Fractionation of sediment phosphorus revisited. I: Fractionation steps and their biogeochemical basis

Abstract

The aim of this work was to assess the validity of a phosphorus fractionation procedure, introduced by Psenner and co-workers and modified by Jensen and Thamdrup, in chemical characterization of sediment P. In this procedure, P is separated into 6 pools: loosely bound (and pore water) P, redox-sensitive P (bound to iron and manganese), P bound to oxides of aluminum and nonreducible Fe, calcium-bound P, and mobile and immobile pools of organic P. The procedure was slightly modified further, and every step of the work is described in detail. Reproducibility of the method and variation within the extracts obtained at each step were investigated with a commercial reference material. The validity of the results considered against the theoretical basis of the P fractionation procedure was evaluated in terms of the elemental composition of the separate extracts. The results showed good reproducibility of the method; variation in amounts of the different P forms in the separate extractions was small (coefficient of variation <15%). In addition, the analysis of selected elements extracted along with P were reliable enough to deduce the origin of the various P forms. The analytical results for P and the other elements were in accordance with the general theoretical basis of the fractionation procedure. Despite some shortcomings, the tested procedure, in combination with the laboratory practices and analytical methods described, gives reliable and valuable results for distinguishing between potentially mobile and immobile P in sediment.