『Abstract
　Phosphorus (P) fractions and their bioavailability in the sediments from the middle and lower reaches of the Yangtze River region were investigated using different chemical extraction methods. The results show that the contents of bioavailable P in the sediments extracted by different extraction procedures varied greatly. But their rank order was similar. Potentially releasable P (PRP) was the largest, followed by algal available P (AAP), NaHCO3 extractable P (Olsen-P), water soluble P (WSP), and readily desorbable P. PRP contributed approximately 60％ to total P (TP) in most sediments, AAP 20％, Olsen-P 15％, WSP 2％, and readily desorbable P (RDP) 0.5％. For the heavily polluted sediments, their bioavailable P extracted from TP mainly originated from inorganic P (IP), IP mainly originated from NaOH-P, the bioavailable P concentrations can be evaluated by measuring the concentrations of TP, NaOH-P, and IP. For the slightly polluted sediments, the bioavailable P can only be evaluated by different chemical extractable methods.

Keywords: Yangtze River region; Sediment; Phosphorus fractions; Bioavailable P; Potential nutrient release; Chemical extraction』

Introduction
Materials and methods
　Study area
　Sediment samples and analyses
　P fractions and bioavailable P
Results
　Sediment characteristic
　Concentrations of the bioavailable P and their contributions to TP
　Relationships between the bioavailable P and different fractions
Discussion
Conclusions
Acknowledgments
References

※分析方法は、Wang et al.（2005）による。