PHOSPHORUS DIAGENESIS IN LAKE-SEDIMENTS - INVESTIGATIONS USING FRACTIONATION TECHNIQUES

A 60-cm sediment core, representing approximately 50 years of depositi on, was collected from the major depositional basin of Onondaga Lake, a calcareous, hypereutrophic system in Syracuse, New York (USA). Seque ntial chemical extractions were performed to obtain fractional phospho rus (P) profiles, and these suggest that the sediment P available for solubilization and recycling to the water column is contained within t he CaCO3-associated, Fe&Al-bound, and extractable biogenic-P fractions . Corrections were applied to account for the presence of refractory P within the CaCO3-associated and Fe&Al-bound fractions. Labile phospho rus comprises similar to 50% of the particulate P at the time of depos ition. Reductions in labile P with depth suggest losses due to diagene sis with subsequent release to the lake water column. Rate constants f or diagenesis were calculated from measurements of labile P on dated c ores. Two labile components were apparent: one, exhibiting 'fast' deca y (k = 4.8 year(-1)), was located within the upper 1 cm of sediment, a nd the other, characterized by 'slow' decay (k = 0.1 year(-1)) was loc ated throughout the sediment to a depth of similar to 30 cm, below whi ch sediment P was refractory. The ratio of the 'fast' to 'slow' fracti ons is approximately 1:1 in freshly deposited sediment. These findings facilitate sediment P modelling and have bearing on the recovery of l akes following reductions in external phosphorus loads.