Abstract: The spatial variation and vertical distribution of different forms of phosphorus in sediments of the Nanhu Lake were studied. The research indicated that the Nanhu Lake was in the state of severe eutrophication. The total phosphorus（TP）showed high levels in sediment. Average level of TP in surface sediments（0 - 20 cm）was as high as 3. 29 g/kg，and site 3# closed to the sewage treatment plant showed the highest ω（TP），reached 6. 42 g/kg . As a major component in the form of total phosphorus，the inorganic phosphorus（IP）content was varied from 0. 15 to 2. 85 g/kg，which accounted for 70% of TP. Influenced by the redox conditions，the ratio of ω（IP）/ ω（TP）showed a decrease trend with the depth increased. Iron and aluminum bound phosphorus（Fe / Al-P）accounted for more than 60% of TP，the content was 0. 21-3. 47 g/kg，and the calcium bound phosphorus content was 0. 09-1. 42 g/kg. Phosphorus load in sediments was the major internal load to cause the lake to be eutrophication. IP and Fe/Al-P were forms of higher bioavailability. Sediments are risky in releasing phosphorus load and great consideration shall be taken on the these characteristics in the future treatment and management.

Key words: Nanhu Lake, sediment, vertical distribution, internal load