Abstract: To explore endogenouspollution and bio-availabilityof different forms of phosphorus (P) in the water and sediments of Lake Chaohu, conventional chemical approaches and diffusive gradients in thin-films (DGT) technology were used in this study to analyze spatial distribution of different forms of P in the water and sediments and P adsorption by sediments in different zones. Results show that the water in the western part of the lake washigher than the waters in the central and eastern parts of the lake in content of total P (TP) and dissolved inorganic P (DIP) and could be sorted into the level of eutrophication. Among the five chemically extractable forms of Pin the sediments, TP, Fe/Al-P (iron/aluminum bound P) and AAP (algal-available P) in the three parts of the lake followed an order of western part > eastern part >centralpart in content; OP (organic P) in an order of eastern part > western part > central part; Ca-P (Calcium bound P) did not vary much between the parts; and DGT-P (P determined with the DGT method) did not either within the lake, but did in the areas of river mouths, indicating that the areas of river mouths were greatly influenced by the pollutants carried by river flows. DGT-P in the sediments was positively related to highly active AAP, Fe/Al-P,OP and DIP, with coefficient R being 0.541, 0.547,0.731(P＜0.01) and 0.438(P＜0.05), respectively, which indicates that the DGT device was effective in monitoring bio-available Pin the sediments. Isothermal adsorption study indicates that the sediments in the western and eastern parts of the lake were both high in P adsorption potentiality, while those in the central part was quite low. However, DGT-P in equilibrium solutions varied sharply, with the highest equilibrium concentrationof the sample from Sampling Site No. 9(0.62mg•L^-1) in the western part of the lake being 9 times as high as that of the sample from Sampling Stie No. 3(0.07mg•L^-1) in the eastern part of the lake, suggesting that sediments may influence, to a quite extent, bio-availability of P in the overlaying water.

Key words: distribution of forms of phosphorus, bio-available phosphorus, diffusive gradients in thin-films, Lake Chaohu