الفهرس 
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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.