Proportion of sedimentary phosphorus (P) forms according to [30] on total P of synthetic vivianite powder (Pviv, surface oxidised, blue appearance) and of a high-density sample (ρ > 2.3 g cm−3) naturally rich in sedimentary vivianite.

P speciation according to [30]: NH4Cl-TP: loosely adsorbed P; BD-TP: redox sensitive P, mainly bound to Fe-(hydr)oxides; NaOH-SRP: metal-bound P, mainly associated with Fe- and Al-oxides; NaOH-NRP: organic-bound P, HCl-TP: P bound in calcium carbonates and apatite; and Res-P: residual P determined after digestion of remaining sediment.P speciation according to [32]: Ex-P: loosely sorbed P; CDB-P: iron(oxyhydr)oxide-bound P, vivianite.The first two steps of the P speciation according to [32] are given in brackets.