| 51. |
- Yu, Changxun, 1983-, et al.
(författare)
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Iron speciation and valence in the upper 1 km of fractured crystalline bedrock on the Baltic shield
- 2017
-
Ingår i: Goldschmidt2017 Abstracts.
-
Konferensbidrag (refereegranskat)abstract
- The widespread networks of open water-conducting fractures in crystalline bedrock are covered by a variety of Fe-bearing minerals. Quantitative information on Fe mineralogy and valence of these minerals is of great importance not only in constraining the biogeochemical cycle of Fe and other related elements in this largely unexplored space, but also in evaluating the mineralogical capacity to reduce oxygen which is one of the key issues in the risk assessment of nuclear waste repositories. Here, we studied Fe mineralogy and valence in fracture coatings, fresh rocks and altered rocks in the upper 1 km of fractured crystalline bedrock at two sites (Laxemar and Forsmark areas, Sweden) on the Baltic shield. Fe3+/∑Fe ratios in these materials were quantified based on the centroid position of the pre-edge feature on Fe XANES spectra, while the speciation of Fe was predicted by reconstructing the sample EXFAS spectra using a linear combination of a large dataset of reference spectra collected previously[1] and in this study. The results were compared with Mössbauer spectra. The fresh and altered rocks showed no systematic difference in Fe3+/∑Fe ratio, indicating that past hydrothermal activities (red-staining on fracture wall-rock) did not lead to a reduction in reducing capacity within the fracture networks. The fracture coatings from the Forsmark area are of clear hydrothermal character (as indicated by an abundance of hematite, hornblende and muscovite) and have not experienced the same degree of low-T oxidative weathering as the samples from the Laxemar area having frequent and abundant illite and ferrihydrite. However, Fe3+/∑Fe ratios of the fracture coatings from the two areas showed similar features, including no depth trend and a similar variability from 0.24-0.85 and 0.12-0.71 which are overall larger than the fresh and altered rocks. This suggests that regional geological events can have a significant impact on the speciation of Fe, but not Fe valence.
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| 52. |
- Yu, Changxun, 1983-, et al.
(författare)
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Iron‑sulfur geochemistry and acidity retention in hydrologically active macropores of boreal acid sulfate soils : Effects of mitigation suspensions of fine-grained calcite and peat
- 2023
-
Ingår i: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 856:Part 2
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Tidskriftsartikel (refereegranskat)abstract
- Acid sulfate soils discharge large amounts of sulfuric acid along with toxic metals, deteriorating water quality and ecosystem health of recipient waterbodies. There is thus an urgent need to develop cost-effective and sustainable measures to mitigate the negative effects of these soils. In this study, we flushed aseptically-prepared MQ water (reference) or mitigation suspensions containing calcite, peat or a combination of both through 15-cm-thick soil cores from an acid sulfate soil field in western Finland, and investigated the geochemistry of Fe and S on the surfaces of macropores and in the solid columnar blocks (interiors) of the soil columns. The macropore surfaces of all soil columns were strongly enriched in total and HCl-extractable Fe and S relative to the interiors, owing to the existence of abundant Fe oxyhydroxysulfates (schwertmannite and partly jarosite) as yellow-to-brownish surface-coatings. The dissolution/hydrolysis of Fe oxyhydroxysulfates (predominantly jarosite) on the macropore surfaces of the reference columns, although being constantly flushed, effectively buffered the permeates at pH close to 4. These results suggest that Fe oxyhydroxysulfates accumulated on the macropore surfaces of boreal acid sulfate soils can act as long-lasting acidification sources. The treatments with mitigation suspensions led to a (near-)complete conversion of jarosite to Fe hydroxides, causing a substantial loss of S. In contrast, we did not observe any recognizable evidence indicating transformation of schwertmannite. However, sulfate sorbed by this mineral might be partially lost through anion-exchange processes during the treatments with calcite. No Fe sulfides were found in the peat-treated columns. Since Fe sulfides can support renewed acidification events, the moderate mineralogical changes induced by peat are desirable. In addition, peat materials can act as toxic-metal scavengers. Thus, the peat materials used here, which is relatively cheap in the boreal zone, is ideal for remediating boreal acid sulfate soils and other similar jarosite-bearing soils.
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| 53. |
- Yu, Changxun, et al.
(författare)
-
Manganese accumulation and solid-phase speciation in a 3.5 m thick mud sequence from the estuary of an acidic and Mn-rich creek, northern Baltic Sea
- 2016
-
Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 437, s. 56-66
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Tidskriftsartikel (refereegranskat)abstract
- In sediments, manganese (Mn) is typically enriched in the form of authigenic Mn hydroxides at the water-sediment interface where intensive redox cycling of Mn occurs. Here we show, based on existing hydrochemical and geochemical (sediment core) data and new detailed chemical and mineralogical characterization of a 3.5 m long sediment core from a Boreal estuary, that the behavior of Mn can be profoundly different and more complex in estuarine settings receiving an abundance of terrestrial Mn. The most notable feature in the 3.5 m long sediment core is two depth intervals (60-155 cm and 181-230 cm) where there are strong fine-scale variations in Mn concentrations with peaks episodically reaching up to 10-25 g kg(-1) and 6.7-12 g kg(-1), respectively. X-ray absorption spectroscopy and sequential chemical extraction show that Mn occurs mainly as authigenic rhodochrosite at these two depth intervals and is mainly surface-sorbed in other sections with relatively low and stable Mn concentrations. The data suggests that the strong fine-scale variations in Mn concentrations are a reflection of the extent of formation and settling of Mn hydroxides, the precursors of the authigenic rhodochrosite (and also of the surface-sorbed Mn), rather than Mn input to the estuary or redox-related Mn translocation within the sediment. There was agreement between the results of linear combination fitting of extended X-ray absorption fine structure data and a 7-step sequential chemical extraction (SCE) in terms of quantification of surface-sorbed Mn species, whereas the SCE experiment failed to fractionate a majority of rhodochrosite into SCE step-2 (1M NH4-acetate at pH 6), which is frequently employed to dissolve carbonate. We ascribe this discrepancy to only partial dissolution of rhodochrosite in the weakly acidic (pH = 6) NH4-acetate leach.
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| 54. |
- Yu, Changxun, 1983-, et al.
(författare)
-
Manganese cycling and transport in boreal estuaries impacted by acidic Mn-rich drainage
- 2024
-
Ingår i: GEOCHIMICA ET COSMOCHIMICA ACTA. - : Elsevier. - 0016-7037 .- 1872-9533 .- 0046-564X. ; 365, s. 136-157
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Tidskriftsartikel (refereegranskat)abstract
- As critical transition zones between the land and the sea, estuaries are not only hotspots of hydrogeochemical and microbial processes/reactions, but also play a vital role in processing and transferring terrestrial fluxes of metals and nutrients to the sea. This study focused on three estuaries in the Gulf of Bothnia. All of them expe-rience frequent inputs of acidic and Mn/metal-rich creek waters due to flushing of acid sulfate soils that are widespread in the creeks catchments. Analyzing existing long-term water chemistry data revealed a strong sea-sonal variation of Mn loads, with the highest values in spring (after snow melt) and autumn (after heavy rains). We sampled surface waters, suspended particulate matter (SPM), and sediments from the estuarine mixing zones and determined the loads and solid-phase speciation of Mn as well as the composition and metabolic potentials of microbial communities. The results showed that the removal, cycling, and lateral transport of Mn were governed by similar phases and processes in the three estuaries. Manganese X-ray absorption spectroscopy data of the SPM suggested that the removal of Mn was regulated by silicates (e.g., biotite), organically complexed Mn(II), and MnOx (dominated by groutite and phyllomanganates). While the fractional amounts of silicate-bound Mn(II) were overall low and constant throughout the estuaries, MnOx was strongly correlated with the Mn loadings of the SPM and thus the main vector for the removal of Mn in the central and outer parts of the estuaries, along with organically complexed Mn(II). Down estuary, both the fractional amounts and average Mn oxidation state of the MnOx phases increased with (i) the total Mn loads on the SPM samples and (ii) the relative abundances of several potential Mn-oxidizing bacteria (Flavobacterium, Caulobacter, Mycobacterium, and Pedobacter) in the surface waters. These features collectively suggested that the oxidation of Mn, probably mediated by the potential Mn-oxidizing microorganisms, became more extensive and complete towards the central and outer parts of the es-tuaries. At two sites in the central parts of one estuary, abundant phyllomanganates occurred in the surface sediments, but were converted to surface-sorbed Mn(II) phases at deeper layers (>3-4 cm). The occurrence of phyllomanganates may have suppressed the reduction of sulfate in the surface sediments, pushing down the methane sulfate transition zone that is typically shallow in estuarine sediments. At the outermost site in the estuary, deposited MnOx were reduced immediately at the water-sediment interface and converted most likely to Mn carbonate. The mobile Mn species produced by the Mn reduction processes (e.g., aqueous Mn(II) and ligand complexed Mn(III)) could partly diffuse into the overlying waters and, together with the estuarine Mn loads carried by the surface waters, transfer large amounts of reactive Mn into open coastal areas and subsequently contribute to Mn shuttling and inter-linked biogeochemical processes over the seafloor. Given the widespread occurrence of acid sulfate soils and other sulfidic geological materials on many coastal plains worldwide, the identified Mn attenuation and transport mechanisms are relevant for many estuaries globally.
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| 55. |
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| 56. |
- Yu, Changxun, 1983-, et al.
(författare)
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Micro-scale isotopic variability of low-temperature pyrite in fractured crystalline bedrock ― A large Fe isotope fractionation between Fe(II)aq/pyrite and absence of Fe-S isotope co-variation
- 2019
-
Ingår i: Chemical Geology. - : Elsevier. - 0009-2541 .- 1872-6836. ; 522, s. 192-207
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Tidskriftsartikel (refereegranskat)abstract
- This study assessed Fe-isotope ratio (56Fe/54Fe, expressed as δ56Fe relative to the IRMM-014 standard) variability and controls in pyrite that has among the largest reported S-isotope variability (maximum δ34S: 140‰). The pyrite occurs as fine-grained secondary crystals in fractures throughout the upper kilometer of granitoids of the Baltic Shield, and was analyzed here for δ56Fe by in situ secondary ion mass spectrometry (SIMS). Part of these pyrite crystals were picked from borehole instrumentation at depths of >400 m below sea level (m.b.s.l.), and thus are modern (known to have formed within 17 years) and can be compared with the δ56Fe of the source dissolved ferrous iron. The δ56Fe values of the modern pyrite crystals (−1.81‰ to +2.29‰) varied to a much greater extent than those of the groundwaters from which they formed (−0.48‰ to +0.13‰), providing strong field evidence for a large Fe isotope fractionation during the conversion of Fe(II)aq to FeS and ultimately to pyrite. Enrichment of 56Fe in pyrite relative to the groundwater was explained by equilibrium Fe(II)aq-FeS isotope fractionation, whereas depletion of 56Fe in pyrite relative to the groundwater was mainly the result of sulfidization of magnetite and kinetic isotopic fractionation during partial transformation of microsized FeS to pyrite. In many pyrite crystals, there is an increase in δ34S from crystal center to rim reflecting Rayleigh distillation processes (reservoir effects) caused by the development of closed-system conditions in the micro-environment near the growing crystals. A corresponding center-to-rim feature was not observed for the δ56Fe values. It is therefore unlikely that the groundwater near the growing pyrite crystals became progressively enriched in the heavy Fe isotope, in contrast to what has been found for the sulfur in sulfate. Other pyrite crystals formed following bacterial sulfate reduction in the time period of mid-Mesozoicum to Quaternary, had an almost identical Fe-isotope variability (total range: −1.50‰ to +2.76‰), frequency-distribution pattern, and relationship with δ34S as the recent pyrite formed on the borehole instrumentation. These features suggest that fundamental processes are operating and governing the Fe-isotope composition of pyrite crystals formed in fractured crystalline bedrock over large time scales.
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| 57. |
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| 58. |
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| 59. |
- Yu, Changxun, 1983-, et al.
(författare)
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Retention and transport of arsenic, uranium and nickel in a black shale setting revealed by a long-term humidity cell test and sequential chemica extractions
- 2014
-
Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 363, s. 134-144
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Tidskriftsartikel (refereegranskat)abstract
- The dispersion of acidic solutions with high levels of metals/metalloids, as a result of oxidative weathering of pyritic geomaterials, is a major environmental problem in areas where these materials are widely distributed and/or were historically mined. In this study, four types of materials encountered in an old black-shale mining area (unweathered black shale, weathered black shale, burnt black shale, and lime-mixed burnt black shale) were subjected to a long-term (up to 137 weeks) humidity cell test (HCT) combined with sequential chemical extractions (SCE), with the aim of examining geochemical controls on the release of Ni, U and As in this kind of pyritic settings. By combining the results of HCT and SCE as well as previously collected groundwater data, it is clearly shown that the degree of pyrite oxidation is the only major factor controlling the release of Ni, resulting in its highly elevated concentrations in acidic groundwaters. Although U followed a similar leaching pattern as observed for Ni and occurred abundantly in acidic groundwaters, a major decrease in the chemical fraction targeting exchangeable and carbonate phases, and a correlation of U concentrations with redox potential in groundwaters collectively suggest that the release of U was largely controlled by the solubilization of sorbed/carbonate U phases by oxidation to the highly soluble form (UO22+). As compared to the HCT, the SCE procedures used in this study delivered equally good estimates of Ni, U and S cumulatively leached, suggesting the strength of the SCE in terms of quantification of these elements during the weathering of pyritic geomaterials. Arsenic X-ray absorption near-edge structure spectroscopy shows that during the HCT (oxidation and leaching) of unweathered black shale, As was oxidized from its reduced form (having the oxidation state of -1 and most probably occurs as arsenian pyrite) to As(+5). Compared to the two cationic metals, As was released to a very limited extent and was not detectable in the leachates having pH between 6 and 3. This is because As was speciated exclusively as negatively-charged oxyanions in these leachates as predicted by MINTEQ modeling, thus was effectively attenuated by concurrently formed iron minerals. These minerals include mainly schwertmannite and K-jarosite as observed by SEM-EDS and also predicted by MINTEQ modeling. Elevated levels of As exclusively occurred in the groundwaters from one tube strongly impacted by seawater intrusion. This was regarded as a reflection of loosely-sorbed As oxyanions reliberated through ion exchange with seawater chloride. In this context, sea-level rise on a global scale as a potential driver for arsenic remobilization in low-lying coastal areas deserves further attention.
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| 60. |
- Yu, Changxun, 1983-, et al.
(författare)
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Storage and Distribution of Organic Carbon and Nutrients in Acidic Soils Developed on Sulfidic Sediments : The Roles of Reactive Iron and Macropores
- 2024
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 58:21, s. 9200-9212
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Tidskriftsartikel (refereegranskat)abstract
- In a boreal acidic sulfate-rich subsoil (pH 3–4) developing on sulfidic and organic-rich sediments over the past 70 years, extensive brownish-to-yellowish layers have formed on macropores. Our data reveal that these layers (“macropore surfaces”) are strongly enriched in 1 M HCl-extractable reactive iron (2–7% dry weight), largely bound to schwertmannite and 2-line ferrihydrite. These reactive iron phases trap large pools of labile organic matter (OM) and HCl-extractable phosphorus, possibly derived from the cultivated layer. Within soil aggregates, the OM is of a different nature from that on the macropore surfaces but similar to that in the underlying sulfidic sediments (C-horizon). This provides evidence that the sedimentary OM in the bulk subsoil has been largely preserved without significant decomposition and/or fractionation, likely due to physiochemical stabilization by the reactive iron phases that also existed abundantly within the aggregates. These findings not only highlight the important yet underappreciated roles of iron oxyhydroxysulfates in OM/nutrient storage and distribution in acidic sulfate-rich and other similar environments but also suggest that boreal acidic sulfate-rich subsoils and other similar soil systems (existing widely on coastal plains worldwide and being increasingly formed in thawing permafrost) may act as global sinks for OM and nutrients in the short run.
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| 61. |
- Zhang, Xiaodong, et al.
(författare)
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Storage of soil phytoliths and phytolith-occluded carbon along aprecipitation gradient in grasslands of northern China
- 2020
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Ingår i: Geoderma. - : Elsevier. - 0016-7061 .- 1872-6259. ; 364, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Climatic factors including mean annual precipitation (MAP) significantly influence the carbon (C) cycle interrestrial ecosystems and Earth overall. Phytolith-occluded carbon (PhytOC) is an important C sequestrationmechanism and as such plays a vital role in global long-term C sequestration. Understanding the spatialvariability in the storage of soil phytoliths and PhytOC and its relationship with climate is critical for evaluatingthe impact of global climate change on terrestrial ecosystem functions. However, little is known about theresponses of soil phytoliths and PhytOC to MAP in grassland ecosystems. This study sampled soil from 24natural, semi-arid steppe sites along a 2,500 km transect with a precipitation gradient of 243–481 mm yr−1 innorthern China. We investigated the influence of precipitation on the spatial distributions of soil phytoliths andPhytOC storage. Storage of soil phytoliths in bulk soil (0–100 cm depth) ranged from 21.3 ± 0.4 to88.4 ± 20.3 t ha−1 along the precipitation gradient. Amounts of soil phytoliths and PhytOC storage weresignificantly and positively correlated with MAP. Multiple regression analysis revealed that phytolith storage inbulk soil was best predicted by MAP (R = 0.5) and soil organic carbon (SOC, R = 0.4), with these two variablesaccounting for about 58% of the total variation observed. Considering the forecasted increase in MAP in theInner Mongolian steppe due to climate change, and the strong influence of MAP on the annual net primaryproductivity (ANPP) and related soil PhytOC input from litter decomposition in this region, we expect thatecosystem primary productivity will increase from deserts to meadow steppe and thereby promote soil PhytOCstorage. These findings have important implications for understanding the dynamics of soil phytoliths, andpredicting the impacts of global climate change on ecosystem functions and management practices in the EastAsian steppe ecosystems.
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| 62. |
- Zheng, Xiaodi, et al.
(författare)
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Biogeochemical cycle and isotope fractionation of copper in plant-soil systems : a review
- 2024
-
Ingår i: Reviews in Environmental Science and Biotechnology. - : Springer. - 1569-1705 .- 1572-9826. ; 23, s. 21-41
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Tidskriftsartikel (refereegranskat)abstract
- Copper (Cu) is a bio-essential element and a potentially toxic pollutant in the plant-soil systems. Analysis of stable Cu isotopes can be a powerful tool for tracing the biogeochemical cycling of Cu in plant-soil systems. In this review, we examined the analysis method of stable Cu isotope ratios in plants and soils, and discussed the biogeochemical processes, including redox reactions, mineral dissolution, abiotic and biotic sorption, which fractionate Cu isotopes in plant-soil systems. We also reviewed the variability of the isotopic signature in different plants and plant tissues, as well as different soil types and profiles to discuss the relationship between the biogeochemical transformation of Cu and its isotope fractionation in plant-soil systems. The collected data show that delta 65Cu values range from - 2.59 to + 1.73 parts per thousand in plant-soil systems, and increment 65Cu values range from - 1.00 to - 0.11 parts per thousand between the plant and soil. The variation in the increment 65Cu value between the plant and soil is mainly in response to the different uptake strategies during the acquisition of Cu from soils. Cu isotope analyses are proved to be a suitable technique during the biogeochemical transformation of Cu in plant-soil systems, especially during redox reactions. Ultimately, research challenges and future directions for Cu isotope techniques as a proxy for Cu biogeochemical cycles are also proposed. This review is beneficial for soil safety, food safety, and the sustainable development of agriculture and human health.
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| 63. |
- Zheng, Xiaodi, et al.
(författare)
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Extreme Copper Isotope Fractionation Driven by Redox Oscillation During Gleysols Weathering in Mun River Basin, Northeast Thailand
- 2023
-
Ingår i: Journal of Geophysical Research - Earth Surface. - : John Wiley & Sons. - 2169-9003 .- 2169-9011. ; 128:3
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Tidskriftsartikel (refereegranskat)abstract
- The fractionation of copper (Cu) isotope is a process related to the redox fluctuation during soil Cu biogeochemical cycling. For Cu isotope composition in weathered gleysols of tropical zones, the increased rates of redox fluctuations are assumed to occur during gleysol evolution due to the seasonal exchange of groundwater and river water. However, the impact of the frequency of redox fluctuations on soil Cu isotope signatures is rarely documented. Here, we analyzed the variations of Cu content and isotope fractionation in two low-humic gleysol profiles with different pedogenetic processes during weathering in the same basin (Mun River Basin), and found that the frequency of redox fluctuations could determine the magnitude of Cu isotope fractionation. We record an increased light Cu isotopes and identify the stable Cu(I) species retained in the residual soils with the increased frequency of redox fluctuation. Several processes contribute to Cu isotope fractionation at different soil horizons, but most isotope fractionation is related to the re-adsorption or re-precipitation by iron and manganese oxyhydroxide (i.e., ferrihydrite and pyrolusite), especially at the iron or manganese-rich zone. Cu isotope fractionation is sensitive to increased redox fluctuations in the terrestrial ecosystem, and may have significant implications for assessing soil ecological vulnerability under future climate change scenarios.
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| 64. |
- Åström, Mats E., 1963-, et al.
(författare)
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Extensive accumulation of rare earth elements in estuarine sediments affected by leaching of acid sulfate soils
- 2020
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Ingår i: Boreal Environment Research. - : Finnish Environmental Inst. - 1239-6095 .- 1797-2469. ; 25, s. 105-120
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Tidskriftsartikel (refereegranskat)abstract
- The concentrations, loads and speciation of rare earth elements (REEs) were studied in a 3.5 m thick mud depositional succession from an estuary in the Gulf of Bothnia. The uppermost 182.5 cm of the mud, estimated to have deposited from the early 1970s to 2011 (sampling year), had very high REE concentrations (596-1456 ppm) and accumulation rates (5.2-28 g m(-2) year(-1)). This was explained by large REE export from acid sulfate soils after they became efficiently drained with modern drainage techniques. Geochemical and synchrotron-based spectroscopic (XANES) analyses showed that the REEs in the mud are relatively firmly bound in non-clastic phases, likely adsorbed by clay minerals and also to some extent by iron oxyhydroxides. Below 182.5 cm, the REE concentrations successively decreased down to background values at the base at 3.5 m, reflecting less efficient drainage and leaching of the acid sulfate soils in previous decades and centuries.
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| 65. |
- Åström, Mats E., 1963-, et al.
(författare)
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Sources, transport and sinks of beryllium in a coastal landscape affected by acidic soils
- 2018
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 232, s. 288-302
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Tidskriftsartikel (refereegranskat)abstract
- Beryllium (Be) sources, transport and sinks were studied in a coastal landscape where acidic soils (acid sulfate soils) have developed after drainage of fine-grained sulfide-bearing sediments. The study included the determination of total abundance and speciation of Be in a variety of solid and aqueous materials in both the terrestrial and estuarine parts of the landscape. A major feature was that despite normal (background) Be concentration in the sulfide-bearing sediments, the Be leaching from these sediments after O2-exposure and acid sulfate soil development were extensive, with concentrations up to 76 μg L−1 in soil water, 39 μg L−1 in runoff and 12 μg L−1 in low-order streams. These high Be concentrations were mainly in the solution form (i.e., passing a 1 kilodalton filter) and modelled to be dominated by free Be2+. The extensive Be release within, and leaching from the acid sulfate soils was controlled by pH, with a critical value of 4.0 below which the Be concentrations increased strongly. Although plagioclase and mica were most likely the main carriers of Be within these soils, it is suggested that other minerals such as Be hydroxides, Al hydroxides carrying Be, and Be sulfides are the main contributors of the abundance of dissolved Be in the acidic waters. When the acidic and Be-rich creek water was neutralized in the estuary of relatively low salinity, the dominating solution form of Be was removed by transformation to particles, reflected in the suspended particulate matter that had hydroxylamine hydrochloride extractable Be up to 17 mg kg−1 and ammonium acetate EDTA extractable Be up to 4 mg kg−1. In corresponding pristine materials (parent material of the acid sulfate soils) in the catchment, the median Be extractability with these reagents were only 0.3 and 0.05 mg kg−1, respectively. As the Be-rich suspended particulate matter ultimately became benthic sediment, the Be was preserved in terms of total concentrations but underwent to some extent changes in speciation, including release from hydroxides and concomitant scavenging by organic matter and particle surfaces.
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| 66. |
- Åström, Mats, et al.
(författare)
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Sura sulfatjordar i Sverige : Ny kunskap och underlag för åtgärder
- 2024
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Målsättningen med projektet har varit att öka kunskapen om sura sulfatjordars utbredning och karaktär i Sverige. De viktigaste resultaten är: Sura sulfatjordar har en betydligt större förekomst och är framförallt betydligt surare och svavelrikare i sydöstra och södra Sverige än vad som tidigare varit känt, medan däremot förekomsten kring Vänern är liten. Norröver (Västerbotten, Norrbotten) är förekomsten hög, vilket varit känt sedan tidigare. Den nationella karteringen som gjordes i studien baserades på gles provtagning, vilket var vad projektets omfattning tillät. Detta innebär emellertid att för mellan-och sydsverige finns ännu ingen detaljkarta över förekomst av sura sulfatjordar. För att kunna genomföra en sådan kartering så effektivt och fort som möjligt, vilket det finns behov av, testades en ny karteringsteknik i ett valt område (väster om sjön Hjälmaren). Tekniken, som gav positiva resultat, genomfördes med maskininlärning och baserades på helikopterburna resistivitetsmätningar, höjddata (Lantmäteriet), nationella marktäckedata (Naturvårdsverket) och SGU:s jordartskarta. Den testades via fältundersökningar och har potential att genomföras på större områden. Med avseende på pH, aciditet samt totalhalter, syralösliga (1M HCl-lakning) halter och vattenlösliga halter av grundämnen är de sura sulfatjordarna relativt likadana runtom i landet med tanke på de rätt stora regionala variationer som förekommer i temperatur, paleosedimentationsmiljöer och markanvändningen. Denna förhållandevis homogena geokemiska karaktär underlättar förståelsen av hur de sura sulfatjordarna fungerar i termer av bland annat historiska, nutida och framtida effekter (försurning och metallbelastning) på miljön. Den förenklar också planering av åtgärder för att minska syra och metalläckage från dessa jordar, och bedömning av vad som är att förvänta vid återskapande av våtmarker på dessa jordar. På lokal nivå kan skillnaderna emellertid vara stora, t.ex. kan i den reducerade zonen där svavelhalten normalt är kring 1 % vara så hög som 5–7 % med avsevärd potentiellt ökad risk för miljön. En betydande övergripande regional fysikalisk-kemisk skillnad finns däremot på så vis att i norr har de sura sulfatjordarna ett betydligt tjockare surt skikt (median 75 cm) än de i söder (median 40 cm). En av konsekvenserna är att de sydliga sura sulfatjordarna sannolikt är mer känsliga för framtida sänkningar i grundvattennivån, d.v.s. det finns större potential för ytterligare omfattande syrabildning och metallfrisättning till följ av grundvattensänkningar förorsakade av långa torrperioder eller effektiverad dränering. Även de mikrobiella samhällena i den sura sulfatjorden är delvis annorlunda i norr än i söder. Till exempel, det finns en högre relativ förekomst av Ktedonobacteraceae i de norra delarna och Gallionellaceae i södra delarna av landet. Dessa skillnader är med största sannolikhet kopplade till temperaturskillnaderna mellan norr och söder, inklusive djup och tidsmässig längd av frost i marken. Kunskap om mer exakt vilka skillnaderna är mellan den mikrobiella aktiviteten i söder och norr kommer att belysas av en pågående mer ingående ”omics” studie där fokus är på de kemiska reaktioner som mikroberna bidrar till att ske eller påskynda.Återvätning av sura sulfatjordar kan åstadkomma positiva miljöeffekter. Detta gäller särskilt när den sekundära järnmineralogin (bildad efter att den sura sulfatjorden uppstått) domineras av schwertmannit och ferrihydrit, vilka mikrober under reducerande förhållanden relativt enkelt förmår bryta ner (reducera) vilket leder till en förhöjning av pH. Det, i sin tur, leder till att ett flertal metaller som blir toxiska redan vid relativt låga halter, såsom kadmium, nickel, mangan och beryllium, kommer att fastläggs istället för att läcka till närmiljön. Återvätning av sura sulfatjordar kan också skapa negativa miljöeffekter. Detta kan ske i form av ökad mobilisering och läckage av spårämnen som arsenik, krom och uran, men i första hand av ökad frisättning och rörlighet av tvåvärt järn. Den sura sulfatjorden har ett exceptionellt stort förråd av järn som kan bidra till detta, bundet i de sekundära mineralen schwertmannit, jarosit och ferrihydrit. I nästan 20 % av de undersökta sura sulfatjordarna motsvarar detta förråd > 2,0 % av hela den sura oxiderade zonens torrvikt, vilket är anmärkningsvärt högt. Det finns därför anledning till oro över vad de stora mängder järn som potentiellt kan frigöras skulle ha på våtmarken i sig på och vattensystem nedströms restaureringen. Sura sulfatjordar förekommer främst i låglänta områden som återfinns under den högsta kustlinjen. Det finns därför risk att metaller som läcker från dessa jordar hamnar i våtmarker, som likaledes förekommer i dessa områden. Detta har skett på ett omfattande sätt på en plats som undersökts i södra Sverige där framförallt järn fällts ut och påverkat både floran och faunan i våtmarken. Detta är ett fenomen att vara uppmärksam på i områden med sur sulfatjord, utöver den mer välkända påverkan i form av försurning och metallkontaminering av vattendrag. Det finns ett antal metoder som utvecklats, framförallt i Finland, för att minska läckage av syra och metaller från sura sulfatjordar under åkermark. På basen av genomgången litteratur och diskussioner med relevanta aktörer, bedöms den bästa metoden vara en kombination av teknikerna reglerbar dränering, underbevattning och injicering av kalkstenssuspension via täckdikningssystem. Denna teknikkombination förväntas leda till: (i) minskad oxidation och högre pH i jordarna, (ii) minskat läckage av syra och metaller till närmiljön, och (iii) positiva effekter på skörden på åkrarna (bör dock undersökas mer systematiskt) och kan därför ge en vinn-vinn situation. Ytterligare rekommenderas undersökning av möjligheter med och effekter av kalkfilterdiken. Att förhindra en sänkning av grundvattenytan i sura sulfatjordar är den viktigaste preventiva åtgärden både på kort och lång sikt. Detta är i sig ingen ny slutsats, men projektet har tagit fram data som mer exakt visar vad som kommer att ske i termer av bildning av aciditet och frisättning av metaller när grundvattennivån når djupare ner i den sura sulfatjordens underliggande reducerade och pH-neutrala grundvattenzon. Redan en sänkning ner i övergångszonen, d.v.s. den zon som ligger strax under det sura skiktet och där pH stiger snabbt, kommer frigöra avsevärda mängder aciditet och metaller med känd giftighet.
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