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Manganese accumulation and solid-phase speciation in a 3.5 m thick mud sequence from the estuary of an acidic and Mn-rich creek, northern Baltic Sea

Artikel i vetenskaplig tidskrift
Författare C. X. Yu
J. J. Virtasalo
P. Osterholm
E. D. Burton
P. Peltola
A. E. K. Ojala
Johan Hogmalm
M. E. Astrom
Publicerad i Chemical Geology
Volym 437
Sidor 56-66
ISSN 0009-2541
Publiceringsår 2016
Publicerad vid Institutionen för geovetenskaper
Sidor 56-66
Språk en
Länkar dx.doi.org/10.1016/j.chemgeo.2016.0...
Ämnesord Estuarine sediments, Mn speciation, X-ray absorption spectroscopy, Rhodochrosite, Acid sulfate soil, ray-absorption spectroscopy, ferruginous lake matano, anoxic, marine-sediments, sulfate soil runoff, black-shale basins, organic-matter, western finland, iron reduction, icp-ms, sulfide, Geochemistry & Geophysics
Ämneskategorier Geovetenskap och miljövetenskap

Sammanfattning

In sediments, manganese (Mn) is typically enriched in the form of authigenic Mn hydroxides at the water-sediment interface where intensive redox cycling of Mn occurs. Here we show, based on existing hydrochemical and geochemical (sediment core) data and new detailed chemical and mineralogical characterization of a 3.5 m long sediment core from a Boreal estuary, that the behavior of Mn can be profoundly different and more complex in estuarine settings receiving an abundance of terrestrial Mn. The most notable feature in the 3.5 m long sediment core is two depth intervals (60-155 cm and 181-230 cm) where there are strong fine-scale variations in Mn concentrations with peaks episodically reaching up to 10-25 g kg(-1) and 6.7-12 g kg(-1), respectively. X-ray absorption spectroscopy and sequential chemical extraction show that Mn occurs mainly as authigenic rhodochrosite at these two depth intervals and is mainly surface-sorbed in other sections with relatively low and stable Mn concentrations. The data suggests that the strong fine-scale variations in Mn concentrations are a reflection of the extent of formation and settling of Mn hydroxides, the precursors of the authigenic rhodochrosite (and also of the surface-sorbed Mn), rather than Mn input to the estuary or redox-related Mn translocation within the sediment. There was agreement between the results of linear combination fitting of extended X-ray absorption fine structure data and a 7-step sequential chemical extraction (SCE) in terms of quantification of surface-sorbed Mn species, whereas the SCE experiment failed to fractionate a majority of rhodochrosite into SCE step-2 (1M NH4-acetate at pH 6), which is frequently employed to dissolve carbonate. We ascribe this discrepancy to only partial dissolution of rhodochrosite in the weakly acidic (pH = 6) NH4-acetate leach.

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