Dynamic Of Phytoplankton And Monitoring Of Microcystis In A Shallow Eutrophication Lake, Lake Xuanwu

With the increasing development of economy and human activities, environmental problems caused by cyanobacterial blooms in various water bodies especially in freshwater lakes has become a concern all over the world. Xuanwu lake, a state-level scenic spot with the typical subtropical climate, which located in the middle and lower reachers of the Yangtze River, formed cyanobacterial bloom in the summer of 2005 and the dominant species were Microcystis spp.. In this study, based on the establishment of the Real-time PCR, variations of cyanobacteria, Microcystis, microcystin-producing Microcystis were surveyed. Relationships between the phytoplankton and the environmental factors were also studied in a long periord. The main results and conclusions were as follows:(1) 17 years monitoring data shows that with the decreasing of the nutrition, there was obvious fluctuation to the phytoplankton biomass. Species construction of phytoplankton was changed form Chlorella, Cyclotella, Dactylococcopsis, Merismopedia, to Microcysti, Merismopedia. Lower nutrient is prone to the break out of the cyanobacteria.(2) To monitor the densities of the population of Microcystis, Cyanobacteria and the potential microcystin-producing Microcystis, we used a quantitative real-time PCR assay trageting the 16S Cyan, 16S Micr, microcystin synthetase gene(mcyB). Quantification based on real-time PCR is a powerful tool for the rapid quantification of cyanobacteria, Microcystis, Microcystin-producing Microcystis in environmental samples, espescially it is too low to be detected by microscope. The detective rate is 100% and the lowest detection is 10 cells·ml^-1.(3) The data shows below:â‘ The abundance of Cyanobacteria cells varied from 4.6×10⁶ to 2.0×10¹⁰ cells·L^-1, the abundance of Microcystis cells varied from 4.4×10⁵ to 9.0×10⁹ cells·L^-1, the ratio of the mcyB subpopulation to the Microcystis varied considerably, from 0.2% to 11.8%.â‘¡During the year-round investigation: there is no significantly correlationship between Microcystis, Microcystin-producing Microcystis and other environmental factors except TP, PO4-P. Cyanobacteria has the positive relationship with TP, PO₄-P and pH, while the negative relationship with TN:TP and SD.â‘¢During the investigation of winter and spring, the increasing of Microcystis in lower layer is more fast than in middle and top layers in the water colony. The Microcystis were closely correlated with the water temperature, PO₄-P and NO₂-N. Microcystin-producing Microcystis were significantly correlated with NO₃-N, TN and water temperature.(4) A method, for DNA extraction from sediment samples of Xuanwu Lake was developed, and purification and efficience of extracted DNAs were evaluated through ultraviolet spectrum OD260/280 ratios and PCR amplification of 16S rDNA specific for Microcystis. The results showed that sediment samples from all sites in the study obtained quite purified genomic DNAs with OD260/OD280 ratios from 1.54 to 1.89, and Microcystis 16S rRNA gene fragments have been detected in all sampling sites, which indicating this method can be used for molecular detection of Microcystis cells in sediments.(5) More than 250 single colonies of M. wesenbergii from 7 waters with different latitudes and climates were used to perform determination of mcyA by multiplex PCR method, and microcystin production was also analyzed for strains of M. wesenbergii isolated from these waters by ELISA and HPLC. Results from both molecular and chemical ways indicated that M. wesenbergii colonies and strains in Chinese waters are not microcystin producers.