An investigation of the origin and mobility of phosphorus in freshwater sediments from Bort-Les-Orgues Reservoir, France

In order to assess the origin and the potential mobility of phosphorus (P) in the sediment of the Bort-Les-Orgues Reservoir, France, two sequential ex traction schemes, i.e., the SMT (modified Williams method)and the Golterman schemes, were compared. Finally, the potential mobility of P in this sedim ent was estimated from results of sequential extraction. The SMT method app eared to be more satisfactory than the Golterman method, which is in accord ance with results from a study currently carried out in the framework of th e European programme Standards, Measurements and Testing. Iron-bound P and organic P were the dominant forms of P in the sediment; these forms are lik ely to be released at the sediment/water interface in case of anoxia and co uld diffuse into the water column, thus increasing the risk of eutrophicati on in this sensitive reservoir. The P stock (330 +/- 66 t) is not negligibl e and should be taken into account in any restoration project of the reserv oir. The SMT procedure seems promising and will provide, in the near future , a valuable tool for water managers in the field of lake restoration.