Vivianite Precipitation and Phosphate Sorption following Iron Reduction in Anoxic Soils
- Lisa Heiberg *a,
- Christian Bender Kochb,
- Charlotte Kjaergaardc,
- Henning S. Jensena and
- B. Hansen Hans Christianb
- a Institute of Biology, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark
b Dep. of Basic Sciences and Environment, Univ. of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C., Denmark
c Dep. of Agroecology and Environment, Aarhus Univ., Blichers Allé 20, DK-8830 Tjele, Denmark. Assigned to Associate Editor Antonio Delgado
Phosphorus retention in lowland soils depends on redox conditions. The aim of this study was to evaluate how the Fe(III) reduction degree affects phosphate adsorption and precipitation. Two similarly P-saturated, ferric Fe-rich lowland soils, a sandy and a peat soil, were incubated under anaerobic conditions. Mössbauer spectroscopy demonstrated that Fe(III) in the sandy soil was present as goethite and phyllosilicates, whereas Fe(III) in the peat soil was mainly present as polynuclear, Fe-humic complexes. Following anoxic incubation, extensive formation of Fe(II) in the solids occurred. After 100 d, the Fe(II) production reached its maximum and 34% of the citrate–bicarbonate–dithionite extractable Fe (FeCBD) was reduced to Fe(II) in the sandy soil. The peat soil showed a much faster reduction of Fe(III) and the maximum reduction of 89% of FeCBD was reached after 200 d. Neoformation of a metavivianite/vivianite phase under anoxic conditions was identified by X-ray diffraction in the peat. The sandy soil exhibited small changes in the point of zero net sorption (EPC0) and Pi desorption with increasing Fe(III) reduction, whereas in the peat soil Pi desorption increased from 80 to 3100 μmol kg−1 and EPC0 increased from 1.7 to 83 μM, after 322 d of anoxic incubation. The fast Fe(III) reduction made the peat soils particularly vulnerable to changes in redox conditions. However, the precipitation of vivianite/metavivianite minerals may control soluble Pi concentrations to between 2 and 3 μM in the long term if the soil is not disturbed.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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