Abstract: Contents of bioavailable phosphorus (BAP) in water and surface sediment of the Shiwuli River in the Chaohu Lake Catchment were analyzed using the conventional chemical analysis method and diffusive gradients in thin-films (DGT) technology, to study N and P distributions in the water and surface sediment of the river. Results show that the concentrations of orthophosphate and total phosphorus ascended first along with the river from the upper reaches downwards and then descended and leveled off above the eutrophication level[ρ（DIP）≥ 0.343 mg·L^-1，ρ（TP）≥ 0.676 mg·L^-1]. The inflow of sewage at the upper reaches is the main cause of the drastic rise of phosphorus concentration in the water and then the concentration decreased in the mid reaches of the river thanks to the reduction of sewage inflow. However, P concentration rose somewhat in the lower reaches, because of the influx of tributaries and agricultural non-point source pollution. In the sediment, four fractions of BAP were found and followed with an order of AAP ＞ Olsen-P ＞ WSP ＞ RDP in concentration. AAP and Olsen-P were significantly correlated with TP content. In the sediments in the mid and lower reaches of the river, P in the pore water tended to transfer into river water, which indicates that certain potential risk existed of P in pore water diffusing into overlaying water. The determination of BAP in the river revealed that significant correlation exists between the DGT technology and the conventional chemical method (P < 0.01). It is, therefore, concluded that the DGT technology can be used as a reliable tool to accurately analyze the water in the Shiwuli River for BAP content in future.

Key words: bioavailable phosphorus, DGT, water, pore water, Shiwuli River