Study On Vertical Migration Of Cyanobacteria And The Effect Of Nitrogen And Phosphorus Released From Sediment On Buoyancy Regulation Of Cyanobacteria

The buoyancy and buoyancy regulation are very important to the dominance of blue-green algae.Lake simulator experiments(4m high and 1m diameter) and Pyrex bottle experiments(10L) were applied here to investigate the buoyancy regulation and vertical distribution of Planktothrix mougeotii in eutrophic lakes at 28℃,Pyrex bottle experiments(10L) were applied here to investigate the response of buoyancy regulation of cyanobacteria to nitrogen and phosphorus released from sediment,Blue-green algal blooms in Lake Taihu and Three Gorges reservoir region,the character of cyanobacterial cells and buoyancy were investigated.The results showed that:1.During light phase,the filaments stratify in the 2～3m after 8h light exposure and the biomass at the layer attach maximum after 12h light exposure.During dark phase, the filaments are tent to migrate to the surface.20%of filaments migrate to the surface after 12h and 50%of filaments migrate to the surface after 48h.The buoyancy regulation under light condition is that filaments stratify in 10μmoL·(m²Â·s)^-1 layers,the filaments above the layer sink down,while those suspended below the layer float up.The amplitude of dial changes in buoyancy is relation to photon irradiance,the change of buoyancy in light[100μmoL·(m²Â·s)^-1]/dark is higher than its in light[25μmoL·(m²Â·s)^-1] /dark.Carbohydrate ballasting may be the only mechanism for buoyancy changes in Planktothrix mougeotii filaments during the period.2.When Microcystis blooms was developing in the enclosure which were sealed off from the sediments at the bottom with a depth of 0.5 m,TP concentration showed a dramatic increase,In contrast to the dramatic increase in phosphorus concentration associated with the outburst of Microcystis blooms,the increase of TN concentration was not significant in the enclosure with blooms,Microcystis cells absorbed nitrogen and phosphorus and reserved high-level nitrogen and phosphorus,but Q_N and Q_P fell down associated with the outburst of Microcystis blooms;cellular gas vesicle volume and cellular protein decreased with the outburst of Microcystis blooms,cellular carbohydrate decreased,the change of cellular carbohydrate is related to N/P,Microcystis buoyancy did not lose with the outburst of Microcystis blooms.3.Cell and buoyancy regulation of Microcystis may be influenced by temperature and nutrient;Blue algal bloom in Lake Taihu in Wuxi in May in 2007,gas vesicle provided much excess buoyancy which eliminated the influence of carbohydrate;Blue algal bloom in Three Gorges reservoir region in December in 2007,cellular carbohydrate of Microcystis accumulated in response to low temperature,gas vesicles of Microcystis were not collapse by turgor pressure,buoyancy regulation of Microcystis may be controlled synthetically by cellular gas vesicle volume 1 and cellular carbohydrate.