『Abstract
　The vertical variation of P forms in sediments of urban shallow lakes in China, Xuanwu Lake, Daming Lake and Mochou Lake, were sequentially extracted and measured with the method of SEDEX. The results indicated the TP content in the sediment profiles ranged from 371.94 to 777.25 mg kg^-1 for Xuanwu Lake, 1,308.14 to 4,632.63 mg kg^-1 for Daming Lake, and 995.49 to 1,860.71 mg kg^-1 for Mochou Lake. The Results of sequential extraction showed that Ca-P and Fe-P were the main fractions. Meanwhile, the proportions of Bio-P to TP were 35.24％ for Muanwu Lake, 29.57％ Daming lake, and 25.26％, for Mochou Lake, indicating a high potential of P releasing. The content of Bio-P was significantly and positively correlated with TP (r = 0.978, P＜0.01). Lake hydrations conditions played an important role in the distribution and contents of Bio-P and TP. In the region with macrophytes, the contents of TP and Bio-P were relatively low. Physicochemical properties of sediments were significantly related to the fraction distribution and P contents, and might play an important role in controlling P activity and mobility. Moreover, Fe showed an evident influence on P fraction and the ratio Fe/P might be good indicator to the contents and composition of active P in sediments.

Keywords: Urban shallow lake; Sediment; P form; Activity』

Introduction
Materials and methods
　Sampling and pre-treatment
　Analysis
Results and discussion
　The vertical distribution of P fractions
　Factor influencing P activity
Conclusions
References