『Abstract
　Phosphorus (P) is the limiting macronutrient for primary production in most lakes. Sediment characteristics are strongly correlated to the internal P loading in lakes. This study investigated speciation of P, Fe, Al, and Ca in sediments of six sampling sites with varying trophic status in Baiyangdian Lake of North China during the period of July 2008 and March 2009. The results of sequential extraction experiments of the top sediments showed that total extractable P ranged approximately from 13 to 28 μmol g^-1 for all sampling sites and the rank order of P-fractions was HCl-P＞NaOH85-P＞NaOH25-P＞BD-P＞NH4Cl-P. BD-P and BD-Fe had a consistent change with seasons. Their concentrations were both much higher in early spring and mid-autumn. BD-Fe, Al extracted with NaOH at 25℃ and 85℃ affected corresponding P concentration in sediments, while high concentration of extractable Ca from sediments showed no direct effects. According to the Kopacek（aの頭に´、cの頭にv） et al. model of the molar ratios of Al:Fe and [NaOH25-Al]:[NH4Cl-P + BD-P], there was potential P release from sediments twice a year for some hypereutrophic sites in early spring and mid-autumn, especially in the former season.

Keywords: Phosphorus; Iron; Aluminum; Calcium; Fraction; Lake sediment』

Introduction
Materials and methods
　Area descriptions
　Sample collection and treatment
　Phosphorus fractionation
Results
　Phosphorus
　Iron
　Aluminum
　Calcium
　Correlations between P and Fe, Al, and Ca
　Al:Fe model
　Ca:Fe ratio
Discussion
Conclusion\]Acknowledgments
References