Quantification of individual phosphorus forms in surface sediments of the Southern Caspian Sea - Iranian Coast: A sequential extraction procedure

Seventy Two sediments from four stations (Anzali, Tonekabon, Noshahr and Amirabad), located in Caspian Sea-Iranian coast were examined on the basis of P-fractionation in autumn and winter of 2013-2014. Several forms of the phosphorus in sediment were separated and extracted according to sequential extraction method. Then the extracted phosphorus in each fraction was determined by UV&ndash;Vis spectrophotometry. In addition, Total concentrations of Ca, Fe and Al in sediment fractions were also measured by Atomic absorption spectroscopy. In autumn the rank order of P-fractions was: Ca-P>Residual-P>BD-P>Al-P>loosely-P and in winter it was: Ca-P>BD-P>Residual-P>Al-P>loosely adsorbed-P. In both season the loosely adsorbed phosphorus (NH4Cl&ndash;P) represented < 1% of the sedimentary inorganic phosphorus, while the reductant phosphorus (BD&ndash;P) ranged from 2.7 to 4%. The calcium bound phosphorus (Ca-P or HCl&ndash;P) showed considerable contribution (89-91%) to the sedimentary inorganic P-loads. The metal oxide bound phosphorus (Al-P or NaOH&ndash;P) was 1.2-1.5% and Residual-P was 2.3-4.5%. Concentration of BD- P increased with increasing depth in all stations and the concentration of other fractions increased in most stations. Sampling seasons had significant effect on variance of most P-fractions and other sediment features. TP and BD-P were positively correlated with Fetot (p<0.05).