Microcystin Dynamics Research Articles

Study of Seasonal Dynamics of Microcystins and Nutrients in Studena Reservoir in 2023

This paper is a synthesis of data from studies conducted in 2023 on the seasonal dynamics of the presence of microcystin-LR and its homologues in water samples from Studena reservoir. A total of ten samples were collected from June to October 2023. The species composition of phytoplankton and the nutrients total nitrogen and total phosphorus were determined. The presence of microcystins was detected in three samples from the months of September and October (microcystin-LR concentration 0.38 and 0.75 μg/L in the water sample and in a scum at the reservoir wall in October; microcystin-RR 0.10 μg/L in September and 0.55 and 0.70 μg/L in the water sample and in a scum at the reservoir wall in October; microcystin-YR 0.27 and 0.48 μg/L in the water sample and in a scum at the reservoir wall in October). Trace amounts of microcystin-LR equivalents other than microcystin-RR and microcystin-YR were observed in water samples in June and July. The phytoplankton communities in the reservoir are persistently inhabited by blue-green algae. The presence of microcystins at concentrations close to the permissible level in the autumn sample indicates that at the time of sampling the bloom of cyanobacteria that produced the microcystins had passed and the toxins released remained in the water. Due to the near acceptable concentration of MC-LR in the autumn sample, serious consideration should be given to monitoring the reservoir during periods favourable for bloom formation.

Seasonal dynamics of microcystins and microcystin-producing Microcystis populations in three water bodies in Mozambique

Seasonal dynamics of microcystins and microcystin-producing Microcystis populations in three water bodies in Mozambique

Microcystin Concentrations, Partitioning, and Structural Composition during Active Growth and Decline: A Laboratory Study.

Microcystin can be present in variable concentrations, phases (dissolved and particulate), and structural forms (congeners), all which impact the toxicity and persistence of the algal metabolite. Conducting incubation experiments with six bloom assemblages collected from the Chowan River, North Carolina, we assessed microcystin dynamics during active growth and biomass degradation. Upon collection, average particulate and dissolved microcystin ranged between 0.2 and 993 µg L-1 and 0.5 and 3.6 µg L-1, respectively. The presence of congeners MC-LA, -LR, -RR, and -YR was confirmed with MC-RR and MC-LR being the most prevalent. Congener composition shifted over time and varied between dissolved and particulate phases. Particulate microcystin exponentially declined in five of six incubations with an average half-life of 10.2 ± 3.7 days, while dissolved microcystin remained detectable until the end of the incubation trials (up to 100 days). Our findings suggest that concerns about food-web transfer via intracellular toxins seem most warranted within the first few weeks of the bloom peak, while dissolved toxins linger for several months in the aftermath of the event. Also, it was indicated there were differences in congener profiles linked to the sampling method. We believe this study can inform monitoring strategies and aid microcystin-exposure risk assessments for cyanobacterial blooms.

Temporal dynamics of microcystins in two reservoirs with different trophic status during the early growth stage of cyanobacteria.

Harmful cyanobacterial blooms are increasing in frequency and severity, which makes their toxic secondary metabolites of microcystins (MCs) have been widely studied, especially in their distribution and influence factors in different habitats. However, the distribution of MCs on the early growth stage of harmful cyanobacteria and its influence factors and risks are still largely unknown. Thus, in the present study, two reservoirs (Lutian Reservoir and Lake Haitang) with different trophic status in China have been studied weekly from March to May in 2018, when the cyanobacteria communities were just in the early growth stage, to investigate the variation of MCs concentration and the relationships between MCs and environmental parameters. During the investigation, Lutian Reservoir and Lake Haitang were found to be mesotrophic and light eutrophic, respectively. In Lutian Reservoir, the concentration of EMCs (extracellular MCs) was obviously higher than that of IMCs (intracellular MCs) with a mean value of 0.323 and 0.264μg/L, respectively. Meanwhile, the concentration of EMCs also fluctuated more sharply than that of IMCs. Congeners of IMC-YR and EMC-LR were respectively dominant in total concentrations of IMCs and EMCs. Unsurprisingly, in Lake Haitang, the concentrations of IMC and EMC were both significantly higher than that in Lutian Reservoir with a mean concentration of 0.482 and 0.472μg/L, respectively. Differently, the concentration of MC-YR was dominant in both IMCs and EMCs, followed by MC-LR. In correlation analysis, the IMCs were significantly and positively correlated with the density and biomass of phytoplankton phyla and potential MCs-producing cyanobacteria and the parameters of water temperature (WT), nutrients, and organic matters. Similar results were also observed for EMCs. While the different variations of MCs in the two reservoirs might be primarily caused by the differences in WT, nutrients (especially phosphorus), organic matters, and the composition of MCs-producing cyanobacteria. In addition, the coexistence of the dominant species of Pseudoanabaena sp., which can produce a taste-and-odor compound of 2-methylisoborneol (2-MIB), might have a significant impact on the concentration and toxicity of MCs. Our results suggested that the risks posed by MCs at the early growth stage of cyanobacteria should also deserve our attention, especially in mesotrophic water bodies.

Dynamics of microcystins and saxitoxin in the Indian River Lagoon, Florida

Harmful algal blooms that can produce toxins are common in the Indian River Lagoon (IRL), which covers ~250 km of Florida's east coast. The current study assessed the dynamics of microcystins and saxitoxin in six segments of the IRL: Banana River Lagoon (BRL), Mosquito Lagoon (ML), Northern IRL (NIRL), Central IRL (CIRL), Southern IRL (SIRL), and the St. Lucie Estuary (SLE). Surface water samples (n=40) collected during the 2018 wet and 2019 dry season were analyzed to determine associations between toxins and temperature, salinity, pH, oxygen saturation, concentrations of dissolved nutrients and chlorophyll-a, presence of biosynthetic genes for toxins, relative abundance of planktonic species, and composition of the microbial community. The potential toxicity of samples was assessed using multiple mammalian cell lines. Enzyme-Linked Immunosorbent Assays were used to determine concentrations of microcystins and saxitoxin. Overall, the microcystins concentration ranged between 0.01-85.70 µg/L, and saxitoxin concentrations ranged between 0.01-2.43 µg/L across the IRL. Microcystins concentrations were 65% below the limit of quantification (0.05 µg/L), and saxitoxin concentrations were 85% below the limit of detection (0.02 µg/L). Microcystins concentrations were higher in the SLE, while saxitoxin was elevated in the NIRL and BRL. Cytotoxicity related to the presence of microcystins was seen in the SLE during the wet season. No significant patterns between cytotoxicity and saxitoxin were identified. Dissolved nutrients were identified as the most highly related parameters, explaining 53% of microcystin and 47% of saxitoxin variability. Multivariate models suggested cyanobacteria, flagellates, ciliates, and diatoms as the subset of microorganisms whose abundances were maximally correlated with saxitoxin and microcystins concentrations. Lastly, biosynthetic genes for microcystins were detected in the SLE and for saxitoxin in the BRL and NIRL. These results highlight the synergistic roles environmental and biological parameters play in influencing the dynamics of toxin production by harmful algae in the IRL.

Toxic cyanobacteria and microcystin dynamics in a tropical reservoir: assessing the influence of environmental variables.

Toxic cyanobacterial blooms (TCBs) have become a growing concern worldwide. The present study investigated the dynamic of toxic cyanobacteria and microcystin (MC) concentrations in the Tri An Reservoir (TAR), a tropical system in Vietnam, with quantitative real-time polymerase chain reaction (qPCR) and high-performance liquid chromatography (HPLC), respectively. The results of the qPCR quantification revealed that Microcystis was the dominant group and the primary MC producer in the TAR. Potentially toxigenic cyanobacteria varied from 1.2 × 104 to 1.58 × 107 cells/mL, and the mean proportion of toxic Microcystis to that of the total toxic cyanobacteria varied from 21 to 88%. Microcystin concentrations in raw water and sediment samples often peaked during June to October as blooms occurred and varied from 0.27 to 6.59μg/L and from 1.79 to 544.9ng/g in wet weight, respectively. The results of this study indicated that conditions favoring Microcystis proliferation lead to the selection of more toxic genotypes. Water temperature and light availability were not driving factor in the formation of TCBs in the TAR. However, the high loads of total nitrogen (TN), phosphate, and total phosphorus (TP) into the water via rainfall runoff in combination with a high total suspended solid (TSS) and decreased water level during the early months of the rainy seasons did lead to a shift in Microcystis blooms and higher proportions of toxic genotypes of Microcystis in the TAR. This research may provide more insight into the occurrence mechanism of TCBs in tropical waters. The strategy to control TCB problems in tropical regions should be focused on these limnological and hydrological parameters, in addition to a reduction in nitrogen and phosphorus loading.

Temporal microcystin dynamics of the source water and finished water in a waterworks of Lake Taihu

水体富营养化导致的有害蓝藻水华仍是目前全世界普遍面临的水环境问题，而有害蓝藻水华所引起的饮用水安全问题亦受到人们的广泛关注.为了解太湖水源地水源水及自来水厂出厂饮用水中微囊藻毒素（MCs）的污染现状，于2014年8月期间对贡湖湾某水厂水源水及出厂水中浮游植物胞内及胞外MCs浓度进行了调查，并同时检测了相关的理化指标.结果表明，水源水中胞内MCs总浓度平均值为7165.5 ng/L，以MC-LR和MC-RR为主，平均浓度分别为3408.7和3398.8 ng/L，其中MC-RR占总MCs比例的平均值为56.1%；而胞外溶解性MCs浓度相对较低，平均浓度为142.6 ng/L，最高浓度仅为512.8 ng/L.水厂出厂水中胞内MCs的检出浓度（平均值为0.77 ng/L）和检出频率都很低，去除率达99.8%以上；而胞外溶解性MCs的检出浓度（平均值为21.71 ng/L）和检出频率相对较高，但浓度仍远低于国家标准1.0 μg/L，其去除率相对较低，仅为62.9%~81.8%.数据分析发现，水源水中胞内与胞外MCs浓度之间呈显著正相关，胞内MCs浓度与总氮（TN）浓度、铵态氮（NH₄⁺-N）浓度、总磷（TP）浓度、高锰酸盐指数（COD_Mn）和浊度呈显著相关，而胞外MCs浓度与TN浓度、TP浓度、COD_Mn、浊度和叶绿素a浓度呈显著正相关；逐步回归结果显示，TP对胞内MCs浓度变化的解释率最高，而胞外MCs浓度变化主要与胞内MCs浓度相关.最终，通过对出厂饮用水中MCs浓度非致癌风险指数的计算发现，出厂饮用水对人类健康的威胁较小，但致癌风险相对较高.;Harmful cyanobacteria blooms, which are caused by water eutrophication, is still one of the serious water environment problems encountered by the whole world. In order to estimate the current status of microcystins (MCs) in the source water and finished water of Lake Taihu, we examined the concentrations of intracellular MC (intraMCs) and extracellular MC (extraMCs) and related physiochemical parameters of the source water and finished water in a waterworks in August 2014. Our results showed that the mean concentration of intraMCs in the source water was 7165.5 ng/L, dominated by MC-LR and MC-RR, with the mean concentration of 3408.7 and 3398.8 ng/L, respectively, and MC-RR accounted for 56.1% of the total MCs. The extraMCs in the source water were still on a low level with the mean and maximum value of 142.6 and 512.8 ng/L, respectively. However, the concentrations of intraMCs in finished water were relatively on a low level (mean value of 0.77 ng/L) with the removal efficiency above 99.98%. Although extraMCs in finished water were also detected on a low level (mean value of 21.71 ng/L), the concentration and detection frequencies of extraMCs were significantly higher than those of intraMCs with removal efficiency of 62.9%-81.8%. Data analysis showed that the significant and positive correlation was observed between concentrations of intraMCs and extraMCs in source water. Meanwhile, intraMCs were significantly correlated with total nitrogen (TN), ammonium (NH₄⁺-N), total phosphorus (TP), chemical oxygen demand (COD_Mn) and turbidity, while extraMCs were significantly and positively correlated with TN, TP, COD_Mn, turbidity and chlorophyll-a. In addition, according to stepwise multiple linear regression analysis, TP could explain most of the variance of intraMCs in source water, while the variations of extraMCs could be primarily explained by intraMCs. Finally, according to non-carcinogenic risk index, MCs in finished water presented a relative low threat to the people there, while the risks will be higher when considering carcinogenic risk.

Relative importance of Microcystis abundance and diversity in determining microcystin dynamics in Lake Erie coastal wetland and downstream beach water.

Microcystis population and microcystin (MC) dynamics were investigated in western Lake Erie coastal wetlands and downstream beach water. A three-dimensional (3-D) model was developed to quantify how Microcystis population size and structure affect MCs. Real-time PCR, denaturing gradient gel electrophoresis (DGGE) and enzyme-linked immunoabsorbent assay (ELISA) were used. A moderate-low level of Microcystis abundance and MCs were detected with a significant increase along the wetland flow and the spatiotemporal homogeneity of Microcystis populations. The proportion of toxigenic and nontoxgenic genotypes appeared to be more affected by the variation in two major Microcystis PC-IGS genotypes. MC dynamics was associated with the changing Microcystis population size and structure. The 3-D model showed that Microcystis population with greater Microcystis PC-IGS abundance (and simultaneously higher diversity) had more MCs. Microcystin variation was significantly affected by Microcystis population size and structure. The 3-D model also revealed the relative importance of Microcystis population size and structure in determining MCs in the Lake Erie costal wetland and downstream beach water. This study enriches our understanding of Microcystis population and microcystin ecology in a western Lake Erie coastal wetland and downstream beach water. Our illustrative model brings a new perspective for understanding the ecological relationship between Microcystis population size and structure and MCs.

Local nutrient regimes determine site-specific environmental triggers of cyanobacterial and microcystin variability in urban lakes

Abstract. Toxic cyanobacterial blooms in urban lakes present serious health hazards to humans and animals and require effective management strategies. Managing such blooms requires a sufficient understanding of the controlling environmental factors. A range of them has been proposed in the literature as potential triggers for cyanobacterial biomass development and cyanotoxin (e.g. microcystin) production in freshwater systems. However, the environmental triggers of cyanobacteria and microcystin variability remain a subject of debate due to contrasting findings. This issue has raised the question of whether the relevance of environmental triggers may depend on site-specific combinations of environmental factors. In this study, we investigated the site-specificity of environmental triggers for cyanobacterial bloom and microcystin dynamics in three urban lakes in Western Australia. Our study suggests that cyanobacterial biomass, cyanobacterial dominance and cyanobacterial microcystin content variability were significantly correlated to phosphorus and iron concentrations. However, the correlations were different between lakes, thus suggesting a site-specific effect of these environmental factors. The discrepancies in the correlations could be explained by differences in local nutrient concentration. For instance, we found no correlation between cyanobacterial fraction and total phosphorous (TP) in the lake with the highest TP concentration, while correlations were significant and negative in the other two lakes. In addition, our study indicates that the difference of the correlation between total iron (TFe) and the cyanobacterial fraction between lakes might have been a consequence of differences in the cyanobacterial community structure, specifically the presence or absence of nitrogen-fixing species. In conclusion, our study suggests that identification of significant environmental factors under site-specific conditions is an important strategy to enhance successful outcomes in cyanobacterial bloom control measures.

The importance of lake sediments as a pathway for microcystin dynamics in shallow eutrophic lakes.

Microcystins are toxins produced by cyanobacteria. They occur in aquatic systems across the world and their occurrence is expected to increase in frequency and magnitude. As microcystins are hazardous to humans and animals, it is essential to understand their fate in aquatic systems in order to control health risks. While the occurrence of microcystins in sediments has been widely reported, the factors influencing their occurrence, variability, and spatial distribution are not yet well understood. Especially in shallow lakes, which often develop large cyanobacterial blooms, the spatial variability of toxins in the sediments is a complex interplay between the spatial distribution of toxin producing cyanobacteria, local biological, physical and chemical processes, and the re-distribution of toxins in sediments through wind mixing. In this study, microcystin occurrence in lake sediment, and their relationship with biological and physicochemical variables were investigated in a shallow, eutrophic lake over five months. We found no significant difference in cyanobacterial biomass, temperature, pH, and salinity between the surface water and the water directly overlying the sediment (hereafter ‘overlying water’), indicating that the water column was well mixed. Microcystins were detected in all sediment samples, with concentrations ranging from 0.06 to 0.78 µg equivalent microcystin-LR/g sediments (dry mass). Microcystin concentration and cyanobacterial biomass in the sediment was different between sites in three out of five months, indicating that the spatial distribution was a complex interaction between local and mixing processes. A combination of total microcystins in the water, depth integrated cyanobacterial biomass in the water, cyanobacterial biomass in the sediment, and pH explained only 21.1% of the spatial variability of microcystins in the sediments. A more in-depth analysis that included variables representative of processes on smaller vertical or local scales, such as cyanobacterial biomass in the different layers and the two fractions of microcystins, increased the explained variability to 51.7%. This highlights that even in a well-mixed lake, local processes are important drivers of toxin variability. The present study emphasises the role of the interaction between water and sediments in the distribution of microcystins in aquatic systems as an important pathway which deserves further consideration.

Microcystin Dynamics in Aquatic Organisms

Eutrophication of surface water has increased significantly during the past decade, resulting in increased occurrences of toxic blooms. Cyanotoxins have become a global health threat to humans, wild animals, or domestic livestock. Hepatotoxic microcystins (MC) are the predominant cyanotoxins, which accumulate in aquatic organisms and are transferred to higher trophic levels. This is an issue of major concern in aquatic toxicology, as it involves the risk for human exposure through the consumption of contaminated fish and other aquatic organisms. The persistence and detoxification of MC in aquatic organisms are important issues for public health and fishery economics. Bioaccumulation of MC depends on the toxicity of the strains, mode of feeding, and detoxication mechanisms. Although mussels, as sessile filter feeders, seem to be organisms that ingest more MC, other molluscs like gastropods, as well as zooplankton and fish, may also retain average similar levels of toxins. Edible animals such as some species of molluscs, crustaceans, and fish present different risk because toxins accumulate in muscle at low levels. Carnivorous fish seem to accumulate high MC concentrations compared to phytophagous or omnivorous fish. This review summarizes the existing data on the distribution and dynamics of MC in contaminated aquatic organisms.

Collapse of a Planktothrix agardhii perennial bloom and microcystin dynamics in response to reduced phosphate concentrations in a temperate lake

Planktothrix agardhii dynamics, microcystin concentration and limnological variables were monitored every 2 weeks for 2 years (2004-2006) in a shallow hypereutrophic artificial lake (BNV, Viry-Châtillon, France). Time-series analysis identified two components in the P. agardhii biomass dynamics: (1) a significant decreasing trend in P. agardhii biomass (65% of the overall variance) and (2) a residual component without significant seasonal periodicity. A path-analysis model was built to determine the main factors controlling the P. agardhii dynamics over the period studied. The model explained 66% of P. agardhii biomass changes. The decreasing trend in P. agardhii biomass was significantly related to a decrease in the PO4(3-) concentration resulting from an improved treatment of the incoming watershed surface water. The residual component was related to zooplankton dynamics (cyclopoid abundances), supporting the hypothesis of a top-down control of P. agardhii, but only when the biomass was low. Forty-nine percent of the variability in the microcystin (MC) concentration (min:<0.1 microg equivalent MC-LR L(-1); max: 7.4 microg equivalent MC-LR L(-1)) could be explained by changes in the P. agardhii biomass. The highest toxin content was observed when P. agardhii biomass was the lowest, which suggests changes in the proportion of microcystin-producing and -nonproducing subpopulations and/or the physiological status of cells.

Seasonal Dynamics of Microcystins with Associated Biotic and Abiotic Parameters in Two Bays of Lake Taihu, the Third Largest Freshwater Lake in China

[Liu, Y. Q.; Xie, P.; Zhang, D. W.; Wen, Z. R.] Chinese Acad Sci, Inst Hydrobiol, Donghu Expt Stn Lake Ecosyst, State Key Lab Freshwater Ecol & Biotechnol, Wuhan 430072, Peoples R China

Microcystis genotype succession in relation to microcystin concentrations in freshwater lakes

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 48:1-12 (2007) - doi:10.3354/ame048001 Microcystis genotype succession in relation to microcystin concentrations in freshwater lakes W. Edwin A. Kardinaal1,3,*, Ingmar Janse2,4,*, Miranda Kamst-van Agterveld2, Marion Meima2, Josje Snoek1, Luuc R. Mur1, Jef Huisman1, Gabriel Zwart1,2,5, Petra M. Visser1,** 1Aquatic Microbiology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Nieuwe Achtergracht 127, 1018 WS, Amsterdam, The Netherlands 2Department of Microbial Wetland Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Centre for Limnology, Rijksstraatweg 6, 3631 AC Nieuwersluis, The Netherlands 3Present address: DHV consultancy, PO Box 1132, 3800 BC Amersfoort, The Netherlands 4Present address: National Institute for Public Health and the Environment, PO Box 1, 3720 BA Bilthoven, The Netherlands 5Present address: Waterboard Peel en Maasvallei, PO Box 3390, 5902 RJ Venlo, The Netherlands *Both authors contributed equally to this work**Corresponding author. Email: petra.visser@science.uva.nl ABSTRACT: Potentially toxic Cyanobacteria, like Microcystis, form a serious threat in recreational waters and drinking-water reservoirs. We monitored the population dynamics of toxic and non-toxic Microcystis strains using rRNA of the internal transcribed spacer region in combination with DGGE to determine whether there is a seasonal succession of toxic and non-toxic Microcystis genotypes in freshwater lakes and, if so, whether this succession can explain seasonal dynamics of the toxin microcystin. We studied 3 lakes in The Netherlands, all dominated by Microcystis during summer. Coexistence of several genotypes was observed in all lakes. The seasonal succession in a deep, stratified lake started with a population consisting of several toxic genotypes at the onset of the bloom, which changed into a population dominated by non-toxic genotypes at the end of the bloom. In this lake, the genotype succession clearly accounted for the observed microcystin dynamics. In 2 unstratified lakes, we also observed a seasonal replacement of Microcystis genotypes; however, the relation between genotype succession and microcystin dynamics was less conspicuous, since toxic strains dominated throughout the bloom period. A seasonal succession of different Microcystis genotypes might often be a key mechanism determining microcystin concentrations in Microcystisdominated lakes. Therefore, factors driving the succession of toxic and non-toxic genotypes deserve further study. KEY WORDS: Harmful cyanobacteria · Microcystis · Microcystins · Genotypes · Succession · ITS · DGGE Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 48, No. 1. Online publication date: June 20, 2007 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2007 Inter-Research.

In situ studies on the distribution patterns and dynamics of microcystins in a biomanipulation fish – bighead carp ( Aristichthys nobilis)

The distribution and dynamics of microcystins in various organs of the phytoplanktivorous bighead carp were studied monthly in Lake Taihu, which is dominated by toxic cyanobacteria. There was a good agreement between LC-MS and HPLC-UV determinations. Average recoveries of spiked fish samples were 63% for MC-RR and 71% for MC-LR. The highest MC contents in intestine, liver, kidney and spleen were 85.67, 2.83, 1.70 and 1.57 μg g −1 DW, respectively. MCs were much higher in mid-gut walls (1.22 μg g −1 DW) than in hind- and fore-gut walls (0.31 and 0.18 μg g −1 DW, respectively), suggesting the importance of mid-gut wall as major site for MC absorption. A cysteine conjugate of MC-LR was detected frequently in kidney. Among the muscle samples analyzed, 25% were above the provisional tolerable daily intake level by WHO. Bighead is strongly resistant to microcystins and can be used as biomanipulation fish to counteract cyanotoxin contamination in eutrophic waters.

Regulation of cyanobacteria and microcystin dynamics in polymictic shallow lakes

A comparative study on seasonal dynamics of cyanobacteria and microcystins in relation to physical and chemical parameters was carried out in three polymictic shallow lakes. Lakes were predominated by Oscillatoriales: Planktothrix agardhii in one lake and Limnothrix spp. in the other two lakes. Considerable populations of Nostocales occurred in two of the lakes prior to mass developments of Oscillatoriales. The lake predominated by P. agardhii differed from the lakes predominated by Limnothrix spp. by higher total phosphorus concentrations and a larger surface area. Phosphorus is discussed as the crucial factor in the competition between Oscillatoriales, with P agardhii as the stronger competitor under higher phosphorus concentrations. Both Oscillatoriales outcompeted Nostocales populations under a declining intensity of PAR (photosynthetically active radiation). The decline of PAR intensity was promoted by the cyanobacteria itself and had a positive feed back on the development of Oscillatoriales but a negative effect on the development of Nostocales populations. Furthermore, the presence and concentration of microcystin was related to the presence and biovolume of P agardhii, respectively. No microcystins were found when only Limnothrix spp. were present.

Evidence for control of microcystin dynamics in Bautzen Reservoir (Germany) by cyanobacterial population growth rates and dissolved inorganic carbon

Laboratory experiments with Microcystis aeruginosa (strain PCC 7806) showed (1) that microcystins (MCYSTs) were synthesized only during the exponential growth phase of the producer, and (2) that MCYST production started when pH exceeded the value of 8.4 indicating a lack of free CO 2 and a beginning decline in HCO 3 - . Both findings were included as basic considerations in a model to simulate MCYST concentrations during a four-year period in the hypertrophic Bautzen Reservoir. The model calculates the particular MCYST production rates of five different species of cyanobacteria which occurred in Bautzen Reservoir. The model simulations show a good correlation between measured and calculated concentrations (r = 0.74). correlation being worse (1 = 0.62) when the pH-switch (no MCYST formation below pH 8.2) is excluded from the model. Since MCYST production is correlated with the growth rates and growth rates usually are controlled by changing environmental variables, no correlation between MCYST concentration and single abiotic or biotic factors can be expected. Consequently, MCYST concentration can be influenced only indirectly by the environmental factors. We conclude that the MCYST production under field conditions is controlled simultaneously by (1) the growth phase of a particular MCYST producer, (2) the species (and/or strain) composition of the cyanobacterial community, and (3) the availability of dissolved inorganic carbon. This complex control pattern may also explain many inconsistent results hitherto published regarding the influence of environmental factors on MCYST production.

In situ evaluation of options for chemical treatment of hepatotoxic cyanobacterial blooms

Closed-bottom limnocorrals were placed in a hardwater lake in central Alberta to compare the effect of two alternative approaches to chemical removal of toxic phytoplankton blooms. Reglone A, which lyses phytoplankton cells, and lime-alum, which precipitates intact phytoplankton cells out of the water column were both effective in removing phytoplankton from the water column. Our results were consistent with laboratory studies in that treatment with Reglone A removed phytoplankton (primarily cyanobacteria) blooms with a concomitant increase in dissolved microcystin (exo-MCYST) and phosphorus concentrations in the surrounding water whereas lime-alum treatment did not. Maximum exo-MCYST concentrations in the water phase of the lime-alum treated limnocorrals were 32-fold lower than those recorded in the Reglone-treated limnocorrals. Treatment with lime alone caused a sharp rise in pH (to &gt;10), and the observed increase in exo-MCYST was likely due to pH shock. Exo-MCYST concentration in the Reglone-treated enclosures remained high for the duration of the experiment (&gt;5 days). As microcystin did not partition onto lake sediments in laboratory studies, our limnocorrals results were probably a good indication of microcystin dynamics in lakes. Thus, the use of chemicals such as lime-alum that precipitate out intact phytoplankton cells lessens the potential health risk where microcystins are present.

A Field Study to Investigate Environmental Factors that Could Effect Microcystin Synthesis of a Microcystis Population in the Bautzen Reservoir

AbstractToxicity of Microcystis blooms to warm‐blooded animals generated by microcystins has bew reported world wide. The ecological relevance of microcystin production for cyanobacteria remains unknown. The microcystin concentration in Microcystis blooms occurring in the Bautzen reservoir Was investigated. The microcystin content of samples were determined by HPLC and ranged from undetectabel to 14.7 μg mg−1. Various chemical and physical parameters were monitored at the same time as Microcystis sampling, however, there was no correlation between these parameters and microcystin dynamics. The spatial distribution of microcystin in the Microcystis population was investigated once and showed no difference between samples taken at five stations. The microcystin concentration in ihc cell free water from the reservoir was below the detection threshold (&lt; 1 μg L−1). Size dependent Fractions of the Microcystis population analyzed for microcystin concentration correlated with colony sim. In the small fraction (&gt;30 &lt;66 μm) microcystin was not detected. In the medium fraction (&gt; 6 h &lt; 100μm) lower microcystin concentrations were detected than in large fraction (&gt;100μm) in which the highest microcystin concentrations were found.