Identification of stoichiometric iron-phosphorus colloids produced in a eutrophic lake |
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| Authors: | Charles-Philippe Lienemann Marc Monnerat Janusz Dominik Didier Perret |
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| Institution: | Institut de Chimie Minérale et Analytique, Université de Lausanne; BCH, CH-1015 Lausanne, Switzerland, CH
Institut F.-A. Forel, Université de Genève, and Centre d'Etudes en Sciences Naturelles de l'Environnement (CESNE); 10 route de Suisse, CH-1290 Versoix, Switzerland, CH
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| Abstract: | : Iron-rich colloids formed at the oxic-anoxic interface of a eutrophic lake (Lake Lugano; CH) were characterized by bulk chemical methods and analytical electron microscopy. Fractionation of raw waters showed that non-dissolved iron is particulate above the oxicline and mainly colloidal in the anoxic part of the hypolimnion, while non-dissolved ortho-phosphate is mostly colloidal through the water column. Because of these differences, filtration did not prove helpful for the determination of the role of iron-rich species in the scavenging of ortho-phosphate. On the other hand, analytical electron microscopy revealed that iron-rich nano-granules (ca. 50nm) are associated to the surface of bacterially produced fibrillar polysaccharides. Iron colloids in these complex entities contain important and constant amounts of phosphorus (PO4]part:Fe]part = 0.48 - 0.11, n = 1096 Fe-rich entities analyzed by electron microscopy), which suggests that phosphates are stoichiometrically incorporated into the hydrous iron oxide phase, with a tentative composition Fe2OOH]1-x(OH)3]xPO4], during its genesis. |
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