Interactions between a cyanobacterial bloom (Microcystis) and the submerged aquatic plant Ceratophyllum oryzetorum Kom.

In aquatic ecosystems, macrophytes and phytoplankton are main primary producers, in which macrophyte plays an important role in maintaining clear water state, while phytoplankton often dominates in turbid waterbodies. In the present study, the growth and photosynthetic activity of the submerged aquatic plant Ceratophyllum oryzetorum Kom. in different cell densities of cyanobacterial bloom are studied. The results show that the plant length and fresh mass of C. oryzetorum are promoted by low cyanobacterial cell densities. Medium and high cyanobacterial cell densities, on the contrary, act as inhibitory. Furthermore, the photosynthetic activity of C. oryzetorum is strongly inhibited by high cyanobacterial cell densities. To a certain extent, the growth of cyanobacteria is inhibited by C. oryzetorurn, but no significant effect is found in this study.

Comparison of three flocculants for heavy cyanobacterial bloom mitigation and subsequent environmental impact

Cyanobacteria can accumulate as a heavy biomass on the leeward side of large eutrophic lakes,posing a potential threat to public health.The mitigating capacity of three flocculants and their potential impacts on the major environmental features of water and sediments was evaluated.Results indicate that polyaluminum chloride(PAC)and ferric chloride(FeCl)are efficient flocculants that can rapidly mitigate cyanobacterial blooms with chlorophyll-a concentrations higher tnan 1500 ug/L within 15 min.In comparison,cationic starch with chitosan could only treat cyanobacterial blooms in chlorophyll-a concentrations of less than 200μg/L.The addition of FeClcaused a decline in the pH value,while dissolved oxygen in the water column dropped to 2 mg/L during cationic starch with chitosan treatment for a high cyanobacterial biomass group.Thus,a combination of flocculants and oxygenators should be considered when treating high-concentration cyanobacterial blooms for emergency purposes.Additionally,the cell lysis of cyanobacteria caused by cationic starch with chitosan can result in an increase in total dissolved phosphorus and total dissolved nitrogen.Furthermore,the high accumlation of nutrients in sediments after the settling of cyanobacteria can cause high internal phosphorus pollution.The increase in the total organic carbon of the sediments can threaten lake restoration achieved by planting submerged macrophytes.

Tidal water exchanges can shape the phytoplankton community structure and reduce the risk of harmful cyanobacterial blooms in a semi-closed lake

For estuaries,inland lakes play a vital role in the ecological balance under the impact of tide s.The effect of tides-induced water exchange on phytoplankton community in a semi-closed lake was studied and compared with that of an adjacent closed lake in the Oujiang River mouth in Zhejiang,East China Sea,from June 29,2020 to June 14,2021.Results show that the dominant species,abundance,dominance,and diversity of the phytoplankton species between the two lakes were significantly different.In the closed lake,cyanobacteria were the dominant species during the study period.However.in the semi-closed lake,the diversification of the dominant species was greater,and some species of diatoms and green algae became dominant.The average phytoplankton abundance in the closed lake was 6 times of that in the semi-closed lake.The average dominance of cyanobacteria in the closed lake was 0.96,and those in the semi-closed lake and the Oujiang River were 0.51 and 0.22,respectively.Cyanobacterial blooms occurred throughout the study time in the closed lake but not in the semi-closed one.Furthermore,the species diversity richness of the phytoplankton in the semi-closed lake was higher than that of the closed one,and the phytoplankton community between the closed lake and semi-closed lake could be divided into distinctly different groups based on non-metic multidimensional scaling analysis(NMDS)and analysis of similarities(ANOSIM)analysis.The salinity of the water was significantly greater and the transparency significantly smaller in the semi-closed lake than those in the closed lake.Therefore,water exchange driven by local tidal movement increased salinity and decreased transparency of water,which consequently shaped the community structures of different phytoplankton and reduced the risk of a cyanobacterial bloom outbreak in the semi-closed lake.

The Correlation between the Variation of Dissolved Inorganic Carbon Content and Cyanobacterial Blooms in Fubao Bay of Dianchi Lake

To explore variation of dissolved inorganic carbon content( DIC) caused by cyanobacterial blooms and provide a basis for formulating effective preventive and control measures of cyanobacterial blooms,the concentration of inorganic carbon and the concentration of planktonic algae were studied by sampling method,and the distribution and variation of the DIC and physicochemical factors in the ecological restoration area of Fubao Bay of Dianchi Lake were analyzed. Results indicated that the distribution of chlorophyll-a was significantly positive correlated with CO_3^(2-)( P < 0. 01) and pH values( P < 0. 05); and the distribution of chlorophyll-a was significantly negative correlated with CO_2( P <0. 01),DIC and HCO_3^-( P < 0. 05). In conclusion,the outbreak and extinction of cyanobacterial blooms is one of the important reasons for the variation of inorganic carbon form and concentration.

Controlling cyanobacterial blooms by managing nutrient ratio and limitation in a large hypereutrophic lake: Lake Taihu, China

Excessive nitrogen（N） and phosphorus（P） loading of aquatic ecosystems is a leading cause of eutrophication and harmful algal blooms worldwide, and reducing nutrient levels in water has been a primary management objective. To provide a rational protection strategy and predict future trends of eutrophication in eutrophic lakes, we need to understand the relationships between nutrient ratios and nutrient limitations. We conducted a set of outdoor bioassays at the shore of Lake Taihu. It showed that N only additions induced phytoplankton growth but adding only P did not. Combined N plus P additions promoted higher phytoplankton biomass than N only additions, which suggested that both N and P were deficient for maximum phytoplankton growth in this lake（TN：TP = 18.9）. When nutrients are present at less than 7.75–13.95 mg/L TN and 0.41–0.74 mg/L TP, the deficiency of either N or P or both limits the growth of phytoplankton. N limitation then takes place when the TN：TP ratio is less than 21.5–24.7（TDN：TDP was 34.2–44.3）, and P limitation occurs above this. Therefore, according to this ratio, controlling N when N limitation exists and controlling P when P deficiency is present will prevent algal blooms effectively in the short term. But for the long term, a persistent dual nutrient（N and P） management strategy is necessary.

Decrease of NH_4^+-N by bacterioplankton accelerated the removal of cyanobacterial blooms in aerated aquatic ecosystem

We used aerated systems to assess the influence of the bacterioplankton community on cyanobacterial blooms in algae/post-bloom of Lake Taihu, China. Bacterioplankton community diversity was evaluated by polymerase chain reaction-denaturing gradient gel electrophoresis （PCR-DGGE） fingerprinting. Chemical analysis and nitrogen dynamic changes illustrated that NH4＋-N was nitrified to NO2^--N and NO3^--N by bacterioplankton. Finally, NHa^＋-N was exhausted and NO3^--N was denitrified to NO2^--N, while the accumulation of NO2^--N indicated that bacterioplankton with completely aerobic denitrification ability were lacking in the water samples collected from Lake Taihu. We suggested that adding completely aerobic denitrification bacteria （to denitrify NO2^--N to N2） would improve the water quality. PCR-DGGE and sequencing results showed that more than 1/3 of the bacterial species were associated with the removal of nitrogen, and Acidovorax temperans was the dominant one. PCR-DGGE, variation of nitrogen, removal efficiencies of chlorophyll-a and canonical correspondence analysis indicated that the bacterioplankton significantly influenced the physiological and biochemical changes of cyanobacteria. Additionally, the unweighted pair-group method with arithmetic means revealed there was no obvious harm to the microecosystem from aeration. The present study demonstrated that bacterioplankton can play crucial roles in aerated ecosystems, which could control the impact of cyanobacterial blooms in eutrophicated fresh water systems.

Off-flavor compounds from decaying cyanobacterial blooms of Lake Taihu

The effect of cyanobacterial bloom decay on water quality and the complete degradation of cyanobacterial blooms in a short period were examined by an enclosure experiment in Gonghu Bay of Lake Taihu,China.Water quality parameters as well as taste and odor compounds during the breakdown of cyanobacterial blooms were measured.Results showed that the decay of cyanobacterial blooms caused anoxic water conditions,decreased pH,and increased nutrient loading to the lake water.The highest concentrations of dimethyl sulfide （DMS）,dimethyl trisulfide （DMTS）,and β-cyclocitral were observed in the anoxic water,at 62331.8,12413.3,and 1374.9 ng/L,respectively.2-Methylisoborneol was dominant during the live growth phase of cyanobacterial blooms,whereas DMS and DMTS were dominant during the decomposition phase.Dissolved oxygen,pH,and chlorophyll a were negatively correlated with DMS,DMTS,and β-cyclocitral,whereas total phosphorus,total nitrogen,and ammonium （NH4＋-N） were positively correlated with DMS,DMTS,β-cyclocitral,and β-ionone.The experimental results suggested that preventing the anaerobic decomposition of cyanobacterial blooms is an important strategy against the recurrence of a malodor crisis in Lake Taihu.

Electrochemical inactivation of cyanobacteria and microcystin degradation using a boron-doped diamond anode-A potential tool for cyanobacterial bloom control

Cyanobacterial blooms are global phenomena that can occur in calm and nutrient-rich （eutrophic） fresh and marine waters. Human exposure to cyanobacteria and their biologically active products is possible during water sports and various water activities, or by ingestion of contaminated water. Although the vast majority of harmful cyanobacterial products are confined to the interior of the cells, these are eventually released into the surrounding water following natural or artificially induced cell death. Electrochemical oxidation has been used here to damage cyanobacteria to halt their proliferation, and for microcystin degradation under in-vitro conditions. Partially spent Jaworski growth medium with no addition of supporting electrolytes was used. Electrochemical treatment resulted in the cyanobacterial loss of cell-buoyancy regulation, cell proliferation arrest, and eventual cell death. Microcystin degradation was studied separately in two basic modes of treatment： batch-wise flow, and constant flow, for electrolytic-cell exposure. Batch-wise exposure simulates treatment under environmental conditions, while constant flow is more appropriate for the study of boron-doped diamond electrode efficacy under laboratory conditions. The effectiveness of microcystin degradation was established using high-performance liquid chromatography-photodiode array detector analysis, while the biological activities of the products were estimated using a colorimetric protein phosphatase-1 inhibition assay. The results indicate potential for the application of electro-oxidation methods for the control of bloom events by taking advantage of specific intrinsic ecological characteristics of bloom-forming cyanobacteria. The applicability of the use of boron-doped diamond electrodes in remediation of water exposed to cyanobacteria bloom events is discussed.

Simultaneous elimination of cyanotoxins and PCBs via mechanical collection of cyanobacterial blooms:An application of“green-bioadsorption concept”

In this study,the distribution,transfer and fate of both polychlorinated biphenyls（PCBs）and cyanotoxins via phytoplankton routes were systematically investigated in two Chinese lakes.Results indicated that PCB adsorption/bioaccumulation dynamics has significantly positive correlations with the biomass of green alga and diatoms.Total lipid content of phytoplankton is the major factor that influences PCB adsorption/bioaccumulation.Cyanobacterial blooms with relatively lower lipid content could also absorb high amount of PCBs due to their high cell density in the water columns,and this process was proposed as major route for the transfer of PCBs in Chinese eutrophic freshwater.According to these findings,a novel route on fates of PCBs via phytoplankton and a green bioadsorption concept were proposed and confirmed.In the practice of mechanical collections of bloom biomass from Lake Taihu,cyanotoxin/cyanobacteria and PCBs were found to be removed simultaneously very efficiently followed this theory.

Seasonal variation and principle of cyanobacterial biomass and forms in the water source area of Chaohu City, China

We investigated seasonal variations in cyanobacterial biomass and the forms of its dominant population （M. aeruginosa） and their correlation with environmental factors in the water source area of Chaohu City, China from December 2011 to October 2012. The results show that species belonging to the phylum Cyanophyta occupied the maximum proportion of phytoplankton biomass, and that the dominant population in the water source area of Chaohu City was M. aeruginosa. The variation in cyanobacterial biomass from March to August 2012 was well fitted to the logistic growth model. The growth rate of cyanobacteria was the highest in June, and the biomass of cyanobacteria reached a maximum in August. From February to March 2012, the main form of M. aeruginosa was the single-cell form; M. aeruginosa colonies began to appear from April, and blooms appeared on the water surface in May. The maximum diameter of the colonies was recorded in July, and then gradually decreased from August. The diameter range ofM. aeruginosa colonies was 18.37-237.77μm, and most of the colonies were distributed in the range 20-200μm, comprising 95.5% of the total number of samples. Temperature and photosynthetically active radiation may be the most important factors that influenced the annual variation in M. aeruginosa biomass and forms. The suitable temperature for cyanobaeterial growth was in the range of 15-30℃. In natural water bodies, photosynthetically active radiation had a significant positive influence on the colonial diameter of M. aeruginosa （P〈0.01）.

Effect of Iron on Growth, Pigmentation and Antioxidative Activity of Bloom Forming Cyanobacteria

Cyanobacterial blooms are ubiquitous in fresh and brackish eutrophic waters in India. The cyanotoxins produced by many bloom forming cyanobacteria severely affect the health of animals, fishes, birds and human beings. Different physical and chemical factors contribute towards bloom formation. Ten bloom forming cyanobacteria were isolated from natural blooms of northern India. The strains were purified and enriched in the laboratory. The aim of this study was to understand the influence of iron on growth, pigmentation and antioxidative activity of enzymes-catalase and ascorbate peroxidase of bloom forming cyanobacteria. Results show that different strains of bloom forming cyanobacteria attain optimum growth at varied concentration of iron. The cyanobacterial strains like Synechocystis aquatalis, Merismopedia glauca, Anabaena variabilis and Anabaena iyengarii exhibit maximum growth at low iron concentration （2 pM） while some species require higher concentration of iron for their optimum growth namely, Arthrospira platensis show optimum growth at 10uM, and Nostocpaludosum shows maximum growth at 100uM concentration of iron. It was also noticed that chlorophyll and phycobiliprotein content also varies with change in iron concentration. The activity of antioxidative enzymescatalase and ascorbate peroxidase was noticed in all ten cyanobacterial strains. In the light of the findings, it seems that Arthrospira platensis possess maximum catalase and ascorbate peroxidase activity. Increment in concentration beyond optimum value leads to deterioration in the growth, pigment content and enzymatic activity of the cyanobacterial strains. Knowledge about the factors influencing growth of bloom forming cyanobacteria will help to work out ways for eradication of hazardous cyanobacterial blooms.

Removal of Agricultural Non-Point Source Pollutants by Artificial Aquatic Food Web System: A Study Case of the Control of Cynobacterial Bloom in Jiyu River

An artificial aquatic food web (AAFW) system was designed to remove the non-point source pollutants in eutrophic Jiyu river. A certain amount of Scenedesmus obliquus and Daphnia pulex was cultured in the system for the control of serious cyanobacterial bloom. The AAFW system was a continuous-flow system including one storage basin of 3 m3 capacity with polluted river water (the total nitrogen-TN: 4.49 mg⋅l-1;the total phosphorus-TP: 0.192 mg⋅l-1), one phytoplankton tank of 3 m3 capacity with an initial concentrations of S. obliquus about 5.8 × 103 ind⋅l-1, and one zooplankton growth chamber of 1.5 m3 capacity with an initial abundance of D. pulex about 22.5 ind⋅l-1. The system was optimized by setting hydraulic retention time of phytoplankton tank as 5 days and the experiments were operated for 45 days. Compared with the polluted river, TN and TP were removed about 28% and 47% by the AAFW system, respectively. The biomass of phytoplankton decrease from 6.33 mg⋅l-1 to 1.48 mg⋅l-1 and the percentage of cyanobacteria decrease from 43.93% to 2.36%, the biomass of Crustacean zooplankton increase from 0.34 mg⋅l-1 to 1.53 mg⋅l-1 and the percentage of D. pulex increase from 19.19% to 57.62%. Our results indicated that the AAFW system not only is an efficient, flexible system for reducing nutrient levels in tributary rivers, but also has an ability to control the cyanobacteria bloom and rebuilding the aquatic ecosystem from the polluted river water.

Succession of Aphanizomenon flos-aquae and Microcystis aeruginosa in direct co-culture experiments at different temperatures and biomasses

Cyanobacterial blooms have become a serious global environmental issue due to their potential risk for releasing detrimental secondary metabolites into aquatic ecosystems,posing a great threat to water quality management for public health authorities.Aphanizomenon,a common filamentous cyanobacterial genus belonging to Nostocales,is under particular concern because its several members are able to form harmful blooms.Furthermore,succession of bloom between A.flos-aquae and Microcystis occurs in many natural lakes.To evaluate the competitiveness of A.flos-aquae vs.M.aeruginosa,two sets of experiments at different ratios of biomass at 15℃and 25℃were conducted.Results show that at 15℃,the two species were able to coexist,and A.flos-aquae showed a specific higher growth rate,and its growth was promoted by the presence of M.aeruginosa.At 25℃,the growth of A.flos-aquae was inhibited by the biomass of M.aeruginosa,and M.aeruginosa suppressed A.flos-aquae in competition.Additionally,the vegetative cell size of A.flos-aquae was significantly influenced by the co-culture with M.aeruginosa,whereas the filament length of A.flos-aquae was not significantly affected.This study confirms that temperature is the dominating factor on the succession of A.flos-aquae and M.aeruginosa of a different biomass.

Community structure of aerobic anoxygenic phototrophic bacteria in algae-and macrophyte-dominated areas in Taihu Lake,China

Aerobic anoxygenic phototrophic bacteria(AAPB)repre sent a major group of bacterioplankton assemblages in many water systems and some are assumed to be closely associated with phytoplankton.However,studies on relationships between AAPB and cyanobacterial blooms are in scarcity.The dynamics of the abundance and diversity of AAPB was compared based on pufM gene in Meiliang Bay(featured by cyanobacterial blooms)and East Bay(featured by macrophyte)of Taihu Lake,a shallow subtropical lake in the East China plain.AAPB abundance was not significantly different between the two sites,and they were positively correlated with dissolved organic carbon(DOC)concentration.The ratios of AAPB to total bacteria varied from 3.4%to 11.5%and peaked in winter in both site s.No significant differences of AAPB community compositions were detected between the two sites,but there was a separation between warm seasons(June,August,and October)and cold seasons(December,February,and April).Rhizobiales and Limnohabitans-like pufM sequences were significantly contributors for the difference between two seasons,and specially enriched in cold seasons.Chlorophyll a(Ch1 a)and DOC were the most significant variables influencing the AAPB community structure.Furthermore,Porphyrobacter and Rhodospirillales-like pufM sequences were positively correlated with Ch1 a,indicating potential influence of cyanobacterial blooms on these AAPB taxa.These results suggested that diverse AAPB ecotypes coexisted in Taihu Lake,and their ecological role in carbon cycling in the lake may not be ignored.

Key physiological traits and chemical properties of extracellular polymeric substances determining colony formation in a cyanobacterium

Colony formation of cyanobacteria is crucial for the formation of surface blooms in lakes.However,the underlying mechanisms of colony formation involving in physiological and cell surface characteristics remain to not well be established.Six cyanobacterial Microcystis strains(including both unicellular and colonial ones)were employed to estimate the influences of their physiological traits and the composition of extracellular polymeric substances(EPS)on colony or aggregate formation.Results show that raising the number of the photosynthetic reaction center and light-harvesting antenna in the PSII and reducing the growth rate were the major physiological strategies of Microcystis to produce excess EPS enhancing colony formation.Tightly bound EPS(T-EPS)was responsible for colony formation,which approximately accounted for 50%of the total amount of EPS.Five fluorescent components(protein-,tryptophan-,and tyrosine-like components and two humic-like components)were found in the T-EPS,although the amounts of these components varied with strains.Importantly,colonial strains contained much higher tyrosine-like substances than unicellular ones.We suggest that tyrosine-like substances might serve as a crosslinking agent to connect other polymers in EPS(e.g.,proteins or polysaccharides)for colony formation.Our findings identified key physiological traits and chemical components of EPS for colony formation in Microcystis,which can contribute to a better understanding on the formation of Microcystis blooms.

Hyperspectral Reflectance Characteristics of Cyanobacteria

Potentially harmful cyanobacterial blooms are an emerging environmental concern in freshwater bodies worldwide. Cyanobacterial blooms are generally caused by high nutrient inputs and warm, still waters and have been appearing with increasing frequency in water bodies used for drinking water supply and recreation, a problem which will likely worsen with a warming climate. Cyanobacterial blooms are composed of genera with known biological pigments and can be distinguished and analyzed via hyperspectral image collection technology such as remote sensing by satellites, airplanes, and drones. Here, we utilize hyperspectral microscopy and imaging spectroscopy to characterize and differentiate several important bloom-forming cyanobacteria genera obtained in the field during active research programs conducted by US Geological Survey and from commercial sources. Many of the cyanobacteria genera showed differences in their spectra that may be used to identify and predict their occurrence, including peaks and valleys in spectral reflectance. Because certain cyanobacteria, such as Cylindrospermum or Dolichospermum, are more prone to produce cyanotoxins than others, the ability to differentiate these species may help target high priority waterbodies for sampling. These spectra may also be used to prioritize restoration and research efforts to control cyanobacterial harmful algal blooms (CyanoHABs) and improve water quality for aquatic life and humans alike.

Seasonal Succession of the Plankton and Microbenthos in a Hypertrophic Shallow Water Reservoir at Modra(W Slovakia)

The seasonal development of the phytoplankton, phytobenthos, zooplankton, and microbenthos in a high eutrophised intravilan water reservoir was studied. Finally, 25 genera with 44 species of Cyanobacteria/Cyanophytes and 67 genera with 102 species as well as infraspecific taxa of different groups of microscopic algae were identified. The phytoplankton in most parts of the water basin was strongly dominated by green colonial alga Golenkiniopsis longispina. From October until December a cyanophyte species Aphanocapsa delicatissima with typical cell dimensions of picoplankton/ was found in large amounts/predominated. As early as spring, a plankton bloom in all its components was observed. At that time, also a high concentration of total phosphorus was recorded, which in the second half of April dropped rapidly. The concentration of chlorophyll-a increased from 162.7 μg/L in March to 2322 μg/L in September. Massive occurrence of benthic protozoa in the plankton, as a consequence of anoxia, has been observed. Further, the detritivore and omnivore ciliate species Coleps hirtus dominated in the microbenthos. Altogether 74 of ciliate taxa were detected. Their abundance and biomass reached peak in April, but these steadily decreased from May until the end of the year. Extreme values of zooplankton density (54,016 ind/L) were recorded in spring followed by a sudden fall in summer and autumn. The contribution of rotifers (Brachionus spp., Filinia longiseta) in the total zooplankton density and biomass was 98%. Relatively a low species richness of crustaceans (4 Cladocera and 3 Copepoda) was observed.

Quantification of microcystin-producing and non-microcystin producing Microcystis populations during the 2009 and 2010 blooms in Lake Taihu using quantitative real-time PCR

Lake Taihu,a large,shallow hypertrophic freshwater lake in eastern China,has experienced lake-wide toxic cyanobacterial blooms annually during summer season in the past decades.Spatial changes in the abundance of hepatotoxin microcystin-producing and nonmicrocystin producing Microcystis populations were investigated in the lake in August of 2009 and 2010.To monitor the densities of the total Microcystis population and the potential microcystin-producing subpopulation,we used a quantitative real-time PCR assay targeting the phycocyanin intergenic spacer（PC-IGS） and the microcystin synthetase gene（mcyD）,respectively.On the basis of quantification by real-time PCR analysis,the abundance of potential toxic Microcystis genotypes and the ratio of the mcyD subpopulation to the total Microcystis varied significantly,from 4.08×104 to 5.22×107 copies/mL,from 5.7% to 65.8%,respectively.Correlation analysis showed a strong positive relationship between chlorophyll-a,toxic Microcystis and total Microcystis;the abundance of toxic Microcystis correlated positively with total phosphorus and ortho-phosphate concentrations,but negatively with TN：TP ratio and nitrate concentrations.Meanwhile the proportion of potential toxic genotypes within Microcystis population showed positive correlation with total phosphorus and ortho-phosphate concentrations.Our data suggest that increased phosphorus loading may be a significant factor promoting the occurrence of toxic Microcystis bloom in Lake Taihu.

Alteration of dominant cyanobacteria in different bloom periods caused by abiotic factors and species interactions

Freshwater cyanobacterial blooms have drawn public attention because they threaten the safety of water resources and human health worldwide.Heavy cyanobacterial blooms outbreak in Lake Taihu in summer annually and vanish in other months.To find out the factors impacting the cyanobacterial blooms,the present study measured the physicochemical parameters of water and investigated the composition of microbial community using the 16S rRNA gene and internal transcribed spacer amplicon sequencing in the months with or without bloom.The most interesting finding is that two major cyanobacteria,Planktothrix and Microcystis,dramatically alternated during a cyanobacterial bloom in 2016,which is less mentioned in previous studies.When the temperature of the water began increasing in July,Planktothrix appeared first and showed as a superior competitor for M.aeruginosa in NO3^−-rich conditions.Microcystis became the dominant genus when the water temperature increased further in August.Laboratory experiments confirmed the influence of temperature and the total dissolved nitrogen(TDN)form on the growth of Planktothrix and Microcystis in a co-culture system.Besides,species interactions between cyanobacteria and non-cyanobacterial microorganisms,especially the prokaryotes,also played a key role in the alteration of Planktothrix and Microcystis.The present study exhibited the alteration of two dominant cyanobacteria in the different bloom periods caused by the temperature,TDN forms as well as the species interactions.These results helped the better understanding of cyanobacterial blooms and the factors which contribute to them.

Effects of elevated CO_2 on dynamics of microcystin-producing and non-microcystin-producing strains during Microcystis blooms

In an attempt to elucidate the effects of different CO2concentrations（270, 380, and 750 μL/L） on the competition of microcystin-producing（MC-producing） and non-MC-producing Microcystis strains during dense cyanobacteria blooms, an in situ simulation experiment was conducted in the Meiliang Bay of Lake Taihu in the summer of 2012. The abundance of total Microcystis and MC-producing Microcystis genotypes was quantified based on the 16 S r DNA and mcy D gene using real-time PCR. The results showed that atmospheric CO2 elevation would significantly decrease the p H value and increase the dissolved inorganic carbon（DIC） concentration.Changes in CO2 concentration did not show significant influence on the abundance of total Microcystis population. However, CO2 concentrations may be an important factor in determining the subpopulation structure of Microcystis. The enhancement of CO2 concentrations could largely increase the competitive ability of non-MC-producing over MC-producing Microcystis, resulting in a higher proportion of non-MC-producing subpopulation in treatments using high CO2 concentrations. Concurrently, MC concentration in water declined when CO2 concentrations were elevated. Therefore, we concluded that the increase of CO2 concentrations might decrease potential health risks of MC for human and animals in the future.