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- 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
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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. |
- Algesten, Grete, et al.
(author)
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Organic carbon budget for the Gulf of Bothnia
- 2006
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In: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 63:3-4, s. 155-161
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Journal article (peer-reviewed)abstract
- We calculated input of organic carbon to the unproductive, brackish water basin of the Gulf of Bothnia from rivers, point sources and the atmosphere. We also calculated the net exchange of organic carbon between the Gulf of Bothnia and the adjacent marine system, the Baltic Proper. We compared the input with sinks for organic carbon; permanent incorporation in sediments and mineralization and subsequent evasion of CO2 to the atmosphere. The major fluxes were riverine input (1500 Gg C year(-1)), exchange with the Baltic Proper (depending on which of several possible DOC concentration differences between the basins that was used in the calculation, the flux varied between an outflow of 466 and an input of 950 Gg C year(-1)), sediment burial (1100 Gg C year) and evasion to the atmosphere (3610 Gg C year(-1)). The largest single net flux was the emission of CO2 to the atmosphere, mainly caused by bacterial mineralization of organic carbon. Input and output did not match in our budget which we ascribe uncertainties in the calculation of the exchange of organic carbon between the Gulf of Bothnia and the Baltic Proper, and the fact that CO2 emission, which in our calculation represented 1 year (2002) may have been overestimated in comparison with long-term means. We conclude that net heterotrophy of the Gulf of Bothnia was due to input of organic carbon from both the catchment and from the Baltic Proper and that the future degree of net heterotrophy will be sensible to both catchment export of organic carbon and to the ongoing eutrophication of the Baltic Proper.
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| 4. |
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| 5. |
- 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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| 6. |
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| 7. |
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| 8. |
- Sobek, Sebastian, et al.
(author)
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A carbon budget of a small humic lake : An example of the importance of lakes for organic matter cycling in boreal catchments
- 2006
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In: Ambio. - 0044-7447 .- 1654-7209. ; 35:8, s. 469-475
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Journal article (peer-reviewed)abstract
- Lakes play an important role in the cycling of organic matter in the boreal landscape, due to the frequently high extent of bacterial respiration and the efficient burial of organic carbon in sediments. Based on a mass balance approach, we calculated a carbon budget for a small humic Swedish lake in the vicinity of a potential final repository for radioactive waste in Sweden, in order to assess its potential impact on the environmental fate of radionuclides associated with organic matter. We found that the lake is a net heterotrophic ecosystem, subsidized by organic carbon inputs from the catchment and from emergent macrophyte production. The largest sink of organic carbon is respiration by aquatic bacteria and subsequent emission of carbon dioxide to the atmosphere. Although the annual burial of organic carbon in the sediment is a comparatively small sink, it results in the build-up of the largest carbon pool in the lake. Hence, lakes may simultaneously disperse and accumulate organic-associated radionuclides leaking from a final repository.
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| 9. |
- Sobek, Sebastian, 1973-
(author)
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Carbon Dioxide Supersaturation in Lakes – Causes, Consequences and Sensitivity to Climate Change
- 2005
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Doctoral thesis (other academic/artistic)abstract
- The global carbon cycle is intimately linked with the earth’s climate system. Knowledge about carbon cycling in the biosphere is therefore crucial for predictions of climate change. This thesis investigates the carbon dioxide balance of Swedish boreal lakes, its regulation, significance to the carbon budget of the boreal landscape, and sensitivity to climate change. Swedish boreal lakes were almost exclusively supersaturated in CO2 with respect to the atmosphere, resulting in an emission of CO2 from lakes to the atmosphere. Lake pCO2 was closely related to the concentration of terrigenous dissolved organic carbon (DOC), indicating that the utilization of terrigenous DOC by lake bacteria is a major source of CO2. This conclusion is supported by independent field studies, showing that net plankton respiration accounts for most of the CO2 emitted from Swedish boreal lakes, while photochemical mineralization and sediment respiration were less important. Mineralization of terrigenous DOC and subsequent emission of CO2 from lakes to the atmosphere was a major carbon loss factor in 21 major Swedish boreal catchments, removing 30-80% of the organic carbon exported from terrestrial soils to surface waters. Lake CO2 emission is in the same order of magnitude as organic carbon accumulation in boreal forest soils, and should therefore be included in the carbon budget of the boreal landscape. In a set of nearly 5000 global lakes, DOC concentration was a much more important regulator of lake pCO2 than temperature. Climate change will therefore affect the carbon balance of lakes primarily via alterations in terrestrial DOC export, rather than via changes in temperature per se. Both current observations and models of future climate suggest an increasing export of terrigenous DOC from many Scandinavian catchments. Hence, there probably is a current trend towards higher CO2 emission from Swedish boreal lakes, which is likely to continue in the future.
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| 10. |
- Sobek, Sebastian, et al.
(author)
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Patterns and regulation of dissolved organic carbon : An analysis of 7,500 widely distributed lakes
- 2007
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In: Limnology and Oceanography. - 0024-3590 .- 1939-5590. ; 52:3, s. 1208-1219
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Journal article (peer-reviewed)abstract
- Dissolved organic carbon (DOC) is a key parameter in lakes that can affect numerous features, including microbial metabolism, light climate, acidity, and primary production. In an attempt to understand the factors that regulate DOC in lakes, we assembled a large database (7,514 lakes from 6 continents) of DOC concentrations and other parameters that characterize the conditions in the lakes, the catchment, the soil, and the climate. DOC concentrations were in the range 0.1-332 mg L-1, and the median was 5.71 mg L-1. A partial least squares regression explained 48% of the variability in lake DOC and showed that altitude, mean annual runoff, and precipitation were negatively correlated with lake DOC, while conductivity, soil carbon density, and soil C:N ratio were positively related with lake DOC. A multiple linear regression using altitude, mean annual runoff, and soil carbon density as predictors explained 40% of the variability in lake DOC. While lake area and drainage ratio (catchment:lake area) were not correlated to lake DOC in the global data set, these two factors explained significant variation of the residuals of the multiple linear regression model in several regional subsets of data. These results suggest a hierarchical regulation of DOC in lakes, where climatic and topographic characteristics set the possible range of DOC concentrations of a certain region, and catchment and lake properties then regulate the DOC concentration in each individual lake.
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