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Abstract Phosphorus (P) is, an essential nutrient element limiting the biological productivity (Redifield, 1958; Codispoti, 1989); especially important on geologic time scales because it lacks a volatile form to facilitate transfer between the ocean, atmosphere and terrestrial biosphere (Holland, 1978; Broecker, 1982). Phosphorus may enter an aquatic system in particulate and dissolved forms; the last may become associated with particles as they settle out of the water column (Bloesch et aI., 1988). Phosphorus constitutes about 0.1 % of the earth’s crust and exists in all known minerals, mainly in hydroxy-apatite {Cas (P04h (OH)}and fluro-apatite {CalO(P04)6 F2}, as orthophosphate. In the aquatic systems, the incorporation of dissolved phosphate in sediments occurs via several mechanisms including precipitation, adsorption onto the settled particles, absorption or uptake by biota and deposition after death as detrital matter. Precipitation and complexation reactions are important in determining the soluble phosphate concentrations in natural waters. The solubility of P is controlled by Fe (Ill), AI (Ill) and Ca (Stumm and Leckie, 1971). The influence of the solid phase, whether it is suspended particles or sediments, is of considerable importance in regulating the dissolved P phase of natural waters systems. Apatite is formed epitaxially on solid calcite surface due to interaction with phosphate ions at pH range of 6.8 to 8.3 (Stumm and Leckie, 1971). Stumm and Zobrist (1971) reported adsorption of phosphate on goethite (a-FeOOH). The adsorption of phosphate on aluminium oxide (a-AI203) and several clay minerals. |