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  • 1.
    Berger, Tobias
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Mathurin, Frédéric A.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Gustafsson, Jon Petter
    Swedish University of Agricultural Sciences ; KTH Royal Inst Technol, Sweden.
    Peltola, Pasi
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Åström, Mats E.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    The impact of fluoride on Al abundance and speciation in boreal streams2015In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 409, p. 118-124Article in journal (Refereed)
    Abstract [en]

    The impact of fluoride on the abundance and speciation of aluminium (Al) was investigated in three boreal streams characterised by overall high concentrations of fluoride and dissolved organic matter. Stream-water sampling was carried out several times a year for at least 4 years, and a chemical equilibrium model (Visual MINTEQ) was applied in order to model the proportion of colloidal and organically/inorganically complexed Al in the waters. The Al concentrations in filtered (0.45 mu m) water samples were inversely correlated with pH, and reached values up to approximately 1 mg/L during low pH conditions (pH < 6.0). In a stream with high fluoride concentrations, as compared to a similar stream with only moderately elevated fluoride concentrations, the Al concentrations were consistently elevated. For the stream with high concentrations of fluoride and Al, the model predicted both high concentrations and proportions of Al-fluoride complexation. This prediction indicates that high fluoride levels contribute to raise both the Al abundance and the ratio of inorganic to organic Al complexation in stream water. In contrast, for another stream with high fluoride concentrations and consistently high (near neutral) pH, there was no evidence of fluoride affecting Al concentration or complexation. These results show that it is important to focus future studies on the role of high levels of dissolved fluoride on both the speciation and the toxicity of Al in stream water.

  • 2. Boman, Anton
    et al.
    Åström, Mats
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Fröjdö, Sören
    Sulfur dynamics in boreal acid sulphate soils rich in metastable iron sulfide – The role of artificial drainage2008In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 255, no 1-2, p. 68-77Article in journal (Refereed)
    Abstract [en]

    The sulfur dynamics of boreal brackish-water sediments rich in metastable iron sulfide (average elemental composition of FeS1.1), which upon oxidation have a huge impact on stream-water chemistry, were studied. Two cores, extending from the upper oxidized layer (acid sulfate soil) into the underlying iron sulfide-bearing sediment (potential acid sulfate soil) were collected at a site close to the sea level and at another site about 40 m above the latter in a region of current isostatic land uplift (Finland). The data clearly show, in contrast to what is often argued, that these notorious acidic soils are formed not as a result of the natural uplift but because of extensive ditching of farmlands. Above the depth of artificial drainage, S and Ni are abundantly lost, while beneath that level pyrite is abundant and metastable iron sulfide is increasing with depth, and the Ni concentration is relatively stable. In the narrow zone between the reduced and oxidized layers, the processes are dynamic and result in preservation of elemental S at one of the locations. The sulfur isotopic composition for metastable iron sulfide and pyrite in the investigated acid sulfate soils were found to be distinctly bimodal and roughly corresponding to a similar distribution in stream-water sulfate earlier reported from the same region. This indicates that pyrite is the main source of sulfate and acidity in some affected drains, while in others it is metastable iron sulfide.

  • 3.
    Maskenskaya, Olga M.
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Drake, Henrik
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Mathurin, Frédéric A.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Åström, Mats E.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    The role of carbonate complexes and crystal habit on rare earth element uptake in low-temperature calcite in fractured crystalline rock2015In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 391, p. 100-110Article in journal (Refereed)
    Abstract [en]

    This study focuses on rare earth element (REE) geochemistry of low-temperature calcite coatings occurring on the walls of fractures throughout the upper kilometer of crystalline rocks of the Baltic Shield. Fifty one calcite coatings were sampled from cores drilled with the triple-tube technique which successfully preserved the fragile calcite coatings on the fracture walls. The calcites, which based on geological and isotopic evidence were precipitated over the last 10 million years, had highly variable Sigma REE concentrations (0.61-2276 ppm) that decreased weakly with the depth the calcite was sampled from. When normalized to shale (and host rock), the REE concentrations of habits with c-axis approximate to a-axes and the closely associated c-axis > a-axes, the most abundant crystal morphologies in the system, decreased strongly and smoothly across the series. In contrast, the REEs of habits with c-axis >> a-axes, identified only in fractures in the uppermost 260m of the bedrock, were flatter and occasionally expressed a weak middle REE enrichment. By using calcite-water partition coefficients derived for REEs in previous laboratory experiments, the La/Yb of the paleogroundwater from which the calcites precipitated was back-calculated and found to be overall similar (range 0.15-452) overlap to the corresponding ratio of the present groundwater (range: 2.1-36.4). In terms of REE/Ca, the values for the back-calculated paleogroundwater (La / Ca 9.9 (*) 10(-11)-3.9 (*) 10(-7); Yb / Ca 1.5 (*) 10(-10)-2.2(*)10(-7)) were similar to those of LaCO3+ / Ca (4.5(*)10(-10)-8.5 (*) 10(-7)) and (YbCO3+ + Yb(CO3)(2)(-)) / Ca (5.4 (*) 10(-11)-1.8 (*) 10(-8)), respectively, in the present groundwater. These patterns indicate that the LREE to HREE and REE to Ca ratios in the groundwater at the site are broadly similar to those existing when the calcites precipitated, and that carbonate complexes present in the paleogroundwater played a crucial role in sequestration and fractionation of REEs in calcite. The findings have implications for bedrock storage of high-level radioactivewaste, which contains actinides for which the REEs can be used as natural analogues. (C) 2014 Elsevier B.V. All rights reserved.

  • 4.
    Peltola, Pasi
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Brun, Christian
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Åström, Mats
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Tomilina, Olga
    High K/Rb ratios in stream waters - Exploring plant litter decay, ground water and lithology as potential controlling mechanisms2008In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 257, no 1-2, p. 92-100Article in journal (Refereed)
  • 5.
    Yu, Changxun
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Lavergren, Ulf
    County Administrative Board of Gotland, Sweden.
    Peltola, Pasi
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Drake, Henrik
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Bergbäck, Bo
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Åström, Mats E.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Retention and transport of arsenic, uranium and nickel in a black shale setting revealed by a long-term humidity cell test and sequential chemica extractions2014In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 363, p. 134-144Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Yu, Changxun
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Virtasalo, Joonas J.
    Geol Survey Finland GTK, Finland.
    Karlsson, Torbjörn
    Umea Univ.
    Peltola, Pasi
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Osterholm, Peter
    Åbo Akad Univ, Finland.
    Burton, Edward D.
    So Cross Univ, Australia.
    Arppe, Laura
    Univ Helsinki, Finland.
    Hogmalm, Johan K.
    Univ Gothenburg.
    Ojala, Antti E. K.
    Geol Survey Finland GTK, Finland..
    Åström, Mats E.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Iron behavior in a northern estuary: Large pools of non-sulfidized Fe(II) associated with organic matter2015In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 413, p. 73-85Article in journal (Refereed)
    Abstract [en]

    The estuaries of the Northern Baltic Sea (Gulf of Bothnia) receive an abundance of diagenetically reactive catchment-derived Fe, which is to a large degree complexed with organicmatter or present as Fe (hydr-) oxides. However, our understanding of sedimentary Fe diagenesis in these estuaries is limited. To address this limitation, the present study examines Fe geochemistry in a 3.5-m-thick estuarine benthic mud layer and three samples of suspended particulate matter of a catchment on the eastern Gulf of Bothnia. The age-depth model of the mud, constructed on the basis of sedimentary features as well as Cs-137 and aquatic plant C-14 determinations, revealed a high average rate of sedimentation (5 cm . yr(-1)) for the upper mud unit (0-182.5 cm, corresponding to 1973-2011), in response to intensive land-use (ditching) in the catchment since the 1960s and 1970s. The intensive land-use has resulted in a strong increase in the Fe accumulation rates, but has not caused a recognizable impact on the diagenetic processes of Fe including features such as degree of sulfidization and solid-phase partitioning. Iron X-ray absorption spectroscopy (XAS) indicated that in the suspended particulate matter, large proportions (47-58%) of Fe occur as Fe(III)-organic complexes and 2-line ferrihydrite. In the mud, the former is completely reduced, and reactive Fe (defined via extraction with 1 MHCl) was high throughout (52-68%, median = 61%) and strongly dominated by Fe(II). This reactive Fe(II) pool was sulfidized to only a limited extent (degree of reactive sulfidization = 11-26%, median = 17%). This phenomenon is attributed to the brackish-water conditions (i.e. low in sulfate) and the abundant input of reactive Fe(III) from the catchment, leading to a surplus of dissolved Fe2+ over dissolved sulfide in the sediment. The low availability of dissolved sulfide, in combination with the high average sedimentation rate, limits the formation of intermediate reduced sulfur compounds at the water-sediment interface, thereby retarding the conversion of FeS into pyrite (ratios of pyrite-S to AVS = 0.17-1.73, median = 0.37; degree of pyritization = 1-17%, median = 3%). Iron XAS, in combination with wavelet transform analysis, of representative sediment segments from the upper and lower mud units suggests that the non-sulfidized Fe(II) pool is dominantly complexed by organic matter, with the remaining Fe(II) occurring as mackinawite. This has implications for the understanding of early Fe diagenesis in settings with a high input of organic matter and relatively low supply of sulfate. (C) 2015 Elsevier B.V. All rights reserved.

  • 7.
    Yu, Changxun
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Virtasalo, Joonas J.
    Geol Survey Finland GTK, Finland.
    Österholm, Peter
    Åbo Akad Univ, Finland.
    Burton, Edward D.
    Southern Cross Univ, Australia.
    Peltola, Pasi
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Ojala, Antti E. K.
    Geol Survey Finland GTK, Finland.
    Högmalm, Johan K.
    University of Gothenburg.
    Åström, Mats E.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    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 Sea2016In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 437, p. 56-66Article in journal (Refereed)
    Abstract [en]

    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. (C) 2016 Elsevier B.V. All rights reserved.

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