Development Of Cyanobacterial Blooms Research Articles

Correlation Abundance Networks for analyzing biological interactions during cyanobacterial blooms

Introduction: Cyanobacterial blooms are becoming increasingly common, and understanding their dynamics can be crucial for proposing appropriate management strategies. While the physical and chemical parameters influence on blooms have been extensively studied, less attention has been put on the susceptibility of the biological communities. Objective: The purpose of this study was to analyze the phytoplankton abundance networks during blooms at different levels of intensity and how bloom-forming cyanobacteria interact with and/or impact phytoplankton community. Methods: We used 22 samplings conducted in the same reservoir located in northern Argentina, which is known for recurrent cyanobacterial blooms. Each sampling was classified into four levels based on the abundance of cyanobacteria. For each level, abundances correlation networks were constructed considering all species. Results: A pattern of decreasing statistically significant abundance correlations was observed as the intensity of the blooms increased: 219 correlations at level 1; 144 at level 2; 80 at level 3, and only 33 at level 4. Bloom-forming cyanobacteria showed to be little correlated with others species in all the levels, which could be associated to certain independence with the community. Increased bloom seems to disconnect the phytoplanktonic correlation abundances network. Conclusion: Analyzing correlation abundances networks should be a valuable tool for understanding the dynamics and development of cyanobacterial blooms, as well as identifying key species in this process.

Patterns and impacts of cyanobacteria in a deep, thermally stratified, oligotrophic lake

AbstractCyanobacterial blooms are a concern in oligotrophic lakes because these systems are often used for multiple purposes (i.e., recreation and public water supplies). Monitoring cyanobacteria impacts is challenging in such cases because of low and heterogeneous concentrations over time, space, and depth. Canandaigua Lake (New York State) is oligotrophic, but has been impacted by blooms since at least the early 2000s, with limited quantification. This study integrated data from established shoreline surveillance and inter‐agency monitoring programs to connect lake processes and evaluate use impacts. Surveys at open‐water locations were conducted to investigate the origination, timing, and magnitude of cyanobacterial bloom development. Impacts on recreation and source water were caused by blooms originating in the epilimnion that moved to shorelines and intake depths. The integration of multiple monitoring programs was critical to understanding impacts. The methods developed here can be adopted to other cases of large, deep, low‐nutrient lakes.

Growth Characteristics and Changes in Elemental Composition of <i>Microcystis</i> sp. under Various N:P Mass Ratios

This study investigated the relationship between nitrogen (N) and phosphorus (P) mass ratio in the medium and cellular N (Nc) and P (Pc) mass ratio in Microcystis cell. Monoculture experiments were conducted with the phosphorus concentration fixed at 0.110 mg L–1 and the initial N:P mass ratios of 1, 10, 18, 50, 70, and 100. The results showed that the cell density of Microcystis sp. was highest at the initial N:P mass ratio of 50. Although it has been disputed that a low total N:P (TN:TP) ratio (< 29) in water was a cause of the development of cyanobacterial blooms or a result of its occurrence, this study could support the latter trend. This assumption could be supported by the results of elemental analysis (i.e., cellular Nc:Pc mass ratio of Microcystis sp.). At the end of the culture experiment, the Nc:Pc ratios ranged from 13.2 to 20.3, which were similar to the initial value (12.7). In general, the dissolved N and P concentrations in lake water are completely consumed when cyanobacterial blooms occur. Therefore, the present study suggests that the low TN:TP ratio may reflect the cellular Nc:Pc ratio of Microcystis sp. following assimilation of N and P in lake water.

Dolichospermum blooms in Lake Superior: DNA-based approach provides insight to the past, present and future of blooms

Cyanobacterial blooms are increasing in frequency, duration, and severity globally in freshwater ecosystems. The Laurentian Great Lakes are prone to toxin-producing cyanobacterial blooms and have experienced annually recurring blooms. Because of its oligotrophic nature, Lake Superior has been relatively free of bloom occurrences. However, in recent years, Dolichospermum blooms have occurred with increasing frequency, especially in the western arm. During a Dolichospermum bloom in 2018, opportunistic samples were collected from the offshore bloom and investigated with shotgun metagenomics. We identified a near-complete Dolichospermum genome that is highly similar to genomes from cultures recovered in Lakes Erie and Ontario. The genomes from the Laurentian Great Lakes are typified by their putative ability to produce a suite of secondary metabolites like anabaenopeptin, but not toxins like microcystin. Additionally, we recovered a Dolichospermum lemmermannii 16S rRNA gene from the bloom and using datasets collected from the epilimnion and sediments in Lake Superior show this organism is ubiquitous and that several strains may exist. While there is much to learn about Lake Superior cyanobacterial bloom development and triggers, understanding this organism is endemic to the region, what its genome is capable of and that specific strains may have provenance within the lake provides a distinct ecological basis for understanding and working towards a predictive framework for future blooms.

Impacts of atmospheric stilling and climate warming on cyanobacterial blooms: An individual-based modelling approach

Harmful algal blooms of the freshwater cyanobacteria genus Microcystis are a global problem and are expected to intensify with climate change. In studies of climate change impacts on Microcystis blooms, atmospheric stilling has not been considered. Stilling is expected to occur in some regions of the world with climate warming, and it will affect lake stratification regimes. We tested if stilling could affect water column Microcystis distributions using a novel individual-based model (IBM). Using the IBM coupled to a three-dimensional hydrodynamic model, we assessed responses of colonial Microcystis biomass to wind speed decrease and air temperature increase projected under a future climate. The IBM altered Microcystis colony size using relationships with turbulence from the literature, and included light, temperature, and nutrient effects on Microcystis growth using input data from a shallow urban lake. The model results show that dynamic variations in colony size are critical for accurate prediction of cyanobacterial bloom development and decay. Colony size (mean and variability) increased more than six-fold for a 20% decrease in wind speed compared with a 2 °C increase in air temperature. Our results suggest that atmospheric stilling needs to be included in projections of changes in the frequency, distribution and magnitude of blooms of buoyant, colony-forming cyanobacteria under climate change.

Methane-Derived Carbon as a Driver for Cyanobacterial Growth.

Methane, a potent greenhouse gas produced in freshwater ecosystems, can be used by methane-oxidizing bacteria (MOB) and can therefore subsidize the pelagic food web with energy and carbon. Consortia of MOB and photoautotrophs have been described in aquatic ecosystems and MOB can benefit from photoautotrophs which produce oxygen, thereby enhancing CH4 oxidation. Methane oxidation can account for accumulation of inorganic carbon (i.e., CO2) and the release of exometabolites that may both be important factors influencing the structure of phytoplankton communities. The consortium of MOB and phototroph has been mainly studied for methane-removing biotechnologies, but there is still little information on the role of these interactions in freshwater ecosystems especially in the context of cyanobacterial growth and bloom development. We hypothesized that MOB could be an alternative C source to support cyanobacterial growth in freshwater systems. We detected low δ13C values in cyanobacterial blooms (the lowest detected value −59.97‰ for Planktothrix rubescens) what could be the result of the use of methane-derived carbon by cyanobacteria and/or MOB attached to their cells. We further proved the presence of metabolically active MOB on cyanobacterial filaments using the fluorescein isothiocyanate (FITC) based activity assay. The PCR results also proved the presence of the pmoA gene in several non-axenic cultures of cyanobacteria. Finally, experiments comprising the co-culture of the cyanobacterium Aphanizomenon gracile with the methanotroph Methylosinus sporium proved that cyanobacterial growth was significantly improved in the presence of MOB, presumably through utilizing CO2 released by MOB. On the other hand, 13C-CH4 labeled incubations showed the uptake and assimilation of MOB-derived metabolites by the cyanobacterium. We also observed a higher growth of MOB in the presence of cyanobacteria under a higher irradiance regime, then when grown alone, underpinning the bidirectional influence with as of yet unknown environmental consequences.

Selective removal of common cyanotoxins: a review.

The development of cyanobacterial blooms can have adverse effects on water bodies and may produce cyanotoxins. Several physical and chemical methods have been applied to remove cyanotoxins, but they have been significantly challenged due to extensive energy footprint and over-used chemicals, which limits practical application on a large scale. Selective removal has been regarded as the most promising approach recently for the elimination of prevalent and major bloom-forming cyanotoxins (e.g., microcystins and cylindrospermopsin) as natural organic matters and radical scavengers are ineluctably present in real scenarios. This paper reviews current advancements in research on selective oxidation and adsorption of cyanotoxins. Its goal is to provide comprehensive information on the treatment mechanism and the process feasibility involved in the cyanotoxin removal from real-world waters. Moreover, perspectives of cyanotoxin control and in situ selective elimination approaches are also reviewed. It is expected that the information gathered and discussed in this review can provide a useful and novel reference and direction for future pilot-scale applications.

Phytoremediation of CYN, MC-LR and ANTX-a from Water by the Submerged Macrophyte Lemna trisulca.

Cyanotoxins are harmful to aquatic and water-related organisms. In this study, Lemna trisulca was tested as a phytoremediation agent for three common cyanotoxins produced by bloom-forming cyanobacteria. Cocultivation of L. trisulca with Dolichospermum flos-aquae in BG11 medium caused a release of the intracellular pool of anatoxin-a into the medium and the adsorption of 92% of the toxin by the plant—after 14 days, the total amount of toxin decreased 3.17 times. Cocultivation with Raphidopsis raciborskii caused a 2.77-time reduction in the concentration of cylindrospermopsin (CYN) in comparison to the control (62% of the total pool of CYN was associated with the plant). The greatest toxin limitation was noted for cocultivation with Microcystis aeruginosa. After two weeks, the microcystin-LR (MC-LR) concentration decreased more than 310 times. The macrophyte also influenced the growth and development of cyanobacteria cells. Overall, 14 days of cocultivation reduced the biomass of D. flos-aquae, M. aeruginosa, and R. raciborskii by 8, 12, and 3 times, and chlorophyll a concentration in comparison to the control decreased by 17.5, 4.3, and 32.6 times, respectively. Additionally, the macrophyte stabilized the electrical conductivity (EC) and pH values of the water and affected the even uptake of cations and anions from the medium. The obtained results indicate the biotechnological potential of L. trisulca for limiting the development of harmful cyanobacterial blooms and their toxicity.

Rising atmospheric CO2 levels result in an earlier cyanobacterial bloom-maintenance phase with higher algal biomass

The effect of rising atmospheric CO2 on freshwater lakes is a subject of considerable debate. However, it is not clear how rising CO2 concentration affects cyanobacterial bloom development under potential nutrient limitation conditions and if CO2 should be taken into account in making nutrient reduction strategy. To fill the knowledge gaps, this study investigated the spatiotemporal variability in aquatic CO2 concentration (pCO2) from 2006 to 2016 in Lake Taihu, where cyanobacterial blooms often occurred from late spring to the early fall. Lake Taihu is an atmospheric CO2 source in May and November, with only 18% and 11% pCO2-undersaturated areas, respectively. During cyanobacterial bloom in August, 81% of the lake areas are pCO2-undersaturated, absorbing ~ 0.53 t C/h of atmospheric CO2. The results demonstrated that CO2 transfer across air-water interface was important in supporting cyanobacterial bloom development. Besides, Field investigation showed that the chlorophyll a level is significantly positively correlated with supersaturated pCO2 (>13.56 µmol/L) in May, but pCO2 decreases with high chlorophyll a levels in August, suggesting that cyanobacterial growth would be promoted by high pCO2 over a threshold. These observations suggested that the effect of rising atmospheric CO2 on freshwater lakes and cyanobacterial blooms should be paid attention to. Further, when the N- and P-levels are >0.3 mg/L and >0.02 mg/L, respectively, high-pCO2 conditions allow a more rapid growth rate of cyanobacteria via improved nutrient-use efficiency. Moreover, cyanobacteria afford maximum N- or P-use efficiency at lower N- or P-concentrations with high CO2 concentration. This improvement would result in an earlier bloom-maintenance phase and higher cyanobacterial biomass. In this case, nutrient reduction is more imperative under future high CO2 conditions.

Drivers shaping episodic and gradual changes in phytoplankton community succession: Taxonomic versus functional groups

Describing temporal changes in phytoplankton communities is complicated owing to (i) multivariate environmental drivers, (ii) inter-specific relationships, and (iii) various species. With long-term research data from the lower Nakdong River from 1993 to 2016, we examined the temporal changes at two scales—episodic (from weekly to monthly) and long-term (yearly)—and screened the potential environmental drivers. Phytoplankton community component patterns were modeled with the drivers as covariates, using multivariate autoregressive state-space (MARSS) models, to assess their response to environmental drivers and biotic interactions. We assumed that compared to taxonomic classification, functional classification would obtain a better identification of community response to temporal variability. Over 24 years, the succession patterns of the dominant taxonomic and functional groups decreased in diversity, with the greatest decreases in biomass of Bacillariophyceae and group D (mainly the diatom Stephanodiscus hantzschii), and coincided with the introduction of group H1 (dinitrogen-fixing nostocaleans). The potential drivers for these changes were precipitation, water level, and total nitrogen (TN) for taxonomic groups and TN, total phosphorus, and euphotic zone depth for functional groups. The results of the MARSS model and temporal trends for each driver indicated that the increases in the water level and light availability were mostly related with the taxonomic and functional groups, respectively. The model for functional groups proposed a total of 24 significant inter-group relationships, where five relationships supported the succession patterns of dominant groups in the Nakdong River. Combined with the effects of increased light availability, a positive relationship between groups H1 and M (mainly Cyanobacteria and Microcystis aeruginosa) appears to induce cyanobacterial bloom development over a long period. These results can be fundamental information for river system management concerning the resulting cascading effects of changes in environmental drivers and inter-group relationships on the phytoplankton community composition.

Dynamics of nutrient and phytoplankton in Epe Lagoon, Nigeria: possible causes and consequences of reoccurring cyanobacterial blooms

The impact of environmental variables and processes of nutrient enrichment on phytoplankton community at Epe lagoon was studied for 18 months (November 2012–April 2014). Two cyanobacterial bloom incidences were observed in the two dry seasons during this period. Rainfall pattern regulated nitrogen limitation which triggered cyanobacterial bloom development and influenced the bloom duration. Nutrient-laden influx from agricultural practices accounted for the increase in nitrate, phosphate and the relatively low silicate. Hypoxic conditions during the two bloom episodes reflected the vulnerability of this lagoon ecosystem. The cyanobacterial blooms were dominated by potentially toxic species; Anabaena circinalis, A. flos-aquae, A. limnetica and A. spiroides. A comparison of ambient nutrient ratios with the Redfield ratio (N/P/Si = 16:1:16) showed clear temporal variations that coincided with phytoplankton dynamics and the bloom regime. Low N/P ratios were recorded during the first 8 months, and there was a shift to higher ratios during the subsequent 8 months, followed by low N/P ratios in the last 2 months. Higher silicate values coincided with decreased cyanobacterial biomass, cyanobacteria bloom collapse and proliferation of diatoms during the first annual cycle. Cyanobacterial abundance exceeded the alert level 1 and almost reached alert level 2 which call for continuous environmental monitoring and management of coastal waters.

Effects of cyanobacterial accumulation and decomposition on the microenvironment in water and sediment

Cyanobacterial blooms pose a serious threat to aquatic environmental health and have emerged as a primary issue in the recovery of eutrophic lakes. In order to comprehensively establish the effects of cyanobacterial blooms on nutrients in the aquatic environment, nutrient migration and transformation were studied in freshwater and sediments during cyanobacterial bloom decomposition. Cyanobacteria and sediments were collected from Zhushan Bay, in Taihu Lake, and the process of cyanobacterial decomposition was simulated in the laboratory. The focus of this research was to assess the effects of cyanobacterial decomposition on physicochemical parameters and nutrient concentrations in water, the vertical distribution of nutrients in sediments. We also determined the moisture content (ΔCw) and organic matter content (ΔOM) in surface sediments. Correlations were assessed between cyanobacterial decomposition and nutrient concentrations in water, with ΔCw and ΔOM in surface sediments simultaneously analyzed. In the water column, electric conductivity (Ec) was found to significantly increase, while dissolved oxygen (DO) and oxidation reduction potential (ORP) rapidly reduced. In addition, pH initially decreased and then increased, while ultraviolet light (UV254) exhibited an opposite trend, which was related to the release and degradation of organic matter during the decomposition of cyanobacteria. Other nutrient concentrations were found to increase gradually with time, with the exception of nitrate nitrogen (NO3−–N), indicating that nutrients undergo temporal transitions between forms during cyanobacterial decomposition. Cyanobacterial decomposition causes ΔOM and ΔCw to increase in surface sediment layers, affecting the vertical distribution of nutrient species in the sediment. The water-sediment interface nutrient flux intensity was ranked in the order total nitrogen (TN) > ammonia nitrogen (NH4+–N) > NO3−–N > total phosphorus (TP), which was related to the settlement of cyanobacterial debris during cyanobacterial decomposition. Good binomial relationships (R2 > 0.90, p < 0.05) were found between cyanobacterial density and nutrient concentrations in the waterbody, as well as between cyanobacterial density and ΔOM or ΔCw in the surface sediment. Cyanobacterial decomposition affected various water quality parameters, leading to nutrient migration and transformation in the water-sediment interface, providing nutrients to drive cyanobacterial bloom development.

Seasonal changes in the bacterial community structure of three eutrophicated urban lakes in Mexico city, with emphasis on Microcystis spp.

Artificial urban lakes commonly have physicochemical conditions that contribute to rapid anthropogenic eutrophication and development of cyanobacterial blooms. Microcystis is the dominat genus in most freshwater bodies and is one of the main producter of microcystins. Using 454-pyrosequencing we characterized the bacterial community, with special emphasis on Microcystis, in three recreational urban lakes from Mexico City in both wet and dry seasons. We also evaluated some physicochemical parameters that might influence the presence of Microcystis blooms, and we associated the relative abundance of heterotrophic and autotrophic bacterial communities with their possible metabolic capacities. A total of 14 phyla, 18 classes, 39 orders, 53 families and 48 bacterial genera were identified in both seasons in the three urban lakes. Cyanobacteria had the highest relative abundance followed by Proteobacteria and Actinobacteria. Microcystis was the dominant taxon followed by Arthrospira, Planktothrix and Synechococcus. We also found heterotrophic bacteria associated with the blooms, such as Rhodobacter, Pseudomonas, Sphingomonas and, Porphyrobacter. The highest richness, diversity and dominance were registered in the bacterial community of the Virgilio Uribe Olympic Rowing-Canoeing Track in both seasons, and the lowest values were found in the Chapultepec Lake. The canonical correspondence analysis showed that dissolved oxygen and NO3–N concentrations might explain the presence of Microcystis blooms. The metabolic prediction indicated that these communities are involved in photosynthesis, oxidative phosphorylation, methane metabolism, carbon fixation, and nitrogen and sulfur metabolism. The lakes studied had a high prevalence of Microcystis, but average values of microcystins did not exceed the maximum permissible level established by the United States Environmental Protection Agency for recreational and cultural activities. The presence of cyanobacteria and microcystins at low to moderate concentrations in the three lakes could result in ecosystem disruption and increase animal and human health risks.

Drivers of cyanobacterial blooms in lakes and reservoirs in Jinan City, China

Cyanobacterial blooms are a serious issue and frequently occur in lakes and reservoirs. Understanding how topography and human activities affect cyanobacterial dominance and blooms can greatly enhance the success of restoration projects to reduce blooms. Therefore, in this study the dominant species of cyanobacteria were determined by calculating the break point of the cumulative dominance curve for multiple sites in Jinan, China. In addition, the key drivers affecting the dominant cyanobacteria species were identified by canonical correspondence analysis and correlations between topography, human activities and the key drivers of the dominant cyanobacteria were investigated using random forests analysis. Merismopedia glauca, Merismopedia tenuissima, Microcystis aeruginosa, Oscillatoria tenuis, Phormidium tenus and Raphidiopsis sinensia were determined to be the dominant species. The key drivers of cyanobacterial bloom development were total phosphorus (TP), ammonium nitrogen (NH3-N), water temperature and total hardness. Topography and human activities were highly correlated with the key driving factors. The higher the altitude, the greater the effect of water temperature on the cyanobacteria community. In the area where sewage irrigation was present and a large amount of chemical fertiliser was used, total hardness had a greater effect on the cyanobacteria community. In areas where the population was more concentrated, TP and NH3-N had greater effects on the cyanobacteria community.

Turbulence exerts nutrients uptake and assimilation of bloom-forming Dolichospermum through modulating morphological traits: Field and chemostat culture studies

Hydrodynamic conditions are closely related to the development and dissipation of cyanobacterial blooms. The morphological features of Dolichospermum under different hydrodynamic conditions were analysed during three blooms in Gaoyang Lake, which is part of the backwater area of the China Three Gorges Reservoir, from 2007 to 2010. The results showed that the length of filaments and the morphology of cells were different in relation to the turbulence caused by the difference in hydraulic retention times. Thus, it was hypothesized that turbulence could shape the morphology and physiology of cyanobacteria. To answer the question regarding what the morphological and physiological responses of cyanobacteria to turbulent mixing mean for these organisms, laboratory experiments in continuous cultivation under different dilution rates were conducted to analyse the effects of specific turbulence intensity on the growth, nutrient uptake and morphology of Dolichospermum flos-aquae. Increasing the turbulence intensity caused synchronous increases in the ratio of the cellular length to the width, in the specific surface area of the filament and the cell and in the nutrient uptake rate; at the same time, the average filament length decreased. These indicated that the turbulence, within the range of our experimental design, could stimulate the growth of Dolichospermum by increasing its nutrient uptake. Additionally, at a high specific growth rate, the nutrient uptake rate of Dolichospermum changed more noticeably with the increasing morphological indicators, indicating that the rapidly growing Dolichospermum was more sensitive to turbulence. These findings explain the role of morphological strategies in the dominance of Dolichospermum within a certain range of turbulence intensity, especially in the early growth stage of blooms. The results also facilitate a greater understanding of the hydrodynamic effects on cyanobacteria and will be instrumental in developing flow regulation to control cyanobacterial blooms in reservoirs.

Dynamic Changes of Nitrogen-Transforming and Phosphorus-Accumulating Bacteria Along with the Formation of Cyanobacterial Blooms

In order to reveal the dynamic changes of nitrogen-transforming and phosphorus-accumulating bacteria in the process of cyanobacterial bloom formation, bacterial community structure and functional genes associated with nitrogen cycling were analyzed using high-throughput sequencing and real-time quantitative PCR (qPCR). The high-throughput sequencing results showed that the diversity of bacterial communities decreased during cyanobacterial blooms, and the lacustrine free-living and bloom-attached bacterial communities varied with increased bloom density. With increasing density of cyanobacteria, the relative abundance of Actinobacteria and Bacteroidetes decreased, whereas that of Firmicutes increased. Moreover, the growth of phosphate-accumulating organisms was increased in the phycosphere of cyanobacterial blooms, while that of nitrifiers was inhibited. Denitrifiers increased significantly under moderate blooms. The qPCR data also revealed that the abundance of nitrification and denitrification genes decreased or disappeared with the development of cyanobacterial blooms, indicating that the nitrogen transformation process might be inhibited, which showed a positive feedback of bacterial community to the development of Microcystis blooms by satisfying the needs of the nutrients budget.

Autoaggregation and adhesion abilities in bacteria associated with colonies of Microcystis

Bacteria associated with Microcystis may play an important role in formation of Microcystis colonies and in development of cyanobacterial blooms. Adhesion to Microcystis cells is a requirement for colonization and long-term association of bacteria with Microcystis colonies. This study aimed to explore the relationship between autoaggregation ability and adhesion ability of Microcystis-associated bacteria, and to evaluate the effects of different environmental factors on their autoaggregation abilities. Twelve bacterial strains were isolated from colonies of three Microcystis morphospecies. All the bacterial isolates exhibited autoaggregation abilities. A positive correlation was found between autoaggregation ability and adhesion ability. Two selected bacterial isolates, HJX5 and HJX9, exhibited strong autoaggregation abilities at pH from 3 to 11. The laboratory experiment revealed the inhibitory effects of metal cations on the autoaggregation abilities of HJX5 and HJX9, but HJX5 and HJX9 could exhibit their autoaggregation abilities in the lake water. Extraction of exopolysaccharides (EPS) decreased significantly their autoaggregation abilities, indicating that EPS can play an important role in autoaggregation. The autoaggregation ability of Microcystis-associated bacteria may be an important trait contributing to their attachment into Microcystis colonies.

Molecular detection of microbial communities associated with Microcystis vs Synechococcus dominated waters in Tianjin, China

Harmful cyanobacterial blooms cause many ecological disasters worldwide. During the development of cyanobacterial blooms, the diversity and domination of cyanobacterial taxa are of a particular concern. In this study, the microbial community structure within a water system, such as in Yuqiao Reservoir and Haihe River in Tianjin City, China, was compared by using next-generation sequencing. A total of 5 001 operational taxonomic units were obtained and clustered from filtered 16S rDNA V3–V4 region sequences. The cyanobacterial and microbial structures greatly differed in these two water areas. Microcystis was dominant in Yuqiao, whereas Synechococcus was dominant in Haihe. Proteobacteria species were dominant among all detected samples. The relative abundances of Bacteroidetes and Planctomycetes were higher in Yuqiao Reservoir than in Haihe River, whereas Firmicutes and Verrucomicrobia were relatively abundant in Haihe River. Further analyses indicated that the domination of both cyanobacteria was strongly related to several environmental factors, such as total nitrogen, total phosphorus, and dissolved oxygen, reflecting the role of trophic states in shaping the dominance of cyanobacterial taxa. The present study provided the example for Microcystis and Synechococcus dominance along a cyanobacterial bloom in north China. Applying highthroughput sequencing could offer a wide field of vision in analyzing microbial community structures.

Increased risk of cyanobacterial blooms in northern high‐latitude lakes through climate warming and phosphorus enrichment

Abstract Harmful cyanobacterial blooms are an increasing problem at many locations throughout the world but are rarely reported in aquatic habitats at high latitudes. Shallow lakes are a major feature of northern permafrost landscapes and are likely to experience large‐scale changes in their limnological properties in the future as a consequence of climate warming. In the present study, we addressed the question of what preconditions would be necessary to stimulate the growth and dominance of bloom‐forming cyanobacteria in northern fresh waters. We analysed the summer phytoplankton of 18 lakes on eroding permafrost (thaw lakes) and on glacier‐scoured rock (rock basin lakes) in subarctic Quebec, Canada, to determine their phytoplankton community structure and the biomass contribution of cyanobacteria. This survey was complemented with an incubation experiment to evaluate the direct warming and indirect phosphorus (P) enrichment effects of climate change on cyanobacterial bloom development. All lakes contained diverse phytoplankton communities, often dominated by chrysophytes, dinoflagellates and chlorophytes. Cyanobacteria were present in all waterbodies, but their contribution to the total community biovolume was highly variable (mean of 8.7%, range 0.1%–47%). Cyanobacterial community biovolumes correlated positively with surface water temperatures, and negatively with dissolved organic carbon, soluble reactive phosphorus, iron and manganese concentrations in the surface waters. Phosphorus enrichment of water from a thaw lake resulted in a fourfold increase of chlorophyll a (Chl‐a) and an increase in the cyanobacterial pigments echinenone and zeaxanthin. The phytoplankton counts showed that there was a sharp decrease in diversity (expressed as decline of the Shannon–Wiener index from 1.69 to 0.16), accompanied by a shift to cyanobacterial dominance, notably by the heterocystous, potentially toxic species Dolichospermum cf. planctonicum. Increased temperature led to an initial doubling of cyanobacterial biovolume, followed by the development of a chrysophyte bloom. Combined warming and P enrichment led to reduced phytoplankton biodiversity, with a community composed of cyanobacteria and chrysophytes. There was also a pronounced response by the picophytoplankton community; picocyanobacteria were strongly stimulated by P enrichment, while picoeukaryotes increased in response to warming. The current inoculum levels of cyanobacteria in subarctic lakes and their responsiveness to temperature and phosphorus indicate the potential for an abrupt increase in their abundance, accompanied by a decrease in phytoplankton diversity. Ongoing climate change will increase the risk of noxious cyanobacterial blooms in northern lakes and ponds, with potentially negative consequences for higher trophic levels.

Interactive effects of phosphorus and zooplankton grazing on cyanobacterial blooms in a shallow temperate lake

Cyanobacterial blooms are becoming increasingly common worldwide. These blooms can be moderated by grazing and/or nutrient availability, but the interactive effects of these processes are not well understood. We examined the interactive effects of phosphate and copepods on growth of phytoplankton (algae and cyanobacteria) in a shallow temperate lake. Field sampling of nutrient and chlorophyll a concentrations was conducted weekly from May through October, 2013. Five two-factorial experiments, spanning pre-, mid-, and post-bloom periods, were conducted with unfiltered lake water incubated with amended copepods, phosphate, or both. Changes in chlorophyll a concentration were used to calculate net phytoplankton biomass growth rates, and cell counts were performed on selected experiments to calculate growth rates of six microplanktonic taxonomic groups. Field data revealed cyanobacterial bloom development in July and decline in September. Experimental results indicated that phytoplankton growth increased with added phosphate pre-bloom, and decreased with added copepod grazers post-bloom, but that a more complex interactive (phosphorus x copepods) effect was observed immediately prior to and during peak bloom times. More specifically, the addition of phosphate and copepods enhanced ciliate growth pre-bloom, while selective grazing by copepods reduced dinoflagellate growth mid-bloom, possibly enhancing cyanobacterial growth and bloom duration via trophic cascade effects.