The availability of phosphorus (P) for the growth of phytoplankton in waterbodies is generally believed to be the controlling factor in eutrophication. The objective of this study was to quantify fractions of phosphorus so as to determine the potential of aquatic sediment as a source of phosphorus supply. Surface sediments from two of the reservoirs in Singapore were collected, analyzed and the general characteristics investigated. Fractionation of phosphorus was carried out to determine the various components such as NH4Cl-P, NAI-P, Apatite-P and Residual-P. In the sediments from MacRitchie Reservoir, total phosphorus (TP) concentrations, in terms of dry weight (dw) of sediment, ranged from 211 μg P/g dw to 448 μg P/g dw. Besides, Residual-P formed the major component in the sediments (74.4% to 81.8% of TP). The P bound with Fe and Al varied from 18.0% to 25.1%. But, in the Kranji Reservoir, the TP concentrations in the sediments were found to be four-to eight-fold higher (1640 μg P/g dw to 1885 μg P/g dw) than that from MacRitchie Reservoir, and the Residual P only accounted for 28.2% to 39.2% of TP. However, the P bound with Fe and Al, was the dominant component (53.0% to 63.0%) of TP. This fraction of phosphorus could be released for the growth of phytoplankton when anoxic conditions prevail at the sediment-water interface. It can be concluded from this fractionation study that sediments in Kranji Reservoir have a larger pool of potential phosphorus supply to support the growth of phytoplankton in the waterbody.

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