Abstract: Water and sediment samples, which were taken from Meiliang Bay, Taihu Lake, were used to mimic a sediment-water system with Chlamydomonas reinhardtii. A variety of phosphorous(P)contents and alkaline phosphatase activities(APA)were measured during C. reinhardtii proliferating, blooming and decaying(76 d), to estimate the contribution of alga to P contents and availabilities at the surface between water column and sediments. The rapid proliferation and blooms for C. reinhardtii resulted in noticeable increases in pH and DO contents with substantial decreases in total P and inorganic P in water column. However, the organic P contents in sediments with alga addition treatment(AT)were averagely 1.5 times higher than those without alga addition treatment(WAT). In addition, water-dissolved P(WP)contents in sediments with AT were observed a clear decrease during the decaying stage, possibly implying that parts of algae survived in the surface of sediments could continue to use WP to a large extent. Moreover, APA in water column was found a 1-3 times higher in average during the decaying stage than those in proliferating and blooming stages, while APA in sediments arrived at the highest level during the proliferating and blooming stages. After then, although APA in sediments for AT decreased over time, it was 2 times above higher than those in WAT. Therefore, C. reinhardtii's blooms accelerated the release of P in a water-sediment system. Parts of algae survived in sediments can proliferate and re-suspend by using the released P. This potentially contributes to the blooms repeatedly occurring during short periods in eutrophic waters.