『Abstract
　Solid phases of phosphorus fractions in the surface and core sediments were studied to understand the biogeochemical cycling and bioavailability of phosphorus in the Pichavaram intertidal mangrove sediments of India. Total P in surface and core sediments ranged between 451-552 and 459-736μg g^-1 respectively and Fe bound P was the dominant fraction. Low levels of Fe bound P in the mangrove zone than the two estuarine zones may be because of high salinity inhibition of phosphate adsorption onto the Fe-oxides/hydroxides. Post-depositional reorganization of P was observed in surface sediments, converting organic P and Fe bound P into the authigenic P. High High levels of organic P in the mangrove zone is primarily due to intensive cycling and degradation of organic matter and adsorption of phosphate on the organic molecules. The burial rates and regeneration efficiency of P in the intertidal mangrove ecosystem ranged from 5.41 to 7.27μmol P cm^-2 year^-1 and 0.122 to 0.233μmol P cm^-2 year^-1, respectively. High burial efficiency (≒99％) of P proves the earlier observation of limiting nature of P for the biological productivity. Further, bioavailable P (exchangeable P + Fe bound P + organic P) constituted a considerable proportion of sedimentary P pool of which an average accounted for 55 and 50％ in surface and core sediments respectively. The results indicate that significant amount of P is locked in sediments in the form of authigenic P and detrital P which makes P as a limiting nutrient for the biological productivity.

Keywords: Phosphorus; Sequential extraction; Organic P; Mangrove; India』

Introduction
Materials and methods
　Research area description
　Sample collection and pretreatment
　Sequential extraction of phosphorus
　Analytical methods
Results
　Sediment characteristics
　Phosphorus fractions in sediments
Discussion
　Phosphorus speciation in surface sediments
　Phosphorus fractions in core sediments
　Phosphorus burial rate and regeneration efficiency
　Bioavailable phosphorus
Summary and conclusion
Acknowledgement
References