title: An innovative approach for sequential extraction of phosphorus in sediments: Ferrous iron P as an independent P fraction.
abstract: Accurate identification of phosphorus (P) forms is crucially important for understanding the geochemical cycle of P; however, until now the role of ferrous iron P (Fe(II)-P) buried in sediments has been completely ignored in nearly all sequential extraction procedures developed. Using sediment cores sampled from Donghu Lake in Wuhan, China, this study explored a modified version of widely used sequential P extraction method (SEDEX; Ruttenberg, 1992) in which Fe(II)-P was identified as an independent fraction. Based on the high selectivity of the extractant (0.2% 2,2'-bipyridine+0.1 M KCl) and the dissolution equilibrium of P, procedures for extracting Fe(II)-P were optimized using a 1:100 solid:liquid ratio and extraction at 50 ± 1 °C for 24 h. The sedimentary P extracted was divided into five fractions: loosely-bound P, Fe(II)-P, CDB-P, Ca-P and O-P. Fe(II)-P was the predominant fraction in fresh sediments in Donghu Lake, accounting for 15.7-49.9% of TP, with a mean of 31.6%. The mean values of Ca-P, O-P, CDB-P and loosely-bound P were 28.4%, 22.7%, 17.1% and 4.3%, respectively. Combined with component analysis of extracts and recovery experiments of standard reference minerals (vivianite, Fe3(PO4)2·8H2O) in natural sediments, extraction of Fe(II)-P with 0.2% 2,2-bipridine and 0.1 M KCl was robust, with a good recovery rate (88.7-100.6%) and little of the Ca-P dissolved. It is possible to use this innovative SEDEX not only to distinguish the contribution of different P matrices in fresh sediments, but also to investigate the transformation of sedimentary P under different redox conditions. Therefore, greater focus on Fe(II)-P is necessary, because it is a major sink for the geochemical process of sedimentary P.
authors.affiliation: Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China; Graduate School of the Chinese Academy of Sciences, Beijing, 100039, China.
authors.forename: Sen
authors.initials: S
authors.lastname: Gu
authors.affiliation: Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.
authors.forename: Yiguang
authors.initials: Y
authors.lastname: Qian
authors.affiliation: Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China.
authors.forename: Yang
authors.initials: Y
authors.lastname: Jiao
authors.affiliation: Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, China. Electronic address: qmli@ihb.ac.cn.
authors.forename: Qingman
authors.initials: Q
authors.lastname: Li
authors.affiliation: OSUR - CNRS, University of Rennes 1, Rennes, 35042, France.
authors.forename: Gilles
authors.initials: G
authors.lastname: Pinay
authors.affiliation: OSUR - CNRS, University of Rennes 1, Rennes, 35042, France.
authors.forename: Gerard
authors.initials: G
authors.lastname: Gruau
mesh_terms: D019015:Geologic Sediments; D007501:Iron; D060106:Lakes; D008903:Minerals; D010758:Phosphorus
chemical_list: D008903:Minerals; D010758:Phosphorus; D007501:Iron
keywords: Ferrous iron phosphorus; Geochemical process; Phosphorus fractionation; SEDEX; Vivianite