Cyanobacteria In Water Research Articles

Biochemical, toxicological and genomic investigation of a high-biomass producing Limnothrix strain isolated from Italian shallow drinking water reservoir

The presence of cyanobacteria in water for drinking and recreational purposes is considered problematic due to their bloom-forming and toxigenic potential. While most cyanotoxins are produced by extensively studied cyanobacteria, little is known about other abundant genera not usually assessed for their toxic potential. Here, a new isolate of Limnothrix redekei from an Italian drinking water reservoir was cultured and investigated using biological, chemical, and genomic methods. Compared to other Limnothrix spp., the isolate yielded high biomass productivity and was mainly constituted by proteins. The isolate had genomic features similar to those of the other 10 genomes of Limnothrix spp. published so far, regardless of their geographical origin. Most genes were implicated in primary metabolism (e.g. photosynthesis, nutrients transport, cell division), while <1 % of the genome was dedicated to secondary metabolism. Two regions encoding for a cyanobactin and a polyketide were found, whereas those for known cyanotoxins were absent. Toxicological investigations based on the crustacean Artemia sp. bioassay revealed potential toxicity of Limnothrix aqueous extracts (mortality >90 %). The highest toxicity was observed in a single fraction of the extract, whose UV spectrum presented carotenoid-like characteristics. Although the structure of the putative toxin was not yet elucidated, these findings pose the basis for further investigations on Limnothrix spp. toxicity, for which the observed toxic aqueous extracts could not exclude possible implications for ecosystems and humans through drinking water resources.

Remote cyanobacteria detection by multispectral drone imagery

Bartelt G, You J, Hondzo M. 2024. Remote cyanobacteria detection by multispectral drone imagery. Lake Reserv Manage. 40:236–247. Cyanobacteria play a crucial role in the ecological services of aquatic environments. Remote detection of cyanobacteria in water using satellite-based sensor images has been proven effective in monitoring eutrophication and harmful algal blooms. Satellite-based sensors are good at tracking large blooms in oceans and lakes, but not in small bodies of water. This study seeks to use remote-sensing techniques on images obtained from a multispectral camera mounted on an unmanned aerial system (UAS). We investigated a small freshwater lake, Brownie Lake, in Minneapolis, Minnesota, using the UAS. We compared the collected imagery to the measurements of chlorophyll and phycocyanin concentrations. Cyanobacterial chlorophyll a (Chl-a) concentrations and multispectral UAS data showed good agreement (r 2 = 0.54) in this study. Chl-a concentration strongly correlated with the presence of the near-infrared band at 840 nm and the red band at 668 nm. The most correlated spectral band combinations were the normalized difference vegetative index (NDVI) and 2 band algorithm (2BDA). Our research demonstrates the usefulness of UAS technologies in water quality monitoring.

Pulse Feature-Enhanced Classification of Microalgae and Cyanobacteria Using Polarized Light Scattering and Fluorescence Signals.

Harmful algal blooms (HABs) pose a global threat to the biodiversity and stability of local aquatic ecosystems. Rapid and accurate classification of microalgae and cyanobacteria in water is increasingly desired for monitoring complex water environments. In this paper, we propose a pulse feature-enhanced classification (PFEC) method as a potential solution. Equipped with a rapid measurement prototype that simultaneously detects polarized light scattering and fluorescence signals of individual particles, PFEC allows for the extraction of 38 pulse features to improve the classification accuracy of microalgae, cyanobacteria, and other suspended particulate matter (SPM) to 89.03%. Compared with microscopic observation, PFEC reveals three phyla proportions in aquaculture samples with an average error of less than 14%. In this paper, PFEC is found to be more accurate than the pulse-average classification method, which is interpreted as pulse features carrying more detailed information about particles. The high consistency of the dominant and common species between PFEC and microscopy in all field samples also demonstrates the flexibility and robustness of the former. Moreover, the high Pearson correlation coefficient accounting for 0.958 between the cyanobacterial proportion obtained by PFEC and the cyanobacterial density given by microscopy implies that PFEC serves as a promising early warning tool for cyanobacterial blooms. The results of this work suggest that PFEC holds great potential for the rapid and accurate classification of microalgae and cyanobacteria in aquatic environment monitoring.

Using FlowCam and molecular techniques to assess the diversity of Cyanobacteria species in water used for food production

Globally, the occurrence of cyanobacteria in water currently remains an important subject as they produce cyanotoxins that pose threat to human health. Studies on the contamination of maize meals during mill grinding processes using cyanobacteria-contaminated water have not been conducted. The present study aimed to assess the diversity of cyanobacteria in the samples (process water, uncooked maize meal, and cooked maize meal (porridge)). Polymerized Chain Reaction (PCR) and Advanced digital flow cytometry (FlowCAM) were used to detect and identify cyanobacterial species available in these samples. 16S Primers (forward and reverse) tailed with Universal Sequences were used for amplification and sequencing of full-length 16S rRNA genes from cyanobacteria found in all samples. Cyanobacterial species from order Nostocales, Pseudanabaenales, Oscillatoriales Chroococcales, Synechococcales, and unclassified cyanobacterial order, some of which have the potential to produce cyanotoxins were amplified and identified in process water, raw maize meal and porridge samples using PCR. Images of the genus Microcystis, Phormidium, and Leptolyngbya were captured in process water samples using FlowCAM. These findings show the presence of cyanobacteria species in process water used for maize meal and the absence in cooked maize meal. The presence of cyanobacteria in process water is likely another route of human exposure to cyanotoxins.

Dynamic monitoring of phycocyanin concentration in Chaohu Lake of China using Sentinel-3 images and its indication of cyanobacterial blooms

• Gradient boosting regression has the great potential in water quality retrieval. • PC concentration in Chaohu Lake has a high temporal consistency with CBs proportion. • PC concentration has the indicative significance for early warning of CBs outbreak. Phycocyanin (PC) is an indicator pigment of cyanobacteria in water. Monitoring the dynamic variation of PC concentration in lakes by satellite remote sensing is of great significance for the effective prevention and control of cyanobacterial blooms (CBs). Few studies have quantitatively monitored the long-term PC concentration variation in water and explored the relationship between PC concentration and CBs based on the advantages of the high temporal and spectral resolution of Sentinel-3 OLCI images. In this study, a retrieval model of PC concentration suitable for Sentinel-3 OLCI images was constructed and applied to the Sentinel-3 image dataset from May 2016 to November 2021 to analyze the spatiotemporal PC concentration variations in Chaohu Lake of China. The factors influencing PC concentration and its indicative significance for CBs outbreak were also explored. The results show that the PC concentration retrieval model based on the gradient boosting regression algorithm has the best performance (R 2 = 0.86, root mean square error = 45.44 ug/L, and mean absolute percentage error = 26.27 %), which has great application potential in the retrieval of other water quality parameters. In summer and autumn, the PC concentration in western Chaohu Lake was higher than that in other lake parts, which was mainly related to the higher nutrient concentration and prevailing wind direction in this part. During 2016–2021, the average PC concentration in Chaohu Lake in 2019 was the highest, and that in 2017 was the lowest, mainly affected by air temperature and precipitation. The variation of PC concentration in Chaohu Lake has a high temporal consistency with the proportion of CBs area, and the PC concentration of 303.9 μg/L is a necessary condition for CBs outbreak. This study revealed that Sentinel-3 OLCI images could provide a useful data source for high-frequency dynamic monitoring of PC concentrations in lakes and reservoirs, and the quantitative monitoring of PC concentrations in water has relevant indicative significance for early warning of CBs in inland water.

Freshwater cyanobacteria in waters intended for human consumption in Serbia: Two decades of changes in diversity

Herein we provide an assessment of cyanobacterial diversity and habitat preferences of potentially toxic and alien taxa, which could be an important tool for human health risk assessment regarding recreational and water-supply waterbodies. The diversity changes of cyanobacteria in waters intended for human consumption in Serbia were analyzed two decades after the first floristic study was published. The examination included phytoplankton and phytobenthic sample analysis from 35 localities in the period between 2012 and 2017, together with published literature records. The results indicate that the number of identified taxa doubled since the first Serbian Flora of Cyanobacteria was released two decades ago. The changes most likely occurred due to environmental factors, including hydrological transformations of habitats, cultural eutrophication and global warming. Many frequently recorded taxa are potentially toxic and bloom-forming. The spread of alien species with potentially invasive characteristics has also been noted. Canonical correspondence analysis (CCA) indicates that shallow waterbodies are the most vulnerable regarding the occurrence and expansion of bloom-forming, potentially toxic and invasive taxa. This shows the urgent need for a more detailed investigation. Additionally, although most of the research was focused on planktonic forms, benthic cyanobacteria represent an important component for public health risk assessment and therefore should be more frequently investigated.

Hydrogen peroxide modified and bismuth vanadate decorated titanium dioxide nanocomposite (BiVO4@HMT) for enhanced visible light photocatalytic growth inhibition of harmful cyanobacteria in water.

The persistence of harmful cyanobacterial algal blooms in aquatic ecosystems leads to health damage for various life forms. In this study, a photocatalyst active in the visible light range was prepared by combining BiVO4 with hydrogen peroxide modified titanium dioxide (BiVO4@HMT; for short), using an impregnation method. The catalyst was used to photocatalytically inhibit the growth of cyanobacteria collected from a bloom site. To infer the optimum pH for cyanobacterial growth, the effect of pH was studied. The growth of cyanobacteria was favoured in an alkaline environment at pH values in the range of 8-9.5 when analysed on the 20th day of incubation. Structural and chemical analysis of pristine and composite nano-powders was performed using XRD, SEM, TEM and XPS, confirming the heterojunction formation, while optical and band gap analysis revealed increased visible light absorption and reduced band gap of the composite. A small strawberry seed-like assembly of BiVO4 particles increased the light absorption in the 15%BiVO4@HMT composite and increased the inhibition efficiency up to 2.56 times compared to pristine HMT at an exposure time of 6 h and cell concentration at 0.1 g L-1 with an optimum catalyst dose of 1 g L-1. The amount of chlorophyll 'a' decreased due to the generation of catalytically reactive species, especially holes (h+), which caused oxidative damage to the cell wall, cell membrane and antioxidants in algal cells. This study reports that visible light active nanocatalysts can be used as a promising method for reducing algal blooms in water bodies.

Regulation of cyanobacteria population density by cyanophage and its effect on material circulation in water

噬藻体是环境中一类以蓝藻为主要宿主的浮游病毒.由于其能特异性裂解蓝藻细胞，因而成为蓝藻种群密度的重要生物调控因子，并被探讨用作蓝藻水华的潜在生物治理方案.噬藻体与蓝藻的相互作用机制可以降低宿主细胞丰度、改变浮游生物群落构成，促进碳、氮、磷等关键生命元素在水体中的生物地球化学循环过程.本文总结了近60年来分离的噬藻体及其对宿主藻的侵染机制，重点介绍了噬藻体对蓝藻种群密度的调节作用，并分析了噬藻体裂解蓝藻对水生态系统中营养物质循环、浮游生物群落变化的影响，并评价了噬藻体对蓝藻水华调控的潜在生态效应.噬藻体实际环境治理应用仍存在较大的挑战，例如噬藻体在水体中易与蓝藻形成共存；噬藻体感染、裂解水华蓝藻后水体中藻毒素消长，在很大程度上决定其安全性，相关科学问题仍需要进一步探索.本文将有助于更加全面地了解噬藻体在水生态系统中的作用，并评估噬藻体对蓝藻群落结构的调控和水体中物质循环过程的影响.;Cyanophage is a kind of planktonic viruses with cyanobacteria as host in the environment. Because it can specifically lytic cyanobacteria cells, it has become an effective biological regulator of cyanobacteria population density and has been discussed as a potential biological treatment scheme for cyanobacteria bloom. The interaction mechanism between cyanophage and cyanobacteria can reduce the abundance of host cells, change the composition of plankton community, and promote the biogeochemical cycle of key life elements such as carbon, nitrogen and phosphorus in water. This paper reviews cyanophage isolated in different water bodies in recent 60 years, summarizes the infection mechanisms of cyanophage, and focuses on the adjustment of cyanophage in cyanobacteria population. The effects of cyanobacteria lysis by cyanophage on nutrient cycling and plankton community changes in aquatic ecosystem are analyzed, and the ecological effects of cyanophage on the regulation of cyanobacteria bloom are evaluated. However, it should be pointed out that there are still great challenges in the practical environmental treatment application of cyanophage. For example, cyanophage is easy to coexist with cyanobacteria in water, and the change trend of cyanotoxins in water after cyanophage infecting still needs to be further explored. This review will contribute to a more comprehensive understanding of cyanophage and evaluate the regulatory effect of cyanophage on cyanobacteria community structure and the process of material circulation in water.

Annual dynamic remote sensing monitoring of phycocyanin concentration in Lake Chaohu based on Sentinel-3 OLCI images

藻蓝素（PC）是水体蓝藻的指示性色素，其浓度反映了蓝藻生物量，利用卫星遥感监测藻蓝素浓度年内动态对蓝藻水华的有效防控有着重要意义.根据不同季节的巢湖藻蓝素浓度实测数据与同期Sentinel-3 OLCI影像，构建机器学习回归反演模型，应用于巢湖2019年OLCI影像集上，对巢湖藻蓝素浓度的空间分布、年内变化进行遥感监测.研究表明：在MUMM和C2RCC水体大气校正方法中，C2RCC的大气校正结果更接近实测光谱反射率；在机器学习回归算法中，基于梯度提升回归的藻蓝素浓度反演模型精度最高，其R²、RMSE和rRMSE分别达到0.84、49.76 μg/L和34.1%.水体藻蓝素浓度在1—4月及12月较低，在5—11月浓度较高且波动频繁，日均气温是水体藻蓝素浓度年内变化的主要原因，而藻蓝素短期剧烈波动主要是受到日降水量和日照时数的影响；在夏、秋季节，西湖区藻蓝素浓度明显高于中、东湖区，主要与入湖河流中氮磷等物质的高输入有关.Sentinel-3 OLCI影像为湖库水体藻蓝素浓度动态监测提供了重要数据源，梯度提升回归算法在富营养化水体藻蓝素浓度反演中具有较大的应用潜力.;Phycocyanin (PC) is an indicator pigment of cyanobacteria in water, and its concentration reflects the biomass of cyanobacteria. Monitoring the annual dynamics of PC concentration by satellite remote sensing is of great significance for the effective prevention and control of cyanobacteria bloom. Based on the measured data of phycocyanin concentration in Lake Chaohu in different seasons and the Sentinel-3 OLCI images of the same period, a machine learning regression retrieval model was constructed and applied to the 2019 OLCI image set of Lake Chaohu to monitor the spatial distribution and annual variation of PC concentration. The results show that among MUMM and C2RCC atmospheric correction methods, the atmospheric correction result of C2RCC is closer to the measured spectral reflectance. Among the machine learning regression algorithms, the retrieval model of PC concentration based on gradient boosting regression has the highest accuracy, its R², RMSE and rRMSE reach 0.84, 49.76 μg/L and 34.1%, respectively. The concentration of PC was low from January to April and December, but high from May to November and fluctuated frequently. The average daily temperature was the main reason for the annual variation of PC concentration, and the short-term fluctuation of PC was mainly affected by the daily precipitation and sunshine duration. In summer and autumn, the PC concentration in the West Lake area was significantly higher than that in the middle and east lake area, which was mainly related to the high input of nitrogen and phosphorus into the lake. Sentinel-3 OLCI images provide important data sources for the dynamic monitoring of PC concentration in lake and reservoir waters, and the gradient boosting regression algorithm has great application potential in the retrieval of PC concentration in eutrophication waters.

In vitro antimicrobial and antioxidant activities of certain brackish water cyanobacteria from Chilika Lake, India

In vitro antimicrobial and antioxidant activities of certain brackish water cyanobacteria from Chilika Lake, India

Monitoring, Modeling and Management of Water Quality

In this special issue, we are able to present a selection of high-level contributions showing the manifold aspects of the monitoring, modeling, and management of water quality. Monitoring aspects range from cyanobacteria in water using spectrophotometry via wide-area water quality monitoring and exploiting unmanned surface vehicles, to using sentinel-2 satellites for the near-real-time evaluation of catastrophic floods. Modeling ranges from small scale approaches by deriving a Bayesian network for assessing the retention efficacy of riparian buffer zones, to national scales with a modification of the MONERIS (Modeling Nutrient Emissions in River Systems) nutrient emission model for a lowland country. Management is specifically addressed by lessons learned from the long-term management of a large (re)constructed wetland and the support of river basin management planning in the Danube River Basin.

Using sodium percarbonate to suppress vertically distributed filamentous cyanobacteria while maintaining the stability of microeukaryotic communities in drinking water reservoirs

The increasing frequency and intensity of blooms of toxin- and taste & odour-producing filamentous cyanobacteria in water sources is a growing global issue. Compared to the common spherical Microcystis genus, the removal of filamentous cyanobacteria is more difficult in drinking water treatment plants; hence, abatement and control of the occurrence and proliferation of harmful filamentous cyanobacteria within drinking water sources is important for water supply. In this study, the solid sodium percarbonate (SPC), Na2CO3·1.5H2O2, was used as an algaecide to eliminate the cyanobacteria distributed throughout the water column in the surface and bottom layer of a reservoir serving as a drinking water source. Results showed that although the oxidation capacity of SPC was higher in the surface water due to the higher light intensity than in the bottom water, 3.0 mg/L SPC can still suppress the harmful cyanobacteria in the bottom water after 36 h because the carbonate ion generated by SPC decomposition can act as an activator of H2O2 to generate many reactive oxygen species — including superoxide radicals, carbonate radical anions, and hydroxyl radicals — even in the light-limited environment. The obtained inactivation rates for the main cyanobacteria in this reservoir followed the order: Pseudanabaena limnetica > Raphidiopsis curvata > Cylindrospermopsis raciborskii. 3.0 mg/L SPC has a slight impact on microeukaryotic communities according to the 18S rRNA gene sequencing, while 6.0 mg/L SPC changed the composition of eukaryotic phytoplankton and zooplankton clearly. Eukaryotic co-occurrence networks showed that although the network of eukaryotic plankton in treated surface water was more compact and clustered, stability of microeukaryotes in the treated surface water was lower than for the treated bottom water, owing to the higher oxidation capacity of SPC in the surface water. The results above not only have important implications for full-scale control of harmful cyanobacteria in drinking water sources, especially filamentous cyanobacteria with vertical distributions, but also help to ensure the health and stability of the whole aquatic ecosystem.

Toxic cyanobacteria in water supply systems: data analysis to map global challenges and demonstrate the benefits of multi-barrier treatment approaches

Abstract The occurrence of toxic cyanobacteria in surface waters and their impact on drinking water treatment plants (WTPs) is a growing, global concern. The main objective of this paper was to assess the presence of cyanobacteria in surface water sources and associated cell removal efficiency in full-scale WTPs across the world. Previously unpublished data was collected from WTPs experiencing cyanobacterial blooms in either their managed surface waters or recreational waters. In total, data were collected from 31 surface water sources and 21 WTPs in North and South America, Europe, Asia, and Australia. The most commonly detected species were identified in both the surface waters, including Microcystis, Anabaena, Nostoc, Oscillatoria, and Planktolyngbya, and water treatment plant intakes, including Microcystis, Cylindrospermopsis, Anabaena, Pseudanabaena, and Aphanizomenon. In the intakes, cyanotoxins and taste and odor (T&amp;O) compounds frequently co-occurred (80%) as did multiple cyanotoxins (39%). Conventional treatment saw a wide range of removal depending on the density of cells, species, and metabolites. Although more than 28% of sampling events displayed negligible or even negative removals of metabolites or cells due to accumulation within the clarifier, filtration, or water recycling, the presence of multiple treatment barriers, particularly advanced treatments like granular activated carbon and nanofiltration, allowed for the cells and their metabolites of concern to be removed to below guideline values. During treatment, total microcystins were often removed without releasing their intracellular fraction, whereas cylindrospermopsin, geosmin, and 2-MIB were commonly detected as entirely extracellular at the plant's intake. The maximum tolerable cell (MTC) counts for cyanotoxin- or T&amp;O-producing cells were calculated using guideline values, average removal efficiency, and the average cell quota derived from data. The 21 WTPs in this work were found to be able to tolerate approximately 74,000 cells/mL for microcystins, 8,000 cells/mL for cylindrospermopsin, and 1,200 cells/mL for geosmin and 2-MIB before exceeding guideline values. These levels provide guidance for water treatment plant operators to assess the potential risk associated with cells capable of producing cyanotoxins or T&amp;O compounds.

Laboratory-scale evaluation of algaecide effectiveness for control of microcystin-producing cyanobacteria from Lake Okeechobee, Florida (USA)

Growth of microcystin-producing cyanobacteria in Lake Okeechobee (Florida, USA) and surrounding waters has resulted in adverse health impacts for humans and endangered species, as well as significant economic losses. As these issues worsen, there is growing pressure for efficacious solutions to rapidly mitigate harmful algal blooms (HABs) and protect critical freshwater resources. Applications of USEPA-registered algaecides as management tactics meet many decision-making criteria often required by water resource managers (e.g., effective, scalable, selective), but have not yet been evaluated on a large scale within the Lake Okeechobee waterway. This study was conducted to bolster the peer-reviewed database for available management tactics against microcystin-producing cyanobacteria in waters of this region. Laboratory-scale experiments can be conducted first to minimize uncertainty at larger scales and improve confidence in decision-making. In this study, samples containing microcystin-producing cyanobacteria collected from Lake Okeechobee were exposed to several USEPA-registered algaecides in laboratory toxicity experiments. Responses of target cyanobacteria were measured 3 days after treatment (DAT) in terms of cell density, chlorophyll-a concentrations, and phycocyanin concentrations. Based on responses of the cyanobacteria, minimum effective exposure concentrations were identified for each algaecide. Microcystin release (i.e. proportion of total microcystins in the aqueous phase) was measured and compared 1 DAT among effective exposures. Total microcystin concentrations were measured in effective treatments at 1, 4, and 9 DAT to discern potential for microcystin persistence following exposures to the effective formulations and exposure concentrations. Overall, several formulations including GreenClean Liquid® 5.0, GreenClean Liquid® 5.0 combined with Hydrothol® 191, and the copper-based algaecides evaluated (Algimycin® PWF, Argos, Captain® XTR, Cutrine® Ultra, and SeClear®) achieved significant and similar effects on target cyanobacteria. The chelated copper-based formulations (Algimycin® PWF, Argos, Captain® XTR, and Cutrine® Ultra) resulted in relatively less microcystin release 1 DAT and lesser total microcystin concentrations 4 DAT. At 9 DAT, total microcystin concentrations were significantly lower than in untreated controls in all treatments evaluated. These results provide the necessary comparative performance data for preliminary decision-making and designing additional studies at larger scales. Importantly, the comparative toxicity data and approach provided in this study demonstrate the initial steps for development of site-specific management strategies for Lake Okeechobee and other areas impacted by harmful algal blooms with large spatial and temporal scales.

Identification of Phytoplankton from Fresh Water and Growth Optimization in Potent Algae by Response Surface Methodology for Enhanced Biomass Production

ABSTRACT Microalgae are photosynthetic microorganisms which have the ability to transform carbon source into biochemicals that can be utilized as biofuels, food, feed and high value bioactive compounds. This study was carried out to evaluate the diversity of phytoplankton including diatoms, microalgae and cyanobacteria in water from two different locations in Salem district of Tamil Nadu, India. In the present study ten water samples were collected from these two sites and their phytoplankton diversity was studied using microscopy. Nearly four cyanobacteria, nine green algae and twenty four diatoms were observed. From them thirteen microalgae and cyanobacteria were isolated and grown in laboratory conditions, nine were able to sustain growth. Algal isolates viz., Chlorella sp. (88 mg/l), Chlorococcum sp. (67 mg/l), Oscillatoria sp. (53 mg/l) and Phormidium sp. (72 mg/l) were selected based on biomass productivity. Higher biochemical profile was found in two microalgae and one cyanobacterium. These three algae were optimized by box benkhen analysis of response surface methodology using varying sources such as carbon, nitrogen, phosphate, pH and temperature. The results revealed that these algae showed maximum biomass production in optimized conditions. The obtained biomass may be used for extraction of bioactive compounds, probiotics, biofuels and other value added products.

Warming and eutrophication effects on the phytoplankton communities of two tropical water systems of different trophic states: An experimental approach

AbstractBoth global warming and eutrophication are predicted to promote cyanobacterial blooms. At the same time, how tropical phytoplankton communities exhibiting different trophic state systems will respond to temperature variations is less clear. To investigate the effects of temperature changes and nutrient additions on phytoplankton communities, and gain insights regarding possible resistance to these effects, the present study focused on testing the hypothesis that temperature variations and nutrient additions will have a stronger effect on cyanobacteria dominance in eutrophic water system than in oligo‐mesotrophic water systems. Experiments were conducted with phytoplankton communities from two aquatic ecosystems exhibiting different trophic states. To this end, water samples from a eutrophic and oligo‐mesotrophic system were collected and incubated at 25 and 30ºC. Samples receiving additional surplus nitrogen (N) and phosphorus (P) inputs were included to serve as eutrophication treatments. The study results indicated that temperature variations alone did not promote cyanobacteria in water from either the oligo‐mesotrophic or eutrophic water system. However, nutrient enrichment of the water from the eutrophic system significantly boosted the cyanobacteria, with the biomass increasing by factor of 10 for both the 25°C and 30°C treatments. In contrast, eutrophication of the water from the oligo‐mesotrophic system did not change the relative contribution of phytoplankton groups, with the response ratios being much lower than those for the water from the eutrophic system. Although based on a simple experimental design, the results of the present study suggest that cyanobacteria dominance is favoured by further nutrient additions for eutrophic water systems, independently of any direct temperature effects, and that more pristine environments possess some resistance against eutrophication effects. Since global warming is assumed to indirectly intensify eutrophication symptoms, the results of the present study underscore the importance of nutrient control.

Free or Protein-Bound Microcystin Accumulation by Freshwater Bivalves as a Tool to Evaluate Water Contamination by Microcystin-Producing Cyanobacteria?

Cyanobacterial proliferations display rapid spatiotemporal variations that can interfere in the assessment of water contamination levels by microcystins (MC), and make necessary the use of integrative tools. This study evaluates the pertinence of bivalves Anodonta anatina and Dreissena polymorpha as bioindicators of the presence of MC-producing cyanobacteria in water. Ingested MC accumulates into two fractions in bivalve tissues—the cellular free and the protein-bound fractions—both forming the total MC fraction. Mussels were exposed to the cyanobacteria Planktothrix agardhii at densities producing an equivalent of 1, 10 and 100 µg/L of intracellular MC, with the evaluation of: (i) cyanobacterial cells and MC daily intake by mussels, (ii) free and total MC kinetics in whole individuals (using all the tissues) or only in the digestive gland, during and after the exposure, (iii) bioaccumulation factors. For each species, the kinetics of the two accumulation fractions were compared to evaluate which one best reflect levels and dynamics of MC-producing cyanobacteria in water. Results showed that the dynamic of free MC in bivalve tissues better highlight the dynamic of intracellular MC in water. Using whole D. polymorpha may be appropriate to reveal and discriminate the water contamination levels above densities of cyanobacteria producing 1 µg MC/L. Digestive glands of A. anatina appeared more sensitive to reveal low environmental concentration, but without direct correlation with levels of water contamination. Further experimentations in situ are necessary to confirm those results in order to propose the use of freshwater bivalves for a biomonitoring of MC-producing cyanobacteria in fresh waters.

A Semianalytical Algorithm for Mapping Proportion of Cyanobacterial Biomass in Eutrophic Inland Lakes Based on OLCI Data

The proportion of cyanobacterial biomass (PCB) can indicate the dominance of cyanobacteria in water, and it provides important information regarding the phytoplankton composition. Variations in the PCB can clarify the cyanobacteria accumulation process. Therefore, using remote sensing to obtain the spatial–temporal distribution of the PCB in inland lakes is very important for understanding the cyanobacterial bloom process. A total of 357 water samples was collected from three Chinese eutrophic inland lakes: Taihu Lake, Dianchi Lake, and Chaohu Lake, over eight field campaigns from 2013 to 2018. A normalized index of the PCB (NIPCB) was proposed using the absorption of chlorophyll-a (Chl-a) at 665 nm ( $a_{\mathrm {chl}}$ (665)) and the absorption of phycocyanin (PC) at 620 nm ( $a_{\mathrm {pc}}$ (620)) to indicate the PCB. A classification method using the PC index (PCI) was developed to identify the water types using the different algae composition features, and the relationship between the NIPCB and PCB in two water types was extensively examined. Finally, a semianalytical algorithm was developed to estimate the PCB based on the NIPCB index and the OLCI bands. The result of the estimated accuracy assessment using the independent validating data set demonstrated that the algorithm performance is satisfactory with mean absolute percentage error (MAPE) of 31.01% and root mean square error (RMSE) of 0.20. The MUMM method was then applied to conduct an OLCI image atmospheric correction with a satisfactory performance with the MAPE calculated between the measured remote sensing reflectance and the retrieved remote sensing from a satellite image of less than 25%. Consequently, the developed algorithm was successfully applied to three OLCI images of Dianchi Lake on April 12, 2017, Taihu Lake on May 18, 2017, and Chaohu Lake on September 8, 2018. The spatial distribution of the PCB in these three inland lakes is reasonable, and it demonstrated that the developed algorithm could be used to effectively monitor PCB at a large scale and provide important assistance in predicting the cyanobacterial blooms in eutrophic inland lakes by using remote sensing.

Monitoring of Cyanobacteria in Water Using Spectrophotometry and First Derivative of Absorbance

Management of cyanobacteria blooms and their negative impact on human and ecosystem health requires effective tools for monitoring their concentration in water bodies. This research investigated the potential of derivative spectrophotometry in detection and monitoring of cyanobacteria using toxigenic and non-toxigenic strains of Microcystis aeruginosa. Microcystis aeruginosa was quantified in deionized water and surface water using traditional spectrophotometry and the first derivative of absorbance. The first derivative of absorbance was effective in improving the signal of traditional spectrophotometry; however, it was not adequate in differentiating between signal and noise at low concentrations. Savitzky-Golay coefficients for first derivative were used to smooth the derivative spectra and improve the correlation between concentration and noise at low concentrations. Derivative spectrophotometry improved the detection limit as much as eight times in deionized water and as much as four times in surface water. The lowest detection limit measured in surface water with traditional spectrophotometry was 392,982 cells/mL, and the Savitzky-Golay first derivative of absorbance was 90,231 cells/mL. The method provided herein provides a promising tool in real-time monitoring of cyanobacteria concentrations and spectrophotometry offers the ability to measure water quality parameters together with cyanobacteria concentrations.

Potential of Opuntia stricta Haw (Mexican elephant ear) in removing cyanobacteria in surface water

In this study, assays were carried out to evaluate the efficiency of cactus Opuntia stricta cladodes as a coagulant for removal of cyanobacteria cells. To carry out the coagulation assays, water from eutrophic reservoir Bodocongo, in Brazilian semiarid, with cyanobacteria bloom of Microcystis aeroginosa, Plankthotrix isothrix and Cylindrospermopsis raciborskii were sampled. This water was submitted to coagulation with different forms of O. stricta cladodes (crude, pulverized and solution), concentration (10; 50 and 100 mg/L) and time (5, 15, 30, 60 and 120 min). In order to assess cell removal, readings were made in aliquots of 5 mL of samples analyzed by triplicates counting on sedimentation chambers using an inverted optical microscope, according to the Utermohl method. Dosage of 100 mg/L from the solution form of O. strica cladodes gave the best cell and turbidity removal. Colonial species were fast removed than filaments. The most removal occurred in the first 30 min of experiments. No significant differences were observed for pH changes in the experiments. O. stricta cladodes gave satisfactory results in reducing cyanobacteria cell in water; however, complete removal was not obtained; further studies are necessary to evaluate the best concentrations and the mechanisms of cyanobacteria removal. Key words: Eutrophication, biobased coagulants, Cactus.