『Abstract
　Settling particulate matter was collected in sediment traps from the major depositional basin of Onondaga Lake, a calcareous, eutrophic lake in Syracuse, New York, U.S.A. Sediment traps were deployed at three depths from July to November and for a brief period under ice cover in February to investigate both vertical and seasonal variations in sedimentation. A sequential chemical extraction (fractionation) method was applied to the collected material to quantify the following phosphorus (P) fractions, or forms: loosely bound-P (sorbed-P, CaCO3 associated-P, and Fe and Al bound-P), extractable biogenic-P (easily degradable organic-P and biogenic inorganic polyphosphates), calcium mineral-P (e.g., apatite), and refractory organic-P. Extractable biogenic-P and refractory organic-P were strongly correlated, suggesting a common, autochthonous origin in plankton. Calcium mineral-P appears to be of terrigenous origin. A dramatic increase in the loosely bound-P content of the particulate matter was observed during fall turnover when dissolved Fe²⁺, which had accumulated in the anoxic hypolimnion, mixed with the surface waters and oxidized with attendant adsorption of P. We estimate that the labile-, or exchangeable-P (i.e. loosely bound- and extractable biogenic-P forms) content of the settling particulates constitutes 〜50％ of the total P influx to the sediments over the period of study. The labile-P flux over the July-November study period was 11 mg P m^-2 day^-1 and the labile-P flux estimated from sediment traps deployed under ice cover was 6 mg P m^-2 day^-1. From these values the annual average labile-P flux to the sediments was estimated to be 9 mg P m^-2 day^-1, only slightly less than the estimated annual average sediment P release rate of 10 mg P m^-2 day^-1. This indicates that the sediments are approximately at steady state with respect to current external P loadings to the lake.

Keywords: Phosphorus; Sedimentation; Fractionation; Speciation; Calcareous』

1. Introduction
2. Study system
3. Methods
4. Results and discussion
　4.1. Seston dry weight and total phosphorus fluxes
　4.2. Seasonal particulate phosphorus speciation
　4.3. labile phosphorus
5. Summary and conclusions
Acknowledgements
References