Dépôt numérique

Non-steady state diagenesis of organic and inorganic sulfur in lake sediments.

Couture, Raoul-Marie; Fischer, Rachele; Van Cappellen, Philippe; Gobeil, Charles (2016). Non-steady state diagenesis of organic and inorganic sulfur in lake sediments. Geochimica et Cosmochimica Acta , vol. 194 . p. 15-33. DOI: 10.1016/j.gca.2016.08.029.

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Sulfur controls the fate of many geochemical elements in lake sediments, including iron, phosphorus and environmentally important trace elements. We measured the speciation of pore-water and sediment-bound sulfur (aqueous sulfate and sulfides, elemental sulfur, iron monosulfide, pyrite, organic sulfur) and supporting geochemical variables (carbon, oxygen, iron) in the sediments of a perennially oxygenated and a seasonally anoxic basin of an oligotrophic lake in Québec, using a combination of pore-water analyses, sequential extractions and X-ray absorption near edge structure. A non-steady state early diagenetic model was developed and calibrated against this extensive dataset to help unravel the pathways and quantify the rates of S transformations. Results suggest that the main source of S to the sediments is the settling of organic ester-sulfate (R-O-SO₃-H). Hydrolysis of these compounds provides an additional source of sulfate for anaerobic microbial oxidation of sedimentary organic matter, releasing sulfide to the pore-water. Reduced solid-bound S species accumulate as thiols (R-SH) and iron sulfides in the perennially oxygenated and seasonally anoxic basin, respectively. The model-estimated rate constant for R-SH formation is lower than previously estimated for this particular lacustrine site, but similar to that proposed for marine shelf sediments. The solid sediment S profiles, however, carry the imprint of the time-dependent sulfate input to the lake. Iron sulfide enrichments formed during past decades of elevated atmospheric SO₄ deposition are presently dissolving. In the sediments of the perennially oxygenated basin this reaction hampers the build-up of Fe(III) (oxy)hydroxide near the sediment–water interface.

Type de document: Article
Mots-clés libres: sulphur; organosulfur compounds; iron sulphides; early diagenetic modeling; seasonal anoxia; oligotrophic lakes; X-ray absorption spectroscopy
Centre: Centre Eau Terre Environnement
Date de dépôt: 04 mai 2018 19:26
Dernière modification: 04 mai 2018 19:26
URI: http://espace.inrs.ca/id/eprint/5660

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