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Yu, C., Berger, T., Drake, H., Song, Z., Peltola, P. & Åström, M. E. (2019). Geochemical controls on dispersion of U and Th in Quaternary deposits, stream water, and aquatic plants in an area with a granite pluton. Science of the Total Environment, 663, 16-28
Open this publication in new window or tab >>Geochemical controls on dispersion of U and Th in Quaternary deposits, stream water, and aquatic plants in an area with a granite pluton
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2019 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 663, p. 16-28Article in journal (Refereed) Published
Abstract [en]

The weathering of U and/or Th rich granite plutons, which occurs worldwide, may serve as a potentially important, but as yet poorly defined source for U and Th in (sub-)surface environments. Here, we assessed the impact of an outcrop of such granite (5 km in diameter) and its erosional products on the distribution of U and Th in four nemo-boreal catchments. The results showed that (i) the pluton was enriched in both U and Th; and (ii) secondary U and Th phases were accumulated by peat/gyttja and in other Quaternary deposits with high contents of organic matter. Movement of the ice sheet during the latest glaciation led to dispersal of U- and Th-rich materials eroded from the pluton, resulting in a progressive increase in dissolved U and Th concentrations, as well as U concentrations in aquatic plants with increasing proximity to the pluton. The accumulation of U in the aquatic plants growing upon the pluton (100–365 mg kg−1, dry ash weight) shows that this rock represents a long-term risk for adjacent ecosystems. Dissolved pools of U and Th were correlated with those of dissolved organic matter (DOM) and were predicted to largely occur as organic complexes. This demonstrates the importance of DOM in the transport of U and Th in the catchments. Large fractions of Ca2UO2(CO3)30(aq) were modeled to occur in the stream with highest pH and alkalinity and thus, explain the strongly elevated U concentrations and fluxes in this particular stream. In future climate scenarios, boreal catchments will experience intensified runoff and warmer temperature that favor the production of hydrologically accessible DOM and alkalinity. Therefore, the results obtained from this study have implications for predicting the distribution and transport of Th and U in boreal catchments, especially those associated with U and/or Th rich granite plutons.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Uranium, Thorium, Nemo-boreal catchments, Climate change, Weathering
National Category
Environmental Sciences Geochemistry
Research subject
Natural Science, Environmental Science; Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-80032 (URN)10.1016/j.scitotenv.2019.01.293 (DOI)000459858500002 ()30708213 (PubMedID)
Available from: 2019-01-30 Created: 2019-01-30 Last updated: 2019-03-15Bibliographically approved
Uddh Söderberg, T., Berggren Kleja, D., Åström, M. E., Jarsjö, J., Fröberg, M., Svensson, P. A. & Augustsson, A. (2019). Metal solubility and transport at a contaminated landfill site – From the source zone into the groundwater. Science of the Total Environment, 668, 1064-1076
Open this publication in new window or tab >>Metal solubility and transport at a contaminated landfill site – From the source zone into the groundwater
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2019 (English)In: Science of the Total Environment, ISSN 0048-9697, E-ISSN 1879-1026, Vol. 668, p. 1064-1076Article in journal (Refereed) Published
Abstract [en]

Risks associated with metal contaminated sites are tightly linked to material leachability and contaminant mobility. In this study, metal solubility and transport were characterized within a glass waste landfill through i) lysimeter-collection of pore water and standardized batch leaching tests, ii) soil profiles extending from the landfill surface, through unsaturated soil underneath, and into the groundwater zone, and iii) groundwater samples upstream, at, and downstream of the landfill. The soil analyzes targeted both pseudo-total and geochemically active concentrations of contaminant metals (As, Cd, Pb, Sb) and basic soil geochemistry (pH, org. C, Fe,Mn). Water samples were analyzed for dissolved, colloid-bound and particulate metals, and speciation modelling of the aqueous phase was conducted. The results revealed a highly contaminated system, with mean metal concentrationsin the waste zone between 90 and 250 times the regional background levels. Despite severe contamination of the waste zone and high geochemically active fractions (80–100%) of all contaminant metals as well as elevated concentrations in landfill pore water, the concentrations of Cd and Pb decrease abruptly at the transition between landfill and underlying natural soil and no indication of groundwater contamination was found. The efficient cation retention is likely due to the high pH. However, the sorption of As and Sb is weaker at such high pH,which explains their higher mobility from the pore water zone into groundwater. The field soil:solution for Pb, ranging from 140 to 2,900,000 l kg−1), despite little variability in basic geochemical variables, which we suggest is due to waste material heterogeneity.

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Soil and groundwater metal pollution, Glass waste, Soil:Solution partitioning (Kd), Leachability, Mobility, Colloids
National Category
Environmental Sciences
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-81555 (URN)10.1016/j.scitotenv.2019.03.013 (DOI)000462776800098 ()
Funder
The Geological Survey of Sweden (SGU), 36-1778/2014
Available from: 2019-04-01 Created: 2019-04-01 Last updated: 2019-04-18Bibliographically approved
Yu, C., Boily, J.-F., Shchukarev, A., Drake, H., Song, Z., Hogmalm, K. J. & Åström, M. E. (2018). A cryogenic XPS study of Ce fixation on nanosized manganite and vernadite: Interfacial reactions and effects of fulvic acid complexation. Chemical Geology, 483, 304-311
Open this publication in new window or tab >>A cryogenic XPS study of Ce fixation on nanosized manganite and vernadite: Interfacial reactions and effects of fulvic acid complexation
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2018 (English)In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 483, p. 304-311Article in journal (Refereed) Published
Abstract [en]

This study investigated interfacial reactions between aqueous Ce(III) and two synthetic nanosized Mn (hydr-) oxides (manganite: γ-MnOOH, and vernadite: δ-MnO2) in the absence and presence of Nordic Lake fulvic acid (NLFA) at circumneutral pH by batch experiments and cryogenic X-ray photoelectron spectroscopy (XPS). The surfaces of manganite and vernadite were negatively charged (XPS-derived loadings of (Na+K)/Cl > 1) and loaded with 0.42–4.33 Ce ions nm−2. Manganite stabilized Ce-oxidation states almost identical to those for vernadite (approximately 75% Ce(IV) and 25% Ce(III)), providing the first experimental evidence that also a Mn (III) phase (manganite) can act as an important scavenger for Ce(IV) and thus, contribute to the decoupling of Ce from its neighboring rare earth elements and the development of Ce anomaly. In contrast, when exposed to Ce (III)-NLFA complexes, the oxidation of Ce by these two Mn (hydr-)oxides was strongly suppressed, suggesting that the formation of Ce(III) complexes with fulvic acid can stabilize Ce(III) even in the presence of oxidative Mn oxide surfaces. The experiments also showed that Ce(III) complexed with excess NLFA was nearly completely removed, pointing to a strong preferential sorption of Ce(III)-complexed NLFA over free NLFA. This finding suggests that the Ce(III)-NLFA complexes were most likely sorbed by their cation side, i.e. Ce(III) bridging between oxide groups on the Mn (hydr-)oxides and negatively-charged functional groups in NLFA. Hence, Ce(III) was in direct contact with the oxidative manganite and vernadite but despite that not oxidized. An implication is that in organic-rich environments there may be an absence of Ce(IV) and Ce anomaly despite otherwise favorable conditions for Ce(III) oxidation.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Cryogenic XPS, Manganite, Vernadite, Oxidative scavenging, Ce anomaly
National Category
Earth and Related Environmental Sciences
Research subject
Natural Science
Identifiers
urn:nbn:se:lnu:diva-72684 (URN)10.1016/j.chemgeo.2018.02.033 (DOI)000429492300027 ()
Available from: 2018-04-13 Created: 2018-04-13 Last updated: 2018-07-10Bibliographically approved
Christel, S., Yu, C., Wu, X., Josefsson, S., Sohlenius, G., Åström, M. E. & Dopson, M. (2018). Comparison of Boreal Acid Sulfate Soil Microbial Communities in Oxidative and Reductive Environments. Research in Microbiology
Open this publication in new window or tab >>Comparison of Boreal Acid Sulfate Soil Microbial Communities in Oxidative and Reductive Environments
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2018 (English)In: Research in Microbiology, ISSN 0923-2508, E-ISSN 1769-7123Article in journal (Refereed) Submitted
Keywords
sulfide mineral; metal; sulfur; 16S rRNA gene; mitigation; wetland
National Category
Microbiology
Identifiers
urn:nbn:se:lnu:diva-77664 (URN)
Available from: 2018-09-10 Created: 2018-09-10 Last updated: 2019-01-23
Lopez-Fernandez, M., Åström, M. E., Bertilsson, S. & Dopson, M. (2018). Depth and Dissolved Organic Carbon Shape Microbial Communities in Surface Influenced but Not Ancient Saline Terrestrial Aquifers. Frontiers in Microbiology, 9, Article ID 2880.
Open this publication in new window or tab >>Depth and Dissolved Organic Carbon Shape Microbial Communities in Surface Influenced but Not Ancient Saline Terrestrial Aquifers
2018 (English)In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 9, article id 2880Article in journal (Refereed) Published
Abstract [en]

The continental deep biosphere is suggested to contain a substantial fraction of the earth's total biomass and microorganisms inhabiting this environment likely have a substantial impact on biogeochemical cycles. However, the deep microbial community is still largely unknown and can be influenced by parameters such as temperature, pressure, water residence times, and chemistry of the waters. In this study, 21 boreholes representing a range of deep continental groundwaters from the Aspo Hard Rock Laboratory were subjected to high-throughput 16S rRNA gene sequencing to characterize how the different water types influence the microbial communities. Geochemical parameters showed the stability of the waters and allowed their classification into three groups. These were (i) waters influenced by infiltration from the Baltic Sea with a "modern marine (MM)" signature, (ii) a "thoroughly mixed (TM)" water containing groundwaters of several origins, and (iii) deep "old saline (OS)" waters. Decreasing microbial cell numbers positively correlated with depth. In addition, there was a stronger positive correlation between increased cell numbers and dissolved organic carbon for the MM compared to the OS waters. This supported that the MM waters depend on organic carbon infiltration from the Baltic Sea while the ancient saline waters were fed by "geogases" such as carbon dioxide and hydrogen. The 16S rRNA gene relative abundance of the studied groundwaters revealed different microbial community compositions. Interestingly, the TM water showed the highest dissimilarity compared to the other two water types, potentially due to the several contrasting water types contributing to this groundwater. The main identified microbial phyla in the groundwaters were Gammaproteobacteria, unclassified sequences, Campylobacterota (formerly Epsilonproteobacteria), Patescibacteria, Deltaproteobacteria, and Alphaproteobacteria. Many of these taxa are suggested to mediate ferric iron and nitrate reduction, especially in the MM waters. This indicated that nitrate reduction may be a neglected but important process in the deep continental biosphere. In addition to the high number of unclassified sequences, almost 50% of the identified phyla were archaeal or bacterial candidate phyla. The percentage of unknown and candidate phyla increased with depth, pointing to the importance and necessity of further studies to characterize deep biosphere microbial populations.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2018
Keywords
16S rRNA gene, amplicon sequencing, deep subsurface, groundwaters, chemistry, microbial diversity
National Category
Microbiology
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-79095 (URN)10.3389/fmicb.2018.02880 (DOI)000451406100001 ()
Funder
Swedish Research Council, 2014-4398; 2012-3892; 2017-04422
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2019-02-27Bibliographically approved
Drake, H., Mathurin, F. A., Zack, T., Schäfer, T., Roberts, N., Whitehouse, M., . . . Åström, M. E. (2018). Incorporation of Metals into Calcite in a Deep Anoxic Granite Aquifer. Environmental Science and Technology, 52(2), 493-502
Open this publication in new window or tab >>Incorporation of Metals into Calcite in a Deep Anoxic Granite Aquifer
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2018 (English)In: Environmental Science and Technology, ISSN 0013-936X, E-ISSN 1520-5851, Vol. 52, no 2, p. 493-502Article in journal (Refereed) Published
Abstract [en]

Understanding metal scavenging by calcite in deep aquifers in granite is of importance for deciphering and modeling hydrochemical fluctuations and water–rock interaction in the upper crust and for retention mechanisms associated with underground repositories for toxic wastes. Metal scavenging into calcite has generally been established in the laboratory or in natural environments that cannot be unreservedly applied to conditions in deep crystalline rocks, an environment of broad interest for nuclear waste repositories. Here, we report a microanalytical study of calcite precipitated over a period of 17 years from anoxic, low-temperature (14 °C), neutral (pH: 7.4–7.7), and brackish (Cl: 1700–7100 mg/L) groundwater flowing in fractures at >400 m depth in granite rock. This enabled assessment of the trace metal uptake by calcite under these deep-seated conditions. Aquatic speciation modeling was carried out to assess influence of metal complexation on the partitioning into calcite. The resulting environment-specific partition coefficients were for several divalent ions in line with values obtained in controlled laboratory experiments, whereas for several other ions they differed substantially. High absolute uptake of rare earth elements and U(IV) suggests that coprecipitation into calcite can be an important sink for these metals and analogousactinides in the vicinity of geological repositories.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018
National Category
Earth and Related Environmental Sciences
Research subject
Natural Science
Identifiers
urn:nbn:se:lnu:diva-70485 (URN)10.1021/acs.est.7b05258 (DOI)000423012200013 ()29251499 (PubMedID)
Available from: 2018-02-05 Created: 2018-02-05 Last updated: 2018-02-08Bibliographically approved
Åström, M. E., Yu, C., Peltola, P., Reynolds, J. K., Österholm, P., Nystrand, M. I., . . . Ojala, A. E. .. (2018). Sources, transport and sinks of beryllium in a coastal landscape affected by acidic soils. Geochimica et Cosmochimica Acta, 232, 288-302
Open this publication in new window or tab >>Sources, transport and sinks of beryllium in a coastal landscape affected by acidic soils
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2018 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 232, p. 288-302Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Earth and Related Environmental Sciences
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-74838 (URN)10.1016/j.gca.2018.04.025 (DOI)
Available from: 2018-06-01 Created: 2018-06-01 Last updated: 2019-02-12Bibliographically approved
Drake, H., Whitehouse, M. J., Heim, C., Reiners, P. W., Tillberg, M., Hogmalm, K. J., . . . Åström, M. E. (2018). Unprecedented 34S-enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks. Geobiology, 16(5), 556-574
Open this publication in new window or tab >>Unprecedented 34S-enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks
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2018 (English)In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 16, no 5, p. 556-574Article in journal (Refereed) Published
Abstract [en]

In the deep biosphere, microbial sulfate reduction (MSR) is exploited for energy. Here, we show that, in fractured continental crystalline bedrock in three areas in Sweden, this process produced sulfide that reacted with iron to form pyrite extremely enriched in S-34 relative to S-32. As documented by secondary ion mass spectrometry (SIMS) microanalyses, the S-34(pyrite) values are up to +132 parts per thousand V-CDT and with a total range of 186 parts per thousand. The lightest S-34(pyrite) values (-54 parts per thousand) suggest very large fractionation during MSR from an initial sulfate with S-34 values (S-34(sulfate,0)) of +14 to +28 parts per thousand. Fractionation of this magnitude requires a slow MSR rate, a feature we attribute to nutrient and electron donor shortage as well as initial sulfate abundance. The superheavy S-34(pyrite) values were produced by Rayleigh fractionation effects in a diminishing sulfate pool. Large volumes of pyrite with superheavy values (+120 +/- 15 parts per thousand) within single fracture intercepts in the boreholes, associated heavy average values up to +75 parts per thousand and heavy minimum S-34(pyrite) values, suggest isolation of significant amounts of isotopically light sulfide in other parts of the fracture system. Large fracture-specific S-34(pyrite) variability and overall average S-34(pyrite) values (+11 to +16 parts per thousand) lower than the anticipated S-34(sulfate,0) support this hypothesis. The superheavy pyrite found locally in the borehole intercepts thus represents a late stage in a much larger fracture system undergoing Rayleigh fractionation. Microscale Rb-Sr dating and U/Th-He dating of cogenetic minerals reveal that most pyrite formed in the early Paleozoic era, but crystal overgrowths may be significantly younger. The C-13 values in cogenetic calcite suggest that the superheavy S-34(pyrite) values are related to organotrophic MSR, in contrast to findings from marine sediments where superheavy pyrite has been proposed to be linked to anaerobic oxidation of methane. The findings provide new insights into MSR-related S-isotope systematics, particularly regarding formation of large fractions of S-34-rich pyrite.

Place, publisher, year, edition, pages
Wiley-Blackwell, 2018
Keywords
continental crust, deep biosphere, microbial sulfate reduction, pyrite, sulfur isotopes
National Category
Environmental Sciences
Research subject
Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-77727 (URN)10.1111/gbi.12297 (DOI)000441436700007 ()29947123 (PubMedID)
Projects
Characteristics and extent of microbial anaerobic methane oxidation and sulfate reduction in the deep terrestrial subsurface over geological time scalesProduction and consumption of the greenhouse gas methane in the crystalline bedroc
Funder
Swedish Research Council, 2017-05186Swedish Research Council Formas, 2017-00766
Available from: 2018-09-13 Created: 2018-09-13 Last updated: 2018-09-13Bibliographically approved
Drake, H., Ivarsson, M., Bengtson, S., Heim, C., Siljeström, S., Whitehouse, M. J., . . . Åström, M. E. (2017). Anaerobic consortia of fungi and sulfate reducing bacteria in deep granite fractures. Nature Communications, 8, 1-9, Article ID 55.
Open this publication in new window or tab >>Anaerobic consortia of fungi and sulfate reducing bacteria in deep granite fractures
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2017 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 8, p. 1-9, article id 55Article in journal (Refereed) Published
Abstract [en]

The deep biosphere is one of the least understood ecosystems on Earth. Although most microbiological studies in this system have focused on prokaryotes and neglected microeukaryotes, recent discoveries have revealed existence of fossil and active fungi in marine sediments and sub-seafloor basalts, with proposed importance for the subsurface energy cycle. However, studies of fungi in deep continental crystalline rocks are surprisingly few. Consequently, the characteristics and processes of fungi and fungus-prokaryote interactions in this vast environment remain enigmatic. Here we report the first findings of partly organically preserved and partly mineralized fungi at great depth in fractured crystalline rock (−740 m). Based on environmental parameters and mineralogy the fungi are interpreted as anaerobic. Synchrotron-based techniques and stable isotope microanalysis confirm a coupling between the fungi and sulfate reducing bacteria. The cryptoendolithic fungi have significantly weathered neighboring zeolite crystals and thus have implications for storage of toxic wastes using zeolite barriers.

Place, publisher, year, edition, pages
Nature Publishing Group, 2017
National Category
Biological Sciences
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-70482 (URN)10.1038/s41467-017-00094-6 (DOI)000444344000001 ()28676652 (PubMedID)
Available from: 2018-02-05 Created: 2018-02-05 Last updated: 2018-12-14Bibliographically approved
Yu, C., Drake, H., Mathurin, F. A. & Åström, M. E. (2017). Cerium sequestration and accumulation in fractured crystalline bedrock: The role of Mn-Fe (hydr-)oxides and clay minerals. Geochimica et Cosmochimica Acta, 199, 370-389
Open this publication in new window or tab >>Cerium sequestration and accumulation in fractured crystalline bedrock: The role of Mn-Fe (hydr-)oxides and clay minerals
2017 (English)In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 199, p. 370-389Article in journal (Refereed) Published
Abstract [en]

This study focuses on the mechanisms of Ce sequestration and accumulation in the fracture network of the upper kilometer of the granitoid bedrock of the Baltic Shield in southeast Sweden (Laxemar area, Sweden). The material includes 81 specimens of bulk secondary mineral precipitates ("fracture coatings") collected on fracture walls identified in 17 drill cores, and 66 groundwater samples collected from 21 deep boreholes with equipment designed for retrieval of representative groundwater at controlled depths. The concentrations of Ce in the fracture coatings, although varying considerably (10-90th percentiles: 67-438 mg kg(-1)), were frequently higher than those of the wall rock (10-90th percentiles: 70-118 mg kg(-1)). Linear combination fitting analysis of Ce L-III-edge X-ray absorption near-edge structure (XANES) spectra, obtained for 19 fracture coatings with relatively high Ce concentrations (>= 145 mg kg(-1)) and a wide range of Ce-anomaly values, revealed that Ce(IV) occurs frequently in the upper 10 m of the fracture network (Ce(IV)/Ce-total = 0.06-1.00 in 8 out of 11 specimens) and is mainly associated with Mn oxides (modeled as Ce oxidatively scavenged by birnessite). These features are in line with the strong oxidative and sorptive capacities of Mn oxide as demonstrated by previous studies, and abundant todorokite and birnessite-like Mn oxides identified in 3 out of 4 specimens analyzed by Mn K-edge X-ray absorption spectroscopy (XAS) in the upper parts of the fracture network (down to 5 m). For a specimen with very high Ce concentration (1430 mg kg(-1)) and NASC-normalized Ce anomaly (3.63), the analysis of Ce XANES and Mn XAS data revealed (i) a predominance of Ce oxide in addition to Ce scavenged by Mn oxide; and (ii) a large fraction of poorly-crystalline hexagonal birnessite and aqueous Mn2+, suggesting a recent or on-going oxidation of Mn2+ in this fracture. In addition, the Ce oxide precipitates on this fracture observed by in situ SEM-EDS contained considerable amounts of Mn. These spectroscopic and microscopic features led us to suggest that the remarkable accumulation of Ce(IV) in this fracture is a result of repeated formation and dissolution of Mn oxides, that is, formation of Mn oxide followed by oxidative scavenging of Ce as Ce oxide nanoparticles, which largely remained during the subsequent reductive dissolution of the Mn oxides. In addition, the XANES data indicate that goethite has the capability to oxidize Ce at near-neutral pH under our experimental conditions (goethite reacted with 0.001M Ce for 48 h in a glove box with O-2 < 1 ppm). This previously unrecognized Ce oxidation pathway also seems to contribute to a minor extent to the oxidative scavenging of Ce in the fracture network. Trivalent Ce in the fracture coatings, in particular below 2.5 m, is mainly sorbed as inner-sphere complexes on clay minerals. Taking into account the facts that Ce in the present groundwater is scarce and modeled to be largely complexed with humic substance, it is argued that the inner-sphere complexes were mainly formed from past (Paleozoic) hydrothermal fluids. (C) 2016 Elsevier Ltd. All rights reserved.

Keywords
Ce anomaly, Ce oxidation states, Oxidative scavenging, X-ray absorption near-edge structure
National Category
Geochemistry
Research subject
Natural Science
Identifiers
urn:nbn:se:lnu:diva-61146 (URN)10.1016/j.gca.2016.11.044 (DOI)000393125500023 ()
Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2017-11-29Bibliographically approved
Projects
Syntrofi och symbios för överlevnad och tillväxt i den djupa terrestra biosfären [202100-6271]; Linnaeus University
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3585-2209

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