Abstract:

In November，2006，sediment and water samples in Jinsha River，the Yangtze River mainstream，Ming River and Tuo River were collected respectively.And then a series of indices of phosphorus of the sediment samples were tested，including total phosphorus，available phosphorus，fixed phosphorus and dissolved phosphorus.The results showed that the available phosphorus in Ming River sediment samples and Tuo River sediment samples were significantly higher than those in Jinsha River and the Yangtze River mainstream，which reflected the phosphorus pollution of the Yangtze River branch in Sichuan Basin was severer than that in the mainstream.The available phosphorus in mainstream samples increases from upstream to downstream，while the fixed phosphorus decreases.It reflects that the sediment in mainstream has absorbed the dissolved phosphorus from the branches in Sichuan Basin，so the fixation capacity of sediment in mainstream was reducing.According to the difference values of available phosphorus in sediment samples from Jinsha River (Yibing Station) and the Yangtze River (Zhutuo Station)，calculated value of dissolved phosphorus absorbed by sediment in Jinsha River was 382 t/a and the capacity of dissolved phosphorus absorbed by sediment in Jinsha River was 6 885 t/a，which account for 26% and 468% of the annual dissolved phosphorus of the Zhutuo Station，respectively.It is likely that the real value of dissolved phosphorus absorbed by sediment in Jinsha River lies between 382~6 885 t/a，which reduced the load of phosphorus entering the Three Gorges Reservoir，although the real value needs further researching.When the Xiluodu Hydropower Project were built up，assuming that the sediment outflow from the reservoir is a fixed value in the 50 years，the value of dissolved phosphorus entering the Three Gorges Reservoir would increase 16%～294%.

Key words: Xiluodu Hydropower Project, sediment retaining, phosphorus, Three Gorges Reservoir, eutrophication