Effects of Microcystis aeruginosa Bloomon Dynamics of Phosphorus at Interface of Water and Sediments: a Simulation Study

Water and sediment were sampled from the Meiliang Bay of the Taihu Lake, China, to build up a simulated sediment-water system with Microcystis aeruginosa added for simulation of the occurrence of Microcystis aeruginosa bloom, with a view to defining how and to what extent alga bloom contributes to variation of Phosphorus in the sediment-water interface. Microcystis aeruginosa in the water column always stayed in a state of alternation of proliferation and suspension during the incubation period (238 day). Proliferation of the algae increased pH in the overlying water by 11%-14%. After the first boom of proliferation of the algae, TP in the water decreased by over 90%, while organic P (Or-P) in the sediment increased substantially. The proportion of water-soluble P (WP) in TP decreased from the initial 93% to 11% during the period of alternation of proliferation and suspension,whilethe content of Or-P alternated decreasing and increasingduring the period. WP contents in both the water and the sediment dropped rapidly to a very low level during the first boom of proliferation of the algae, but afterwards, the content bounced back on average by 2.7 times in the waterand 1.7 times in the sediments. In the sediment, activity of alkaline phosphatase was negatively correlated with Or-P content (P<0.05) and positively correlated with WP content (P<0.01). Hence, it is believed that quite a portion of alga cells rapidly decayed and decomposed during the bloom releasing a considerable amount of WP, which to a certain extent sustained the population of Microcystis aeruginosa in alternation of proliferation and suspension.