| 1. |
- Chmiel, Hannah Elisa, 1983-, et al.
(författare)
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The role of sediments in the carbon budget of a small boreal lake
- 2016
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 61:5, s. 1814-1825
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the role of lake sediments as carbon (C) source and sink in the annual C budget of a small (0.07 km2), shallow (mean depth 3.4 m), and humic lake (mean DOC concentration 17 mg L-1) in boreal Sweden. Organic carbon (OC) burial and mineralization in sediments were quantified from 210Pb-dated sediment and laboratory sediment incubation experiments, respectively, and upscaled to the entire basin and to one whole year, by using sediment thickness derived sub-bottom profiling, basin morphometry, and water column monitoring data of temperature and oxygen concentration. Furthermore, catchment C import, open water metabolism, photochemical mineralization as well as carbon dioxide (CO2) and methane (CH4) emissions to the atmosphere, were quantified to relate sediment processes to other lake C fluxes. We found that on a whole-basin and annual scale, sediment OC mineralization was three times larger than OC burial, and contributed about 16% to the annual CO2 emission from the lake to the atmosphere. Remaining contributions to the CO2 emission were attributed to water column metabolism (31%), photochemical mineralization (6%), and catchment imports via inlet streams and inflow of shallow groundwater (47%). We conclude that on an annual and whole-basin scale 1) sediment OC mineralization dominated over OC burial, 2) water column OC mineralization contributed more than sediments to lake CO2 emission, and 3) catchment import of C to the lake was greater than lake-internal C cycling.
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| 2. |
- Fridh, Maria, et al.
(författare)
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Subjective health complaints and exposure to peer victimization among disabled and non-disabled adolescents: A population-based study in Sweden.
- 2018
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Ingår i: Scandinavian journal of public health. - : SAGE Publications. - 1651-1905 .- 1403-4948. ; 46:2
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Tidskriftsartikel (refereegranskat)abstract
- To investigate subjective health complaints (SHCs) (psychological and somatic, respectively) among disabled and non-disabled adolescents, focusing on the impact of traditional bullying and cyber harassment, and furthermore to report psychological and somatic SHCs across different types of disability.Data from the public health survey of children and adolescents in Scania, Sweden, 2012 was used. A questionnaire was answered anonymously in school by 9791 students in the 9th grade (response rate 83%), and 7533 of these with valid answers on key questions were included in this study. Associations with daily SHCs were investigated by multi-adjusted logistic regression analyses.Any disability was reported by 24.1% of boys and 22.0% of girls. Disabled students were more exposed to cyber harassment (boys: 20.0%; girls: 28.2%) than non-disabled peers (boys: 11.8%; girls: 18.1%). Exposure to traditional bullying showed the same pattern but with a lower prevalence. Disabled students had around doubled odds of both daily psychological SHCs and daily somatic SHCs in the fully adjusted models. In general, the odds increased with exposure to cyber harassment or traditional bullying and the highest odds were seen among disabled students exposed to both cyber harassment and traditional bullying. Students with ADHD/ADD had the highest odds of daily psychological SHCs as well as exposure to traditional bullying across six disability types.Disabled adolescents report poorer health and are more exposed to both traditional bullying and cyber harassment. This public health issue needs more attention in schools and in society in general.
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| 3. |
- Gudasz, Cristian, et al.
(författare)
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Temperature sensitivity of organic carbon mineralization in contrasting lake sediments
- 2015
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : American Geophysical Union (AGU). - 2169-8953 .- 2169-8961. ; 120:7, s. 1215-1225
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Tidskriftsartikel (refereegranskat)abstract
- Temperature alone explains a great amount of variation in sediment organic carbon (OC) mineralization. Studies on decomposition of soil OC suggest that (1) temperature sensitivity differs between the fast and slowly decomposition OC and (2) over time, decreasing soil respiration is coupled with increase in temperature sensitivity. In lakes, autochthonous and allochthonous OC sources are generally regarded as fast and slowly decomposing OC, respectively. Lake sediments with different contributions of allochthonous and autochthonous components, however, showed similar temperature sensitivity in short-term incubation experiments. Whether the mineralization of OC in lake sediments dominated by allochthonous or autochthonous OC has different temperature sensitivity in the longer term has not been addressed. We incubated sediments from two boreal lakes that had contrasting OC origin (allochthonous versus autochthonous), and OC characteristics (C/N ratios of 21 and 10) at 1, 3, 5, 8, 13, and 21 degrees C for five months. Compared to soil and litter mineralization, sediment OC mineralization rates were low in spite of low apparent activation energy (E-a). The fraction of the total OC pool that was lost during five months varied between 0.4 and 14.8%. We estimate that the sediment OC pool not becoming long-term preserved was degraded with average apparent turnover times between 3 and 32years. While OC mineralization was strongly dependent on temperature as well as on OC composition and origin, temperature sensitivity was similar across lakes and over time. We suggest that the temperature sensitivity of OC mineralization in lake sediments is similar across systems within the relevant seasonal scales of OC supply and degradation.
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| 4. |
- Köhler, Birgit, et al.
(författare)
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Reactivity continuum modeling of leaf, root, and wood decomposition across biomes
- 2015
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 120:7, s. 1196-1214
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Tidskriftsartikel (refereegranskat)abstract
- Large carbon dioxide amounts are released to the atmosphere during organic matter decomposition. Yet the large-scale and long-term regulation of this critical process in global carbon cycling by litter chemistry and climate remains poorly understood. We used reactivity continuum (RC) modeling to analyze the decadal data set of the Long-term Intersite Decomposition Experiment, in which fine litter and wood decomposition was studied in eight biome types (224 time series). In 32 and 46% of all sites the litter content of the acid-unhydrolyzable residue (AUR, formerly referred to as lignin) and the AUR/nitrogen ratio, respectively, retarded initial decomposition rates. This initial rate-retarding effect generally disappeared within the first year of decomposition, and rate-stimulating effects of nutrients and a rate-retarding effect of the carbon/nitrogen ratio became more prevalent. For needles and leaves/grasses, the influence of climate on decomposition decreased over time. For fine roots, the climatic influence was initially smaller but increased toward later-stage decomposition. The climate decomposition index was the strongest climatic predictor of decomposition. The similar variability in initial decomposition rates across litter categories as across biome types suggested that future changes in decomposition may be dominated by warming-induced changes in plant community composition. In general, the RC model parameters successfully predicted independent decomposition data for the different litter-biome combinations (196 time series). We argue that parameterization of large-scale decomposition models with RC model parameters, as opposed to the currently common discrete multiexponential models, could significantly improve their mechanistic foundation and predictive accuracy across climate zones and litter categories.
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| 5. |
- 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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| 6. |
- Mostovaya, Alina, et al.
(författare)
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Effects of compositional changes on reactivity continuum and decomposition kinetics of lake dissolved organic matter
- 2016
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 121:7, s. 1733-1746
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Tidskriftsartikel (refereegranskat)abstract
- To address the link between the composition and decomposition of freshwater dissolved organic matter (DOM), we manipulated the DOM from three boreal lakes using preincubations with UV light to cleave large aromatic molecules and polyvinylpyrrolidone (PVP) to remove colored phenolic compounds. Subsequently, we monitored the dissolved organic carbon (DOC) loss over 4months of microbial degradation in the dark to assess how compositional changes in DOM affected different aspects of the reactivity continuum, including the distribution of the apparent decay coefficients. We observed profound effects on decomposition kinetics, with pronounced shifts in the relative share of rapidly and more slowly decomposing fractions of the DOM. In the UV-exposed treatment initial apparent decay coefficient k(0) was almost threefold higher than in the control. Significantly higher relative DOC loss in the UV-exposed treatment was sustained for 2months of incubation, after which decay coefficients converged with those in the control. The PVP removed compounds with absorbance and fluorescence characteristics representative of aromatic compounds, which led to slower decomposition, compared to that in the control. Our results demonstrate the reactivity continuum underlying the decomposition of DOM in freshwaters and highlight the importance of intrinsic properties of DOM in determining its decomposition kinetics.
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| 7. |
- Müller, Roger A., et al.
(författare)
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Hourly, daily, and seasonal variability in the absorption spectra of chromophoric dissolved organic matter in a eutrophic, humic lake
- 2014
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Ingår i: Journal of Geophysical Research - Biogeosciences. - 2169-8953 .- 2169-8961. ; 119:10, s. 1985-1998
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Tidskriftsartikel (refereegranskat)abstract
- The short-term (hourly and daily) variation in chromophoric dissolved organic matter (CDOM) in lakes is largely unknown. We assessed the spectral characteristics of light absorption by CDOM in a eutrophic, humic shallow mixed lake of temperate Sweden at a high-frequency (30 min) interval and during a full growing season (May to October). Physical time series, such as solar radiation, temperature, wind, and partial pressures of carbon dioxide in water and air, were measured synchronously. We identified a strong radiation-induced summer CDOM loss (25 to 50%) that developed over 4 months, which was accompanied by strong changes in CDOM absorption spectral shape. The magnitude of the CDOM loss exceeded subhourly to daily variability by an order of magnitude. Applying Fourier analysis, we demonstrate that variation in CDOM remained largely unaffected by rapid shifts in weather, and no apparent response to in-lake dissolved organic carbon production was found. In autumn, CDOM occasionally showed variation at hourly to daily time scales, reaching a maximum daily coefficient of variation of 15%. We suggest that lake-internal effects on CDOM are quenched in humic lake waters by dominating effects associated with imported CDOM and solar exposure. Since humic lake waters belong to one of the most abundant lake types on Earth, our results have important implications for the understanding of global CDOM cycling.
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