems, and that substantial transfer of LMWC from terrestrial sources to lake consumers can occur within a few days. Sequestration of LMWC of terrestrial origin, thus, helps explain high shares of terrestrial carbon in lake organisms and implies that lake food webs can be closely dependent on recent terrestrial PP.
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| 4. |
- Bergström, Ann-Kristin, et al.
(author)
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Phytoplankton responses to nitrogen and phosphorus enrichment in unproductive Swedish lakes along a gradient of atmospheric nitrogen deposition
- 2008
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In: Aquatic Biology. - : Inter-Research Science Center. - 1864-7782 .- 1864-7790. ; 4, s. 55-64
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Journal article (peer-reviewed)abstract
- Lake sampling and in situ nutrient enrichment enclosure experiments with nitrogen (N) and phosphorus (P) were conducted in unproductive Swedish lakes along a gradient of increasing atmospheric N-deposition. The regional and seasonal patterns of nutrient limitation of phytoplankton were clearly related to the amounts of N-deposition and N-inputs the lakes received. In areas of low N-deposition in northern Sweden, N-limitation of phytoplankton was evident throughout the summer season due to high catchment N-retention and very low dissolved inorganic N (DIN) inputs during the early summer. High N-deposition in the south was accompanied by high lake DIN-concentrations during the early summer and subsequent P-limitation of phytoplankton. However, P-limitation did not persist over the summer and, as a consequence of a declining DIN-pool, the lakes switched to dual- and co-limitation by N and P, and then to N-limitation. Generally, the lakes were N-limited rather than P-limited during the summer. We conclude that N-limitation is probably a natural state of the unproductive lakes studied, but P-limitation of variable intensity and duration has been induced by elevated atmospheric N-deposition.
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| 5. |
- Jansson, Mats, et al.
(author)
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Impact of allochthonous organic carbon on microbial food web carbon dynamics and structure in Lake Örträsket
- 1999
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In: Archiv für Hydrobiologie. - 0003-9136. ; 144:4, s. 409-428
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Journal article (peer-reviewed)abstract
- Bacterial utilization of allochthonous organic carbon and the subsequent fate of the bacterial production in the pelagic food web were estimated in Lake Örträsket, a large humic lake in northern Sweden. Bacterial production relied mainly on allochthonous DOC and exceeded primary production in the epilimnion. Bacterial productivity was clearly stimulated during high flow episodes, increasing the input of bacteria degradable organic material to the lake. Bacterioplankton were exploited mainly by mixotrophic flagellates which probably used bacteria as a source of carbon, phosphorus and nitrogen. The possibly extremely low availability of inorganic P during periods with high bacterial production may have allowed the mixotrophs to outcompete obligate autotrophs and help them become dominant phytoplankters during large parts of the summer. The results from Lake Örträsket indicated that the total production depended on bacterial energy mobilization from allochthonous organic carbon compounds and that heterotrophic mobilized energy was linked via mixotrophs to higher levels in the food chain.
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| 6. |
- Jansson, Mats, et al.
(author)
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Nutrient limitation of bacterioplankton, autotrophic and mixotrophic phytoplankton, and heterotrophic nanoflagellates in Lake Örträsket
- 1996
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In: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 41:7, s. 1552-1559
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Journal article (peer-reviewed)abstract
- Enrichment experiments with P and N were conducted in humic Lake Örträsket in northern Sweden. The composition of the microplankton community showed a dominance by bacterioplankton, followed by mixotrophic sind potentially mixotrophic phytoplankton, heterotrophic nanoflagellates, and autotrophic phytoplankton. Bacterioplankton was P limited for most of the ice-free period, and phytoplankton biomass and primary production mostly increased after enrichment with N, but not with P. The dominant group of phytoplankton, the mixotrophic flagellates, was stimulated by N bur not by P, while obligate autotrophic species were stimulated only by P+N. It is suggested that N limitation in mixotrophic species is induced by grazing of P-rich bacteria. The results suggest that primary productivity in humic lakes can be limited by N and indicate the importance of phagocytosis as a means of nutrition in phytoplankton. A link is suggested to exist in humic lakes whereby heterotrophic bacterioplankton, which use humic compounds as their principal energy source, can transfer energy and nutrients to potentially autotrophic organisms, with subsequent utilization by other components of the food web.
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| 7. |
- Jonsson, Anders, et al.
(author)
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Integrating aquatic carbon fluxes in a boreal catchment carbon budget
- 2007
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In: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 334:1-2, s. 141-150
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Journal article (peer-reviewed)abstract
- In this paper, we assess the extent to which the export of terrestrially fixed carbon to aquatic systems and the aquatic metabolism of this carbon affect the overall accumulation of organic carbon in a boreal catchment. We estimated the contribution of stocks and processes in aquatic environments to the carbon balance of a boreal catchment in northern Sweden. We used published data concerning the net ecosystem exchange (NEE) of CO2 in terrestrial environments, and calculations of loss of terrestrial carbon to surface water and the turnover of terrestrial carbon in aquatic systems. The NEE of terrestrial environments was estimated to be 139 g C/m2 of catchment area per year. The export of terrestrially fixed carbon to aquatic systems was 8.6 g C/m2/yr, resulting in a net accumulation of organic carbon in terrestrial systems of 131 g C/m2/yr. Almost 45% of the terrestrial export was mineralized in streams and lakes and evaded as CO2, while most of the remaining (approximately 55%) terrestrial export was transported to the sea as organic carbon or as dissolved inorganic carbon emanating from soil respiration. The sedimentation of organic carbon and input of organic carbon via aquatic primary production were insignificant when compared to the mineralization and river transport of terrestrial organic carbon. Aquatic fluxes were small compared to the terrestrial NEE, which we consider to be largely a consequence of the studied catchment being subject to intensive forestry resulting in a large annual accumulation of carbon in growing tree biomass.
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| 8. |
- Jonsson, Anders, et al.
(author)
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Whole-lake mineralization of allochthonous and autochthonous organic carbon in a large humic lake (Örträsket, N. Sweden)
- 2001
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In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 46:7, s. 1691-1700
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Journal article (peer-reviewed)abstract
- Organic carbon mineralization was studied. in a large humic lake (Lake Örträsket) in northern Sweden during a well-defined summer stratification period following high water flow during snowmelt. Several independent methods including plankton counts, measurements of bacterioplankton and phytoplankton production, stable isotope monitoring, sediment trapping, and mass balance calculations were used. Total organic carbon mineralization showed a summer mean of 0.3 g C m(-2) d(-1) and was partitioned about equally between water and sediment. In the water column, organic matter was mineralized by bacteria (60%) and protozoan and metazoan zooplankton (30%), as well as by photooxidation (10%). Most of the mineralized organic carbon was of allochthonous origin. Primary production in the lake contributed at most 5% of the total organic carbon input and about 20% of the total organic carbon mineralization. Total carbon mineralization in. the epilimnion and metalimnion agreed well with an estimate of CO2 evasion from the stratified lake, while CO2 accumulation in the hypolimnion matched the O-2 consumption and resulted in a very negative delta C-13 of DIC before autumn overturn (-23 parts per thousand). Isotopic compositions of DIC and POC confirmed the dominant influence of terrestrial organic input on the cycling of both organic and inorganic carbon in the lake.
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| 9. |
- Pers, C, et al.
(author)
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Modelling dissolved organic carbon turnover in humic Lake Ortrasket, Sweden
- 2001
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In: Environmental Modelling and Assessment. - 1420-2026 .- 1573-2967 .- 0167-6369 .- 1573-2959. ; 6:3, s. 159-172
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Journal article (peer-reviewed)abstract
- The organic carbon balance of a lake with high input of allochthonous organic carbon is modelled integrating physical, chemical and biological processes. The physical model captures the behaviour of real thermal stratification in the lake for different flow situations during the period 1993-1997. The dissolved organic carbon model is based on simulated trajectories of water parcels. By tracking parcels, account is kept of environmental factors such as temperature and radiation as well as DOC quality for each parcel, The DOC concentration shows seasonal variations primarily dependent on inflow. The organic matter degradation (bacterial- and photodegradation) in the lake amounts to 1.5-2.5 mg C l(-1) yr(-1), where photooxidation is responsible for approximately 10%. The estimated DIC production in the lake is large compared to sediment mineralisation and primary production. The main conclusion is that the model with the selected parameterisations of the degradation processes reasonably well describes the DOC dynamics in a forest lake.
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