IRON CONTENT OF SEDIMENT AND PHOSPHATE ADSORPTION PROPERTIES

Phosphorus can occur in sediments in different forms and accordingly i ts availability varies. The distinction between the phosphorus fractio ns is made with two chemical extraction methods; an ammonium oxalate-o xalic acid extraction and an extraction according to Hieltjes & Lijkle ma (1980). The iron and aluminum liberated with the ammonium oxalate-o xalic acid extraction method is linearly correlated (r2 = 0.73) with t he phosphorus liberated in the first two steps of the Hieltjes and Lij klema extraction by: P=0.035(Fe+Al)+0.001(P, Fe and Al in mmol g-1). T he iron and aluminum (hydr)oxides are very important fractions in the sediment adsorption capacity for phosphorus. The phosphorus sorption c apacity (PSC) is 0.080 mol P (mol (Fe+Al))-1 and the adsorption consta nt (k) is 11.9 mumol P l-1. Here it is assumed that iron and aluminum (hydr)oxide have the same affinity for phosphorus.