Fractionation of phosphate in sediments of four representative mangrove stages (French Guiana)

Phosphate was fractionated in Guianese mangrove sediments. Fe(OOH)approximate to P was extracted using a Ca-EDTA + Na-dithionite solution buffered at pH 8. CaCO(3)approximate to P was extracted using Na-2-EDTA solution at pH 4.5. Next, Acid Soluble Organic Phosphate (ASOP) was extracted by H2SO4 0.5 N. Finally, Residual Organic Phosphate (ROP) was digested with H2SO4 + H2O2. Four representative mangrove stages have been studied: sea edge pioneer mangroves, mature coastal mangroves, mixed riverine mangroves, and declining to dead mangroves. The sum of the P-fractions varied between 638 to 804 mu g g(-1) in pioneer and mixed mangroves respectively. In all the stages, the percentage of inorganic phosphate was larger than 50% of the total P. Fe(OOH)approximate to P varied between 221 (pioneer mangrove) to 426 mu g g(-1) (dead mangrove). CaCO(3)approximate to P varied between 75 to 102 mu g g(-1) in mixed, dead or mature mangroves and attained 125 mu g g(-1) in pioneer mangrove. The sum of the concentrations of organic phosphate (ASOP + ROP) increased markedly from the dead mangrove (189 mu g g(-1)) to the mixed mangrove (380 mu g g(-1)). Guianese mangroves, are relatively rich in total phosphate, possibly because they are narrowly related to the 'Amazon dispersal system'. Each mangrove stage can be characterised by a prevailing form of phosphate. The concentrations of these different forms were ascribed to the marked relations with the seawater which controls import or export of suspended matters and to the wave action which controls the resuspension of the sediments and subsequently exchange of phosphate between the suspended matter and the water column.