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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.

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.

In order to investigate the spatial variations of the over-winter cyanobacteria in different areas of Lake Taihu, sediment and water samples were collected monthly in 14 sites in winters from 2007 to 2008. The phycocyanobilin concentration (PC) of samples was measured by the fluorometry analysis of pigments to confirm the difference of PC’s spatial variations among three areas of Lake Taihu. The result shows that, differing from summer, the winter PC in both sediment and water from northern part was lower than western and southern part of Lake Taihu. Even in December, in some parts of western and southern areas the cyanobacteria was still blooming, and PC of surface sediment was also high. According to the result, it is clear that the over-winter cyanobacteria was mainly distributed in western and southern areas of Lake Taihu during the investigation winter seasons.

Of all the cloudless 340 satellite imageries 11 were shot by Landsat MSS/TM/ETM sensor since 1979, 216 by EOS MODIS sensor since 2002, 10 by CEBERS CCD sensor since 2005 and 3 by IRS P6 LISS-3 sensor in 2007. On the basis of the spectral analysis, an applicable model was developed to extract the cyanobacteria bloom information from multi-source remote sensing images. And then, the model was used to acquire cyanobacteria bloom-covered area and its spatial distribution. The result showed that the initial time of cyanobacteria bloom was moved from June or July to March or April at present, three-four months advanced than the normal. The statistics showed that the cyanobacteria bloom occurs most frequently in June or July and the second was in October or November. Additionally, the duration of cyanobacteria bloom is becoming longer and longer and almost over time of March to December at present. The most intensity of cyanobacteria bloom occurred in September and the second was in June. The north of Lake Taihu, including Meiliang Bay and Zhushan Bay, was the initial location of cyanobacteria bloom and also the heavy disaster area, where the cyanobacteria bloom occurred every year since its first time. However, cyanobacteria bloom also occurred along the south bank of Lake Taihu almost every year since 2001, where the cyanobacteria bloom-covered area was becoming larger and larger and the duration time was becoming longer and longer, and which was becoming the earliest location of cyanobacteria bloom. It was noticeable that the cyanobacteria bloom was pervading gradually from the north, the west and the south to the center since 2003, and it sometimes covered almost the whole non-vegetation area. Additionally, there were cyanobacteria blooms occurring at Gonghu Bay since 2005, and it occurred more frequently in 2007.

Stable isotope analysis is commonly used in studying flows of mass and energy through food webs and trophic relationships in aquatic ecosystems. However, different sample processing methods can influence the measurement of these stable isotope rates, which may result in errors in the resulting food web models and the comparing results between different studies. In particular, errors may result from four different sources, that is, preservation, separation, acidification and dehydration. The collectted particulate/dissolved organic matter, bacteria, zooplankton, algae, hydrophyte, fish and zoobenthos were rinsed with de-ionized water to clean off epibionts, and then stored at -20℃. Acidification by adding 1mol/L HC1 drop-by-drop was needed for carbon isotope analysis in samples of sediment organic matter, invertebrates with calcareous structures, and plankton. For nitrogen analysis, acidification should be avoided. Finally, dehydration was required by the analytical methods used in the determination of isotopic abundance. Both freeze-drying and drying at 40-70℃were acceptable. In addition, materials preserved with formalin and ethanol stocks was suitable for current ecological applications of isotopic analysis and open up the possibility to reconstruct food webs and biogeochemical changes at scales of tens or hundreds of years. In this review we summarize different sample processing prior to the analytical determination of stable isotope ratios and the influence mechanism of some processing methods, which are fundamental for further methodology research.

To explore the effects of different types of phosphate on the growth of Microcystis aeruginosa and Chlorella pyrenoidosa, three types of phosphate salts: dipotassium hydrogen phosphate (K2HPO4), sodium pyrophosphate(Na4P2O7) and sodium polyphosphate (Na5P3O10) were used as phosphate sources in this experiment. The growth curves showed that, at early stage of growth in the K2HPO4 medium, the growth rate of C. pyrenoidosa was significantly higher than that of M. aeruginosa, but on the 16th day, the growth rate of M. aeruginosa and its cell density were all higher than those of C. pyrenoidosa. The growth rate of M. aeruginosa and C. pyrenoidosa in K2HPO4 medium were significantly higher than those in other two phosphate media. Both in the media of sodium pyrophosphate and sodium polyphosphate, the growth rate of C. pyrenoidosa was higher than that of M. aeruginosa. The changes of unicell alkaline phosphatase (APA) suggestted that, the phosphate utilization of C. pyrenoidosa was higher than that of M. aeruginosa. The results suggestted that the phosphate utilization capability of C. pyrenoidosa was higher than that of M. aeruginosa, indicated that phosphate utilization was not the main cause which resulted in the dominance of M. aeruginosa in water-bloom formation.

In this study,the responses of Microcystis aeruginosa growth to oxidation reduction potential (ORP) re- ducing were studied by momospecies culture and mixed culture with Scenedesmus obliquus.Cell size,esterase activ- ity and chlorophyll fluorescence intensity of M.aeruginosa were measured by flow cytometry.The results showed that oxidation reduction potential of medium was reduced by exogenous glutathione (GSH).In monospecies culture groups,M.aeruginosa has a significant higher growth rate than S.obliquus,and no significant effects of ORP on the two algae were found.However,in mixed culture groups,the growth of the two algae were obviously inhibited and the cell concentration of M.aeruginosa was still dominant.While ORP was reduced,the growth rate of M. aeruginosa was enhanced and that of S.obliquus was inhibited.Furthermore,Cell size,esterase activity and chloro- phyll fluorescence intensity of M.aeruginosa were increased after ORP was changed.All these changes play an im- portant role in enhancing growth rate of M.aerugionsa.

The phylogenetic diversity and seasonal variation of the bacterioplankton communities were determined using denaturing gradient gel electrophoresis(DGGE)of PCR-amplified bacterial 16s rRNA genes at Meiliang Bay and lake center in Taihu.Results indicated that the bacterioplankton community composition was diverse in Lake Taihu.At the two sampling stations,bacterioplankton abundance,DGGE band number,Shannon-Wiener index, Simpson index,and Pielou index all showed significantly seasonal variation during the sampling period.Bacterio- plankton abundance,diversity and evenness were all higher in summer and autumn than in winter and spring.The phylogenetic types of the bacterioplankton communities changed during the sampling period.The abundance of bac- terioplankton was significantly higher at Meiliang Bay than at the open lake.The main edificators of the bacterio- plankton communities may have different phylogenic types at Meiliang Bay and lake center.

Photochemical vitality of overwintering phytoplankton including cyanobacteria chlorophyta and bacillario- phyta was not known because of the general small biomass.In present study,Phyto-PAM (Pulse Amplitude Modu- lation) was applied to measure Fv/Fm (ratio of variable to maximal fluorescence) and rapid light curves of phyto- plankton to study the photochemical vitality in situ of overwintering phytoplankton sampled from LakeTaihu,Lake Chaohu and Lake Xuanwu.Both microscopic determination of cyanobacteria,chlorophyta and bacillariophyta and treatment of copper sulfate and Lugol's solution to water samples were performed.The results from microscopy de- termination showed that there were chlorophyta and bacillariophyta but without cyanobacteria in Lake Taihu and Lake Xuanwu.However,a large amount of cyanophyta was detected in Lake Chaohu besides chlorophyta and bacil- lariophyta.Fv/Fm and rapid light curves from Phyto-PAM showed that there was no photochemical vitality of cya- nobacteria in Lake Taihu and Lake Xuanwu but presented with photochemical vitality of chlorophyta and bacillario- phyta(Fv/Fm was about 0.5).In Lake Chaohu,all the three kinds of phytoplankton showed photochemical vitality (Fv/Fm was about 0.5 in chlorophyta and bacillariophyta;Fv/Fm was about 0.3 in cyanophyta).Samples treated with copper sulfate only showed the bacillariophyta photochemical vitality,while even this disappeared when treated with Lugol's solution.The results from Phyto-PAM combined with chemical treatment experiments suggested that the photochemical vitality of phytoplankton was still active in overwintering period.

Cyanobaeteria recruitment from sediments is an important seed bank for their pelagic abundance. We estimated cyanobacteria recruitment from sediments with migration traps in Lake Taihu from March to June 2005, measured in situ growth rate of cyanobacteria in the water column in specially designed chambers, and compared the siy.es of both processes. Meanwhile the effect of zooplankton grazing on cyanobacteria growth rate was also measured. Cyanobacteria recruitment increased with some degree of fluctuation from March to June, peaking in April; in situ growth rate of cyanobacteria also showed a general increase at the same time, only reached maximum in early May. No obvious effect of zooplankton grazing was observed on the in situ cyanobacteria growth rate. Cyanobacteria recruitment only accounted for a small portion of the pelagic growth ( 2.5% ) thereby suggesting that future research on cyanobacteria bloom development be focused on the pelagic populations in water column.

To detect the influences of different temperatures on Microcystis aeruginosa dominance, this experiment researched competition between Microcystis aeruginosa and Chlorella pyrenoidosa under different temperatures by flow cytometry, cell density ratio and chlorophyll-a fluorescence intensity in two species of algae cell were measured. Results displayed under this experimental condition Microcystis aeruginosa dominance became more evident together with temperature rised( 18℃,25℃and 32℃). Higher temperature enhanced chlorophyll-a fluorescence intensity in Chlorella pyrenoidosa cell but reduced chlorophyll-a fluorescence intensity in Microcystis aeruginosa cell. This experiment indicated under suitable light and high nutrition salt condition, higher temperature promoted Microcystis aeruginosa dominance obviously and influenced water bloom forming.

The experiment investigated the relationship of growth characters and phosphorus uptake of Microsystems aerugionosa from Lake Taihu under laboratory conditions. With phosphate and nitrate in oligotrophic level, the growth rate of the alga supported the “N∶P rule”while in hypereutrophic level did not. It is concluded from this study that the “N∶P rule”does not apply to the conditions which P and N were enough. Growth of algae was strongly affected by phosphorus availability. The half saturation constant of P uptake of algae Km was 17.66μM and P half saturation constant for algae growth Ks was16.21μM.The P subsistence quota of algae K=4.36μg /mg(dw). As affected by the initial cellular P quota, the P uptake rates were different. Maximum uptake rate for algae when P is deficient (Vmax,d) was 1.66μg /(L·mg·h) and sufficient maximum P uptake rate (Vmax,s) was 0.06μg/(L·mg·h). P luxury storage coefficient Q0/Qmax=0.14.