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  • 1. Alessi, Daniel S.
    et al.
    Lezama-Pacheco, Juan S.
    Stubbs, Joanne E.
    Janousch, Markus
    Bargar, John R.
    Persson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Bernier-Latmani, Rizlan
    The product of microbial uranium reduction includes multiple species with U(IV)-phosphate coordination2014Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 131, s. 115-127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Until recently, the reduction of U(VI) to U(IV) during bioremediation was assumed to produce solely the sparingly soluble mineral uraninite, UO2(s). However, results from several laboratories reveal other species of U(IV) characterized by the absence of an EXAFS U-U pair correlation (referred to here as noncrystalline U(IV)). Because it lacks the crystalline structure of uraninite, this species is likely to be more labile and susceptible to reoxidation. In the case of single species cultures, analyses of U extended X-ray fine structure (EXAFS) spectra have previously suggested U(IV) coordination to carboxyl, phosphoryl or carbonate groups. In spite of this evidence, little is understood about the species that make up noncrystalline U(IV), their structural chemistry and the nature of the U(IV)-ligand interactions. Here, we use infrared spectroscopy (IR), uranium L-III-edge X-ray absorption spectroscopy (XAS), and phosphorus K-edge XAS analyses to constrain the binding environments of phosphate and uranium associated with Shewanella oneidensis MR-1 bacterial cells. Systems tested as a function of pH included: cells under metal-reducing conditions without uranium, cells under reducing conditions that produced primarily uraninite, and cells under reducing conditions that produced primarily biomass-associated noncrystalline U(IV). P X-ray absorption near-edge structure (XANES) results provided clear and direct evidence of U(IV) coordination to phosphate. Infrared (IR) spectroscopy revealed a pronounced perturbation of phosphate functional groups in the presence of uranium. Analysis of these data provides evidence that U(IV) is coordinated to a range of phosphate species, including monomers and polymerized networks. U EXAFS analyses and a chemical extraction measurements support these conclusions. The results of this study provide new insights into the binding mechanisms of biomass-associated U(IV) species which in turn sheds light on the mechanisms of biological U(VI) reduction. (C) 2014 Elsevier Ltd. All rights reserved.

  • 2.
    Bengtsson, Åsa
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Shchukarev, Andrey
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Persson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Sjöberg, Staffan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    A solubility and surface complexation study of a non-stoichiometric hydroxyapatite2009Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, nr 2, s. 257-267Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dissolution and surface complexation of a non-stoichiometric hydroxyapatite (Ca8.4(HPO4)1.6(PO4)4.4(OH)0.4), (HAP) was studied in the pH range 3.5 – 10.5, at 25 ºC in 0.1 M Na(Cl). The results from well-equilibrated batch experiments, potentiometric titrations, and zeta-potential measurements were combined with information provided by Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The information from the analyses was used to design an equilibration model that takes in to account dissolution, surface potential, solution and surface complexation, as well as possible phase transformations. The results from the XPS measurements clearly show that the surface of the mineral has a different composition than the bulk and that the Ca/P ratio of the surface layer is 1.4 ± 0.1. This ratio was also found in solution in the batches equilibrated at low pH where the dominating reaction is dissolution. In the batches equilibrated at near neutral pH values, however, the Ca/P ratio in solution attains values as high as 25, which is due to re-adsorption of phosphate ions to the HAP surface. The total concentration of protons as well as the total concentration of dissolved calcium and phosphate in solution were used to calculate a model for the dissolution and surface complexation of HAP. The constant capacitance model was applied in designing the following surface complexation model.

  • 3. Björkvald, L
    et al.
    Giesler, Reiner
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Ekologi, miljö och geovetenskap.
    Humborg, C
    Mörth, C-M
    Landscape variations in stream water SO4 and d34S-SO4 in a boreal stream network2009Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 73, s. 4648-4660Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Despite reduced anthropogenic deposition during the last decades, deposition sulphate may still play an important role in the biogeochemical cycles of S and many catchments may act as net sources of S that may remain for several decades. The aim of this study is to elucidate the temporal and spatial dynamics of both SO42− and δ34SSO4 in stream water from catchments with varying percentage of wetland and forest coverage and to determine their relative importance for catchment losses of S. Stream water samples were collected from 15 subcatchments ranging in size from 3 to 6780 ha, in a boreal stream network, northern Sweden. In forested catchments (<2% wetland cover) S–SO42− concentrations in stream water averaged 1.7 mg L−1 whereas in wetland dominated catchments (>30% wetland cover) the concentrations averaged 0.3 mg L−1. A significant negative relationship was observed between S–SO42− and percentage wetland coverage (r2 = 0.77, p < 0.001) and the annual export of stream water SO42− and wetland coverage (r2 = 0.76, p < 0.001). The percentage forest coverage was on the other hand positively related to stream water SO42− concentrations and the annual export of stream water SO42− (r2 = 0.77 and r2 = 0.79, respectively). The annual average δ34SSO4 value in wetland dominated streams was +7.6‰ and in streams of forested catchments +6.7‰. At spring flood the δ34SSO4 values decreased in all streams by 1‰ to 5‰. The δ34SSO4 values in all streams were higher than the δ34SSO4 value of +4.7‰ in precipitation (snow). The export of S ranged from 0.5 kg S ha−1 yr−1 (wetland headwater stream) to 3.8 kg S ha−1 yr−1 (forested headwater stream). With an average S deposition in open field of 1.3 kg S ha−1 yr−1 (2002–2006) the mass balance results in a net export of S from all catchments, except in catchments with >30% wetland. The high temporal and spatial resolution of this study demonstrates that the reducing environments of wetlands play a key role for the biogeochemistry of S in boreal landscapes and are net sinks of S. Forested areas, on the other hand were net sources of S.

  • 4.
    Boily, Jean-Francois
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Kozin, Philipp A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Particle Morphological and Roughness Controls on Mineral Surface Charge Development2014Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 141, nr 15 September, s. 567-578Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Effects of mineral particle morphology and roughness on potential determining ion (p.d.i.; H+, OH) loadings achieved at synthetic lepidocrocite (γ-FeOOH) surfaces were predominantly investigated by potentiometry and thermodynamic modeling. Nanosized rod- (RL) and lath-shaped (LL) particles exhibiting different proportions of the same predominant crystallographic faces acquired largely comparable pH, ionic strength and counterion (NaCl, NaClO4) dependencies on p.d.i. loadings. These results supported previous claims that faces ideally containing proton silent sites only, are likely populated by additional proton active sites. This concept was supported further by results of roughened LL-like particles (LLR) also showing highly congruent pH-, ionic strength- and composition-dependent p.d.i. loadings with those of LL and RL. These loadings thereby correspond to maximal levels allowed by net attractive and repulsive forces at each solution composition, irrespective of particle morphology. Contrasting equilibration times required to achieve these loadings revealed considerably slower exchange of p.d.i. and electrolyte ions near the point of zero charge in the rough LLR than in the more idealized LL and RL particles.

    Thermodynamic modeling was used to test various concepts accounting for these results. The model made use of a novel framework capable of isolating electrostatic contributions from different faces, and of accounting for ion-specific double-layer properties within a single crystallographic face. These efforts made use of capacitance values for each electrolyte ions within the framework of a recently developed Variable Capacitance Model. Attempts at modeling all three particle types were used to suggest that the (0 1 0) face contains ∼0.9 site nm−2 of proton active sites, a value notably constrained by recently published Na+, Cl, and ClO4 loadings derived by cryogenic X-ray photoelectron spectroscopy. The model presented in this work thus provides a means to predict p.d.i. loadings on multifaceted mineral particle surfaces, and can therefore be used to constrain further our understanding of mineral/water interface reactivity.

  • 5.
    Boily, Jean-François
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Chatman, Shawn
    Rosso, Kevin M
    Inner-Helmholtz potential development at the hematite (α-Fe2O3) (0 0 1) surface2011Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 75, nr 15, s. 4113-4124Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electric potentials of the (0 0 1) surface of hematite were measured as a function of pH and ionic strength in solutions of sodium nitrate and oxalic acid using the single-crystal electrode approach. The surface is predominantly charge-neutral in the pH 4–14 range, and develops a positive surface potential below pH 4 due to protonation of μ-OH0 sites (pK1,1,0,int = −1.32). This site is resilient to deprotonation up to at least pH 14 (−pK−1,1,0,int ≫ 19). The associated Stern layer capacitance of 0.31–0.73 F/m2 is smaller than typical values of powders, and possibly arises from a lower degree of surface solvation. Acid-promoted dissolution under elevated concentrations of HNO3 etches the (0 0 1) surface, yielding a convoluted surface populated by sites. The resulting surface potential was therefore larger under these conditions than in the absence of dissolution. Oxalate ions also promoted (0 0 1) dissolution. Associated electric potentials were strongly negative, with values as large as −0.5 V, possibly from metal-bonded interactions with oxalate. The hematite surface can also acquire negative potentials in the pH 7–11 range due to surface complexation and/or precipitation of iron species (0.0038 Fe/nm2) produced from acidic conditions. Oxalate-bearing systems also result in negative potentials in the same pH range, and may include ferric-oxalate surface complexes and/or surface precipitates. All measurements can be modeled by a thermodynamic model that can be used to predict inner-Helmholtz potentials of hematite surfaces.

  • 6. Colla, Christopher A.
    et al.
    Casey, William H.
    Ohlin, C. André
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Computational prediction of Mg-isotope fractionation between aqueous [Mg(OH2)6]2+ and brucite2018Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 227, s. 64-74Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The fractionation factor in the magnesium-isotope fractionation between aqueous solutions of magnesium and brucite changes sign with increasing temperature, as uncovered by recent experiments. To understand this behavior, the Reduced Partition Function Ratios and isotopic fractionation factors (Δ26/24Mgbrucite-Mg(aq)) are calculated using molecular models of aqueous [Mg(OH2)6]2+ and the mineral brucite at increasing levels of density functional theory. The calculations were carried out on the [Mg(OH2)6]2+·12H2O cluster, along with different Pauling-bond-strength-conserving models of the mineral lattice of brucite. Three conclusions were reached: (i) all levels of theory overestimate 〈Mg‒O〉 bond distances in the aqua ion complex relative to Tutton’s salts; (ii) the calculations predict that brucite at 298.15 K is always enriched in the heavy isotope, in contrast with experimental observations; (iii) the temperature dependencies of Wimpenny et al. (2014) and Li et al. (2014) could only be achieved by fixing the 〈Mg‒O〉 bond distances in the [Mg(OH2)6]2+·12H2O cluster to values close to those observed in crystals that trap the hydrated ion.

  • 7.
    Drotz, Stina Harrysson
    et al.
    Department of Forest Ecology & Management, Swedish University of Agricultural Sciences. Umeå.
    Sparrman, Tobias
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Schleucher, Jürgen
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    Nilsson, Mats
    Department of Forest Ecology & Management, Swedish University of Agricultural Sciences. Umeå.
    Öquist, Mats G
    Department of Forest Ecology & Management, Swedish University of Agricultural Sciences. Umeå.
    Effects of soil organic matter composition on unfrozen water content and heterotrophic CO2 production of frozen soils2010Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, nr 8, s. 2281-90Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Several recent studies have highlighted the importance of soil organic matter (SOM) mineralization at high latitudes during winter for ecosystem carbon (C) balances, and the ability of the soil to retain unfrozen water at sub-zero temperatures has been shown to be a major determinant of C mineralization rates. Further, SOM is believed to strongly influence the liquid water contents in frozen surface layers of boreal forest soils and tundra, but the mechanisms and specific factors involved are currently unknown. Here we evaluate the effects of the chemical composition of SUM on the amount of unfrozen water, the pore size equivalents in which unfrozen water can exist, and the microbial heterotrophic activity at sub-zero temperatures in boreal forest soils. To do this, we have characterized the chemical composition of SUM in forest soil samples (surface O-horizons) using solid state CP-MAS (cross polarization magic angle spinning) NMR spectroscopy. The acquired information was then used to elucidate the extent to which different fractions of SUM can explain the observed variations in unfrozen water content, pore size equivalents, and biogenic CO2 production rates in the examined soil samples under frozen conditions (-4 degrees C). The data evaluation was done by the use of principal component analysis (PCA) and projections to latent structures by means of partial least square (PLS). We conclude that aromatic, O-aromatic, methoxy/N-alkyl and alkyl C are the major SOM components affecting frozen boreal forest soil's ability to retain unfrozen water and sustain heterotrophic activity (95% confidence level). Our results reveal that solid carbohydrates have a significant negative impact (95% confidence level) on CO2 production in frozen boreal spruce forest soils, in contrast to the positive effects of carbohydrate polymers during unfrozen conditions. We conclude that the hierarchy of environmental factors controlling SOM mineralization changes as soils freeze. The effect of SUM composition on pore size distribution and unfrozen water content has a superior influence on SUM mineralization and hence on heterotrophic CO2 production of frozen soils. (C) 2010 Elsevier Ltd. All rights reserved.

  • 8.
    Hagvall, Kristoffer
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Persson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Karlsson, Torbjörn
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Spectroscopic characterization of the coordination chemistry and hydrolysis of gallium(III) in the presence of aquatic organic matter2014Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 146, nr 0, s. 76-89Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract Interactions between metals and natural organic matter (NOM) are of great environmental importance and one of the key factors influencing hydrolysis, solubility, and speciation of the metals. However, studying geochemically relevant metals like Al, Fe, and Cu is sometimes associated with analytical problems; for example Fe and Cu are both redox active. Gallium (Ga) is a non-redox active metal that usually occurs at very low concentrations in environmental samples and therefore a wide concentration range of metal(III)–NOM species can be explored by adding Ga(III) to such samples. This makes Ga(III) a good probe and analogue for other metal ions, in particular Al. In addition, due to the increased usage of Ga in society, a better understanding of how Ga interacts with NOM is of importance but such studies are scarce. In this work, Ga(III) interactions with two different organic materials (Suwannee River natural organic matter and Suwannee River fulvic acid) were studied using infrared (IR) and extended X-ray absorption fine structure (EXAFS) spectroscopy in a large experimental range (101–84,076 μg Ga g−1 dry weight; pH 3–8). Our IR spectroscopic results showed that Ga(III) is bonded mainly to carboxylic functional groups and suggested that only a fraction of the total number of carboxylic sites in the samples was actively involved in the bonding. Modeling of the EXAFS data revealed that Ga(III) formed mononuclear chelate complexes with NOM that strongly suppressed the hydrolysis and polymerization of Ga(III). At low Ga(III) concentrations (1675–16,649 μg g−1) organic complexes, consisting of 1–3 chelate ring structures, were the dominating species in the entire pH range while at higher concentrations (67,673–84,076 μg g−1, pH 3.0–7.0) we detected mixtures of mononuclear organic Ga(III) complexes, Ga(III) (hydr)oxide, and free Ga(III) (here defined as the hydrated Ga(III) ion and its soluble hydrolysis products). Moreover, the EXAFS results showed significantly higher contribution from second-shell C atoms (9–11) for the Ga(III)–organic complexes at the lowest concentration (101–125 μg g−1, pH 4.9–5.1), indicating formation of cage-like structures similar to Ga(III)–EDTA. Our combined results showed that Ga(III)–NOM interactions can be of importance for the solubility and speciation of Ga in environmental systems. Furthermore, the similarities between Ga(III) and previous Fe(III) results demonstrate that Ga(III) can be utilized as a probe for metal(III)–NOM interactions over an extended experimental range (e.g., pH and metal concentration) and thereby improve our knowledge about these interactions in general.

  • 9. Harley, Steven J.
    et al.
    Ohlin, C. Andre
    Casey, William H.
    Geochemical kinetics via the Swift-Connick equations and solution NMR2011Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 75, nr 13, s. 3711-3725Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Signal analysis in Nuclear Magnetic Resonance spectroscopy is among the most powerful methods to quantify reaction rates in aqueous solutions. To this end, the Swift-Connick approximations to the Bloch-McConnell equations have been used extensively to estimate rate parameters for elementary reactions. The method is primarily used for O-17 NMR in aqueous solutions, but the list of geochemically relevant nuclei that can be used is long, and includes Si-29, Al-27, F-19, C-13 and many others of particular interest to geochemists. Here we review the derivation of both the Swift-Connick and Bloch-McConnell equations and emphasize assumptions and quirks. For example, the equations were derived for CW-NMR, but are used with modern pulse FT-NMR and can be applied to systems that have exchange rates that are shorter than the lifetime of a typical pulse. The method requires a dilute solution where the minor reacting species contributes a negligible amount of total magnetization. We evaluate the sensitivity of results to this dilute-solution requirement and also highlight the need for chemically well-defined systems if reliable data are to be obtained. The limitations in using longitudinal relaxation to estimate reaction rate parameters are discussed. Finally, we provide examples of the application of the method, including ligand exchanges from aqua ions and hydrolysis complexes, that emphasize its flexibility. Once the basic requirements of the Swift-Connick method are met, it allows geochemists to establish rates of elementary reactions. Reactions at this scale lend themselves well to methods of computational simulation and could provide key tests of accuracy. (C) 2011 Elsevier Ltd. All rights reserved.

  • 10.
    Karlsson, Torbjörn
    et al.
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Persson, Per
    Umeå universitet, Teknisk-naturvetenskaplig fakultet, Kemi.
    Coordination chemistry and hydrolysis of Fe(III) in a peat humic acid studied by X-ray absorption spectroscopy2010Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, nr 1, s. 30-40Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The speciation of iron (Fe) in soils, sediments and surface waters is highly dependent on chemical interactions with natural organic matter (NOM). However, the molecular structure and hydrolysis of the Fe species formed in association with NOM is still poorly described. In this study extended X-ray absorption fine structure (EXAFS) spectroscopy was used to determine the coordination chemistry and hydrolysis of Fe(III) in solution of a peat humic acid (5010–49,200 μg Fe g−1 dry weight, pH 3.0–7.2). Data were analyzed by both conventional EXAFS data fitting and by wavelet transforms in order to facilitate the identification of the nature of backscattering atoms. Our results show that Fe occurs predominantly in the oxidized form as ferric ions and that the speciation varies with pH and Fe concentration. At low Fe concentrations (5010–9920 μg g−1; pH 3.0–7.2) mononuclear Fe(III)–NOM complexes completely dominates the speciation. The determined bond distances for the Fe(III)–NOM complexes are similar to distances obtained for Fe(III) complexed by desferrioxamine B and oxalate indicating the formation of a five-membered chelate ring structure. At higher Fe concentrations (49,200 μg g−1; pH 4.2–6.9) we detect a mixture of mononuclear Fe(III)–NOM complexes and polymeric Fe(III) (hydr)oxides with an increasing amount of Fe(III) (hydr)oxides at higher pH. However, even at pH 6.9 and a Fe concentration of 49,200 μg g−1 our data indicates that a substantial amount of the total Fe (>50%) is in the form of organic complexes. Thus, in environments with significant amounts of organic matter organic Fe complexes will be of great importance for the geochemistry of Fe. Furthermore, the formation of five-membered chelate ring structures is in line with the strong complexation and limited hydrolytic polymerization of Fe(III) in our samples and also agrees with EXAFS derived structures of Fe(III) in organic soils.

  • 11. Kohler, Stephan J.
    et al.
    Lidman, Fredrik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Laudon, Hjalmar
    Landscape types and pH control organic matter mediated mobilization of Al, Fe, U and La in boreal catchments2014Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 135, s. 190-202Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this study we present data from a seven-year time series from 15 nested streams within a 68 km(2) catchment, covering a pH gradient of almost three units. We demonstrate that the two landscape types, forest and wetlands, control the relative mobilization of Al and Fe in this boreal landscape. The La/U ratio is almost constant across the whole catchment despite large variations in pH, Al/Fe and TOC, whereas U and La mobilization increases with increasing contribution of deeper soils and groundwater further downstream. High Al/TOC ratios in the forested catchments suggest that Al originates from the underlying mineral soils, and low Al/TOC ratios derive from wetlands where Al is retained. We observe a competition effect on the binding to TOC between Al and La and also that the relationship between TOC, Al and La changes from the smaller (0.05-2 km(2)) catchments to larger (3-68 km(2)) downstream locations. As pH increase downstream, Al and Fe are gradually removed from the aqueous phase by precipitation of particulate gibbsite-like phases and ferrihydrite. This selective removal of Al and Fe from TOC binding sites results in higher La, and U concentrations downstream. Observed element patterns (U, La) and the range of upper continental crust normalized (La/Nd)(UCC) and (La/Yb)(UCC) in the near stream, riparian zone were very similar to the observed ratios across the whole catchment. The rising (La/Nd)(UCC) over (La/Yb)(UCC) may be due to a selective removal of REE binding to ferrihydrate in the riparian soil, the result of two distinctly different end-members but most probably not due to the in-stream precipitation of ferrihydrate or gibbsite-like phases. (C) 2014 Elsevier Ltd. All rights reserved.

  • 12. Kylander, Malin E.
    et al.
    Martinez-Cortizas, Antonio
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Greenwood, Sarah L.
    Mörth, Carl-Magnus
    Rauch, Sebastien
    Potentials and problems of building detailed dust records using peat archives: An example from Store Mosse (the "Great Bog"), Sweden2016Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 190, s. 156-174Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mineral dust deposition is a process often overlooked in northern mid-latitudes, despite its potential effects on ecosystems. These areas are often peat-rich, providing ample material for the reconstruction of past changes in atmospheric deposition. The highly organic (up to 99% in some cases) matrix of atmospherically fed mires, however, makes studying the actual dust particles (grain size, mineralogy) challenging. Here we explore some of the potentials and problems of using geochemical data from conservative, lithogenic elements (Al, Ga, Rb, Sc, Y, Zr, Th, Ti and REE) to build detailed dust records by using an example from the 8900-yr peat sequence from Store Mosse (the "Great Bog"), which is the largest mire complex in the boreo-nemoral region of southern Sweden. The four dust events recorded at this site were elementally distinct, suggesting different dominant mineral hosts. The oldest and longest event (6385-5300 cal yr BP) sees a clear signal of clay input but with increasing contributions of mica, feldspar and middle-REE- rich phosphate minerals over time. These clays are likely transported from a long-distance source (< 100 km). While dust deposition was reduced during the second event (5300-4370 cal yr BP), this is the most distinct in terms of its source character with [Eu/Eu*] UCC revealing the input of plagioclase feldspar from a local source, possibly active during this stormier period. The third (2380- 2200 cal yr BP) and fourth (1275-1080 cal yr BP) events are much shorter in duration and the presence of clays and heavy minerals is inferred. Elemental mass accumulation rates reflect these changes in mineralogy where the relative importance of the four dust events varies by element. The broad changes in major mineral hosts, grain size, source location and approximated net dust deposition rates observed in the earlier dust events of longer duration agree well with paleoclimatic changes observed in northern Europe. The two most recent dust events are much shorter in duration, which in combination with evidence of their local and regional character, may explain why they have not been seen elsewhere. 

  • 13. Martinez Cortizas, A.
    et al.
    Peiteado Varela, E.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Biester, H.
    Cheburkin, A.
    Reconstructing historical Pb and Hg pollution in NW Spain using multiple cores from the Chao de Lamoso bog (Xistral Mountains)2012Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 82, s. 68-78Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We have applied a single-bog multi-core approach to reconstruct historical Pb and Hg accumulation in an ombrotrophic bog from NW Spain, Chao de Lamoso (Xistral Mountains). Mercury was determined using a LECO-ALTEC AMA-254 analyzer, Pb with an EMMA-XRF analyzer and stable lead isotopes (four cores) by Quadrupole ICP-MS. Maximum concentrations were 74-122 mu g g(-1) for Pb and 142-300 ng g(-1) for Hg. Higher variability was found for Hg than for Pb (2-3 times and 1.5 times, respectively). The slopes of the relationship between Hg and Pb cumulative inventories also suggested differences in relative accumulation of both elements. This substantial spatial variability indicates that, compared with Pb, a more extended sampling may be needed for an accurate estimation of Hg accumulation in mires. The isotopic records showed higher and almost constant Pb-206/Pb-207 ratios (average 1.174 +/- 0.004) in the lower sections and a continuous decrease to the surface (minimum 1.141). By using the change in the isotopic composition of Pb we estimated a chronology for the last similar to 200 years which enabled and approximation of the temporal trends in metal pollution. Based on the average isotopic composition of the studied cores and the application of a simple binary mixing model, six periods with increasing proportions of pollution Pb were identified: prior to similar to 1875 AD, with an average proportion lower than 16%; similar to 1875-1910 AD, increasing up to 24%; similar to 1910-1950 AD, up to 35%; similar to 1950-1970, up to 54%; similar to 1970-1980 AD, up to 74%; and after similar to 1980 AD, increasing up to 80%. The period with the highest rate of increase in recent (since similar to 1900 AD) pollution Pb (equivalent to 2% year(-1)) seems to have started at the maximum in Pb accumulation around the early 1970s. The Hg records showed a more simple evolution with four main phases: prior to similar to 1875 AD with enrichments around 1.5-fold the background, similar to 1875-1955 AD with increasing enrichments; from similar to 1955 AD to similar to 1980 AD with maximum values (up to 4.2-fold); and from similar to 1980 AD to present, with a steady decline to 2.4-fold. For the most recent period (after similar to 1980 AD), the combination of decreasing Pb and Hg concentrations and accumulation rates/enrichments, and low Pb-206/Pb-207 ratios, may point to a higher relative importance of local sources (i.e. coal burning in a nearby power plant) in atmospheric metal pollution in the area.

  • 14. Naafs, B. D. A.
    et al.
    Inglis, G. N.
    Zheng, Y.
    Amesbury, M. J.
    Biester, H.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Blewett, J.
    Burrows, M. A.
    del Castillo Torres, D.
    Chambers, F. M.
    Cohen, A. D.
    Evershed, R. P.
    Feakins, S. J.
    Galka, M.
    Gallego-Sala, A.
    Gandois, L.
    Gray, D. M.
    Hatcher, P. G.
    Honorio Coronado, E. N.
    Hughes, P. D. M.
    Huguet, A.
    Kononen, M.
    Laggoun-Defarge, F.
    Lahteenoja, O.
    Lamentowicz, M.
    Marchant, R.
    McClymont, E.
    Pontevedra-Pombal, X.
    Ponton, C.
    Pourmand, A.
    Rizzuti, A. M.
    Rochefort, L.
    Schellekens, J.
    De Vleeschouwer, F.
    Pancost, R. D.
    Introducing global peat-specific temperature and pH calibrations based on brGDGT bacterial lipids2017Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 208, s. 285-301Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Glycerol dialkyl glycerol tetraethers (GDGTs) are membrane-spanning lipids from Bacteria and Archaea that are ubiquitous in a range of natural archives and especially abundant in peat. Previous work demonstrated that the distribution of bacterial branched GDGTs (brGDGTs) in mineral soils is correlated to environmental factors such as mean annual air temperature (MAAT) and soil pH. However, the influence of these parameters on brGDGT distributions in peat is largely unknown. Here we investigate the distribution of brGDGTs in 470 samples from 96 peatlands around the world with a broad mean annual air temperature (-8 to 27 degrees C) and pH (3-8) range and present the first peat-specific brGDGT-based temperature and pH calibrations. Our results demonstrate that the degree of cyclisation of brGDGTs in peat is positively correlated with pH, pH = 2.49 x CBTpeat + 8.07 (n = 51, R-2 = 0.58, RMSE = 0.8) and the degree of methylation of brGDGTs is positively correlated with MAAT, MAAT(peat) (degrees C) = 52.18 x MBT'(5me) - 23.05 (n = 96, R-2 = 0.76, RMSE = 4.7 degrees C). These peat-specific calibrations are distinct from the available mineral soil calibrations. In light of the error in the temperature calibration (similar to 4.7 degrees C), we urge caution in any application to reconstruct late Holocene climate variability, where the climatic signals are relatively small, and the duration of excursions could be brief. Instead, these proxies are well-suited to reconstruct large amplitude, longer-term shifts in climate such as deglacial transitions. Indeed, when applied to a peat deposit spanning the late glacial period (similar to 15.2 kyr), we demonstrate that MAAT(peat) yields absolute temperatures and relative temperature changes that are consistent with those from other proxies. In addition, the application of MAAT(peat) to fossil peat (i.e. lignites) has the potential to reconstruct terrestrial climate during the Cenozoic. We conclude that there is clear potential to use brGDGTs in peats and lignites to reconstruct past terrestrial climate. 

  • 15.
    Norén, Katarina
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Persson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Adsorption of monocarboxylates at the water/goethite interface: The importance of hydrogen bonding2007Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 71, nr 23, s. 5717-5730Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption of monocarboxylates (acetate, benzoate and cyclohexanecarboxylate) at the water/goethite interface was studied as a function of pH and ionic strength by means of quantitative adsorption measurements and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. ATR-FTIR spectra were obtained of suspensions prepared in both H2O and D2O. In order to identify the number of predominating surface complexes and to improve the resolution of overlapping peaks the ATR-FTIR spectra were subjected to a 2D correlation spectroscopic analysis. The adsorption envelopes of acetate, benzoate and cyclohexanecarboxylate are similar and depend strongly on pH and ionic strength, but the pH dependence is also correlated to the slightly different pKa values of the monocarboxylic acids. At the molecular level, the ATR-FTIR spectroscopic results reveal two surface complexes: one solvent-surface hydration-separated ion pair and one surface hydration-shared ion pair. The former predominates at circumneutral pH values while the latter forms mainly in the acidic pH range. We find no evidence for direct inner-sphere coordination between the carboxylic oxygens and the Fe(III) ions present at the surface. The identification of surface hydration-shared ion pairs emphasizes the importance of comparatively strong ionic hydrogen-bonding interactions for adsorption processes at the water/goethite interface.

  • 16. Panasci, Adele F.
    et al.
    McAlpin, J. Gregory
    Ohlin, C. Andre
    Christensen, Shauna
    Fettinger, James C.
    Britt, R. David
    Rustad, James R.
    Casey, William H.
    Cooperation between bound waters and hydroxyls in controlling isotope-exchange rates2012Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 78, s. 18-27Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mineral oxides differ from aqueous ions in that the bound water molecules are usually attached to different metal centers, or vicinal, and thus separated from one another. In contrast, for most monomeric ions used to establish kinetic reactivity trends, such as octahedral aquo ions (e.g., Al(H(2)O)(6)(3+)), the bound waters are closely packed, or geminal. Because of this structural difference, the existing literature about ligand substitution in monomer ions may be a poor guide to the reactions of geochemical interest. To understand how coordination of the reactive functional groups might affect the rates of simple water-exchange reactions, we synthesized two structurally similar Rh(III) complexes, [Rh(phen)(2)(H(2)O)(2)](3+) [1] and [Rh(phen)(2)(H(2)O)Cl](2+) [2] where (phen) = 1,10-phenanthroline. Complex [1] has two adjacent, geminal, bound waters in the inner-coordination sphere and [2] has a single bound water adjacent to a bound chloride ion. We employed Rh(III) as a trivalent metal rather than a more geochemically relevant metal like Fe(III) or Al(III) to slow the rate of reaction, which makes possible measurement of the rates of isotopic substitution by simple mass spectrometry. We prepared isotopically pure versions of the molecules, dissolved them into isotopically dissimilar water, and measured the rates of exchange from the extents of (18)O and (16)O exchange at the bound waters. The pH dependency of rates differ enormously between the two complexes. Pseudo-first-order rate coefficients at 298 K for water exchanges from the fully protonated molecules are close: k(0)(298) = 5 x 10(-8) (+/- 0.5 x 10(-8)) s(-1) for [1] and k(0)(298) = 2.5 x 10(-9)(+/- 1 x 10(-9)) for [2]. Enthalpy and entropy activation parameters (Delta H(double dagger) and Delta S(double dagger)) were measured to be 119(+/- 3) kJ mol(-1), and 14(+/- 1) J mol(-1) K(-1), respectively for [1]. The corresponding parameters for the mono-aquo complex, [2], are 132(+/- 3) kJ mol(-1) and 41.5(+/- 2) J mol(-1) K(-1). Rates increase by many orders of magnitude upon deprotonation of one of the bound waters in complex [1] because of the close proximity of a transferable proton that can convert the bound hydroxyl to a bound water. This interconversion allows the oxygen to exchange as a bound water, rather than as a bound hydroxyl, which is slow at near-neutral pH conditions. (C) 2011 Elsevier Ltd. All rights reserved.

  • 17. Pearson, Emma J.
    et al.
    Juggins, Steve
    Talbot, Helen M.
    Weckstrom, Jan
    Rosén, Peter
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Ryves, David B.
    Roberts, Stephen J.
    Schmidt, Roland
    A lacustrine GDGT-temperature calibration from the Scandinavian Arctic to Antarctic: Renewed potential for the application of GDGT-paleothermometry in lakes2011Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 75, nr 20, s. 6225-6238Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Quantitative climate reconstructions are fundamental to understand long-term trends in natural climate variability and to test climate models used to predict future climate change. Recent advances in molecular geochemistry have led to calibrations using glycerol dialkyl glycerol tetraethers (GDGTs), a group of temperature-sensitive membrane lipids found in Archaea and bacteria. GDGTs have been used to construct temperature indices for oceans (TEX(86) index) and soils (MBT/CBT index). The aim of this study is to examine GDGT-temperature relationships and assess the potential of constructing a GDGT-based palaeo-thermometer for lakes. We examine GDGT-temperature relationships using core top sediments from 90 lakes across a north-south transect from the Scandinavian Arctic to Antarctica including sites from Finland, Sweden, Siberia, the UK, Austria, Turkey, Ethiopia, Uganda, Chile, South Georgia and the Antarctic Peninsula. We examine a suite of 15 GDGTs, including compounds used in the TEX(86) and MBT/CBT indices and reflecting the broad range of GDGT inputs to small lake systems. GDGTs are present in varying proportions in all lakes examined. The TEX(86) index is not applicable to our sites because of the large relative proportions of soil derived and methanogenic components. Similarly, the MBT/CBT index is also not applicable and predicts temperatures considerably lower than those measured. We examine relationships between individual GDGT compounds and temperature, pH, conductivity and water depth. Temperature accounts for a large and statistically independent fraction of variation in branched GDGT composition. We propose a GDGT-temperature regression model with high accuracy and precision (R(2) = 0.88; RMSE = 2.0 degrees C; RMSEP = 2.1 degrees C) for use in lakes based on a subset of branched GDGT compounds and highlight the potential of this new method for reconstructing past temperatures using lake sediments. (C) 2011 Elsevier Ltd. All rights reserved.

  • 18.
    Rydberg, Johan
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Karlsson, Jon
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Nyman, Roger
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Wanhatalo, Ida
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Näthe, Kerstin
    Institute of Environmental Geology (IUG), Technical University of Braunschweig, Post Box 3329, D-38023 Braunschweig, Germany.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Importance of vegetation type for mercury sequestration in the northern Swedish mire, Rödmossamyran:  2010Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, nr 24, s. 7116-7126Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Even if mires have proven to be relatively reliable archives over the temporal trends in atmospheric mercury deposition, there are large discrepancies between sites regarding the magnitude of the anthropogenic contribution to the global mercury cycle. A number of studies have also revealed significant differences in mercury accumulation within the same mire area. This raises the question of which factors, other than mercury deposition, affect the sequestration of this element in peat. One such factor could be vegetation type, which has the potential to affect both interception and retention of mercury. In order to assess how small-scale differences in vegetation type can affect mercury sequestration we sampled peat and living plants along three transects on a northern Swedish mire. The mire has two distinctly different vegetation types, the central part consists of an open area dominated by Sphagnum whereas the surrounding fen, in addition to Sphagnum mosses, has an understory of ericaceous shrubs and a sparse pine cover. A few main patterns can be observed in our data; (1) Both peat and Sphagnum-mosses have higher mercury content (both concentration and inventory) in the pine-covered fen compared to the open Sphagnum area (100% and 71% higher for peat and plants, respectively). These differences clearly exceed the 33% difference observed for lead-210, which is considered as a good analogue for atmospheric mercury deposition. (2) The differences in mercury concentration between peat profiles within a single vegetation type can largely be attributed to differences in peat decomposition. (3) When growing side by side in the open Sphagnum area, the moss species Sphagnum subsecundum has significantly higher mercury concentrations compared to S. centrale (24 ± 3 and 18 ± 2 ng Hg g−1, respectively). Based on these observations we suggest that species composition, vegetation type and decomposition can affect the mercury sequestration in a peat record, and that any changes in these properties over time, or space, have the potential to modify the mercury deposition signal recorded in the peat.

  • 19. Schellekens, Judith
    et al.
    Bindler, Richard
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
    Martínez-Cortizas, Antonio
    McClymont, Erin L.
    Abbott, Geoffrey D.
    Biester, Harald
    Pontevedra-Pombal, Xabier
    Buurman, Peter
    Preferential degradation of polyphenols from Sphagnum-4-Isopropenylphenol as a proxy for past hydrological conditions in Sphagnum-dominated peat2015Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 150, s. 74-89Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The net accumulation of remains of Sphagnum spp. is fundamental to the development of many peatlands. The effect of polyphenols from Sphagnum on decomposition processes is frequently cited but has barely been studied. The central area of the Rodmossamyran peatland (Sweden) is an open lawn that consists mostly of Sphagnum spp. with a very low contribution from vascular plants. In order to determine the effects of decay on sphagnum phenols, 53 samples of a 2.7 m deep core from this lawn were analysed with pyrolysis gas chromatography-mass spectrometry (pyrolysis-GC-MS) and compared with more traditional decomposition proxies such as C/N ratio, UV light transmission of alkaline peat extracts, and bulk density. Factor analysis of 72 quantified pyrolysis products suggested that the variation in 4-isopropenylphenol was largely determined by aerobic decomposition instead of Sphagnum abundance. In order to evaluate the effects of aerobic decay in Sphagnum peat, down-core records from different climatic regions were compared using molecular markers for plant biopolymers and C/N ratio. These included markers for lignin from vascular plants ((di) methoxyphenols), polyphenols from Sphagnum spp. (4-isopropenylphenol), and cellulose (levoglucosan). Our results indicate that polyphenols from Sphagnum are preferentially degraded over polysaccharides; consequently the variability of the marker for sphagnum acid, 4-isopropenylphenol, was found indicative of decomposition instead of reflecting the abundance of Sphagnum remains. The fact that 4-isopropenylphenol is aerobically degraded in combination with its specificity for Sphagnum spp. makes it a consistent indicator of past hydrological conditions in Sphagnum-dominated peat. In contrast, the variability of C/N records in Sphagnum-dominated peat was influenced by both vegetation shifts and decomposition, and the dominant effect differed between the studied peatlands. Our results provide direction for modelling studies that try to predict possible feedback mechanisms between peatlands and future climate change, and indicate that the focus in Sphagnum decay studies should be on carbohydrates rather than on phenolic compounds.

  • 20.
    Simanova, Anna A.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Persson, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Loring, John S.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Evidence for ligand hydrolysis and Fe(III) reduction in the dissolution of Goethite by desferrioxamine-B2010Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, nr 23, s. 6704-6720Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Desferrioxamine-B (DFOB) is a bacterial trihydroxamate siderophore and probably the most studied to date. However, the manner in which DFOB adsorbs at mineral surfaces and promotes dissolution is still under discussion. Here we investigated the adsorption and dissolution reactions in the goethite–DFOB system using both in situ infrared spectroscopic and quantitative analytical methods. Experiments were carried out at a total DFOB concentration of 1 μmol/m2, at pH 6, and in the absence of visible light. Our infrared spectroscopic results indicated that the adsorption of DFOB was nearly complete after a 4-h reaction time. In an attempt to determine the coordination mode at the goethite surface, we compared the spectrum of adsorbed DFOB after a 4-h reaction time to the spectra of model aqueous species. However, this approach proved too simplistic in the case of such a complex ligand as DFOB, and we suggest that a more detailed investigation (IR in D2O, EXAFS of adsorbed model complexes) is needed to elucidate the structure of the adsorbed siderophore. Between a 4-hand 4-day reaction time, we observed the growth of carboxylate stretching bands at 1548 and 1404 cm-1, which are indicators of DFOB hydrolysis. Acetate, a product of DFOB hydrolysis at its terminal hydroxamate group, was quantified by ion chromatography. Its rate of formation was linear and nearly the same as the rate of Fe(III) dissolution. The larger hydrolysis product, a hydroxylamine fragment, was not detected by LC–MS. However, a signal due to the oxidized form of this fragment, a nitroso compound, was found to increase linearly with time, which is an indirect indication for Fe(III) reduction. Based on these findings, we propose that DFOB undergoes metal-enhanced hydrolysis at the mineral surface followed by the reduction of surface Fe(III). While Fe(II) was not detected in solution, this is likely because it remains adsorbed at the goethite surface or becomes buried in the goethite crystal by electron conduction. Taking into account the extent and similarity between the rates of hydrolysis and dissolution, we suggest that a reductive mechanism could play an important part in the dissolution of goethite by DFOB. This possibility has not been considered previously in the absence of light and at circumneutral pH.

  • 21.
    Sun, Xiaole
    et al.
    Stockholm Univ.
    Olofsson, Martin
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Andersson, Per S.
    Swedish Museum Nat Hist.
    Fry, Brian
    Griffith Univ, Australian Rivers Inst, Nathan, Qld 4111, Australia.
    Legrand, Catherine
    Linnéuniversitetet, Institutionen för biologi och miljö (BOM).
    Humborg, Christoph
    Stockholm Univ.
    Morth, Carl-Magnus
    Stockholm Univ.
    Effects of growth and dissolution on the fractionation of silicon isotopes by estuarine diatoms2014Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 130, s. 156-166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Studies of silicon (Si) isotope fractionation during diatom growth in open ocean systems have documented lower Si isotopic values (delta Si-30) in the biogenic silica of diatom frustules compared to dissolved silicon. Recent findings also indicate that Si isotope fractionation occurs during dissolution of diatom frustules, producing higher delta Si-30 values in the remaining biogenic silica. This study focuses on diatoms from high production areas in estuarine and coastal areas that represent approximately 30-50% of the global marine primary production. Two species of diatoms, Thalassiosira baltica and Skeletonema marinoi, were isolated from the brackish Baltic Sea, one of the largest estuarine systems in the world. These species were used for laboratory investigations of Si isotope fractionation during diatom growth and the subsequent dissolution of the diatom frustules. Both species of diatoms give an identical Si isotope fractionation factor during growth of -1.50 +/- 0.36 parts per thousand (2 sigma) for Si-30, which falls in the range of -2.09 parts per thousand to -0.55 parts per thousand of published data. Our results also suggest a dissolution-induced Si isotope fractionation factor of -0.86 parts per thousand at early stage of dissolution, but this effect was observed only in DSi and no significant Si isotope change was observed for BSi. The growth and dissolution results are applied to a Baltic Sea sediment core to reconstruct DSi utilization by diatoms, and found to be in agreement with the observed DSi uptake rates in the overlying water column during diatom growth.

  • 22.
    Sundman, Anneli
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Karlsson, Torbjörn
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Sjöberg, Staffan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Persson, Per
    Complexation and precipitation reactions in the ternary As(V)–Fe(III)–OM (organic matter) system2014Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 145, s. 297-314Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The predominant forms of arsenic (As) in anoxic and oxic environments are As(III) and As(V), respectively, and the fate of these forms is influenced by interactions with mineral surfaces and organic matter (OM). Interactions between As(V) and OM are believed to occur mainly via iron(Fe)-bridges in ternary Fe–arsenate complexes, but direct evidence for these interactions are scarce. Furthermore, since the speciation of Fe in the presence of organic matter varies as a function of pH and Fe concentration, a central question is how different chemical conditions will affect the As–Fe–OM interactions. In order to answer this, the As(V)–Fe(III)–OM system have been studied under a large range of experimental conditions (6485–67,243 ppm Fe(III) and Fe(III):As(V) ratios of 0.5–20 at pH 3–7), with Suwannee River natural organic matter and Suwannee River fulvic acid as sources of OM, using Fe and As K-edge X-ray absorption spectroscopy (XAS), infrared (IR) spectroscopy and chemical equilibrium modeling. Our collective results showed that interactions in the ternary As(V)–Fe(III)–OM system were strongly influenced by pH, total concentrations and ratios among the reactive species. In particular, the high stability of the Fe(III)–OM complexes exerted a strong control on the speciation. The predominant species identified were mononuclear Fe(III)–OM complexes, Fe(III) (hydr)oxides and FeAsO4 solids. The experimental results also showed that at low concentrations the Fe(III)–OM complexes were sufficiently stable to prevent reaction with arsenate. The chemical equilibrium models developed corroborated the spectroscopic results and indicated that As(V) was distributed over two solid phases, namely FeAsO4(s) and Fe(OH)1.5(AsO4)0.5(s). Thus, neither ternary As(V)–Fe(III)–OM complexes nor As(V) surface complexes on Fe(III) (hydr)oxides were necessary to explain the collective results presented in this study.

  • 23. Taubald, H.
    et al.
    Tonderski, K.
    Andersson, L.
    Ronnberg, R.
    Ahlgren, J.
    Oxygen isotopes in phosphate as a tracer for sources and pathways of catchment P in stream water2010Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 74, nr 12, s. A1030-A1030Artikkel i tidsskrift (Annet vitenskapelig)
  • 24. Tinnacher, Ruth M.
    et al.
    Holmboe, Michael
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen. Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, United States.
    Tournassat, Christophe
    Bourg, Ian C.
    Davis, James A.
    Ion adsorption and diffusion in smectite: Molecular, pore, and continuum scale views2016Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 177, s. 130-149Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Clay-rich media have been proposed as engineered barrier materials or host rocks for high level radioactive waste repositories in several countries. Hence, a detailed understanding of adsorption and diffusion in these materials is needed, not only for radioactive contaminants, but also for predominant earth metals, which can affect radionuclide speciation and diffusion. The prediction of adsorption and diffusion in clay-rich media, however, is complicated by the similarity between the width of clay nanopores and the thickness of the electrical double layer (EDL) at charged clay mineral-water interfaces. Because of this similarity, the distinction between 'bulk liquid' water and 'surface' water (i.e., EDL water) in clayey media can be ambiguous. Hence, the goal of this study was to examine the ability of existing pore scale conceptual models (single porosity models) to link molecular and macroscopic scale data on adsorption and diffusion in compacted smectite. Macroscopic scale measurements of the adsorption and diffusion of calcium, bromide, and tritiated water in Na-montmorillonite were modeled using a multi-component reactive transport approach while testing a variety of conceptual models of pore scale properties (adsorption and diffusion in individual pores). Molecular dynamics (MD) simulations were carried out under conditions similar to those of our macroscopic scale diffusion experiments to help constrain the pore scale models. Our results indicate that single porosity models cannot be simultaneously consistent with our MD simulation results and our macroscopic scale diffusion data. A dual porosity model, which allows for the existence of a significant fraction of bulk liquid water-even at conditions where the average pore width is only a few nanometers-may be required to describe both pore scale and macroscopic scale data.

  • 25. Wang, Zheming
    et al.
    Zachara, John M
    Boily, Jean-François
    Pacific Northwest National Laboratory, Richland, USA.
    Xia, Yuanxian
    Resch, Tom C
    Moore, Dean A
    Liu, C
    Determining individual mineral contributions to U(VI) adsorption in a contaminated aquifer sediment: a fluorescence spectroscopy study2011Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 75, nr 10, s. 2965-2979Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The adsorption and speciation of U(VI) was investigated on contaminated, fine grained sediment materials from the Hanford 300 area (SPP1 GWF) in simulated groundwater using cryogenic laser-induced U(VI) fluorescence spectroscopy combined with chemometric analysis. A series of reference minerals (montmorillonite, illite, Michigan chlorite, North Carolina chlorite, California clinochlore, quartz and synthetic 6-line ferrihydrite) was used for comparison that represents the mineralogical constituents of SPP1 GWF. Surface area-normalized Kd values were measured at U(VI) concentrations of 5 × 10−7 and 5 × 10−6 mol L−1 that displayed the following affinity series: 6-line-ferrihydrite > North Carolina chlorite ≈ California clinochlore > quartz ≈ Michigan chlorite > illite > montmorillonite. Both time-resolved spectra and asynchronous two-dimensional (2D) correlation analysis of SPP1 GWF at different delay times indicated that two major adsorbed U(VI) species were present in the sediment that resembled U(VI) adsorbed on quartz and phyllosilicates. Simulations of the normalized fluorescence spectra confirmed that the speciation of SPP1 GWF was best represented by a linear combination of U(VI) adsorbed on quartz (90%) and phyllosilicates (10%). However, the fluorescence quantum yield for U(VI) adsorbed on phyllosilicates was lower than quartz and, consequently, its fractional contribution to speciation may be underestimated. Spectral comparison with literature data suggested that U(VI) exist primarily as inner-sphere complexes with surface silanol groups on quartz and as surface U(VI) tricarbonate complexes on phyllosilicates.

  • 26.
    Zhu, Wei
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Song, Yu
    Adediran, Gbotemi A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Jiang, Tao
    Reis, Ana T.
    Pereira, Eduarda
    Skyllberg, Ulf
    Björn, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Mercury transformations in resuspended contaminated sediment controlled by redox conditions, chemical speciation and sources of organic matter2018Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 220, s. 158-179Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mercury (Hg) contaminated sediments can be significant sources of Hg in aquatic ecosystems and, through re-emission processes, to the atmosphere. Transformation and release of Hg may be enhanced by various sediment perturbation processes, and controlling biogeochemical factors largely remain unclear. We investigated how rates of Hg transformations in pulp-fiber enriched sediment contaminated by Hg from chlor-alkali industry were controlled by (i) transient redox-changes in sulfur and iron chemistry, (ii) the chemical speciation and solubility of Hg, and (iii) the sources and characteristics of organic matter (OM). Sediment-bottom water microcosm systems were exposed to four combinations of air and nitrogen gas for a total time of 24 h. The treatments were: 24 h N-2, 0.5 h air + 23.5 h N-2, 4 h air + 20 h N-2 and 24 h of air exposure. As a result of these treatments, microcosms spanned a wide range of redox potential, as reflected by the dissolved sulfide concentration range of <= 0.3-97 mu M. Four different chemical species of inorganic divalent Hg (Hg-II) and methyl mercury (MeHg), enriched in different Hg isotope tracers, were added to the microcosms: 201 Hg(NO3)(2)(aq), Hg-202(II) adsorbed to OM (Hg-202(II)-OM(ads)), Hg-198(II) as microcrystalline metacinnabar (beta-(HgS)-Hg-198(s)) and (MeHgCl)-Hg-204(aq). Microcosm systems were composed of bottom water mixed with sediment taken at 0-2, 0-5 and 0-10 cm depth intervals. The composition of OM varied with sediment depth such that compared to deeper sediment, the 0-2 cm depth-interval had a 2-fold higher contribution of labile OM originating from algal and terrestrial inputs, serving as metabolic electron-donors for microorganisms. The potential methylation rate constant (k(meth)) of Hg tracers and net formation of ambient MeHg (MeHg/THg molar ratio) increased up to 50% and 400%, respectively at intermediate oxidative conditions, likely because of an observed 2-fold increase in sulfate concentration stimulating the activity of sulfate reducing bacteria with a capability of methylating Hg-II. Due to differences in Hg-II water-sediment partitioning, k(meth) varied by a factor of 11-70 for the different isotope-enriched Hg tracers. The chemical form of Hg-II was a major controlling factor for k(meth) and its response to the resuspension-oxidation of the system. The beta-(HgS)-Hg-198(s) tracer had the lowest k(meth) and it was mainly constrained by redox-driven Hg-II solubility. The Hg-202(II)-OM(ads) tracer showed an intermediate value on k(meth). It was controlled by both Hg-II solubility and availability of electron donors and acceptors, regulating bacterial activity. The Hg-201(NO3)(2)(aq) tracer had the highest value on k(meth) which was limited mainly by bacterial activity. The k(meth) was up to a factor of 3 higher in the 0-2 cm sediment depth-interval than in 0-5 and 0-10 cm intervals due to a larger contribution of labile OM in the 0-2 cm sediment. Reduction of Hg-II to Hg-0 followed by volatilization exclusively occurred at high sulfidic conditions in the top 0-2 cm sediment. Aromatic moieties of terrestrial OM, present mainly in the top sediment, is suggested to control the reduction of Hg-II. The Hg-0 volatilization rate constant for the Hg-202(II)-OM (ads) tracer exceeded that for beta-(HgS)-Hg-198(s) by one order of magnitude. Our results suggest that contaminated sediments posing a high risk for reactivation of legacy Hg following transient redox resuspension events are characterized by depletion of sulfate in the sediment porewater prior to resuspension, predominance of Hg-II species with solubility exceeding that of crystalline beta-HgS(s), and conditions promoting in situ formation and/ or import of labile OM from algal and terrestrial sources.

  • 27.
    Åkerblom, Staffan
    et al.
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Bishop, Kevin
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Björn, Erik
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Lambertsson, Lars
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Eriksson, Tobias
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Nilsson, Mats B.
    Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, Umeå, Sweden.
    Significant interaction effects from sulfate deposition and climate on sulfur concentrations constitute major controls on methylmercury production in peatlands2013Inngår i: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 102, s. 1-11Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Transformation of inorganic mercury (Hg) to methyl mercury (MeHg) in peatlands is a key process in making boreal catchments a source of MeHg to freshwater ecosystems. Due to the importance of sulfur-reducing bacteria (SRB) for this process, past atmospheric deposition of sulfate (SO42-) may have increased net terrestrial Hg methylation. A long-term (14-year) factorial design field experiment was used to investigate the effect of enhanced SO42- deposition and raised temperature using a greenhouse (GH) treatment (air temperature similar to+4 degrees C; soil temperature 20 cm below mire surface similar to+2 degrees C) on sulfur (S) turnover, net Hg methylation, MeHg and total Hg concentrations in a boreal mire in northern Sweden. Of the SO42--S added during 14 years, 50% was retained in the plots without GH treatment while the combination of SO42- addition and GH treatment resulted in 15% S retention. The addition of SO42- (7-fold ambient SO42--deposition) increased (p < 0.05) the net Hg methylation (200%) as well as the store of S (150%) and MeHg (120%) in the peat. A combination of enhanced SO42- deposition and GH treatment decreased both the net Hg methylation rate constant (0.018 +/- 0.006 d(-1)) and MeHg content (1.2 +/- 0.2 ng g(-1) dry weight (dw)) relative to the sites with enhanced SO42- deposition without GH treatment (0.065 +/- 0.013 d(-1) and 3.7 +/- 0.6 ng g(-1) dw, respectively). The concentration of Hg in the peat declined (p < 0.05) in response to experimental addition of SO42-. Despite the decrease in Hg in response to SO42- deposition, these plots had the highest amounts of MeHg as well as the highest Hg methylation rate constants. This indicates that the concentration of S is more important than the concentration of Hg for the production of MeHg in this boreal landscape. These results also show that long-term chronic SO42- deposition at rates similar to those found in polluted areas of Europe and North America increase the capacity of wetlands to methylate Hg and store MeHg, which can ultimately be released to streams and lakes. This study also, for the first time, indicates that the enhancing effect of SO42- on the production of MeHg might be counteracted by increased temperature. 

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