| 51. |
- Kylander, Malin E., et al.
(author)
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Potentials and problems of building detailed dust records using peat archives : An example from Store Mosse (the "Great Bog"), Sweden
- 2016
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In: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533 .- 0046-564X. ; 190, s. 156-174
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Journal article (peer-reviewed)abstract
- 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.
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| 52. |
- Sjöberg, Susanne, et al.
(author)
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Rare Earth element enriched birnessite in water-bearing fractures, the Ytterby mine, Sweden
- 2017
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In: Applied Geochemistry. - Amsterdam : Elsevier. - 0883-2927 .- 1872-9134. ; 78, s. 158-171
-
Journal article (peer-reviewed)abstract
- Characterization of a black substance exuding from fractured bedrock in a subterranean tunnel revealed a secondary manganese oxide mineralisation exceptionally enriched in rare earth elements (REE). Concentrations are among the highest observed in secondary ferromanganese precipitates in nature. The tunnel is located in the unsaturated zone at shallow depth in the former Ytterby mine, known for the discovery of yttrium, scandium, tantalum and five rare earth elements.Elemental analysis and X-ray diffraction of the black substance establish that the main component is a manganese oxide of the birnessite type. Minor fractions of calcite, other manganese oxides, feldspars, quartz and about 1% organic matter were also found, but no iron oxides were identified. The Ytterby birnessite contains REE, as well as calcium, magnesium and traces of other metals. The REE, which constitute 1% of the dry mass and 2% of the metal content, are firmly included in the mineral structure and are not released by leaching at pH 1.5 or higher. A strong preference for the trivalent REE over divalent and monovalent metals is indicated by concentration ratios of the substance to fracture water. The REE-enriched birnessite has the general formula Mx(Mn3+,Mn4+)2O4·(H2O)n with M = (0.37–0.41) Ca + 0.02 (REE + Y), 0.04 Mg and (0.02–0.03) other metals, and with [Mn3+]/[Mn4+] = 0.86–1.00.The influence of microorganisms on the accumulation of this REE enriched substance is demonstrated by electron paramagnetic resonance spectroscopy. Results show that it is composed of two or more manganese phases, one of which has a biogenic signature. In addition, the occurrence of C31 to C35 extended side chain hopanoids among the identified lipid biomarkers combined with the absence of ergosterol, a fungal lipid biomarker, indicate that the in-situ microbial community is bacterial rather than fungal.
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| 53. |
- Uddh Söderberg, Terese, 1976-, et al.
(author)
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Metal solubility and transport at a contaminated landfill site – From the source zone into the groundwater
- 2019
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In: Science of the Total Environment. - : Elsevier. - 0048-9697 .- 1879-1026. ; 668, s. 1064-1076
-
Journal article (peer-reviewed)abstract
- 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.
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| 54. |
- Bonaglia, Stefano, et al.
(author)
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The fate of fixed nitrogen in marine sediments with low organic loading : an in situ study
- 2017
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In: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 14:2, s. 285-300
-
Journal article (peer-reviewed)abstract
- Over the last decades, the impact of human activities on the global nitrogen (N) cycle has drastically increased. Consequently, benthic N cycling has mainly been studied in anthropogenically impacted estuaries and coasts, while in oligotrophic systems its understanding is still scarce. Here we report on benthic solute fluxes and on rates of denitrification, anammox, and dissimilatory nitrate reduction to ammonium (DNRA) studied by in situ incubations with benthic chamber landers during two cruises to the Gulf of Bothnia (GOB), a cold, oligotrophic basin located in the northern part of the Baltic Sea. Rates of N burial were also inferred to investigate the fate of fixed N in these sediments. Most of the total dissolved fixed nitrogen (TDN) diffusing to the water column was composed of organic N. Average rates of dinitrogen (N-2) production by denitrification and anammox (range: 53-360 mu mol Nm(-2) day(-1)) were comparable to those from Arctic and subarctic sediments worldwide (range: 34-344 mu mol Nm(-2) day(-1)). Anammox accounted for 18-26% of the total N2 production. Absence of free hydrogen sulfide and low concentrations of dissolved iron in sediment pore water suggested that denitrification and DNRA were driven by organic matter oxidation rather than chemolithotrophy. DNRA was as important as denitrification at a shallow, coastal station situated in the northern Bothnian Bay. At this pristine and fully oxygenated site, ammonium regeneration through DNRA contributed more than one-third to the TDN efflux and accounted, on average, for 45% of total nitrate reduction. At the offshore stations, the proportion of DNRA in relation to denitrification was lower (0-16% of total nitrate reduction). Median value and range of benthic DNRA rates from the GOB were comparable to those from the southern and central eutrophic Baltic Sea and other temperate estuaries and coasts in Europe. Therefore, our results contrast with the view that DNRA is negligible in cold and well-oxygenated sediments with low organic carbon loading. However, the mechanisms behind the variability in DNRA rates between our sites were not resolved. The GOB sediments were a major source (237 kt yr(-1), which corresponds to 184% of the external N load) of fixed N to the water column through recycling mechanisms. To our knowledge, our study is the first to document the simultaneous contribution of denitrification, DNRA, anammox, and TDN recycling combined with in situ measurements.
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| 55. |
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| 56. |
- Gustafsson, Jon Petter, 1964-, et al.
(author)
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Aluminium and base cation chemistry in dynamic acidification models - need for a reappraisal?
- 2018
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In: SOIL. - : COPERNICUS GESELLSCHAFT MBH. - 2199-3971 .- 2199-398X. ; 4:4, s. 237-250
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Journal article (peer-reviewed)abstract
- Long-term simulations of the water composition in acid forest soils require that accurate descriptions of aluminium and base cation chemistry are used. Both weathering rates and soil nutrient availability depend on the concentrations of Al3+, of H+, and of base cations (Ca2+, Mg2+, Na+, and K+). Assessments of the acidification status and base cation availability will depend on the model being used. Here we review in what ways different dynamic soil chemistry models describe the processes governing aluminium and base cation concentrations in the soil water. Furthermore, scenario simulations with the HD-MINTEQ model are used to illustrate the difference between model approaches. The results show that all investigated models provide the same type of response to changes in input water chemistry. Still, for base cations we show that the differences in the magnitude of the response may be considerable depending on whether a cation-exchange equation (Gaines-Thomas, Gapon) or an organic complexation model is used. The former approach, which is used in many currently used models (e.g. MAGIC, ForSAFE), causes stronger pH buffering over a relatively narrow pH range, as compared to state-of-the-art models relying on more advanced descriptions in which organic complexation is important (CHUM, HD-MIN PLQ). As for aluminium, a "fixed" gibbsite constant, as used in MAGIC, SMART/VSD, and ForSAFE, leads to slightly more pH buffering than in the more advanced models that consider both organic complexation and Al(OH)(3) (s) precipitation, but in this case the effect is small. We conclude that the descriptions of acid-base chemistry and base cation binding in models such as MAGIC, SMART/VSD, and ForSAFE are only likely to work satisfactorily in a narrow pH range. If the pH varies greatly over time, the use of modern organic complexation models is preferred over cation-exchange equations.
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| 57. |
- Ju, YeoJin, et al.
(author)
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Long-term change in uranium migration processes in highly eroded granite, demonstrated by uranium series disequilibrium in fracture-filling materials
- 2023
-
In: Applied Geochemistry. - : Elsevier. - 0883-2927 .- 1872-9134. ; 148
-
Journal article (peer-reviewed)abstract
- The mineralization and mobilization of uranium (U) are strongly associated with subsurface redox processes, which can affect the U inventory of deep geological repositories of nuclear waste and are to be considered in safety assessments. The Korea Atomic Energy Research Institute (KAERI) underground research tunnel (KURT) is located in an active groundwater recharge area in granitic bedrock, where oxidizing meteoric water infiltrates the subsurface through permeable zones of highly weathered granite, forming multiple redox fronts. Fracture-filling materials (FFMs) are U-enriched, with concentrations of up to ∼50 mg/kg. We examined long-lived radioactive isotopes of 230Th, 232Th, 234U, 235U, and 238U and other redox-sensitive elements and isotopes, e.g., Fe, δ56Fe, and Ce/Ce*, in the FFMs to understand fluctuations in redox conditions in the granitic fracture system. The primary focus was on U migration processes and to decipher the depths of meteoric water infiltration over geological timescales. Enrichment of uranium and other redox-sensitive elements occurred in FFMs at relatively shallow depths (∼180 m below ground level, bgl), implying that the U distribution was associated with redox interactions of the intruding groundwater that precipitated the secondary minerals. Interaction of FFMs with groundwater caused activity ratios (AR) of the FFMs to deviate moderately from secular equilibrium (AR = 1); 234U/238U AR of 0.87–1.25, and 230Th/238U AR of 0.76–1.22. A dynamic redox transition zone, witnessed by uranium series disequilibrium, shows both deposition and complex redistribution in the 120–205 Ka time frame, is confined to the upper ∼180 m bgl of the fractured rock. The results provide new insights into the long-term paleo-redox processes in the complex granitic fracture systems, which are analogs of potential deep-seated geological repositories for high-level radioactive waste.
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| 58. |
- Routh, Joyanto, 1968-, et al.
(author)
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Sedimentary geochemical record of humanï¿œinduced environmental changes in the Lake Brunnsviken watershed, Sweden
- 2004
-
In: Limnology and Oceanography. - : John Wiley & Sons. - 0024-3590 .- 1939-5590. ; 49:5, s. 1560-1569
-
Journal article (peer-reviewed)abstract
- Environmental changes in Lake Brunnsviken, its watershed, and the greater Stockholm region since the middle of the nineteenth century have left interpretable geochemical imprints in the bottom sediments. These human-induced perturbations within the lakeï¿œs watershed included agriculture, urbanization, sewage and industrial disposal, and water column aeration. Smaller d15Ntotal values, high organic carbon mass accumulation rates, low C:N ratios, and larger d13Corg values identify periods of increased nutrient delivery and elevated primary productivity in the lake. C: S ratios that change from high to low trace the transition from an oxic hypolimnion to an anoxic one during the periods of high productivity. Accumulations of redox-sensitive trace elements increase during the anoxic period and are further magnified during a time of industrial waste discharge into the lake. A recent decrease in black carbon concentrations in sediments reflects the conversion from wood and coal to cleaner forms of energy.
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| 59. |
- Routh, Joyanto, 1968-, et al.
(author)
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Sedimentary organic matter sources and depositional environment in the Yegua formation (Brazos County, Texas)
- 1999
-
In: Organic Geochemistry. - : Elsevier. - 0146-6380 .- 1873-5290. ; 30:11, s. 1437-1453
-
Journal article (peer-reviewed)abstract
- The complex depositional environment of the Eocene Yegua formation (Brazos County, Texas) can be better understood by integrating organic matter (OM) geochemistry with stratigraphy. Yegua sediments represent parasequences separated by exposure surfaces. Organic petrography and geochemistry (biomarkers, C/N ratios, and carbon isotopes) indicate the presence of both terrestrial and marine OM in transgressive sediments. In contrast, regressive sediments contain only terrestrial OM. These differences relate to contrasting OM sources and depositional styles on the shelf. OM in the sediments is immature and the potential for generating hydrocarbons is poor. The study suggests that organic geochemical data can help in distinguishing transgressive and regressive environments in sedimentary formations.
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| 60. |
- Hylén, Astrid, 1991, et al.
(author)
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Enhanced benthic nitrous oxide and ammonium production after natural oxygenation of long-term anoxic sediments
- 2022
-
In: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 67:2, s. 419-433
-
Journal article (peer-reviewed)abstract
- Coastal and shelf sediments are central in the global nitrogen (N) cycle as important sites for the removal offixed N. However, this ecosystem service can be hampered by ongoing deoxygenation in many coastal areas.Natural reoxygenation could reinstate anoxic sediments as sites wherefixed N is removed efficiently. To investi-gate this further, we studied benthic N cycling in previously long-term anoxic sediments, following a largeintrusion of oxygenated water to the Baltic Sea. During three campaigns in 2016–2018, we measured in situsediment–waterfluxes of ammonium (NHþ4), nitrate (NO3), oxygen (O2), dissolved inorganic carbon, and NO3reduction processes using benthic chamber landers. Sediment microprofiles of O2, nitrous oxide (N2O), andhydrogen sulfide were measured in sediment cores. At a permanently oxic station, denitrification to N2was themain NO3reduction process. Benthic N2O production appeared to be linked to nitrification, although no netN2Ofluxes from the sediment were detected. At newly oxygenated sites, dissimilatory NO3reduction to NHþ4comprised almost half of the total NO3reduction. At these stations, the removal offixed N was inefficient dueto high effluxes of NHþ4. Sedimentary N2O production was associated with incomplete denitrification, account-ing for 41–88% of the total denitrification rate. Microprofiling revealed algae aggregates as potential hotspots ofseafloor N2O production. Our results show that transient oxygenation of euxinic systems initiates benthic NO3reduction, but may not lead to efficient sedimentary removal offixed N. Instead, recycling of N compounds ispromoted, which may accelerate the return to anoxia.
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