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The effect of cyanobacterial blooms on aquatic ecosystems has received wide attention, yet little is known about their impacts on zooplankton genetic structure.For 26 months (April 2012–May 2014), we monitored zooplankton in a warm‐temperate ice‐free lake in Eastern China, with an emphasis on seasonal population dynamics of the cladoceran, Daphnia galeata. There was a seasonal succession in the zooplanktonic community (composed of Cladocera, Copepoda, and Rotifera).Genetic analysis (based on 14 microsatellite loci) of the 21 monthly samples in which D. galeata was present demonstrated that several clones could successfully overwinter and/or persist for many months. However, all clones, including these long‐lived clones, were completely replaced by new ones after October 2013, probably due to cyanobacteria blooms in that summer. A high clonal richness coupled with high turnover rate was observed in the D. galeata population overall, suggesting frequent sexual reproduction.Daphnia galeata experimentally fed with a diet of Microcystis aeruginosa (the most abundant toxic cyanobacterial species in the lake) had a substantially reduced survivorship, consistent with the field observations.Our findings highlight the changes of zooplanktonic population dynamics in terms of both community and clonal structure in a warm‐temperate ice‐free lake, and call for further investigation on ecological responses of zooplankton to cyanobacterial blooms. [ABSTRACT FROM AUTHOR]

Effects of laser irradiation on photosystem II (PS II) photochemical efficiencies, growth, and other physiological responses of Microcystis aeruginosa were investigated in this study. Results indicate that laser irradiation (wavelengths 405, 450, 532, and 650 nm) could effectively inhibit maximal PS II quantum yield (Fv/Fm) and maximal electron transport rates (ETR) of M. aeruginosa, while saturating light levels (E) of M. aeruginosa did not change significantly. Among the four tested wavelengths, 650 nm laser (red light) showed the highest inhibitory efficiency. Following 650 nm laser irradiation, the growth of M. aeruginosa was significantly suppressed, and contents of cellular photosynthetic pigments (chlorophyll a, carotenoid, phycocyanin, and allophycocyanin) decreased as irradiation dose increased. Meanwhile, laser irradiation enhanced the enzyme activities of superoxide dismutase (SOD) and peroxidase (POD) in M. aeruginosa cells. Lower irradiation doses did not change the intracellular microcystin contents, but higher dose irradiation (>1284 J cm) caused the release of microcystin into the culture medium. Transmission electron microscope examination showed that the ultrastructure of M. aeruginosa cells was destructed progressively following laser irradiation. Effects of laser irradiation on M. aeruginosa may be a combination of photochemical, electromagnetic, and thermal effects. [ABSTRACT FROM AUTHOR]

The critical role of nitrogen in the global proliferation of cyanobacterial blooms is arousing increasing attention. However, the mechanism underlying the algal responses to differential nitrogen forms remains unclarified. The physiological and transcriptomic changes of Microcystis aeruginosa supplied with different nitrogen forms (nitrate and ammonium) were highlighted in this study. The results indicated that ammonium behaves better in stimulating the initial growth in N-limited cells than nitrate. However, a concomitant side effect is that cellular growth and photosynthesis decreased due to photosystem II damage induced by excess absorbed light energy under 10 mg L−1 ammonium. By contrast, adequate nitrate supply favored more efficient photosynthesis, higher biomass yield and microcystin quotas than ammonium. Depending on the supplied nitrogen form, different transcriptomic patterns were observed in M. aeruginosa. Under nitrate, the upregulation of genes involved in Arg biosynthesis, ornithine-urea cycle and photosynthesis increased nitrogen storage and cellular growth, while genes involved in cyclic electron flow around photosystem I and CO 2 −concentrating mechanism were heightened to dissipate excess energy under high ammonium. These insights provided important clues for understanding the physiological and molecular effects of available nitrogen forms on the frequent outbreaks of cyanobacteria. [Display omitted] ● Initial growth of N-limited algae was better stimulated by ammonium than by nitrate. ● Nitrate supply supported a higher cell density and MC quota. ● Excess ammonium supply led to PSII damage. ● The CEF-PSI and CCM were enhanced to dissipate light energy. ● The ornithine-urea pathway facilitated nitrogen storage in Microcystis aeruginosa. [ABSTRACT FROM AUTHOR]

We describe the phytoplankton dynamics and structure in Xiangxi Bay, Three Gorges Reservoir. Samples were collected monthly in the surface waters between August 2007 and July 2008. We identified 10 principle functional groups. C-strategists and S/R-strategists with a wide range of tolerance dominated the phytoplankton assemblage. Seasonal variation was related to water column stability because of changes in hydraulic operation in October, January, and May. Functional group C ( Asterionella formosa) and P ( Aulacoseria granulata) dominated in August and September, whereas group Lo ( Peridiniopsis niei) was the most abundant between February and April, forming a dinoflagellate bloom. Group B ( Stephanodiscus hantzschii), X2 ( Komma acudata), and Y ( Cryptomonas erosa) were present throughout most of the year but were most abundant in late spring. A cyanobacterial bloom occurred from June to July, during which group M ( Microcystis aeruginosa, M. wesenbergii) and H1 ( Anabaena flos-aquae) were dominant. Green algae, characterized by group G ( Eudorina sp., Pandorina sp., Pyramidomonas sp.) and J ( Pediastrum spp., Coelastrum spp., Scenedesums spp.), were abundant after the bloom degraded. This sequence was corroborated by canonical correspondence analysis (CCA). The summary sequence of functional groups resulting from CCA was: C/P → Lo → H1/M/J/G. The dynamics of the phytoplankton community may be explained by the stability of water column, irradiance, water temperature, and nutrient structure. [ABSTRACT FROM AUTHOR]

Aquatic ecosystems and drinking water supply systems worldwide are increasingly affected by taste and odor episodes. In this study, molecular approaches including next-generation sequencing (NGS) and quantitative polymerase chain reaction (qPCR) were used to study the diversity and dynamics of cyanobacteria and 2-methylisoborneol (2-MIB)-producing cyanobacteria in Yuqiao Reservoir, a eutrophicated drinking water reservoir in Tianjin city, northern China. NGS revealed that the entire cyanobacterial community consisted of 16 genera, with Planktothrix (28.8%), Pseudanabaena (18.4%), Cylindrospermosis (7.8%), and Microcystis (7.6%) being the dominant genera, while microscopic examination identified only eight cyanobacterial genera. NGS of the 2-MIB synthesis gene revealed that Pseudanabaena and Planktothricoides were the main 2-MIB producers, with Pseudanabaena being dominant. This finding demonstrated that NGS can identify 2-MIB producers quickly and accurately and it can thus play an important role in the practical monitoring of aquatic ecology. The qPCR test showed 2-MIB synthesis gene with 4.27 × 106 copies/L to 2.24 × 109copies/L occurring at the three sampling sites. The mic gene copy number increased before the 2-MIB concentration increased, indicating that forecasting role in dealing with the 2-MIB concentration by gene copy number. Predicting 2-MIB by qPCR in the field must be verified with additional studies. The combination of NGS and qPCR can be an even more comprehensive method to provide early warning information to managers of reservoirs and water utilities facing taste and odor incidents. This is the first amplicon NGS dataset based on 2-MIB gene to study the diversity and dynamics of 2-MIB-producing cyanobacteria. [Display omitted] • Diversity of 2-MIB-producing cyanobacteria by next-generation sequencing. • qPCR can predict 2-MIB production in advance. • Next-generation sequencing makes up for lack of microscopic examination. [ABSTRACT FROM AUTHOR]

• Changes in water regimes influence algal blooms by field reservoir regulation experiments. • Water level decline and increased velocity correlated with algal biomass reductions. • Dominant phytoplankton community changed from Cyanobacteria to Chlorophyceae. • Water level fluctuations lead to a 50–57 % reduction in cyanobacterial blooms. • Hydrodynamic management helps mitigate ecological impacts of algal blooms. Gaining insight into the impact of reservoir regulation on algal blooms is essential for comprehending the dynamic changes and response mechanisms in the reservoir ecosystem. In this study, we conducted a comprehensive field investigation linking physiochemical parameters, and phytoplankton community to different water regimes in the Three Gorges Reservoir. Our aim was to explore the effects of reservoir regulation on the extinction of cyanobacterial blooms. The results showed that during the four regulatory events, the water levels decreased by 2.02–4.33 m, and the average water velocity increased 68 % compared to before. The average total phosphorus and total nitrogen concentrations reduced by up to 20 %, and the cyanobacterial biomass correspondingly declined dramatically, between 66.94 % and 75.17 %. As the change of water level decline increasing, there was a significant increase of algal diversity and a notable decrease of algal cell density. Additionally, a shift in the dominant phytoplankton community from Cyanobacteria to Chlorophyceae was observed. Our analysis indicated that water level fluctuations had a pronounced effect on cyanobacterial extinction, with hydrodynamic changes resulting in a reduction of cyanobacterial biomass. This research underlined the potential for employing hydrodynamic management as a viable strategy to mitigate the adverse ecological impacts of cyanobacterial blooms, providing a solution for reservoir's eco-environmental management. [Display omitted] [ABSTRACT FROM AUTHOR]

Hydrogen peroxide (HP) is a feasible algicide to control cyanobacterial blooms, but its application in the waters with strong reductive power is still a problem. The rapid decomposition rate of HP results in a short residence time in the waters, which renders the failure of bloom mitigation. In this study, the damage of Microcystis aeruginosa (M. aeruginosa) by HP, the optimization method for Microcystis bloom control and its field effects were investigated. Results of microcosm experiments indicated M. aeruginosa was vulnerable to HP. The HP-induced damage was mainly attributed to the impairments of HP detoxification pathways and photosystem. Repetitive additions of HP, which could prolong the residence time, were conducted in the mesocosm experiments. HP concentration ranged from 96 μM to 165 μM for 2 h could successfully mitigate Microcystis bloom, even though HP decomposition rate reached 109 μM per h. Besides the removal of M. aeruginosa , contents of total dissolved nitrogen, total dissolved phosphate, dissolved organic carbon and chromophoric dissolved organic matter in water column increased significantly (p < 0.05). The enrichment of nutrients promoted the growth of chlorophytes but the growth of M. aeruginosa couldn't be observed. The dominant species thrived in the HP-treated waters was Chlamydomonas sp. Results in this study confirmed that HP was a promising algicide for cyanobacterial blooms control. The optimization method further demonstrated that repetitive additions of HP could favor the mitigation of cyanobacterial blooms. • H 2 O 2 is a feasible algaecide in mitigating Microcystis bloom. • Repetitive additions of H 2 O 2 can favor the bloom control. • Enrichment of nutrients after H 2 O 2 treatment promotes the growth of chlorophytes. [ABSTRACT FROM AUTHOR]

Knowledge of phytoplankton limiting factors is essential for cost-efficient lake eutrophication management. Herein, we propose a statistical framework to explore site-specific phytoplankton limiting factors and their dependence on water depth (WD) in 54 lakes in the Chinese Eastern Plains ecoregion. First, the maximal chlorophyll a (Chl a) response to total N (TN) or P (TP), representing a region-specific "standard" model where phytoplankton were primarily N- or P-limited, was quantified using a 95% quantile regression. Second, site-specific limiting factors were identified using analogical residual analysis. N- or P-limitation was inferred if Fraction TN (i.e. fraction of Chl a observed and predicted by the "standard" model for a given TN) > 0.95 or Fraction TP >0.95; if both Fraction TN and Fraction TP <0.95 in a specific environmental condition (e.g. high non-algal turbidity), light limitation was suggested. As a result, 5%, 7%, 4%, 36%, 16%, 2%, and 30% of the sampling sites were limited by N, P, N+P, light availability, rapid flushing, abundant macrophytes, and unmeasured factors, respectively. Bloom control suggestions in the short run are proposed considering these actual limiting factors. Furthermore, the maximal Fraction TN or Fraction TP response to WD was explored, reflecting the effect of WD on Fraction TN (or Fraction TP) without significant confounders. The results indicated that phytoplankton in the studied freshwaters would be potentially light-limited, N-limited, N+P-co-limited, or P-limited depending on WD (<1.8, 1.8–2.1, 2.1–5.2, or >5.2 m, respectively), because N will gradually become surplus with increasing WD, while at very shallow depths, strong sediment re-suspension induces light limitation. This finding implies that long-term nutrient management strategies in the studied freshwaters that have WDs of 0–2.1, 2.1–5.2, and >5.2 m can entail control of N, N+P, and P, respectively. This study provides essential information for formulating context-dependent bloom control for lakes in our study area and serves as a valuable reference for developing a cost-efficient eutrophication management framework for other regions. • Site-specific algal limiting factors were identified for the studied 54 freshwaters. • Algae in 16% and 84% sites were limited by nutrient and non-nutrient factors, respectively. • Algae in the studied freshwaters would be potentially P-limited with depths of >5.2 m. • Alleviating lake blooms by nutrient reduction requires different strategies depending on depths. [ABSTRACT FROM AUTHOR]