Evidence for vivianite formation and its contribution to long-term phosphorus retention in a recent lake sediment: a novel analytical approach

Abstract

Abstract. Vivianite, Fe3(PO4)2 × 8 H2O, is a ferrous iron phosphate mineral which forms in waterlogged soils and sediments. The phosphorus (P) bound in its crystal lattice is considered to be immobilised because vivianite is stable under anoxic, reducing, sedimentary conditions. Thus, vivianite formation can make a major contribution to P retention during early diagenesis. Much remains unknown about vivianite in sediments, because technical challenges have rendered direct identification and quantification difficult. To identify vivianite and assess its significance for P burial during early diagenesis we studied the consequences of a 1992/1993 in-lake application of FeCl3 and Fe(OH)3 aimed at restoring Lake Groß-Glienicke (Berlin, Germany). In a novel approach, we firstly applied a heavy-liquid separation to the iron-rich surface sediments which allowed direct identification of vivianite by X-ray diffraction in the high-density (ρ > 2.3 g cm−3) sediment fraction. Secondly, we assessed the contribution of vivianite to P retention, combining results from chemical digestion with magnetic susceptibility data derived from magnetic hysteresis measurements. Scanning electron microscopy revealed that the dark blue spherical vivianite nodules were 40–180 μm in diameter, and formed of platy- and needle shaped crystal aggregates. Although equilibrium calculations indicated supersaturation of vivianite throughout the upper 30 cm of the sediment, the vivianite deposits were homogeneously distributed within, and restricted to, the upper 23 cm only. Thus, supersaturated pore water alone cannot serve as a reliable predictor for the in-situ formation of vivianite. In Lake Groß -Glienicke, vivianite formation continues to be triggered by the artificial iron amendment more than 20 years ago, significantly contributing to P retention in surface sediments.

Experimental iron amendment suppresses toxic cyanobacteria in a hypereutrophic lake

“…However, the direct identification of Fe(II) phosphate minerals, such as vivianite, is technically challenging, as demonstrated by a recent study which concluded that vivianite cannot be identified by X‐ray diffraction of bulk sediment samples (Rothe et al. ). By applying a heavy‐liquid separation to sediments, Rothe et al.…”

Internal phosphorus loading in Canadian fresh waters: a critical review and data analysis

“…Vivianite is thought to occur at less than 1% concentration, which has made its direct identification challenging; despite this, several studies show convincing spectroscopic evidence of vivianite in lake sediments (e.g., Manning et al 1991;Fagel et al 2005;Sapota et al 2006;Rothe et al 2014). Additionally, its presence has been inferred from thermodynamic calculations (e.g., Nriagu and Dell 1974;Matisoff 1980).…”

Vivianite formation and its role in phosphorus retention in Lake Ørn, Denmark

“…Vivianite is known to retain phosphorus in lakes under reducing conditions in iron rich systems (Moore et al 1998;Sapota et al 2006;Rothe et al 2014). However, vivianite formation and stability in SiFe-C rich lake sediments are rarely studied (Müller and Förstner, 1973;Fagel et al 2005;Owen et al 2010).…”

“…However, vivianite formation and stability in SiFe-C rich lake sediments are rarely studied (Müller and Förstner, 1973;Fagel et al 2005;Owen et al 2010). In addition, the quantitative contribution of vivianite to phosphorus retention has only rarely been quantified (Rothe et al 2014).…”