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

Abstract

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