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Advancing Knowledge on Cyanobacterial Blooms in Freshwaters

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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Water Quality and Contamination".

Deadline for manuscript submissions: closed (31 May 2020) | Viewed by 45356

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Special Issue Editors

Prof. Dr. Elisabeth (Savi) Vardaka

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Guest Editor

Department of Nutritional Sciences and Dietetics, School of Health Sciences, International Hellenic University, Alexander Campus, Thessaloniki, Greece
Interests: aquatic microbial ecology; cyanobacteria; cyanotoxins; bacterioplankton; phytoplankton; human microbiome
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Konstantinos Ar. Kormas

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Guest Editor

Department of Ichthyology & Aquatic Environment, Faculty of Agricultural Sciences, University of Thessaly, 384 46 Volos, Greece
Interests: aquatic microbial ecology
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Cyanobacterial blooms are a water quality problem that has been widely acknowledged to cause detrimental ecological and economic effects in drinking and recreational waters supplies, and fisheries. There is increasing evidence that cyanobacterial blooms have increased globally and are likely to expand in water resources due to climate change. Of most concern are cyanotoxins, along with mechanisms that induce their release and fate in the aquatic envirornment. These secondary metabolites pose a potential hazard to human health and agricultural and aquaculture products directed for animal and human consumption; therefore, strict and reliable control of cyanotoxins is crucial for assessing risk. In this direction, a deeper understanding of the mechanisms that determine cyanobacterial bloom structures and toxin production become a target for managing practices.This Special Issue aims to bring together recent research of multi- and interdisciplinary approaches from the field to the laboratory and back again, driven by working hypotheses based on any aspect from ecological theory to applied research on mitigating cyanobacterial blooms. Of special interest are papers that suggest the use of complementary approaches, from the most recently developed molecular-based methods to more classical approaches and experimental and mathematical modeling regarding factors (abiotic and/or biotic) that control the diversity of not only the key bloom forming cyanobacterial species, but also their interactions to other biota, either in frehswater systems or their adjacent habitats, and their role in preventing and/or promoting cyanobacterial growth and toxin production and/or degradation.

Prof. Dr. Elisabeth (Savi) Vardaka
Prof. Dr. Konstantinos Ar. Kormas
Guest Editors

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Keywords

Cyanobacteria
Cyanotoxins
Molecular ecology
Human and animal health
Risk assessment
Nutrients
Climate change
Eutrophication

Published Papers (12 papers)

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Editorial

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4 pages, 184 KiB

Open AccessEditorial

Advancing Knowledge on Cyanobacterial Blooms in Freshwaters

by Elisabeth Vardaka and Konstantinos Ar. Kormas

Water 2020, 12(9), 2583; https://doi.org/10.3390/w12092583 - 16 Sep 2020

Cited by 4 | Viewed by 1901

Abstract

Cyanobacterial blooms have become a frequent phenomenon in freshwaters worldwide; they are a widely known indicator of eutrophication and water quality deterioration. Information and knowledge contributing towards the evaluation of the ecological status of freshwaters, particularly since many are used for recreation, drinking water, and aquaculture, is valuable. This Special Issue, entitled “Advancing Knowledge on Cyanobacterial Blooms in Freshwaters”, includes 11 research papers that will focus on the use of complementary approaches, from the most recently developed molecular-based methods to more classical approaches and experimental and mathematical modelling regarding the factors (abiotic and/or biotic) that control the diversity of not only the key bloom-forming cyanobacterial species, but also their interactions with other biota, either in freshwater systems or their adjacent habitats, and their role in preventing and/or promoting cyanobacterial growth and toxin production. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

Research

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15 pages, 2887 KiB

Open AccessArticle

Seasonal Succession of Phytoplankton Functional Groups and Driving Factors of Cyanobacterial Blooms in a Subtropical Reservoir in South China

by Lingai Yao, Xuemin Zhao, Guang-Jie Zhou, Rongchang Liang, Ting Gou, Beicheng Xia, Siyang Li and Chang Liu

Water 2020, 12(4), 1167; https://doi.org/10.3390/w12041167 - 19 Apr 2020

Cited by 17 | Viewed by 3483

Abstract

Freshwater phytoplankton communities can be classified into a variety of functional groups that are based on physiological, morphological, and ecological characteristics. This classification method was used to study the temporal and spatial changes in the phytoplankton communities of Gaozhou Reservoir, which is a large municipal water source in South China. Between January 2015 and December 2017, a total of 155 taxa of phytoplankton that belong to seven phyla were identified. The phytoplankton communities were classified into 28 functional groups, nine of which were considered to be representative functional groups (relative biomass > 10%). Phytoplankton species richness was greater in the summer and autumn than in the winter and spring; cyanobacterial blooms occurred in the spring. The seasonal succession of phytoplankton functional groups was characterized by the occurrence of functional groups P (Staurastrum sp. and Closterium acerosum) and Y (Cryptomonas ovata and Cryptomonas erosa) in the winter and spring, and functional groups NA (Cosmarium sp. and Staurodesmus sp.) and P (Staurastrum sp. and Closterium acerosum) in the summer and autumn. The temperature, nitrogen, and phosphorus levels were the main factors driving seasonal changes in the phytoplankton communities of Gaozhou Reservoir. The functional group M (Microcystis aeruginosa) dominated the community during the cyanobacterial blooms in spring 2016, with the maximum algal cell density of 3.12 × 10⁸ cells L⁻¹. Relatively low temperature (20.8 °C), high concentrations of phosphorus (0.080–0.110 mg L⁻¹), suitable hydrological and hydrodynamic conditions (e.g., relatively long retention time), and relatively closed geographic location in the reservoir were the key factors that stimulated the cyanobacterial blooms during the early stages. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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21 pages, 3281 KiB

Open AccessArticle

Cyanobacterial Blooms in Lake Varese: Analysis and Characterization over Ten Years of Observations

by Nicola Chirico, Diana C. António, Luca Pozzoli, Dimitar Marinov, Anna Malagó, Isabella Sanseverino, Andrea Beghi, Pietro Genoni, Srdan Dobricic and Teresa Lettieri

Water 2020, 12(3), 675; https://doi.org/10.3390/w12030675 - 01 Mar 2020

Cited by 17 | Viewed by 4650

Abstract

Cyanobacteria blooms are a worldwide concern for water bodies and may be promoted by eutrophication and climate change. The prediction of cyanobacterial blooms and identification of the main triggering factors are of paramount importance for water management. In this study, we analyzed a comprehensive dataset including ten-years measurements collected at Lake Varese, an eutrophic lake in Northern Italy. Microscopic analysis of the water samples was performed to characterize the community distribution and dynamics along the years. We observed that cyanobacteria represented a significant fraction of the phytoplankton community, up to 60% as biovolume, and a shift in the phytoplankton community distribution towards cyanobacteria dominance onwards 2010 was detected. The relationships between cyanobacteria biovolume, nutrients, and environmental parameters were investigated through simple and multiple linear regressions. We found that 14-days average air temperature together with total phosphorus may only partly explain the cyanobacteria biovolume variance at Lake Varese. However, weather forecasts can be used to predict an algal outbreak two weeks in advance and, eventually, to adopt management actions. The prediction of cyanobacteria algal blooms remains challenging and more frequent samplings, combined with the microscopy analysis and the metagenomics technique, would allow a more conclusive analysis. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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14 pages, 5392 KiB

Open AccessArticle

Effects of Light Intensity and Exposure Period on the Growth and Stress Responses of Two Cyanobacteria Species: Pseudanabaena galeata and Microcystis aeruginosa

by Guligena Muhetaer, Takashi Asaeda, Senavirathna M. D. H. Jayasanka, Mahendra B. Baniya, Helayaye D. L. Abeynayaka, M. Harun Rashid and HongYu Yan

Water 2020, 12(2), 407; https://doi.org/10.3390/w12020407 - 03 Feb 2020

Cited by 23 | Viewed by 5925

Abstract

Light is an important factor that affects cyanobacterial growth and changes in light can influence their growth and physiology. However, an information gap exists regarding light-induced oxidative stress and the species-specific behavior of cyanobacteria under various light levels. This study was conducted to evaluate the comparative effects of different light intensities on the growth and stress responses of two cyanobacteria species, Pseudanabaena galeata (strain NIES 512) and Microcystis aeruginosa (strain NIES 111), after periods of two and eight days. The cyanobacterial cultures were grown under the following different light intensities: 0, 10, 30, 50, 100, 300, and 600 μmol m⁻² s⁻¹. The optical density (OD₇₃₀), chlorophyll a (Chl-a) content, protein content, H₂O₂ content, and the antioxidative enzyme activities of catalase (CAT) and peroxidase (POD) were measured separately in each cyanobacteria species. P. galeata was negatively affected by light intensities lower than 30 μmol m⁻² s⁻¹ and higher than 50 μmol m⁻² s⁻¹. A range of 30 to 50 μmol m⁻² s⁻¹ light was favorable for the growth of P. galeata, whereas M. aeruginosa had a higher tolerance for extreme light conditions. The favorable range for M. aeruginosa was 10 to 100 μmol m⁻² s⁻¹. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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19 pages, 3297 KiB

Open AccessArticle

Linking Stoichiometric Organic Carbon–Nitrogen Relationships to planktonic Cyanobacteria and Subsurface Methane Maximum in Deep Freshwater Lakes

by Santona Khatun, Tomoya Iwata, Hisaya Kojima, Yoshiki Ikarashi, Kana Yamanami, Daichi Imazawa, Tanaka Kenta, Ryuichiro Shinohara and Hiromi Saito

Water 2020, 12(2), 402; https://doi.org/10.3390/w12020402 - 02 Feb 2020

Cited by 6 | Viewed by 3881

Abstract

Our understanding of the source of methane (CH₄) in freshwater ecosystems is being revised because CH₄ production in oxic water columns, a hitherto inconceivable process of methanogenesis, has been discovered for lake ecosystems. The present study surveyed nine Japanese deep freshwater lakes to show the pattern and mechanisms of such aerobic CH₄ production and subsurface methane maximum (SMM) formation. The field survey observed the development of SMM around the metalimnion in all the study lakes. Generalized linear model (GLM) analyses showed a strong negative nonlinear relationship between dissolved organic carbon (DOC) and dissolved inorganic nitrogen (DIN), as well as a similar curvilinear relationship between DIN and dissolved CH₄, suggesting that the availability of organic carbon controls N accumulation in lake waters thereby influences the CH₄ production process. The microbial community analyses revealed that the distribution of picocyanobacteria (i.e., Synechococcus), which produce CH₄ in oxic conditions, was closely related to the vertical distribution of dissolved CH₄ and SMM formation. Moreover, a cross-lake comparison showed that lakes with a more abundant Synechococcus population exhibited a greater development of the SMM, suggesting that these microorganisms are the most likely cause of methane production. Thus, we conclude that the stoichiometric balance between DOC and DIN might cause the cascading responses of biogeochemical processes, from N depletion to picocyanobacterial domination, and subsequently influence SMM formation in lake ecosystems. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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23 pages, 3684 KiB

Open AccessFeature PaperArticle

Protected Freshwater Ecosystem with Incessant Cyanobacterial Blooming Awaiting a Resolution

by Nada Tokodi, Damjana Drobac Backović, Jelena Lujić, Ilija Šćekić, Snežana Simić, Nevena Đorđević, Tamara Dulić, Branko Miljanović, Nevena Kitanović, Zoran Marinović, Henna Savela, Jussi Meriluoto and Zorica Svirčev

Water 2020, 12(1), 129; https://doi.org/10.3390/w12010129 - 31 Dec 2019

Cited by 8 | Viewed by 4451

Abstract

For 50 years persistent cyanobacterial blooms have been observed in Lake Ludoš (Serbia), a wetland area of international significance listed as a Ramsar site. Cyanobacteria and cyanotoxins can affect many organisms, including valuable flora and fauna, such as rare and endangered bird species living or visiting the lake. The aim was to carry out monitoring, estimate the current status of the lake, and discuss potential resolutions. Results obtained showed: (a) the poor chemical state of the lake; (b) the presence of potentially toxic (genera Dolichospermum, Microcystis, Planktothrix, Chroococcus, Oscillatoria, Woronichinia and dominant species Limnothrix redekei and Pseudanabaena limnetica) and invasive cyanobacterial species Raphidiopsis raciborskii; (c) the detection of microcystin (MC) and saxitoxin (STX) coding genes in biomass samples; (d) the detection of several microcystin variants (MC-LR, MC-dmLR, MC-RR, MC-dmRR, MC-LF) in water samples; (e) histopathological alterations in fish liver, kidney and gills. The potential health risk to all organisms in the ecosystem and the ecosystem itself is thus still real and present. Although there is still no resolution in sight, urgent remediation measures are needed to alleviate the incessant cyanobacterial problem in Lake Ludoš to break this ecosystem out of the perpetual state of limbo in which it has been trapped for quite some time. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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12 pages, 2558 KiB

Open AccessFeature PaperArticle

Ecological Connectivity in Two Ancient Lakes: Impact Upon Planktonic Cyanobacteria and Water Quality

by Matina Katsiapi, Savvas Genitsaris, Natassa Stefanidou, Anastasia Tsavdaridou, Irakleia Giannopoulou, Georgia Stamou, Evangelia Michaloudi, Antonios D. Mazaris and Maria Moustaka-Gouni

Water 2020, 12(1), 18; https://doi.org/10.3390/w12010018 - 19 Dec 2019

Cited by 8 | Viewed by 3193

Abstract

The ancient lakes Mikri Prespa and Megali Prespa are located in SE Europe at the transnational triangle and are globally recognized for their ecological significance. They host hundreds of flora and fauna species, and numerous types of habitat of conservational interest. They also provide a variety of ecosystem services. Over the last few decades, the two lakes have been interconnected through a surface water channel. In an attempt to explore whether such a management practice might alter the ecological properties of the two lakes, we investigated a series of community metrics for phytoplankton by emphasizing cyanobacteria. Our results demonstrate that the cyanobacterial metacommunity structure was affected by directional hydrological connectivity and high dispersal rates, and to a lesser extent, by cyanobacterial species sorting. Cyanobacterial alpha diversity was twofold in the shallow upstream Lake Mikri Prespa (Simpson index average value: 0.70) in comparison to downstream Lake Megali Prespa (Simpson index average value: 0.37). The cyanobacterial assemblage of the latter was only a strict subset of that in Mikri Prespa. Similarly, beta diversity components clearly showed a homogenization of cyanobacteria, supporting the hypothesis that water flow enhances fluvial translocation of potentially toxic and bloom-forming cyanobacteria. Degrading of the water quality in the Lake Megali Prespa in anticipation of improving that of the Lake Mikri Prespa is an issue of great concern for the Prespa lakes’ protection and conservation. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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15 pages, 4271 KiB

Open AccessArticle

Dynamics of Cyanobacteria and Related Environmental Drivers in Freshwater Bodies Affected by Mitten Crab Culturing: A Study of Lake Guchenghu, China

by Hongmin Li, Huihui Chen, Xiaohong Gu, Zhigang Mao, Qingfei Zeng and Huiping Ding

Water 2019, 11(12), 2468; https://doi.org/10.3390/w11122468 - 23 Nov 2019

Cited by 5 | Viewed by 2550

Abstract

Mitten crab aquaculture is prevalent in China, however, knowledge about the threat of cyanobacteria in mitten crab aquaculture-impacted water bodies is limited. Here, seasonal variations of cyanobacteria and their relationships with environmental factors were investigated for Lake Guchenghu area. Results suggested the changes of cyanobacteria community in crab ponds distinguished from the adjacent lake. In the lake, cyanobacterial biomass (3.86 mg/L, 34.6% of the total phytoplankton) was the highest in autumn with the dominance of Oscillatoria, Aphanocapsa and Pesudanabaena. By contrast, in crab ponds, cyanobacteria (46.80 mg/L, 97.2% of the total phytoplankton biomass) were the most abundant in summer when Pesudanabaena and Raphidiopsis were the dominant species. Of particular note was that obviously higher abundance of filamentous and potentially harmful species (e.g., Raphidiopsis raciborskii and Dolichospermum circinale) were observed in ponds compared to the lake. Specifically, water depth (WD), permanganate index (COD_Mn), total phosphorus (TP), N:P ratio, and

{NO}_{2}

⁻-N were the key environmental variables affected cyanobacteria composition. For crab ponds, N:P ratio, water temperature (WT) and TP were the potential environmental drivers of cyanobacteria development. This study highlighted the fact that mitten crab culture had non-negligible influences on the cyanobacteria community and additional attention should be paid to the cyanobacteria dynamics in mitten crab culture-impacted water bodies, especially for those potentially harmful species. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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17 pages, 4574 KiB

Open AccessArticle

Impact of Nutrient and Stoichiometry Gradients on Microbial Assemblages in Erhai Lake and Its Input Streams

by Yang Liu, Xiaodong Qu, James J. Elser, Wenqi Peng, Min Zhang, Ze Ren, Haiping Zhang, Yuhang Zhang and Hua Yang

Water 2019, 11(8), 1711; https://doi.org/10.3390/w11081711 - 17 Aug 2019

Cited by 10 | Viewed by 4017

Abstract

Networks of lakes and streams are linked by downslope flows of material and energy within catchments. Understanding how bacterial assemblages are associated with nutrients and stoichiometric gradients in lakes and streams is essential for understanding biogeochemical cycling in freshwater ecosystems. In this study, we conducted field sampling of bacterial communities from lake water and stream biofilms in Erhai Lake watershed. We determined bacterial communities using high-throughput 16S rRNA gene sequencing and explored the relationship between bacterial composition and environmental factors using networking analysis, canonical correspondence analysis (CCA), and variation partitioning analysis (VPA). Physicochemical parameters, nutrients, and nutrient ratios gradients between the lake and the streams were strongly associated with the differences in community composition and the dominant taxa. Cyanobacteria dominated in Erhai Lake, while Proteobacteria dominated in streams. The stream bacterial network was more stable with multiple stressors, including physicochemical-factors and nutrient-factors, while the lake bacterial network was more fragile and susceptible to human activities with dominant nutrients (phosphorus). Negative correlations between bacterial communities and soluble reactive phosphorus (SRP) as well as positive correlations between bacterial communities and dissolved organic carbon (DOC) in the network indicated these factors had strong effect on bacterial succession. Erhai Lake is in a eutrophic state, and high relative abundances of Synechococcus (40.62%) and Microcystis (16.2%) were noted during the course of our study. CCA indicated that nutrients (phosphorus) were key parameters driving Cyanobacteria-dominated community structure. By classifying the environmental factors into five categories, VPA analyses identified that P-factor (total phosphorus (TP) and SRP) as well as the synergistic effect of C-factor (DOC), N-factor (NO₃⁻), and P-factor (TP and SRP) played a central role in structuring the bacterial communities in Erhai Lake. Heterogeneous physicochemical conditions explained the variations in bacterial assemblages in streams. This study provides a picture of stream–lake linkages from the perspective of bacterial community structure as well as key factors driving bacterial assemblages within lakes and streams at the whole watershed scale. We further argue that better management of phosphorus on the watershed scale is needed for ameliorating eutrophication of Erhai Lake. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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19 pages, 4579 KiB

Open AccessArticle

An Ecological Function Approach to Managing Harmful Cyanobacteria in Three Oregon Lakes: Beyond Water Quality Advisories and Total Maximum Daily Loads (TMDLs)

by Eric S. Hall, Robert K. Hall, Joan L. Aron, Sherman Swanson, Michael J. Philbin, Robin J. Schafer, Tammy Jones-Lepp, Daniel T. Heggem, John Lin, Eric Wilson and Howard Kahan

Water 2019, 11(6), 1125; https://doi.org/10.3390/w11061125 - 29 May 2019

Cited by 9 | Viewed by 4155

Abstract

The Oregon Department of Environmental Quality (ODEQ) uses Total Maximum Daily Load (TMDL) calculations, and the associated regulatory process, to manage harmful cyanobacterial blooms (CyanoHABs) attributable to non-point source (NPS) pollution. TMDLs are based on response (lagging) indicators (e.g., measurable quantities of NPS (nutrients: nitrogen {N} and phosphorus {P}), and/or sediment), and highlight the negative outcomes (symptoms) of impaired water quality. These response indicators belatedly address water quality issues, if the cause is impaired riparian functions. Riparian functions assist in decreasing the impacts of droughts and floods (through sequestration of nutrients and excess sediment), allow water to remain on the land surface, improve aquatic habitats, improve water quality, and provide a focus for monitoring and adaptive management. To manage water quality, the focus must be on the drivers (leading indicators) of the causative mechanisms, such as loss of ecological functions. Success in NPS pollution control, and maintaining healthy aquatic habitats, often depends on land management/land use approaches, which facilitate the natural recovery of stream and wetland riparian functions. Focusing on the drivers of ecosystem functions (e.g., vegetation, hydrology, soil, and landform), instead of individual mandated response indicators, using the proper functioning condition (PFC) approach, as a best management practice (BMP), in conjunction with other tools and management strategies, can lead to pro-active policies and approaches, which support positive change in an ecosystem or watershed, and in water quality improvement. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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13 pages, 6156 KiB

Open AccessArticle

An Improved Logistic Model Illustrating Microcystis aeruginosa Growth Under Different Turbulent Mixing Conditions

by Haiping Zhang, Fan Huang, Feipeng Li, Zhujun Gu, Ruihong Chen and Yuehong Zhang

Water 2019, 11(4), 669; https://doi.org/10.3390/w11040669 - 31 Mar 2019

Cited by 5 | Viewed by 2725

Abstract

To overcome the limitations of the normal logistic equation, we aimed to improve the logistic model under hydrodynamic conditions for the examination of the responses of cyanobacterium, coupled turbulence mixing, and growth of cyanobacterium in population dynamics models. Selecting Microcystis aeruginosa and experimenting with the ideal conditions in a laboratory beaker, the chlorophyll-a concentration reached the corresponding maximum under each turbulent condition compared with the control. According to the experiment results, the theory of mass transfer, turbulence mixing, and the logistic equation are organically combined. The improved logistic growth model of Microcystis aeruginosa and competition growth model in the symbiont Scenedesmus quadricauda under turbulent conditions were established. Using the MATLAB multi-parameter surface fitting device, both models produced good fitting effects, with R > 0.95, proving that the results fit the models, and demonstrating the relationship of the unity of nutrient transfer and algae growth affected by turbulence mixing. With continuous increases in turbulent mixing, the fitted curve became smoother and steadier. Algae stimulated by turbulence accelerate reproduction and fission to achieve population dominance. The improved logistic model quantitatively explains the Microcystis aeruginosa response to turbulence and provides a basis to represent ecological and biogeochemical processes in enclosed eutrophic water bodies. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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12 pages, 6005 KiB

Open AccessArticle

Effect of Phenyl-Acyl Compounds on the Growth, Morphology, and Toxin Production of Microcystis aeruginosa Kützing

by Natalia Herrera, Maria Teresa Florez, Juan Pablo Velasquez and Fernando Echeverri

Water 2019, 11(2), 236; https://doi.org/10.3390/w11020236 - 30 Jan 2019

Cited by 9 | Viewed by 3711

Abstract

The proliferation of cyanobacteria and, consequently, the production of cyanotoxins is a serious public health concern; for their control, several alternatives have been proposed, including physical, chemical, and biological methods. In the search for new alternatives and a greater understanding of the biochemical process involved in the blooms’ formation, we report here the effect of eight phenyl-acyl compounds in the growth of Microcystis aeruginosa Kützing (assesed as cell density/count and Chl a fluorescence concentration) morphology, and production of the toxin microcystin-LR (MC-LR). Caffeic acid and eugenol decreased the growth of M. aeruginosa Kützing and the levels of Chl a. However, 3,5-dimethoxybenzoic acid and syringic acid caused the opposite effect in the growth; 2′and 4′only affected the Chl a. A reduction in the concentration of the MC-LR toxin was detected after treatment with syringic acid, caffeic acid, and eugenol. According to HPLC/MS (High Performance Liquid Chromatography coupled to Mass Spectrometry), a redox process possibly occurs between caffeic acid and MC-LR. The optical microscopy and Scanning Electron Microscopy analyses revealed morphological changes that had been exposed to caffeic acid and vanillin, specifically in the cell division and presence of mucilage. Finally, assays in Daphnia pulex De Geer neonates indicated that caffeic acid had a non-toxic effect at concentrations as high as 100 mg/L at 48 h. Full article

(This article belongs to the Special Issue Advancing Knowledge on Cyanobacterial Blooms in Freshwaters)

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