Fractional phosphate composition in sediments from a tropical river (Catatumbo River, Venezuela)

The distribution of phosphate species in the Catatumbo River, Venezuela, was studied using a sequential extraction scheme. Extraction was performed using 1.0 M NH₄Cl, 0.1 M Na₂S₂O₄–NaHCO₃, 1.0 M NaOH and 0.5 M HCl. Total phosphate was in the range between 121 and 581 g g^–1 D.W. About 64% of the total phosphate is inorganic and present the following composition: 1% NH₄Cl-P, 10% BD-P, 20% NaOH-P, 33% HCl-P; while org-P is 36%. The main form of P in sediment from the Catatumbo River is calcium bound-P, like apatite. The metal concentrations present in sediment are in the following order: Fe> Al > Ca > Mg > Mn. Relationships between P and Fe, Al and Ca were found. Cluster analysis showed that speciation is not dependent on the inorganic matrix of the sediments. Analysing the influence of NaOH concentration and duration of the extraction invalidated the use of NaOH as extracting agent in P-speciation.