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- Widerlund, Anders, et al.
(författare)
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Early diagenesis of arsenic in sediments of the Kalix River estuary, northern Sweden
- 1995
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Ingår i: Chemical Geology. - 0009-2541 .- 1872-6836. ; 125:3-4, s. 185-196
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Tidskriftsartikel (refereegranskat)abstract
- Solid-phase As, Fe, Mn, S and Al and pore-water total As, Fe, Mn and S have been determined for two cores from the Kalix River estuary. At the same station, the depositional flux of arsenic was measured sediment traps. Fe(III)-oxides persist in the anoxic zone of the sediment and act as a carrier for arsenic down to depths of 10-15 cm. The release of arsenic into the pore water is controlled by the reduction/dissolution of these oxides. As a result, internal cycling of arsenic, i.e. upward diffusion in pore water, re-adsorption onto Fe(III)-oxides in the oxidized surface layer and reburial occurs in the uppermost 10-15 cm. At the base of the arsenic cycling zone, solid-phase arsenic maxima (160-170 μg g-1) of probable diagenetic origin occur. The quantity of arsenic diffusing back towards the oxidized surface layer (2.2 μg cm-2 yr-1 As) is close to 75% of the quantity of arsenic being deposited due to sedimentation (2.9 μg cm-2 yr-1 As). However, a mass balance for the surface layer indicates that re-adsorption of arsenic onto Fe(III)-oxides may effectively prevent diffusion of dissolved arsenic back into the overlying water column. It is concluded that the interpretation of sedimentary arsenic profiles may be severely complicated due to post-depositional migration of arsenic
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- Widerlund, Anders
(författare)
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Early diagenetic remobilization of copper in near-shore marine sediments : a quantitative pore-water model
- 1996
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203 .- 1872-7581. ; 54:1-2, s. 41-53
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Tidskriftsartikel (refereegranskat)abstract
- Solid-phase and pore-water Cu have been determined for two cores in the low-salinity (2-3‰) Kalix River estuary, Sweden. The pore-water Cu concentration in the oxidized surface layer of the sediment (32-42 nmol l-1) exceeded the Cu concentration in the overlying bottom water (10-11 nmol l-1) by a factor of 3-4. Assuming that organic matter degradation follows first-order kinetics, a multi-G model with two organic matter fractions of different reactivity was used to describe the early diagenetic decomposition of organic matter. An estimated Cu/C mole ratio of 5.10-5 was obtained from sediment trap data. By combining this ratio with a steady-state pore-water Cu model, the early diagenetic remobilization of Cu was linked to the decomposition of organic matter. The rate constant for the reaction that releases Cu could be set equal to the decay constant of the highly reactive organic matter fraction (2.0 yr-1). This highly reactive fraction was decomposing under aerobic conditions close to the sediment-water interface. Early diagenetic remobilization of Cu in these sediments thus appears to be entirely controlled by aerobic decomposition of organic matter. An estimate of the diffusive benthic efflux of Cu (2.9 nmol cm-2 yr-1) suggests that ˜ 3% of the amount of Cu being deposited is released back into the water column.The pore-water model supports the idea that the Redfield model for the biological control of nitrogen and phosphorus can be extended to certain bioreactive trace elements.
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- Widerlund, Anders, et al.
(författare)
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Redox cycling of iron and manganese in sediments of the Kalix River estuary, northern Sweden
- 1996
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Ingår i: Aquatic geochemistry. - 1380-6165 .- 1573-1421. ; 2:2, s. 185-201
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Tidskriftsartikel (refereegranskat)abstract
- Iron and manganese redox cycling in the sediment - water interface region in the Kalix River estuary was investigated by using sediment trap data, pore-water and solid-phase sediment data. Nondetrital phases (presumably reactive Fe and Mn oxides) form substantial fractions of the total settling flux of Fe and Mn (51% of Fetotal and 84% of Mntotal). A steady-state box model reveals that nondetrital Fe and Mn differ considerably in reactivity during post-depositional redox cycling in the sediment. The production rate of dissolved Mn (1.6 mmol m-2 d-1) exceeded the depositional flux of nondetrital Mn (0.27 mmol m-2 d-1) by a factor of about 6. In contrast, the production rate of upwardly diffusing pore-water Fe (0.77 mmol m-2 d-1) amounted to only 22% of the depositional flux of nondetrital Fe (3.5 mmol m-2 d-1). Upwardly diffusing pore-water Fe and Mn are effectively oxidized and trapped in the oxic surface layer of the sediment, resulting in negligible benthic effluxes of Fe and Mn. Consequently, the concentrations of nondetrital Fe and Mn in permanently deposited, anoxic sediment are similar to those in the settling material. Reactive Fe oxides appear to form a substantial fraction of this buried, non-detrital Fe. The in-situ oxidation rates of Fe and Mn are tentatively estimated to be 0.51 and 0.16-1.7 mol cm-3 d-1, respectively
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