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.
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;Department of Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany;Department of Freshwater Conservation, Brandenburg University of Technology Cottbus-Senftenberg, Bad Saarow, Germany;UFZ-Department of Lake Research, Helmholtz Centre for Environmental Research, Magdeburg, Germany;Institute of Environmental Physics, University of Bremen, Bremen, Germany;Department of Chemical Analytics and Biogeochemistry, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany
Recommended Citation:
Matthias Rothe,Andreas Kleeberg,Björn Grüneberg,et al. Sedimentary Sulphur:Iron Ratio Indicates Vivianite Occurrence: A Study from Two Contrasting Freshwater Systems[J]. PLOS ONE,2015-01-01,10(11)