| 1. |
- Tranvik, Lars J., et al.
(författare)
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Lakes and reservoirs as regulators of carbon cycling and climate
- 2009
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 54:6:2, s. 2298-2314
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Forskningsöversikt (refereegranskat)abstract
- We explore the role of lakes in carbon cycling and global climate, examine the mechanisms influencing carbon pools and transformations in lakes, and discuss how the metabolism of carbon in the inland waters is likely to change in response to climate. Furthermore, we project changes as global climate change in the abundance and spatial distribution of lakes in the biosphere, and we revise the estimate for the global extent of carbon transformation in inland waters. This synthesis demonstrates that the global annual emissions of carbon dioxide from inland waters to the atmosphere are similar in magnitude to the carbon dioxide uptake by the oceans and that the global burial of organic carbon in inland water sediments exceeds organic carbon sequestration on the ocean floor. The role of inland waters in global carbon cycling and climate forcing may be changed by human activities, including construction of impoundments, which accumulate large amounts of carbon in sediments and emit large amounts of methane to the atmosphere. Methane emissions are also expected from lakes on melting permafrost. The synthesis presented here indicates that (1) inland waters constitute a significant component of the global carbon cycle, (2) their contribution to this cycle has significantly changed as a result of human activities, and (3) they will continue to change in response to future climate change causing decreased as well as increased abundance of lakes as well as increases in the number of aquatic impoundments.
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| 2. |
- Guillemette, Francois, et al.
(författare)
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Preferential sequestration of terrestrial organic matter in boreal lake sediments
- 2017
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : AMER GEOPHYSICAL UNION. - 2169-8953 .- 2169-8961. ; 122:4, s. 863-874
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Tidskriftsartikel (refereegranskat)abstract
- The molecular composition and origin has recently been demonstrated to play a critical role in the persistence of organic matter in lake water, but it is unclear to what degree chemical attributes and sources may also control settling and burial of organic matter in lake sediments. Here we compared the annual contribution of allochthonous and autochthonous sources to the organic matter settling in the water column and present in the sediments of 12 boreal lakes. We used the fluorescence properties and elemental composition of the organic matter to trace its origin and found a consistent pattern of increasing contribution of terrestrial compounds in the sediments as compared to the settling matter, with an annual average allochthony of similar to 87% and similar to 57%, respectively. Seasonal data revealed a predominance of in-lake-produced compounds sinking in the water column in summer. Yet only a slight concurrent decrease in the contribution of terrestrial C to lake sediments was observed during the same period, and sediment allochthony increased again to high levels in autumn. Our results reveal a preferential preservation of allochthonous matter in the sediments and highlight the role of lakes as sequesters of organic carbon primarily originating from the surrounding landscape.
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| 3. |
- Kothawala, Dolly N., et al.
(författare)
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Selective loss and preservation of lake water dissolved organic matter fluorescenceduring long-term dark incubations
- 2012
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Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697 .- 1879-1026. ; 433, s. 238-246
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Tidskriftsartikel (refereegranskat)abstract
- The biogeochemical processing of dissolved organic matter (DOM) in inland waters is inherently related to its molecular structure and ecological function. Controlled bioassays are a valuable tool to analyze these relationships, but are seldom conducted and compared at temporal scales that typically prevail in natural inland waters. Here we incubated water from six boreal lakes in the dark and examined changes to the initial fluorescence and absorbance after 3.5 years. We identified five fluorescence components with parallel factor (PARAFAC) analysis (CC, CM, CA, CX and CT) and found a consistent change in the relative intensity of two dominant PARAFAC components (increase in CA:CC, corresponding to Peak A:Peak C), commonly found in lake water, that represent terrestrially-derived DOM. Surprisingly, we only found minor changes to specific absorbance (SUVA), and did not find any changes to other spectral indexes including the fluorescence index, humification index and freshness index. By incorporating lakes spanning a wide range of initial total organic carbon concentrations (3.7 to 32.5 mg L− 1), water residence times, and spectral characteristics (e.g. SUVA 1.13 to 3.77 L·mg C− 1·m− 1), we found that the relative intensities of two humic-like peaks were the most revealing of changes to DOM structure during dark incubations. We also verified that inner filter effects were adequately corrected within the concentration range of incubated samples. Thus, the processing of DOM under dark conditions, including microbial decomposition and flocculation, may have a greater influence on the humic-like peaks, particularly CC (Peak C), with negligible changes to more commonly used spectral indexes.
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| 4. |
- Köhler, Birgit, et al.
(författare)
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Reactivity continuum of dissolved organic carbon decomposition in lake water
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. G01024-
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Tidskriftsartikel (refereegranskat)abstract
- We determined microbial decomposition of dissolved organic carbon (DOC) over 3.7-year long dark bioassays of six Swedish lake waters. The overall lost DOC fraction was similar in clearwater lakes (34.8 {plus minus} 2.4%) and brownwater lakes (37.8 {plus minus} 1.9%). Reactivity continuum modeling revealed that the most labile DOC fraction, degrading at rates >0.01 day-1, was larger in the clearwater (11.1 {plus minus} 1.2%) than the brownwater lakes (0.8 {plus minus} 0.1%). The initial apparent first-order decay coefficients k was fivefold larger in the clearwater (0.0043 {plus minus} 0.0012 day-1) than the brownwater lakes (0.0009 {plus minus} 0.0003 day-1). Over time, k decreased more steeply in the clearwater than the brownwater lakes, reaching the k of the brownwater lakes within five months. Finally, k averaged 0.0001 day-1 in both lake categories. In the brownwater lakes, CDOM absorption decayed with an initial k twice as large (0.0018 {plus minus} 0.0008 day-1) as that of DOC. The initial k was inversely correlated with initial specific UV absorption and colored dissolved organic matter (CDOM) absorption, and positively correlated with initial tryptophan-like fluorescence as proxy for autochthonous DOC. Exposure to simulated sunlight at the end of the incubations caused loss of color in the clearwater lakes and loss of DOC in the brownwater lakes, where subsequent mineralization was also stimulated. The DOC lost in the absence of photochemical processes fell below previously reported watershed-scale losses in Sweden by 25% at most. This suggests that a major part of the in situ DOC loss could potentially be attributed to dark reactions alone.
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| 5. |
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| 6. |
- Premke, Katrin, et al.
(författare)
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Stable isotope analysis of benthic fauna and their food sources in boreal lakes
- 2010
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Ingår i: Journal of The North American Benthological Society. - : University of Chicago Press. - 0887-3593 .- 1937-237X. ; 29:4, s. 1339-1348
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Tidskriftsartikel (refereegranskat)abstract
- The origin of organic C supporting zoobenthic communities in 8 boreal lakes with different concentrations of dissolved organic C (DOC) was assessed by stable-isotope analysis. Profundal zoobenthos was depleted in C-13 compared to littoral zoobenthos, and this difference increased with decreasing DOC concentration. The delta C-13 of littoral zoobenthos suggested reliance on benthic algae, whereas depleted C-13 of profundal zoobenthos could be explained by contributions from allochthonous and autochthonous C sources. In deeper lakes, profundal zoobenthos diets also included C processed by methanotrophic bacteria. Littoral zoobenthos delta C-13 decreased with increasing DOC concentration in the lake water. Our results suggest that littoral benthic fauna are mainly supported by benthic algae in low-DOC lakes and by phytoplankton and allochthonous organic C in high-DOC lakes and that this difference is a result of light absorbance and energy supply by allochthonous organic C. Increasing allochthonous DOC inputs, as expected in a warmer and wetter climate, might reduce benthic algal production and alter the organic C base for benthic food webs in lake ecosystems.
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| 7. |
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