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Lake Taihu is a large(2338 km2),shallow(mean depth 2.0 m),hypereutrophic and well mixed year-round(polymictic) lake.For the past three decades,seasonal blooms of Microcystis spp.have regularly formed in the lake,usually starting around April and persisting through October.It has long been known that microcystin-producing and non microcystin-producing strains can be isolated from one water sample,and the waxing and waning of microcystin-producing versus non-microcystin-producing strains has been suggested as a most important factor regulating net microcystin production in water.However,the quantification of microcystin producers versus non-microcystin-producers was for a long time impeded because of the morphological similarity between strains differing in microcystin production.Quantitative real-time PCR(qPCR) has been successfully applied to track quantities of microcystin-producing Microcystis genotypes in natural populations.So far,the effects of environmental factors on the abundance of microcystin-producing and non-toxic Microcystis genotypes have been studied in a relatively limited scale.In this study,We attempted to verify the environmental factors related to the spatial and temporal dynamics of the abundance of toxic and non-toxic Microcystis in the Lake Taihu.Water samples were collected in three sampling sites(Meiliang Bay(N2),Gonghu Bay(N4) and the center area(S4) at monthly intervals from April to September,2010.The abundance and subpopulation proportion of toxic Microcystis genotypes was quantified using a quantitative real-time PCR with two primers sets for the cpcBA-IGS and mcyA gene.QPCR data showed that the abundance and proportion of toxic Microcystis genotypes in three studying sites increased gradually from April to August,and then decreased in September,with both values being higher in Meiliang Bay than in the other two sites.The proportion of toxic Microcystis genotypes in Meiliang,GonghuBay and the center area varied considerably,ranging from(26.2± 0.8)% to(64.3 ±2.2)%,from(4.4±0.2)% to(22.1±1.8)% and from(10.4±0.4)% to(20.6±1.5)%,respectively.Correlation analysis revealed a significantly positive relationship between chlorophyll a,toxic Microcystis and total Microcystis.Meanwhile all the three components were strongly related to water temperature(P0.05).The change of the proportion of toxic Microcystis genotypes was closed related to water temperature(P0.01) and phosphorus concentration(P0.05),suggesting that water temperature and phosphorus concentration are critical environmental factors for determining the abundance and proportion of toxic Microcystis genotypes in Lake Taihu.

Genetic diversity of photosynthetic picoeukaryotes has been investigated at two stations located in Meiliang Bay and East Taihu in Lake Taihu,respectively.Genetic libraries of chloroplast 16S rRNA gene have been constructed by using primer set PLA491F/OXY1313R,biased towards chloroplast of marine algae.The results show that most of photosynthetic picoeukaryotic sequences belong to Cryptophyta,and the rest of them are affiliated with Bacillariophyta,Chrysophyta and Haptophyta.The study can help us take knowledge of the community structure and ecological function of phytoplankton in Lake Taihu.

Nitrogen isotopic technique was used to study the nitrate pollution of four inflowing rivers of Lake Chaohu in different seasons.Our results showed that River Shiwulihe was the most polluted river,while River Shuangqiaohe as the least polluted one.Nitrogen Stable isotopic values demonstrat that nitrate sources differ in various seasons for those four rivers.The dominate pollution sources of nitrate for River Shiwulihe and River Nanfeihe are human sewage and industry discharge.In the case of River Paihe,nitrate is mainly derived from industry discharge in winter,which is originated from agriculture and rainfall in spring and summer,respectively.For River Shuangqiaohe,nitrate contamination is mainly caused by agriculture in winter and spring,but is influenced by rainfall in summer.In addition,our results imply that ammonium is the main nitrogen pollution compound in those four rivers,and δ15 NH+4 value should be detected for the identification of ammonium sources in further study.

Based on 11004 satellite images from CBERS CCD and Landsat TM/ETM, changes in the spatial characteristics of all lakes in China were determined following pre-established interpretation rules. This dataset was supported by 6843 digital raster images (1:100000 and 1:50000), a countrywide digital vector dataset (1:250000), and historical literature. Comparative data were corrected for seasonal variations using precipitation data. There are presently 2693 natural lakes in China with an area greater than 1.0 km2, excluding reservoirs. These lakes are distributed in 28 provinces, autonomous regions and municipalities and have a total area of 81414.6 km2, accounting for ∼0.9% of China’s total land area. In the past 30 years, the number of newly formed and newly discovered lakes with an area greater than 1.0 km2 is 60 and 131, respectively. Conversely, 243 lakes have disappeared in this time period.

The present article described the importance of prevention, forecast and warning of cyanobacteria bloom. The recent progresses of formation and forecast of cyanobacteria bloom were reviewed. Based on the theory of "four phases of cyanobacteria bloom development" and the temporal and spatial distribution of cyanobacteria overwintering, recruitment and bloom formation in Lake Taihu, the processes of cyanobacteria blooms and the dominant ecological factors during their development phases were studied. Field observations and laboratory simulating studies were performed to investigate horizontal distribution and life characteristics during the overwintering period. The threshold temperature for the recruitment of cyanobacteria was about 9℃ in the field research. It was found that there was a positive relationship between effective accumulated temperatures and recruitment biomass of cyanobacteria. By the methods of frequency of dividing cells, the calculation of the growth rates in situ showed that the growth rates of Microcystis were from 0.2 to 0.4. The dynamics of vertical distribution of cyanobacteria in the transport process between different lake areas were investigated under different meteorological conditions, and the results supported the viewpoint that bloom formation is a shift in the vertical positioning of the cyanobacteria biomass which previously distributed through the water column, since the coefficients of variation of the vertical cyanobacteria distribution at different depths were negatively related to wind speeds. On the basis of the establishment of key factors and their thresholds of bloom formation, the bloom forecast model and flow chart of cyanobacteria bloom forecast and warning were established. The bloom forecasts in 2007, 2008 and analysis of bloom trends of 2008 were implemented. The retrospective assessment of the forecast showed that it is possible to forecast the probability, location and extent of cyanobacteria bloom. The future research directions were also suggested.

Dynamics of composition of different Microcystis spp. genotypes from June to November, 2008 in Meiliang Bay of Lake Taihu in China were investigated based on denaturing gradient gel electrophoresis analysis of PCR-amplified ITS (internal transcribed spacer sequence) fragments. Simultaneously, we investigated the relative abundance of microcystin-producing Microcystis spp. (the ratio of the toxic Microcystis to total Microcystis) based on microcystin synthetase gene (mcyA) and partial Microcystis-specific 16S rDNA sequence using real-time PCR. The results of this study indicated that there were shifts of composition of different Microcystis genotypes during algae bloom in Lake Taihu. The most abundant genotypes were found in the late of August, September and October. Genotypes M5 and M10 were found every month. A total of twelve main genotypes were found, and the relative abundance of each genotype changed during the development of algae bloom. Quantitative real-time PCR (qRT-PCR) revealed that the abundance of toxic Microcystis increased from 0.75% to 32.16% from June to October and decreased significantly in November.