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(3) Dolichospermum cf. pseudocompactum general aspect of the filament with regular coiled, one filament twisted inside the other; (4) Radiocystis fernandoi; (5) Dolichospermum cf. pseudocompactum trichoma with one akinete; (6) D. cf. pseudocompactum trichome with one heterocyte. Scale bar 20 µm.
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The Uruguay River is the second most important river in the Río de la Plata Basin. Taxonomical composition, abundance and distribution of cyanobacteria collected at nine sampling stations in the Lower Uruguay River (Uruguay) were analyzed seasonally from 2006 to 2009. A total of 24 taxa were identified, including 13 Chroococcales, 4 Oscillatoriales...
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Massive cyanobacterial blooms frequently occur in the Uruguay River, one of the largest rivers in South America. A heterocytous morphospecies of unique morphology has been repeatedly observed in the river since 2006 in rather high abundances. This morphospecies was preliminarily reported as Anabaena spiroides and Dolichospermum cf. pseudocompactum,...
Citations
... bloom in the Uruguay river basin particularly in the Gualeguaychú river. In the Uruguay river basin, potentially toxic cyanobacteria blooms have been reported in the Salto Grande reservoir (Crettaz-Minaglia & Bordet, 2013), Nuevo Berlín, Fray Bentos and, Las Cañas (Ferrari et al., 2011). Moreover, during dinoflagellate bloom in the Gualeguaychú river, cyanobacterial blooms were reported in the Uruguay river through Programa de Vigilancia de Playas de la Comisión Administradora del Río Uruguay (Beaches Monitoring Program of the Administrative Commission of the Uruguay River, CARU). ...
Gualeguaychú river is a freshwater continental located in the Center-Eastern of Argentina corresponding to the Neotropical region. Several uses can be identified such as the conservation of aquatic life, recreation (primary and secondary contact), navigation, recreational and subsistence fishing, and human and animal consumption. From February to April 2018, a bloom of Gymnodinium sp. (Dinophyceae) was reported in the low basin of the Gualeguaychú river. The bloom was extended from the Parque Unzué (33º 00' 16.38" S - 58º 29' 21.15" W) to the discharge of the El Cura stream (33º 02' 27.00" S - 50º 20' 29.01" W). This was the first record of a bloom of Gymnodinium sp. in that region where potentially toxic cyanobacteria blooms usually have an annual frequency. Consequently, this finding could be interpreted as a global indicator of change. Therefore, it is necessary to advance in systematic monitoring to develop an early warning system in the Gualeguaychú River.
... bloom in the Uruguay river basin particularly in the Gualeguaychú river. In the Uruguay river basin, potentially toxic cyanobacteria blooms have been reported in the Salto Grande reservoir (Crettaz-Minaglia & Bordet, 2013), Nuevo Berlín, Fray Bentos and, Las Cañas (Ferrari et al., 2011). Moreover, during dinoflagellate bloom in the Gualeguaychú river, cyanobacterial blooms were reported in the Uruguay river through Programa de Vigilancia de Playas de la Comisión Administradora del Río Uruguay (Beaches Monitoring Program of the Administrative Commission of the Uruguay River, CARU). ...
Gualeguaychú river is a freshwater continental located in the Center-Eastern of Argentina corresponding to the Neotropical region. Several uses can be identified such as the conservation of aquatic life, recreation (primary and secondary contact), navigation, recreational and subsistence fishing, and human and animal consumption. From February to April 2018, a bloom of Gymnodinium sp. (Dinophyceae) was reported in the low basin of the Gualeguaychú river. The bloom was extended from the Parque Unzué (33º 00' 16.38" S - 58º 29' 21,15" W) to the discharge of the El Cura stream (33º 02' 27.00" S - 50º 20' 29.01" W). This was the first record of a bloom of Gymnodinium sp. in that region where potentially toxic cyanobacteria blooms usually have an annual frequency. Consequently, this finding could be interpreted as a global indicator of change. Therefore, it is necessary to advance in systematic monitoring to develop an early warning system in the Gualeguaychú River.
... The obtained positive relationship between precipitation and water flow is coincident with studies evaluating larger periods in the lower reaches of the basin (Barros et al., 2015;Díaz et al., 2020;Saurral et al., 2008;Ungerovich et al., 2021). In addition, previous studies described how water flow modulates cyanobacterial blooms (Adloff et al., 2018;Ferrari et al., 2011;Mitrovic et al., 2011;O'Farrell & Izaguirre, 2014). However, our results evidenced that in the long run (years-decades), land use change and its effect on eutrophication were hierarchically more important than hydrology. ...
Toxic cyanobacterial blooms are globally increasing with negative effects on aquatic ecosystems, water use and human health. Blooms’ main driving forces are eutrophication, dams construction, urban waste, replacement of natural vegetation with croplands, and climate change and variability. The relative effects of each driver have not still been properly addressed, particularly in large river basins. Here, we performed a historical analysis of cyanobacterial abundance in a large and important ecosystem of South America (Uruguay river, c.a. 1,900 km long, 365,000 km2 basin). We evaluated the interannual relationships between cyanobacterial abundance and land use change, river flow, urban sewage, temperature and precipitation from 1963 to the present. Our results indicated an exponential increase in cyanobacterial abundance during the last two decades, congruent with an increase in phosphorus concentration. A sharp shift in the increase rate of cyanobacterial abundance after the year 2000 was identified, resulting in abundance levels above public health alert since 2010. Path analyses showed a strong positive correlation between cyanobacteria and cropland area at the entire catchment level, while precipitation, temperature and water flow effects were negligible. Present results help to identify high nutrient input agricultural practices and nutrient enrichment as the main factors driving toxic bloom formation. These practices are already exerting severe effects on both aquatic ecosystems and human health and projections suggest these trends will be intensified in the future. To avoid further water degradation and health risk for future generations, a large scale (transboundary) change in agricultural management towards agroecological practices will be required.
... The new revision of the taxonomic system of cyanobacteria by Komárek et al. (2014) has already transferred the genus Radiocystis into the family Microcystaceae from Synechococcaceae, indicating the similarities between Radiocystis and Microcystis [8]. In particular, Radiocystis fernandoi is the most common species of the genus in tropical regions, and some strains of this species in Brazil have been shown to form heavy blooms and produce microcystins in freshwaters in different tropical and subtropical regions of the continent [37][38][39][40][41][42]. R. fernandoi has been reported to contribute more than 70% of the total cyanobacterial biomass in some blooms [38,[42][43][44]; therefore, this species is regarded as having great ecological importance in tropical regions. ...
Microcystis-dominated blooms cause environmental and ecological impacts worldwide. However, it is sometimes challenging to correctly identify Microcystis and its related genera. Radiocystis fernandoi Komárek et Komáková-Legnerová 1993, characterized by large cells and correspondingly large colonies with gas vesicles, has been frequently found in cyanobacterial blooms in Brazil. However, its molecular and phylogenetic identity is unknown because no valuable DNA sequences are available in GenBank. In this study, a strain with R. fernandoi morphology was successfully isolated from a cyanobacterial bloom sample in Lake Erhai, a subtropical plateau lake in China. Molecular characterization and phylogenetic analyses based on 16S rRNA and cpcBA genes revealed that the strain is different from the type species of the genus Radiocystis but formed a well-supported clade with the Microcystis species. The comparative results of the ITS region between 16S–23S rRNA genes also showed that the strain had very similar secondary structures to the species of Microcystis, supporting it as a new member of the genus Microcystis. Therefore, we propose the transfer of Radiocystis fernandoi into Microcystis fernandoi comb. nov. The correct identification and further taxonomic procedure for the bloom-forming cyanobacterial genera, such as Microcystis, Radiocystis, and Sphaerocavum, are also discussed in this study.
... In total, 36 water samples were analyzed. The system presents strong temporal and spatial gradients in terms of temperature, conductivity (a proxy of salinity), and turbidity (37,(76)(77)(78). The highest surface water temperatures in the Salto Grande reservoir are usually recorded during summer (January to March, 33°C), while the lowest temperatures belong to the outer marine zone of the Río de la Plata during winter to early spring (June to October, 11°C). ...
... The melting curves (RFU) were first represented in a functional basis using a nonperiodic b-splin basis of order 4 (this was the optimal choice after several experiments). The multivariate CART (77,81) was used to model these coefficients (output variables) using the following explanatory variables as input: total nutrients (total nitrogen [TN] and total phosphorus [TP]), wind intensity (WI), water temperature (WT), turbidity (Turb), and conductivity (K). Cross-validation was used to optimize the size (number of leaves) of the final tree. ...
Addressing the ecological and evolutionary processes underlying biodiversity patterns is essential to identify the mechanisms shaping community structure and function. In bacteria, the formation of new ecologically distinct populations (ecotypes) is proposed as one of the main drivers of diversification. New ecotypes arise when mutations in key functional genes or acquisition of new metabolic pathways by horizontal gene transfer allow the population to exploit new resources, permitting their coexistence with the parental population. We previously reported the presence of microcystin-producing organisms of the Microcystis aeruginosa complex (toxic MAC) through an 800 km environmental gradient ranging from freshwater to estuarine-marine waters in South America. We hypothesize that the success of toxic MAC in such a gradient is due to the existence of very closely related populations that are ecologically distinct (ecotypes), each specialized to a specific arrangement of environmental variables. Here, we analyzed toxic MAC genetic diversity through qPCR and high-resolution melting analysis (HRMA) of a functional gene ( mcyJ , microcystin synthetase cluster). We explored the variability of the mcyJ gene along the environmental gradient by multivariate classification and regression trees ( m CART). Six groups of mcyJ genotypes were distinguished and associated with different combinations of water temperature, conductivity and turbidity. We propose that each mcyJ variant associated to a defined environmental condition is an ecotype (or species) whose relative abundances vary according to their fitness in the local environment. This mechanism would explain the success of toxic MAC in such a wide array of environmental conditions.
Importance
Organisms of the Microcystis aeruginosa Complex form harmful algal blooms (HABs) in nutrient-rich water bodies worldwide. MAC HABs are difficult to manage owing to the production of potent toxins (microcystins) that resist water treatment. Besides, the role of microcystins in the ecology of MAC organisms is still elusive, meaning that the environmental conditions driving the toxicity of the bloom are not clear. Furthermore, the lack of coherence between morphology-based and genomic-based species classification makes it difficult to draw sound conclusions about when and where each member species of the MAC will dominate the bloom. Here, we propose that the diversification process and success of toxic MAC in a wide range of waterbodies involves the generation of ecotypes, each specialized in a particular niche, whose relative abundance varies according to its fitness in the local environment. This knowledge can improve the generation of accurate prediction models of MAC growth and toxicity, helping to prevent human and animal intoxication.
... Reservoir conditions thus typically promote a higher phytoplankton growth rate and biomass than upstream reaches (Soares et al., 2008;Aubriot et al., 2020;Kruk et al., 2021). On the other hand, rivers may also exhibit high availability of nutrients but the low residence time, turbulent regime, and moderate light intensity due to high inorganic turbidity are all limiting factors for microalgae biomass and bloom formation (Reynolds and Descy, 1996;Ferrari et al., 2011;O'Farrell and Izaguirre, 2014;Somma et al., 2021). In this sense, BC2021 analyzed mixed lentic and lotic data (37 lotic and 6 I. Alcántara et al. ...
A recent paper by Beretta-Blanco and Carrasco-Letelier (2021) claims that agricultural eutrophication is not one of the
main causes for cyanobacterial blooms in rivers and artificial reservoirs. By combining rivers of markedly different hydrological characteristics e.g., presence/absence and number of dams, river discharge and geological setting, the study speculates about the role of nutrients for modulating phytoplankton chlorophyll-a. Here, we identified serious flaws, from
erratic and inaccurate data manipulation. The study did not define how erroneous original dataset values were treated,
how the variables below the detection/quantification limit were numerically introduced, lack of mandatory variables
for river studies such as flow and rainfall, arbitrary removal of pH > 7.5 values (which were not outliers), and finally
how extreme values of other environmental variables were included. In addition, we identified conceptual and procedural
mistakes such as biased construction/evaluation of model prediction capability. The study trained the model using pooled
data from a short restricted lotic section of the (large) Uruguay River and from both lotic and reservoir domains of the
Negro River, but then tested predictability within the (small) Cuareim River. Besides these methodological considerations,
the article shows misinterpretations of the statistical correlation of cause and effect neglecting basic limnological knowledge of the ecology of harmful algal blooms (HABs) and international research on land use effects on freshwater quality.
The argument that pH is a predictor variable for HABs neglects overwhelming basic paradigms of carbon fluxes and
change in pH because of primary productivity. As a result, the article introduces the notion that HABs formation are
not related to agricultural land use and water residence time and generate a great risk for the management of surface
waterbodies. This reply also emphasizes the need for good practices of open data management, especially for public databases in view of external reproducibility.
... Tendencias temporales de la biomasa y toxinas de cianobacterias, y el uso del suelo en el Río Negro La mayoría de las floraciones estuvieron dominadas por Dolichospermum y Microcystis (o Radiocystis), las cianobacterias más frecuentes en los cuerpos de agua lénticos y lóticos eutróficos del país (Bonilla, et al., 2015;Ferrari, et al., 2011;Haakonsson, et al., 2017). Estos taxa son potencialmente tóxicos, y pueden producir lipopolisacáridos (dermatotoxinas), microcistinas (hepatotoxinas) y potentes neurotoxinas (saxitoxina, anatoxina-a y anatoxina-a(S)) (van Apeldoorn, et al., 2007;Furtado, et al., 2009). ...
Toxic cyanobacterial blooms generate negative environmental, economic and health impacts. We carried out an analysis of historical limnological data (1989-2020, n = 423) and we performed a nutrient enrichment experiment to study the cyanobacteria of Río Negro, the largest internal river of Uruguay. We defined four hazard levels of exposure to toxic cyanobacteria based on quantitative indicators (biovolume and abundance of cyanobacterial cells and visual observation). The most common cyanobacteria (Microcystis sp. and Dolichospermum sp.) are potential producers of various toxins, including some that have not yet been analyzed in Uruguay. Accelerating environmental deterioration since 2000 has been caused by an increase of cyanobacteria biomass and concentrations of toxins (microcystins). Nutrient concentrations indicated advanced eutrophication, associated with the increase in the area devoted to agriculture of the watershed. Experimental results demonstrated the key role of nutrients and residence time in favoring these organisms. Toxic cyanobacterial blooms seriously threaten the multiple ecosystem services provided by the river, making it essential to implement cyanobacteria monitoring, and management plans to control eutrophication in the long term.
(Article in Spanish)
... The dynamics, growth, and abundance of phytoplankton in temperate freshwater bodies are better documented in temperate regions (e.g., Elser et al. 1990, e.g., Dokulil and Teubner 2000, Downing et al. 2001, Yang et al. 2020) than in tropical regions (Soares et al. 2007, e.g., Dao et al. 2016. In tropical rivers, the studies often focused on only one phytoplankton group such as cyanobacteria (Ferrari et al. 2011, e.g., DC Oliveira et al. 2019 or diatoms (e.g., Bellinger et al. 2006;Duong et al. 2019;Triest et al. 2012;Dalu and Froneman 2016) rather than on both microalgae and cyanobacteria (e.g., Soares et al. 2007;Varol and Şen 2018). The dynamics of phytoplankton in rivers from Southeast Asia are poorly reported and understood (Hoang et al. 2018;Duong et al. 2019), and some environmental parameters like trace metals are rarely considered during the investigations . ...
The spatiotemporal variation of phytoplankton and their relationship with environmental variables were analyzed in the Saigon River-a tropical river in Southern Vietnam. Two longitudinal profiles were conducted during dry and rainy season at 18 sampling sites covering more than 60 km long in the river. Besides, a biweekly monitoring conducted in the upstream, urban area (Ho Chi Minh City-HCMC), and downstream of Saigon River was organized from December 2016 to November 2017. The major phytoplankton were diatoms (e.g., Cyclotella cf. meneghiniana, Leptocylindrus danicus, Aulacoseira granulata), cyanobacteria (Microcystis spp., Raphidiopsis raciborskii, Pseudanabaena sp.), and euglenoids (Trachelomonas volvocina). Commonly freshwater phytoplankton species and sometimes brackish water species were dominant during the monitoring. Phytoplankton abundances in dry season were much higher than in rainy season (>100 times) which was explained by a shorter riverine water residence time and higher flushing capacity during the dry season. There was a clear separation of phytoplankton abundance between the urban area and the remaining area of Saigon River because of polluted urban emissions of HCMC. Redundancy analysis shows that the environmental variables (TOC, nitrogen, pH, salinity, Mo, Mn) were the driving factors related to the dominance of L. danicus and Cyclotella cf. meneghiniana in the upstream river and urban section of Saigon River. The dominance of cyanobacterium Microcystis spp. in the downstream of Saigon River was related to higher salinity, Mg, Cu concentrations, and lower concentrations of nutrients, Mn, Co, and Mo. The dominance of potentially toxic cyanobacteria in Saigon River possesses health risk to local residents especially upon the increasing temperature context and nutrient loading into the river in the next decades.
... En Uruguay se registraron floraciones de cianobacterias en el Río de la Plata y aguas continentales hace más de tres décadas, solo en 2018 estas alcanzaron las costas de Rocha. Se han encontrado floraciones tóxicas en el Río Uruguay y en el Río Negro, en los embalses de Salto Grande y del Río Negro, y en lagos y lagunas como Lago Javier, Laguna Blanca, Laguna de Rocha y Laguna de Castillos (Bonilla et al, 2015;Ferrari et al., 2011). en las últimas décadas el aumento de nutrientes provenientes de los desechos orgánicos de la industria, de asentamientos humanos y de la escorrentía de suelos con fertilizante, junto al aumento de temperatura a nivel mundial, han favorecido la formación de floraciones de cianobacterias en los ambientes acuáticos. ...
Las cianobacterias son un grupo muy particular de organismos procariotas que poseen clorofila-a y llevan a cabo la fotosíntesis. Poseen además ficobilinas, un pigmento
accesorio que solo se encuentran en las cianobacterias y les da el color típico verde azulado. Algunas especies son capaces de fijar el nitrógeno al agua gracias a células diferenciadas. en las últimas décadas el aumento de nutrientes provenientes de la escorrentía, junto al aumento de temperatura a nivel mundial, han favorecido la formación de floraciones de cianobacterias en los ambientes acuáticos. En el marco de un proyecto interinstitucional, INIA se plantea abordar el tema de las floraciones y la sostenibilidad de los sistemas de producción agropecuaria sobre aguas continentales en el embalse Rincón del Bonete, el cual recibe nutrientes provenientes de distintas actividades agropecuarias, principalmente la ganadería y la agricultura.
... En Uruguay se registraron floraciones de cianobacterias en el Río de la Plata y aguas continentales hace más de tres décadas, solo en 2018 estas alcanzaron las costas de Rocha. Se han encontrado floraciones tóxicas en el Río Uruguay y en el Río Negro, en los embalses de Salto Grande y del Río Negro, y en lagos y lagunas como Lago Javier, Laguna Blanca, Laguna de Rocha y Laguna de Castillos (Bonilla et al, 2015;Ferrari et al., 2011). en las últimas décadas el aumento de nutrientes provenientes de los desechos orgánicos de la industria, de asentamientos humanos y de la escorrentía de suelos con fertilizante, junto al aumento de temperatura a nivel mundial, han favorecido la formación de floraciones de cianobacterias en los ambientes acuáticos. ...
En las últimas décadas el aumento de nutrientes provenientes de la escorrentía, junto al aumento de temperatura a nivel mundial, han favorecido la formación de floraciones de cianobacterias en los ambientes acuáticos. En el marco de un proyecto interinstitucional, INIA se plantea abordar el tema de las floraciones y la sostenibilidad de los sistemas de producción agropecuaria sobre aguas continentales en el embalse Rincón del Bonete, el cual recibe nutrientes provenientes de distintas actividades agropecuarias, principalmente la ganadería y la agricultura.
