| 1. |
- Škerlep, Martin, et al.
(författare)
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Spruce forest afforestation leading to increased Fe mobilization from soils
- 2022
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 157:3, s. 273-290
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Tidskriftsartikel (refereegranskat)abstract
- Increasing exports of Fe and DOC from soils, causing browning of freshwaters, have been reported in recent decades in many regions of the northern hemisphere. Afforestation, and in particular an increase of Norway spruce forest in certain regions, is suggested as a driver behind these trends in water chemistry. In this study, we tested the hypothesis that the gradual accumulation of organic soil layers in spruce forests, and subsequent increase in organic acid concentrations and acidity enhances mobilization of Fe. First generation Norway spruce stands of different ages (35, 61, 90 years) and adjacent arable control plots were selected to represent the effects of aging forest. Soil solutions were sampled from suction lysimeters at two depths (below organic soil layer and in mineral soil) during two years, and analyzed for Fe concentration, Fe speciation (XAS analysis), DOC, metals, major anions and cations. Solution Fe concentrations were significantly higher in shallow soils under older spruce stands (by 5- and 6-fold) than in control plots and the youngest forest. Variation in Fe concentration was best explained by variation in DOC concentration and pH. Moreover, Fe in all soil solutions was present as mononuclear Fe(III)-OM complexes, showing that this phase is dominating Fe translocation. Fe speciation in the soil was also analyzed, and found to be dominated by Fe oxides with minor differences between plots. These results confirmed that Fe mobilization, by Fe(III)-OM complexes, was higher from mature spruce stands, which supports that afforestation with spruce may contribute to rising concentrations of Fe in surface waters.
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| 2. |
- Andersson, Erik, et al.
(författare)
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Ambio fit for the 2020s
- 2022
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Ingår i: Ambio. - : Springer Nature. - 0044-7447 .- 1654-7209. ; 51:5, s. 1091-1093
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Tidskriftsartikel (refereegranskat)
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| 3. |
- Björnerås, Caroline, et al.
(författare)
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High sulfate concentration enhances iron mobilization from organic soil to water
- 2019
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 0168-2563 .- 1573-515X. ; 144:3, s. 245-259
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Tidskriftsartikel (refereegranskat)abstract
- Widespread increases in iron (Fe) concentrations are contributing to ongoing browning of northern freshwaters, but the driver/s behind the trends are not known. Fe mobilization in soils is known to be controlled by redox conditions, pH, and DOC availability for complexation. Moreover, high sulfate concentrations have been suggested to constrain Fe in transition from soil to water, and declining sulfate deposition to have the opposite effect. We studied the effect of these Fe mobilization barriers in a microcosm experiment, applying high (peak S deposition) and low (present day) sulfate treatments and oxic versus anoxic conditions to boreal (O horizon) soil slurries. We hypothesized that anoxic conditions would favor Fe release. On the contrary we expected high sulfate concentrations to suppress Fe mobility, through FeS formation or by lowering pH and thereby DOC concentrations. Anoxia had positive effects on both Fe and DOC concentrations in solution. Contrasting with our hypothesis, Fe concentrations were enhanced at high sulfate concentrations, i.e. increasing acidity in high sulfate treatments appeared to promote Fe mobilization. Establishment of the basidiomycete fungus Jaapia ochroleuca in the oxic treatments 44 days into the experiment had a major impact on Fe mobilization by increasing total Fe concentrations in solution. Thus, anoxia and acidity, along with fungi mediated mobilization, were important in controlling Fe release from soil to the aqueous phase. While Fe is often assumed to precipitate as Fe(oxy)hydroxides in the transition from anoxic to oxic water in the riparian zone, Fe from anoxic treatments remained in solution after introduction of oxygen. Our results do not support reduced atmospheric S deposition as a driver behind increasing Fe concentrations in boreal freshwaters, but confirm the importance of reducing conditions—which may be enhanced by higher soil temperature and moisture—for mobilization of Fe across the terrestrial-aquatic interphase.
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| 4. |
- Ekström, Sara, et al.
(författare)
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Effect of Acid Deposition on Quantity and Quality of Dissolved Organic Matter in Soil-Water.
- 2011
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Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 1520-5851 .- 0013-936X. ; 45:11, s. 4733-4739
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to explore how acid deposition may affect the concentration and quality of dissolved organic matter (DOM) in soil-water. This was done by a small-scale acidification experiment during two years where 0.5 × 0.5 m(2) plots were artificially irrigated with water with different sulfuric acid content, and soil-water was sampled using zero-tension lysimeters under the O-horizon. The DOM was characterized using absorbance, fluorescence, and size exclusion chromatography analyses. Our results showed lower mobility of DOM in the high acid treatment. At the same time, there was a significant change in the DOM quality. Soil-water in the high acid treatment exhibited DOM that was less colored, less hydrophobic, less aromatic, and of lower molecular weight, compared to the low acid treatment. This supports the hypothesis that reduction in sulfur deposition is an important driver behind the ongoing brownification of surface waters in many regions.
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| 5. |
- Ekström, Sara M., et al.
(författare)
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Reactivity of dissolved organic matter in response to acid deposition
- 2016
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Ingår i: Aquatic Sciences. - : Springer. - 1015-1621 .- 1420-9055. ; 78:3, s. 463-475
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Tidskriftsartikel (refereegranskat)abstract
- Fluvial export of organic matter from the terrestrial catchment to the aquatic system is a large and increasing carbon flux. The successful reduction in sulfuric acid deposition since the 1980s has been shown to enhance the mobility of organic matter in the soil, with more terrestrially derived dissolved organic matter (DOM) reaching aquatic systems. Changes in soil acidity also affect the quality of the DOM. In this study we explore the consequences this may have on the reactivity and turnover of the terrestrially derived DOM as it reaches the aquatic system. DOM of different quality (estimated by absorbance, fluorescence and size exclusion chromatography) was produced through extraction of boreal forest O-horizon soils from podzol at two sulfuric acid concentrations corresponding to natural throughfall in spruce forest in Southern Sweden around 1980 and today. Extraction was done using two different methods, i.e. field leaching and laboratory extraction. The DOM extracts were used to assess if differences in acidity generate DOM of different reactivity. Three reactivity experiments were performed: photodegradation by UV exposure, biodegradation by bacteria, and biodegradation after UV exposure. Reactivity was assessed by measuring loss of dissolved organic carbon and absorbance, change in fluorescence and molecular weight, and bacterial production. DOM extracted at lower sulfuric acid concentration was more susceptible to photooxidation, and less susceptible to bacterial degradation, than DOM extracted at a higher sulfuric acid concentration. Thus the relative importance of these two turnover processes may be altered with changes in acid deposition.
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| 6. |
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| 7. |
- Logue, Jürg Brendan, et al.
(författare)
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Experimental insights into the importance of aquatic bacterial community composition to the degradation of dissolved organic matter
- 2016
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 10:3, s. 533-545
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Tidskriftsartikel (refereegranskat)abstract
- Bacteria play a central role in the cycling of carbon, yet our understanding of the relationship between the taxonomic composition and the degradation of dissolved organic matter (DOM) is still poor. In this experimental study, we were able to demonstrate a direct link between community composition and ecosystem functioning in that differently structured aquatic bacterial communities differed in their degradation of terrestrially derived DOM. Although the same amount of carbon was processed, both the temporal pattern of degradation and the compounds degraded differed among communities. We, moreover, uncovered that low-molecular-weight carbon was available to all communities for utilisation, whereas the ability to degrade carbon of greater molecular weight was a trait less widely distributed. Finally, whereas the degradation of either low-or high-molecular-weight carbon was not restricted to a single phylogenetic clade, our results illustrate that bacterial taxa of similar phylogenetic classification differed substantially in their association with the degradation of DOM compounds. Applying techniques that capture the diversity and complexity of both bacterial communities and DOM, our study provides new insight into how the structure of bacterial communities may affect processes of biogeochemical significance.
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| 8. |
- Meklesh, Viktoriia, et al.
(författare)
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Characterization of the Colloidal Properties of Dissolved Organic Matter From Forest Soils
- 2022
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Ingår i: Frontiers in Soil Science. - : Frontiers Media SA. - 2673-8619.
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Tidskriftsartikel (refereegranskat)abstract
- Components of dissolved organic matter (DOM) span from sub-nm molecules to colloidal aggregates of several hundred nm. The colloidal fraction is important for the transport of organic matter and associated elements in the environment, and for the stability of DOM constituents with respect to microbial decomposition. This study focuses on the colloidal properties of DOM extracted from spruce forest soils of a chronosequence. The DOM samples were obtained by common water extraction procedures at 21 and 100°C, respectively. We applied an experimental approach combining chemical analysis with light and X-ray scattering techniques that informed on the colloidal size, charge, and structure of DOM. Results showed that two main types of colloids were present: semi-flexible cylinders and fractal aggregates. The cylinders consisted of carbohydrates, presumably hemicelluloses, while the aggregates were a composite material containing a large fraction of carbohydrates together with aliphatics and clay particles. These fractal aggregates dominated the cold-water extracts whereas the strong increase in total organic carbon by hot-water extraction caused a concomitantly strong increase of semi-flexible cylinders, which became the predominant species. Comparison between the chronosequence soils showed that with increasing forest age, the amount of carbon extracted per gram of soil declined and the concentration of the semi-flexible cylinders decreased. Thus, the distribution between the fractal aggregates and cylinders in the forest soil DOM samples depends on the composition of the soil organic matter and the leaching temperature. Changes in this distribution may have important implications for the reactivity and stability of DOM colloids.
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| 9. |
- Östman, Örjan, et al.
(författare)
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Regional invariance among microbial communities
- 2010
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 13:1, s. 118-127
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Tidskriftsartikel (refereegranskat)abstract
- Microbial ecology has focused much on causes of between-site variation in community composition. By analysing five data-sets each of aquatic bacteria and phytoplankton, we demonstrated that microbial communities show a large degree of similarity in community composition and that abundant taxa were widespread, a typical pattern for many metazoan metacommunities. The regional abundance of taxa explained on average 85 and 41% of variation in detection frequency and 58 and 31% of variation in local abundances for bacteria and phytoplankton, respectively. However, regional abundance explained less variation in local abundances with increasing environmental variation between sites within data-sets. These findings indicate that the studies of microbial assemblages need to consider similarities between communities to better understand the processes underlying the assembly of microbial communities. Finally, we propose that the degree of regional invariance can be linked to the evolution of microbes and the variation in ecosystem functions performed by microbial communities.
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