The Ecological Research On The Microcystis Bloom In Eutrophic Water Bodies

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. The characteristic of eutrophication in freshwater ecosystem is the annual cyanobacterial blooms during the high temperature season, which could not only break the structure and the balance of hydrophytic ecology in the water but also pose serious health threats due to the production of toxic compounds. Eutrophication has become a serious environmental problem in most lakes of China. As a prerequisite to the ecosystem management for the cyanobacterial bloom events, it is essential to determine the relationship between the biomass distribution of MC- and non MC-Microcystis and the related environmental factors during the development of the bloom in freshwater ecosystem. However, few systematic investigations in the community structure of Microcystis have been conducted on eutrophic lakes.To better understand the basic characteristics of Microcystis blooms in Lake Taihu, samples were collected from December 2008 to October 2010 and analyzed morphologically via the distribution and dynamics of different Microcystis morphotypes and genetically via sequencing the clone library of the internal transcribed spacer of the rRNA operon (ITS). We also conducted quantitative PCR to assess total Microcystis abundance and the proportion of microcystin-producing subpopulation. Marked succession of the Microcystis populations in both morphotypes and genotypes occurred during the course of the Microcystis bloom. The T1 genotype, characterized by strains of Microcystis flos-aquae, was the most dominant genotype in Lake Taihu during winter and spring around the whole lake and likely acted as the main inoculum for forming blooms the following year. The 4600 ITS sequences were obtained and were revealed to have 1260 Microcystis genotypes, the highest genetic diversity of Microcystis reported in Lake Taihu. Water temperature temporally affected the succession of both Microcystis genotypes and morphotypes, whereas wind-driven disturbance and the micro-environment influenced spatial distribution of Microcystis genotypes and morphotypes. High ratios of mcyD containing Microcystis subpopulations were detected during the onset and later phase of blooms. Redundancy analysis (RDA) indicated that water temperature and PO4-P were major factors controlling total Microcystis abundance and proportions of microcystin-producing Microcystis population at hyper-eutrophic waters.To determine the Microcystis population and its spatial distributions along the reaches in Qinhuai River, a convenient approach was applied genetically by sequencing the internal transcribed spacer of the rRNA operon (ITS). The TCS analysis showed that 9 groups were classified from the main 24 genotypes and each group was dominated by one highly represented root sequence. Marked changes in the composition and proportion of the Microcystis ITS genotype were detected from/along the upper to the lower reaches. The possible seed sources of the bloom were located in 4 different locations. Furthermore, it was found that pH was the primary factor affecting the spatial distribution of the main genotype group between samples.