Sequential extractions of inorganic and org-Phosphate from fish pond sediments (Deroua station, Beni Mellal, Morocco) by different fractionation methods

The carp ponds of Deroua station (Beni Mellal, Centre of Morocco) receive a large quantity of fertilizers, particularly urea and triple super phosphat e during the entire period of culture. Only a small part of that is necessa ry to promote an adequate development of phytoplankton, the base of the foo d chain. A large part of the phosphate added to the ponds is stocked in pon d soils and can be released under specific conditions. Although some phosph ate is necessary for the development of aquatic populations, too large of a n input causes problems. Therefore, knowledge of the external load and the mobility of the internal pool is essential for the purpose of management ag ainst eutrophication. In order to assess the inorganic and organic fraction s of phosphate present in sediments, different methods of P fractionation w ere compared. The methods do not give the same results. In the Deroua sedim ents, calcium-bound phosphate represents the major part of total phosphate between 86% and 91% according to the different methods. The org-Phosphate r epresents a small part and varies considerably depending on the different m ethods between 0.87 and 5%. EDTA extractions (Golterman, 1996) have an adva ntage over other methods such as the Sedex, the Hieltjes & Lijklema and the Bonzongo procedures.