Spatial Evolution of Phosphorus Fractionation in the Sediments of Rhumel River in the Northeast Algeria

The objective of the present study is the characterization of the spatial evolution of phosphorus forms in sediments of Rhumel River located in northeast Algeria during winter conditions. Sediments samples were collected along the river in Constantine city during the year 2012. The samples were subjected to physicochemical characterization and metals analysis. Phosphorus was fractionated by sequential extractions procedure in exchangeable, oxyhydroxides bound; calcium bound; organic and residual fractions. The distribution of the different forms of phosphorus in the sediments appears to be influenced by the physicochemical characteristics, which depend on the sampling location. Phosphorus speciation along the river is characterized by the predominance of inorganic phosphorus forms. The exchangeable fraction is the lowest. Phosphorus concentration in this fraction does not exceed 20 mg/kg. The fraction bound to calcium is the most important in retaining inorganic phosphorus with concentrations varying from 328 to 490 mg/kg. Phosphorus bound to oxyhydroxides represents an average of 172 mg/kg. Along the river, the contribution of the different fractions in the phosphorus retention follows the order: exchangeable < bound to oxyhydroxides ~ organic < bound to calcium < residual. As estimated by the sum of exchangeable, bound to oxyhydroxides and bound to organic matter, an average of about 28% of the total phosphorus can become bioavailable. The predominant fraction in the Rhumel sediments changes from residual at upstream Constantine city to bound to calcium at downstream from it.