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

Abstract

Internal phosphorus (P) loading leading to accelerated eutrophication of marine systems has made acute the research on P chemistry in sediments. Studies on the P chemistry in lake and marine sediments are commonly based on fractionation, where P compounds are divided into several pools according to their solubility in or reactivity with various chemical solutions. Procedures typically begin with dilute extractants, which remove the most loosely bound P forms, and they proceed stepwise toward stronger extractants, attacking P forms more strongly bound to the solid phase (e.g., Ruttenberg 1992).Solutions may contain anions able to displace phosphate (PO 4 -P) from its adsorption sites through competition, anions able to alter the chemical state of the adsorption surface, or anions able to dissolve P-bearing compounds.A wide variety of extraction procedures for soil and sediment P have been developed, varying with the aim of the study and the P fractions targeted (for reviews, see Boström et al. 1982, Van Eck 1982, Pettersson et al. 1988, Ruban et al. 1999. The P forms commonly separated include soluble and loosely sorbed (labile) PO 4 -P, redox-sensitive iron (Fe)-bound P, and P bound to hydrated oxides of (Al) and nonreducible Fe (surface-bound), calcium (Ca)-bound P (apatite-P), and organic P. The organic P is sometimes divided into refractory and labile fractions. In addition to organic P, the refractory fraction is assumed to contain some inorganic P (e.g., Ruttenberg 1992), possibly as occluded P forms.Extraction procedures are often poorly explained in the literature, and the theoretical basis of the P fractions separated using the procedure often remains unclear. In addition, the procedures are often difficult to follow because the practical work is inaccurately described. For instance, the determination of PO 4 -P may be complicated by interference from extractant-derived ions. In this study, a commercial reference material was fractionated using a procedure developed by Psenner AbstractThe 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%)...

Caractérisation de la charge interne de phosphore du lac Nairne, Charlevoix (Québec)

“…La concentration de PT a été déterminée à l'aide de la méthode standard SW 846-6010B de la United States Environmental Protection Agency. Les concentrations de s-P et de Fe-P ont été mesurées par extraction séquentielle selon une méthode décrite dans LUKKARI et al (2007a). Tous les résultats ont été reportés en poids sec (mg•g -1 ).…”

Phosphorus in sediments of high-elevation lakes in the Sierra Nevada (California): implications for internal phosphorus loading

“…In our procedure, NH 4 Cl was replaced with NaCl in the first step of the extraction to minimize the dissolution of Ca-bound P (Lukkari et al 2007). For each sediment, a 0.5 g (dry weight) sample was sequentially extracted with (1) 0.46 M NaCl under an N 2 environment for 1 h to obtain loosely bound and pore water P; (2) 0.11 M sodium dithionite (Na 2 S 2 O 4 ) in 0.11 M sodium bicarbonate (NaHCO 3 ) buffer (pH 7) under an N 2 environment for 1 h to obtain P bound primarily to redox-sensitive Fe-oxides (NaBD-P i ) and organic P that is easily mineralized (NaBD-P o ); (3) 0.1 M NaOH for 18 h to obtain inorganic P (NaOH-P i ) associated with amorphous and some crystalline Al oxides but that may contain Fe-associated P not extracted in the previous step, as well as organic P (NaOH-P o ) associated with humic compounds and polyphosphates; (4) 0.5 M HCl for 1 h to extract Ca-associated P found predominantly in apatite minerals (HCl-P i ); and (5) 1 M NaOH at 85°C for 1 h to extract residual and recalcitrant forms of occluded P (85°NaOH-P).…”

“…Organic P (P o ) was estimated as the difference between P t and P i . NaBD extracts were sparged with He to remove dithionite prior to determining P colorimetrically, as it interferes with the development of the phosphomolybdate complex (Lukkari et al 2007). …”

Evaluation of a well‐established sequential phosphorus fractionation technique for use in calcite‐rich lake sediments: identification and prevention of artifacts due to apatite formation

“…Plausibility tests determining simultaneously mobilized metals (Jensen and Thamdrup 1993, Ulrich 1997, Kopaček et al 2005, Lukkari et al 2007, the use of model substances such as activated sludge (Uhlmann et al 1990), or combining sequential P extraction with other structural analyses such as X-rays (Hupfer et al 1995) and 31 P NMR spectroscopy (Hupfer et al 2004, Ahlgren et al 2005 have shown that individual P species can be assigned accurately to a specific chemical fraction. Dissolution and subsequent rebinding of P within one step, however, negatively affects accurate P assignment (Barbanti et al 1994).…”