title: Sedimentary Sulphur:Iron Ratio Indicates Vivianite Occurrence: A Study from Two Contrasting Freshwater Systems.
abstract: An increasing number of studies constrain the importance of iron for the long-term retention of phosphorus (P) under anoxic conditions, i.e. the formation of reduced iron phosphate minerals such as vivianite (Fe3(PO4)2⋅8H2O). Much remains unknown about vivianite formation, the factors controlling its occurrence, and its relevance for P burial during early sediment diagenesis. To study the occurrence of vivianite and to assess its relevance for P binding, surface sediments of two hydrologically contrasting waters were analysed by heavy-liquid separation and subsequent powder X-ray diffraction. In Lake Arendsee, vivianite was present in deeper sediment horizons and not in the uppermost layers with a sharp transition between vivianite and non-vivianite bearing layers. In contrast, in lowland river Lower Havel vivianite was present in the upper sediment layers and not in deeper horizons with a gradual transition between non-vivianite and vivianite bearing layers. In both waters, vivianite occurrence was accompanied by the presence of pyrite (FeS2). Vivianite formation was favoured by an elevated iron availability through a lower degree of sulphidisation and was present at a molar ratio of total sulphur to reactive iron smaller than 1.1, only. A longer lasting burden of sediments by organic matter, i.e. due to eutrophication, favours the release of sulphides, and the formation of insoluble iron sulphides leading to a lack of available iron and to less or no vivianite formation. This weakening in sedimentary P retention, representing a negative feedback mechanism (P release) in terms of water quality, could be partly compensated by harmless Fe amendments.
authors.affiliation: Department of Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.|Department of Geography, Humboldt-Universität zu Berlin, Berlin, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Rothe
authors.affiliation: Department of Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kleeberg
authors.affiliation: Department of Freshwater Conservation, Brandenburg University of Technology Cottbus-Senftenberg, Bad Saarow, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Grüneberg
authors.affiliation: UFZ-Department of Lake Research, Helmholtz Centre for Environmental Research, Magdeburg, Germany.
authors.forename: Kurt
authors.initials: K
authors.lastname: Friese
authors.affiliation: Institute of Environmental Physics, University of Bremen, Bremen, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Pérez-Mayo
authors.affiliation: Department of Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Hupfer
mesh_terms: D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments / Q000032:analysis*; D013455:Sulfur / Q000032:analysis*; D014961:X-Ray Diffraction
chemical_list: D013455:Sulfur