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- Hansson, Sophia V., 1981-
(författare)
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Incorporation and preservation of geochemical fingerprints in peat archives
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present status of the environment, including environmental problems such as heavy metal accumulation in aquatic and terrestrial ecosystems, is in part the consequence of long-term changes. Cores from peatlands and other natural archives provide us with the potential to study aspects of the atmospheric cycling of elements, such as metal pollutants, on timescales much longer than the decade or two available to us with atmospheric deposition monitoring programs. The past decade especially has seen a rapid increase in interest in the biogeochemical record preserved in peat, particularly as it relates to environmental changes (e.g. climate and pollution). Importantly, recent studies have shown that carbon dynamics, i.e., organic matter decomposition, may influence the record of atmospherically derived elements such as halogens and mercury. Other studies have shown that under certain conditions some downward movement of atmospherically deposited elements may also occur, which adds complexity to establishing reliable chronologies as well as inherent problems of estimating accurate accumulation rates of peat and past metal deposition. Thus, we still lack a complete understanding of the basic biogeochemical processes and their effects on trace element distributions. While many studies have validated the general temporal patterns of peat records, there has been a limited critical examination of accumulation records in quantitative terms. To be certain that we extract not only a qualitative record from peat, it is important that we establish a quantitative link between the archive and the few to several decades of data that are available from contemporary monitoring and research. The main objective of this doctoral thesis was to focus on improving the link between the long-term paleorecord and the contemporary monitoring data available from biomonitoring and direct deposition observations. The main research questions have therefore been: Are peat archives an absolute or relative record? And how are geochemical signals, including dating, incorporated in the peat archive? What temporal resolution is realistic to interpret by using peat cores?
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| 2. |
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| 3. |
- Kylander, Malin, 1977-, et al.
(författare)
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Natural lead isotope variations in the atmosphere
- 2010
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 290:1-2, s. 44-53
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Tidskriftsartikel (refereegranskat)abstract
- Stable lead (Pb) isotope data from pre-contamination peat sections has the potential to contribute to our understanding of earth system processes (e.g., atmospheric circulation, erosion, volcanic activity) in the past. Key questions arise however. Can the Pb isotopes archived in peat records be used for assessing aerosol dynamics on a hemispheric scale or do they mainly reflect inputs from local soils? What natural Pb sources are important and do contributions vary over time? In order to answer these questions we have synthesized all available Pb isotope data from pre-contamination peat sections in Europe, Australia, North America and South America. We specifically examine the spatial and temporal variability of the Pb isotope records and identify regionally important trends and Pb sources. A pooling of all available pre-contamination peat data generated an average natural 206Pb/207Pb background ratio of 1.21±0.05 (2σ, n=300)(206Pb/204Pb= 18.90±0.86, 207Pb/204Pb= 15.66±0.10 and 208Pb/204Pb= 38.74±0.57, n=207). The majority of the records showed limited temporal and compositional agreement, suggesting that the peat record receives mainly inputs from local (<10 km) and/or regional (10-500 km) sources. Three-isotope plots also support local and regional control and evidence a wide natural spread at some sites, particularly those located in radiogenic geological settings. A temporally synchronous isotope excursion to values between 1.16-1.18 at sites across Europe ca 4000-3000 B.C. was detected, however. While usually associated with anthropogenic sources, there are indeed natural aerosols having 206Pb/207Pb signatures as low as 1.16 as evidenced in several peat and ice core records globally. Three-isotope plots suggest that this unlikely to be a signal of mineral dust contributions, which tend to have 206Pb/207Pb ratios ≥1.19, but rather sourced to volcanic emissions. These results stress caution when using estimates of the upper continental crust to constrain natural Pb sources in, e.g., mixing equations. Considering the strong influence from local and regional sources on Pb-containing aerosols in the peat record, the assessment of aerosol dynamics at lower latitudes is likely best achieved using a compliment of archives rather than just polar ice cores, for example.
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| 4. |
- Rauch, Sebastien, 1971, et al.
(författare)
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Anthropogenic Forcings on the Surficial Osmium Cycle
- 2010
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 44:3, s. 881-887
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Tidskriftsartikel (refereegranskat)abstract
- Osmium is among the least abundant elements in the Earth's continental crust. Recent anthropogenic Os contamination of the environment from mining and smelting activities, automotive catalytic converter use, and hospital discharges has been documented. Here we present evidence for anthropogenic overprinting of the natural Os cycle using a ca. 7000-year record of atmospheric Os deposition and isotopic composition from an ombrotrophic peat bog in NW Spain. Preanthropogenic Os accumulation in this area is 0.10 +/- 0.04 ng m(-2) y(-1). The oldest strata showing human influence correspond to early metal mining and processing on the Iberian Peninsula (ca. 4700-2500 cal. BP). Elevated Os accumulation rates are found thereafter with a local maximum of 1.1 ng m(-2) y(-1) during the Roman occupation of the Iberian Peninsula (ca. 1930 cal. BP)and a further increase starting in 1750 AD with Os accumulation reaching 30 ng m(-2) y(-1) in the most recent samples. Osmium isotopic composition (Os-187/Os-188) indicates that recent elevated Os accumulation results from increased input of unradiogenic Os from industrial and automotive sources as well as from enhanced deposition of radiogenic Os through increased fossil fuel combustion and soil erosion. We posit that the rapid increase in catalyst-equipped vehicles, increased fossil fuel combustion, and changes in land-use make the changes observed in NW Spain globally relevant.
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| 5. |
- Rodríguez, Nathalie Pérez
(författare)
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Biotic and abiotic isotope fractionation of copper and iron : From the lab to the field scale
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The distribution of the stable isotopes of Cu and Fe in nature is susceptible to isotope fractionation processes during the biogeochemical cycle. Since Cu and Fe are redox sensitive metals, differences in their oxidation states can lead to variations in the stable isotope composition of the aquatic species or compounds that they form. Stable isotopes of Cu and Fe have recently been used to trace metal redox cycles, nutrient pathways, metal contaminant sources and to develop isotopic biosignatures. The objective of this project was to study the geochemical processes governing the isotopic fractionation of Cu and Fe in mine impacted sites, including processes related to mineral processing. One of the key questions was to explain the role of bacteria in the variations of the isotopic composition of Cu and Fe. First, bioleaching and electroleaching of a chalcopyrite concentrate were performed. During the chalcopyrite leaching in both experiments the first release of Cu to the leachate is enriched in the heavier Cu isotope as a product of oxidative dissolution. At the later stages of leaching, the δ65Cu values for the leachate are similar to the initial material, confirming an equilibrium fractionation in a closed system. In the case of Fe isotope fractionation the dissolution of pyrite at redox potentials higher than 600mV leads to an enrichment of the heavier Fe isotope in the leachate in the bioleaching experiment, mainly regulated by the formation of secondary minerals such as jarosite. Soil bacteria were studied in three different experimental scales using pot, lysimeters and field experiments, amended with autochthonous plant growth promoting bacteria. Roots and plants from pots showed no variation in their Fe and Cu isotope composition compared to non-amended samples. However, plants growing in the amended substrates regardless of their experimental scale, showed variations in the Fe and Cu isotope composition of their roots with an increase in the heavier Cu isotope. Siderophores released either by bacteria or the plant can complexate available Cu and Fe in the soil, causing a change in the isotope fractionation of those metals. The second question is related to the biogeochemical cycle of Cu and Fe. In mine tailings the sulphide oxidation resulted in an enrichment of the lighter Cu isotope in secondary phases in the oxidized zone of the tailings compared to the original isotope composition in the unoxidised mineral. Precipitation of covellite at the oxidation front of the tailings profile resulted in a significant enrichment of the lighter Cu isotope in the bulk soil with a δ65Cu value as low as -4.35 ±0.02 ‰. Fe isotope fractionation in the Kristineberg test cell varied due to processes such as Fe(II)-Fe(III) equilibrium and precipitation of Fe-(oxy)hydroxides at the oxidation front, where δ56Fe values were higher than in the initial material. As a way to link the obtained results from this thesis, a self-restored mine site was studied. A variation towards higher δ65Cu values was seen from rocks, to water and biofilms. Cu absorption mainly by extrapolymeric substances and secondary mineral precipitation regulates the isotopic composition of the biofilm. Oxidative weathering of sulphide minerals and further precipitation of Fe-(oxy)hydroxides are considered to be the main causes for Fe isotope fractionation in this area. Summing up, this thesis provides several field studies to corroborate the data observed in the lab regarding processes that are important for the biogeochemical cycling of metals and could be further applied to the extraction of metals or for remediation purposes.
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