title: Redox sensitivity of iron in phosphorus binding does not impede lake restoration.
abstract: Iron salts have been regarded as unsuitable precipitants for sustainable sedimentary P retention, because Fe-bound P is released at low redox potential. The longevity of an Fe(3+) application (500 g m(-2)) in 1992 was studied in a dimictic lake. Release of Fe and P as well as their co-precipitation were observed dependent on artificial aeration in 2010 and only natural oxygenation in 2011. Sediment core stratigraphy by μX-ray fluorescence analysis revealed that Fe is relocating towards the surface, representing a dynamic P trap with a molar Fe:P ratio of 7. Even at this favourable ratio, P release cannot be suppressed. Settling fluxes of Fe, Mn and P, determined by a multi trap at two day resolution, during aeration and oxygenation, showed that released P can be efficiently precipitated independent of the nature of the oxygen supply. Thus, P release is not relevant for the P supply to the epilimnion, since at overturn most P is co-precipitated by the concurrently hypolimnetically accumulated Fe. To increase the availability of reactive (dithionite extractable) Fe for P binding, our Fe dosage calculation considers Fe in surplus. Beside external and internal P sources to be precipitated in a stoichiometric Fe:P ratio of 5, additional Fe equivalents of 25% for sedimentary organic carbon and to bind soluble sulfides are required. A long-term effect can be achieved only if the external P loading is sufficiently reduced, and Fe is added to ≥ 200 g m(-2).
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 301, 12587 Berlin, Germany. kleeberg@igb-berlin.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Kleeberg
authors.forename: Christiane
authors.initials: C
authors.lastname: Herzog
authors.forename: Michael
authors.initials: M
authors.lastname: Hupfer
mesh_terms: D004784:Environmental Monitoring; D019015:Geologic Sediments / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D060106:Lakes; D010084:Oxidation-Reduction; D010758:Phosphorus / Q000737:chemistry*
chemical_list: D010758:Phosphorus; D007501:Iron