Fractionation trends of phosphorus associating with iron fractions: An explanation by the simultaneous extraction procedure

Abstract

Phosphorus biogeochemical cycle presented a close coupling relationship with Fe cycle. In this work, the fractionation trends of phosphorus (P) associating with iron fractions were investigated using a sequential extraction procedure. The results showed that Feprs (poorly reactive sheet silicate) presented as the dominant fraction of all extractable Fe fractions in surface and core sediments. The spatial and vertical distributions of magnetite (Femag), the environmental characteristics of Lake Daihai (DH) basin and the significant associations of Femag with Feox1 (easily reducible oxides) and Feox2 (reducible oxides) jointly suggested the multisource of Femag including terrigenous origins (workings of erosion and transport processes) and authigene formation (the transformation between magnetite and highly reactive fractions of iron induced by microbial effects). In DH surface sediments, although Feox1 and Feox2 were not the dominant Fe fractions, the simultaneous extractable P (SEP) associating with these two Fe fractions, namely P-NH2OH·HCl and P-Na2S2O4 respectively, were the most abundant fractions of the total extractable P; Coupling with the ratio of (ΣFe)/w(ΣP) (54.8), it was convinced that P release was subject to Fe oxides/hydroxides, especially highly reactive Fe (Feox1 and Feox2), due to the SEP simultaneous extracted with these two Fe fractions accounted about 70% of the total extractable P. It was indicated that fractionation trends of P were associating with Fe fractions caused by the interface process of P on Fe oxides surface (amorphous iron oxide and hydration oxide). The trends of spatial and vertical distributions for Fe and SEP fractions archived in sediments well recorded and responded the environmental conditions in the drainage basin of DH. This work is very helpful to update the knowledge of the coupling cycle effects of Fe and P on lakes eutrophication.