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Eutrophication is recognized as the main water quality problem worldwide, mainly due to the prevalence of harmful cyanobacterial blooms. Submerged macrophytes can control cyanobacterial biomass by removing nutrients from the water column or producing allelopathic compounds. As a result, they are highlighted as a potential strategy for restoring eutrophic waters. However, studies in semi-arid tropical ecosystems have shown inconsistent results regarding the effects of submerged macrophytes on cyanobacterial communities and cyanotoxin production. The aim of this study was to assess the effect of submerged macrophytes on cyanobacterial community structure and microcystin production in a tropical semi-arid reservoir subject to intense periods of water level drawdown. Submerged macrophyte cover, surface water physical and chemical variables, cyanobacterial community biovolume and microcystin concentration were measured monthly between October 2014 and July 2015 at the entrance of the river (Zone I) and dam zones (Zone II) of a reservoir. Although both zones were dominated by the submerged macrophyte Egeria densa, there were significant differences in macrophyte cover: Zone I had greater submerged macrophyte cover and Zone II had lower submerged macrophyte cover. Higher total cyanobacterial biovolume, potential microcystin producer biovolume and microcystin concentrations were observed in the zone with the greater submerged macrophyte cover. Moreover, our results showed that nutrient concentrations (total phosphorous, total nitrogen and ammonium) and physical variables (water temperature and turbidity) were also associated with the zone with greater submerged macrophyte cover. This study highlights that the water level drawdown of the reservoir appears to have favored an increase in nutrient concentration, especially in the zones with dense vegetation, which may have contributed to the coexistence of the high cyanobacteria biomass, high submerged macrophyte coverage and high microcystin concentration. Thus, developing strategies for the management of submerged macrophyte cover during water level drawdown events is essential for improving water quality and reducing the risk of harmful cyanobacterial blooms at the ecosystem level in tropical semi-arid aquatic ecosystems.

Os padrões de distribuição e abundância das espécies são regidos por um conjunto de condições ambientais que delineiam as áreas apropriadas para o estabelecimento e manutenção das populações, funcionando como filtros ambientais. Levando isto em consideração, este trabalho teve como objetivo comparar as estruturas da comunidade fitoplanctônica (composição e abundância) entre um ambiente lótico e um lêntico, que são conectados em cascata, e compreender quais fatores ambientais melhor explicam a estruturação dessas comunidades. Para isto, foram feitas coletas trimestrais durante maio e novembro de 2021, no reservatório Epitácio Pessoa e em um trecho do rio Paraíba, ambos localizados no Estado da Paraíba. As amostras coletadas foram conservadas e levadas para identificação em laboratório, onde foram realizadas também as análises estatísticas através da abundância relativa das espécies, da diversidade de Shannon e de uma GLM, no programa RStudio. Os resultados mostraram que não houve diferença significativa na diversidade entre os dois ambientes (p>0,05). No entanto, a análise da abundância relativa revelou diferentes estruturas para os ambientes, onde, no reservatório, o grupo que se destacou foi o das cianobactérias, com 41,68%, apresentando relação negativa com a alcalinidade e os sólidos em suspensão. Enquanto no trecho do rio foram as clorofíceas que se destacaram, com 45,20% da abundância relativa, sendo positivamente relacionada à condutividade elétrica, pH, sólidos dissolvidos, sólidos suspensos totais, turbidez e temperatura da água e do ar, e negativamente relacionada com a alcalinidade, cloreto total e oxigênio. A prevalência de cianobactérias em um ambiente de abastecimento público deve servir como alerta aos gestores e pesquisadores, visto que a toxicidade desses organismos pode afetar as comunidades presentes nesse ecossistema e também a saúde e a economia das pessoas que utilizam desse recurso. Além disso, o aumento da frequência dos eventos de eutrofização, facilita o domínio de cianobactérias, gerando mais custos para restauração.

Predictions of more frequent and intense toxic cyanobacterial blooms in the future arise due to the synergistic effects of eutrophication combined with climate change. Thus, the intensification of dry conditions in arid and semiarid areas promotes a reduction in the water level of aquatic ecosystems and favors the growth of cyanobacteria. Among these conditions, there is a lack of consensus on the role of nitrogen (N) or phosphorus (P) limitation, particularly when cyanobacterial communities are dominated by N-fixing taxa. The present study evaluated the effects of water volume reduction on cyanobacterial abundance and heterocyst production in semiarid tropical reservoirs during a period of prolonged drought. Physicochemical variables and the phytoplankton community were analyzed, and a structural equation model was built to identify the variables that explain the heterocystous cyanobacteria and heterocysts. The reduction in water volume increased the cyanobacterial biomass due to the increase in the biomass of heterocystous filamentous cyanobacteria associated with higher production of heterocysts. Heterocysts were correlated with an increase in the trophic status, low light availability and high salinity maintained under the lower volume conditions. In addition, contrary to expectations, heterocysts were not correlated with the N:P ratio, which suggests that in the tropics, N fixation does not necessarily occur when the N:P ratio is low, and N is limiting. These results indicate the potential for dominance of heterocystous filamentous cyanobacteria in future climate change scenarios, and therefore, we recommend that bloom mitigation strategies prioritize the reduction of N and P associated with the control of variables that favor heterocystous filamentous (i.e., light and salinity). We also recommend including cyanotoxin analysis in the relationship with lowering the water level to determine whether cell-bound toxin production and the associated risk to aquatic biota and humans are increased in the dry period.

The Floc and Sink technique promotes, through the application of coagulants and clays, the removal of phosphorus and algal biomass from the water column by flocculation and sedimentation. Although it is a promising technique for mitigating harmful cyanobacterial blooms, little is known about the impacts on other phytoplankton species as well as it is not known how species with mechanisms of resistance to sedimentation respond to the application of these products. In this study, a laboratory experiment was carried out with water from a eutrophic reservoir to assess the impact of applying aluminum-based coagulants, aluminum sulfate and polyaluminium chloride, and chitosan, alone and combined with lanthanum modified bentonite and natural bentonite on the phytoplankton community, in a functional approach based on morphology (Morphology-Based Functional Groups - MBFG, Kruk et al., 2010 and Reynolds et al., 2014), with an emphasis on the characteristics that provide resistance to sedimentation. We tested two hypotheses: phytoplankton species with adaptive mechanisms that provide buoyancy to cells are more resistant to the removal from the water column by coagulants and clays; and coagulants based on metals and modified clays are more efficient in sedimentation of microalgal cells compared to natural products, regardless of the presence of an adaptive mechanism of resistance to sedimentation. Our results showed that aluminum sulfate and polyaluminium chloride alone or combined with lanthanum modified bentonite and natural bentonite effectively sedimented the cells, regardless of the presence of buoyancy mechanisms. In contrast, the natural coagulant chitosan alone or combined with lanthanum modified bentonite and natural bentonite removed only those species that were small-celled or small colonial without specialized structures or with the presence of spines, arms and siliceous exoskeleton. In the case of species with aerotopes and flagella, the removal was not effective and still caused an increase in algal biomass due to the formation of suspended cell aggregates on the surface of the water column of the experimental units. Therefore, we concluded that the Floc and Sink technique has an impact on the phytoplankton community because it removes from the water column species that are not the target of coagulants and clays, but that are considered important sources of energy in freshwater trophic webs. This result differs according to the type of product used as well as it is related to the morphological adaptations that favor the buoyancy of cells in the water column. Species with aerotopes and flagella are more resistant to sedimentation and may make the use of products applied in the Floc and Sink technique unfeasible. Nevertheless, these results represent only an immediate effect of the technique on the phytoplankton community, thus requiring a longer time scale evaluation to determine the algae that can effectively recover water column. Therefore, we also emphasize that algae of nutritional value can recover over time and make the long-term application of the technique acceptable.

Aim To test the hypothesis that zooplankton changes the structure of phytoplankton in tropical reservoirs by reducing the biomass of algal species susceptible to herbivory. Methods We experimentally evaluated the species-specific responses of phytoplankton to zooplankton within eutrophic reservoirs with different phytoplankton community structure in northeastern of Brazil. Water samples were collected from the subsurface in coastal regions of the Apipucos and Mundaú reservoirs in January/2012 and November/2014, respectively, and transported to the laboratory. The experiments were performed in Erlenmeyer flasks (1 liter) filled with water from the sample sites and were maintained for five days in the laboratory conditions. Two treatments were maintained (1) with phytoplankton and the presence of the native zooplankton and (2) without native zooplankton. Results Zooplankton proved to be an important factor, modifying the structure of the phytoplankton community, especially in the Apipucos reservoir. In this reservoir, we observed a significant reduction of biomass in diatom Cyclotella meneghiniana, and the chlorophyte Chlamydomonas sp., and an increase in the biomass of Raphidiopsis raciborskii. In the Mundaú reservoir, we observed a significant reduction of C. meneghiniana and R. raciborskii, while cyanobacteria Microcystis aeruginosa increased their biomasses in the presence of zooplankton. Conclusions These results show the importance of the microalgae community structure in phytoplankton-zooplankton interactions for food webs in tropical environments, as well as support the role of zooplankton in fostering cyanobacterial growth and maintain algal blooms. Resumo: Objetivo Testar a hipótese de que o zooplâncton altera a estrutura do fitoplâncton em reservatórios tropicais, reduzindo a biomassa de espécies de algas susceptíveis a herbivoria. Métodos Avaliamos experimentalmente as respostas espécie-específicas do fitoplâncton ao zooplâncton em reservatórios eutróficos com diferentes estruturas da comunidade fitoplanctônica no nordeste do Brasil. Amostras de água foram coletadas da subsuperfície nas regiões costeiras dos reservatórios Apipucos e Mundaú em janeiro/2012 e novembro/2014, respectivamente, e transportadas para o laboratório. Os experimentos foram realizados em frascos Erlenmeyer (1 litro) cheios de água dos locais das amostras e mantidos por cinco dias nas condições laboratoriais. Dois tratamentos foram mantidos (1) com fitoplâncton e presença do zooplâncton nativo e (2) sem zooplâncton nativo. Resultados O zooplâncton provou ser um fator importante, modificando a estrutura da comunidade fitoplanctônica, principalmente no reservatório de Apipucos. Neste reservatório, observamos uma redução significativa na biomassa de Cyclotella meneghiniana e Chlamydomonas sp., e um incremento na biomassa de Raphidiopsis raciborskii. No reservatório Mundaú, observamos uma redução significativa de C. meneghiniana e R. raciborskii, enquanto a cianobactéria Microcystis aeruginosa aumentou sua biomassa na presença de zooplâncton. Conclusões Estes resultados mostram a importância da estrutura da comunidade de microalgas nas interações fitoplancton-zooplâncton para as cadeias alimentares em ambientes tropicais, bem como, apoiam o papel do zooplâncton na promoção do crescimento de cianobactérias e na manutenção da proliferação de algas.

Phosphorus (P) is the main nutrient responsible for the harmful effects caused by the enrichment of aquatic systems, and submerged macrophytes play an important role in this process, since they can both remove and release this nutrient in environmental compartments. The present study aimed to evaluate the influence of submerged macrophytes on P in the water, sediment, and water-sediment interface in a eutrophic reservoir in a semiarid region and to evaluate the relationship between the concentration of this nutrient in macrophyte tissue and that available in the different compartments. Were performed ten collection campaigns, in three reservoir locations: at the entrance of the Paraíba River; in the intermediate area between the river entrance and the dam and at the dam. We observed a difference in the P concentration inside and outside macrophyte banks, and this difference was determined by the abundance and intensity of macrophyte growth and decomposition. In sites with extensive vegetation banks and where decomposition was more intense, macrophytes released P to the water-sediment interface and sediment compartments. By contrast, in sites with smaller vegetation banks and where macrophytes did not show reduced abundance, P was removed from these compartments. The entry of new water originating from river water transfer was an important modifying factor of the physical and chemical characteristics and macrophyte abundance. The zone where the river enters the reservoir was the area most affected by the water transfer. The macrophyte decomposition in this zone resulted in the highest P concentration in the water-sediment interface and sediment compartments, which demonstrates the importance of macrophytes in the fertilization of water bodies and, consequently, in the eutrophication process. In turn, in the dam zone, where the macrophyte banks were more stable and without large variations in abundance, P was removed from the compartments. A relationship between P in macrophyte tissue and that available in the environment was observed, particularly at the water-sediment interface, indicating that this compartment was the main P source for these plants, which demonstrated that these plants store higher amounts of P in nutrient-rich sediment and water, functioning as an indicator of the nutritional status of a reservoir.

A pesquisa em questão trata-se da construção do conhecimento de alunos do ensino fundamental sobre Educação Ambiental atrelada a conservação de aves da caatinga. Participaram da pesquisa 18 alunos, com faixa etária entre 8 a 9 anos e foram realizadas atividades dentro da sala de aula. Aplicou-se um formulário semiestruturado com questões discursivas e objetivas e este mesmo foi reaplicado no fim das atividades. Realizaram-se também atividades práticas como jogos e elaboração de bebedouros/comedouros para aves com garrafas PETS. Através do resultado das analises dos formulários e relatos de experiência pode-se verificar que as atividades contribuíram para uma aprendizagem significativa dos alunos na construção de conhecimento sobre as aves da caatinga e práticas de Educação Ambiental.

Cyanobacteria harmful algal blooms (CyanoHABs) have become increasingly frequent and intense in public supply reservoirs as a result of eutrophication and global climate change. The semi-arid region of Brazil has a well documented history of CyanoHABs but the underlying factors that control the excessive proliferation of these organisms and the production of their bioactive secondary metabolites are not comprehensively understood. This study aimed to identify the environmental factors that explain the spatial and temporal variations in the abundance of cyanobacteria and the concentration of cyanotoxins (microcystins, saxitoxins, and cylindrospermopsin) in semi-arid reservoirs. The following hypotheses were tested: (a) the largest biovolumes of potential toxin producing cyanobacteria occur when cyanotoxin concentrations are highest; and (b) the environmental factors that explain variations in biovolume of cyanobacteria also explain changes in cyanotoxins concentrations. Samples were taken from four reservoirs located in the Northeast region of Brazil, over a three-month period (October 2016 and February and June 2017). Of the 24 species of cyanobacteria identified, 13 were potentially toxin-producing. Physicochemical variables such as water volume of the reservoir, water transparency, soluble reactive phosphorus, and total phosphorus explained the abundance of cyanobacteria and the levels of cyanotoxins. These results corroborate the hypothesis that similar physicochemical conditions influence the abundance and diversity of cyanobacteria and cyanotoxins. Cyanobacterial blooms composed of more than one potential toxin producing species were observed in the studied reservoirs, where potential microcystin-producing species were the most common. Microcystins and saxitoxins were detected in all the reservoirs studied, while cylindrospermopsin and the cyanobacterium Cylindrospermopsis raciborskii were simultaneously recorded in only one reservoir (Camalaú Reservoir). Cylindrospermopsin was only detected in a reservoir for the first time in the State of Paraíba. Canonical redundancy analysis showed that the cyanotoxins were related to potential toxin producing species. These results corroborate the proposed hypothesis that there is a correlation between cyanotoxins and the biomass of potential producers. Also, there were situations where cyanotoxins were detected without the presence of potential producers. These results demonstrate the need for reassessment of potential toxin producing species of cyanobacteria in semi-arid reservoirs. This may lead to the identification and characterization of novel producers of these bioactive secondary metabolites.

Geoengineering techniques have been used to control phosphorus and cyanobacteria in lakes promising greater and quicker chemical and ecological recovery. Techniques that use coagulants and clays to remove particulates and dissolved phosphorus from the water column have received great. In this study, bench-scale "flock & sink" assays were carried out to evaluate the efficiency of the coagulants aluminium sulphate (SUL), polyaluminium chloride (PAC) and chitosan (CHI), alone and combined with natural bentonite clays (BEN) and lanthanum-modified bentonite (LMB), to remove of phosphorus from a eutrophic reservoir in a semi-arid region of Brazil. In addition, the study seeks to assess the effects on the cyanobacteria density and the intra- and extracellular concentrations of cyanotoxins after the application of these geoengineering materials. The SUL and PAC coagulants effectively reduced the total phosphorus (TP), reactive soluble phosphorus (SRP), turbidity, chlorophyll-a, cyanobacteria density and intracellular microcystin, whereas CHI showed a low removal efficiency. Lanthanum-modified bentonite proved to be more effective than BEN; however, the application of the coagulants only was sufficient to successfully remove phosphorus and cyanobacteria from the water column. In addition, the efficiency of the "flock & sink" technique in cell removal varied among the cyanobacteria species. Small colonial species such as Aphanocapsa delicatissima, Merismopedia glauca and Merismopedia tenuissima were removed regardless of the treatment used, including those with CHI and BEN. As for the filamentous cyanobacteria, Cylindrospermopsis raciborskii, Geitlerinema amphibium, Planktothrix agardhii and Pseudanabaena catenata, removal was achieved only using PAC, SUL and LMB alone or when combined. The intracellular concentrations of saxitoxin and cylindrospermopsin and the extracellular fraction of these cyanotoxins and of microcystin were not influenced by the application of coagulants and clays. This indicates that cell lysis did not occur with the addition of the geoengineering materials. These results demonstrate that the "flock & sink" technique could be used for restoration of eutrophic waters.

Zooplankton are important biocontrol agents for algal blooms in temperate lakes, while their potential in tropical and subtropical environments is not well understood. The aim of the present study was to evaluate the influence of increased zooplankton biomass on phytoplankton community and cyanotoxins (microcystins and saxitoxin) content of a tropical reservoir (Ipojuca reservoir, Brazil) using in situ mesocosms. Mesocosms consisted of 50L transparent polyethylene bags suspended in the reservoir for twelve days. Phytoplankton populations were exposed to treatments having 1 (control), 2, 3 and 4 times the biomass of zooplankton found in the reservoir at the beginning of the experiment. Filamentous cyanobacteria such as Planktothrix agardhii and Cylindrospermopsis raciborskii were not negatively influenced by increasing zooplankton biomass. In contrast, the treatments with 3 and 4 times zooplankton biomass negatively affected the cyanobacteria Aphanocapsa sp., Chroococcus sp., Dolichospermum sp., Merismopedia tenuissima, Microcystis aeruginosa and Pseudanabaena sp.; the diatom Cyclotella meneghiniana; and the cryptophyte Cryptomonas sp. Total microcystin concentration both increased and decreased at different times depending on zooplankton treatment, while saxitoxin level was not significantly different between the treatments and control. The results of the present study suggest that zooplankton biomass can be manipulated to control the excessive proliferation of non-filamentous bloom forming cyanobacteria (e.g. M. aeruginosa) and their associated cyanotoxins.

O presente artigo tem como objetivo provocar uma reflexão sobre o paradigma da educação inclusiva, a partir do estudo da concepção de meio ambiente levantada na escola Liceu Paraibano em João Pessoa - PB. Esta pesquisa foi desenvolvida com o intuito de realizar uma caracterização da percepção ambiental dos alunos, porém tornou-se um polêmico debate sobre a problemática da inclusão pedagógica de portadores de necessidades especiais no ensino regular. O processo de inclusão deve ser entendido como um posicionamento político e social em prol da educação especial, e que vem crescendo no ambiente escolar, de forma a alcançar relações mais igualitárias para todos. Porém, a pesquisa se deparou com o contexto real dessas “salas de aula de inclusão”. Percebeu-se que para se evitar que alguém esteja em risco de ser excluído de um dado contexto na sala de aula, acaba excluindo outro sujeito do processo de ensino-aprendizagem, transcorrendo de toda forma em situações de desvantagem, seletividade e preconceitos.

The aim of this study was to evaluate the phytoplankton–zooplankton interaction, using phytoplankton morphology-based functional groups, in two reservoirs that have different trophic state indices (TSIs). We hypothesised that the herbivorous relationships of zooplankton with the phytoplankton community would differ between reservoirs with different TSIs. In order to test this hypothesis, field collections to study the phytoplankton, zooplankton and abiotic variables were undertaken between July 2016 and April 2017 from the subsurface layer and in situ experiments were conducted using biomanipulation of the micro- and mesozooplankton. In situ experiments consisted of 18 microcosms in 5-L transparent plastic bottles (in triplicate). The mesotrophic reservoir showed predominance of chlorophytes (Group IV) and mesozooplankton during the study period. In the presence of zooplankton, all phytoplankton groups showed negative growth rates and higher ingestion values, mainly Group IV. In the supereutrophic reservoir, ingestion rates showed that micro- and mesozooplankton reduced the biomass of colonial (Group VII) and filamentous (Group III) cyanobacteria respectively. The findings of the present study reveal that Copepoda Calanoida, as well as small cladocerans, may be the most suitable zooplankton groups for biomass biomanipulation of different morphofunctional phytoplankton groups in mesotrophic reservoirs, and for the control of cyanobacteria in supereutrophic reservoirs.

This study aims to analyse the influence of a cascade of reservoirs on the density, richness and functional groups of phytoplankton in the Contas River, a tropical river of Brazil. This river has two dams along its course, forming the Pedra and Funil reservoirs. Samples were collected over three consecutive years (Dec., 2007 to Dec., 2010) at 28 sampling stations along the river. We identified 198 species and the stretches downstream from the reservoirs showed greater richness. Chlorophyceae, followed by Bacillariophyceae and Cyanophyceae were the dominant groups and highest density was recorded during the rainy season. Overall, a longitudinal pattern in algal densities was found for both seasons, with the lowest values recorded in sections of the Pedra and Funil reservoirs and the highest densities in the downstream sections. Nine functional groups were identified (C, F, J, MP, S1, Sn, Td, Y, Ws); of these, F and J grouped the species with the highest relative abundance during the dry season, while the S1 group, represented by the cyanobacterium Planktothrix agardhii, was dominant in the rainy season. The present study showed a high longitudinal variation in the phytoplankton richness and density, attributed to the hydrological change between the lotic and lentic stretches. Furthermore, the effects of the cascade of reservoirs on phytoplankton, such as reduced density, increased richness and changes in algal associations, were strongly influenced by habitat heterogeneity found in this environment, as well as the rainfall in the region.

This study aims to analyze the effects of nutrients and predation by zooplankton on phytoplankton biomass (chlorophyll a) in a eutrophic reservoir in Brazil (Apipucos Reservoir, State of Pernambuco), through experiments in microcosms. For this, samples of water were placed in 1 L Erlenmeyer flasks and kept for seven days. Treatments included the addition of nutrients (nitrogen combined with phosphorus and isolated additions of nitrogen and phosphorus), with presence and absence of zooplankton and a control which contained the reservoir water without any manipulation. The addition of nutrients did not stimulate phytoplankton growth. However, zooplankton significantly decreased phytoplankton biomass in the treatments it was added to (p < 0.05). The results of this study showed that for the reservoir studied, predation by zooplankton is the most significant factor in the regulation of phytoplankton, contradicting several studies which show that phytoplankton biomass is more strongly controlled by nutrients (bottom-up control) than by predation (top-down control).

The influence of temperature and nutrients on the co-occurrence of Cylindrospermopsis raciborskii and Microcystis panniformis in Mundaú reservoir was investigated. Samples were collected bimonthly from September 2008 to March 2009 with a Van Dorn bottle at two depths (surface and bottom) (n = 16). Water temperature was greater than 22.50 °C; pH values ranged from 6.09 to 8.42; and nitrogen-phosphorus ratios were low (0.11-1.46). The low N:P ratios indicated high phosphorus input, and an eutrophic to hypereutrophic condition in the reservoir. A significant positive correlation of spatial and temporal distribution of C. raciborskii with M. panniformis was observed. Canonical correlation analysis (CCA) results revealed significant association of the biomass of most cyanobacterial species with temperature and nutrients concentration. However, these factors did not explain the co-occurrence of C. raciborskii and M. panniformis. On the other hand, morphological and physiological adaptations such as the possession of aerotopes and production of mucilage, and co-operation between the two species permitted niche overlap, and consequently the co-occurrence of C. raciborskii and M. panniformis in Mundaú reservoir. Resumo Este estudo analisou a possível influência da temperatura e nutrientes (fósforo total ortofosfato, fósforo total dissolvido, nitrogênio total, nitrito e nitrato) na coocorrência de Cylindrospermopsis raciborskii e Microcystis panniformis no reservatório Mundaú, um ecossistema do semiárido do nordeste do Brasil. Amostras foram coletadas bimestralmente com uma garrafa de Van Dorn, de setembro 2008 a março 2009, em duas profundidades (superfície e fundo) em uma estação amostral, totalizando 16 amostras. A temperatura esteve sempre acima de 22.50 °C e o pH variou entre ácido a alcalino (6.09-8.42). A relação nitrogênio-fósforo foi baixa (0.11-1.46), indicando um aumento da concentração de fósforo, contudo, o reservatório esteve de eutrófico a hipertrófico dependendo do período de amostragem. Mudanças na distribuição espacial e temporal das biomassas de C. raciborskii e M. panniformis foram similares para ambas as espécies, as quais foram confirmadas pela correlação positiva entre elas. A Análise de Correlação Canônica (ACC) mostrou uma forte correlação entre a biomassa da maioria das espécies de cianobactérias com as variáveis abióticas, principalmente temperatura e nutrientes. Apesar disto, estes fatores não explicaram a coocorrência de C. raciborskii e M. panniformis. Por outro lado, as adaptações morfológicas e fisiológicas, tais como a posse de aerótopos e produção de mucilagem, e cooperação entre as duas espécies permitiram a sobreposição de nichos e, consequentemente, a co-ocorrência de C. raciborskii e M. panniformis no reservatório Mundaú.

Experiments were conducted to evaluate the N:P ratio, as well as the effects of the interaction between this ratio and zooplankton, on phytoplankton in a tropical reservoir. Three experiments were performed in the presence (+Z) or absence (–Z) of zooplankton and the addition of N and P in different ratios (N:P molar ratio of 5, 16 and 60).In Experiment I, the total phytoplankton biomass and biomass by taxonomic class and species of the N:P 16–Z treatment did not differ significantly from that of the control, whereas for N:P 16+Z, there was a reduction in total phytoplankton. In Experiment II, there was a significant increase in Bacillariophyceae and the biomass of two species in the N:P 60–Z treatment. For the N:P 60+Z treatment, a significant reduction was observed in the total phytoplankton biomass and the biomass of three phytoplankton classes and three species. In Experiment III, there was an increase in the biomass of Dinophyceae with the N:P 5–Z treatment. In the N:P 5+Z treatment, there was a significant reduction in total phytoplankton biomass and the biomass of the phytoplankton class and five species. The findings of the present study reveal that zooplankton species native to a tropical reservoir can change the structure of the phytoplankton community and the response of these organisms to variations in nutrients.

Phytoplankton composition in lotic environments has received less attention than that of lentic environments. The aim of the present study was to describe the micro-phytoplankton of the Contas River, which is one of the five most important water bodies in the state of Bahia, Brazil. Collections were carried out at 28 sampling sites at three-month intervals over a three-year period between December 2007 and September 2010. The micro-phytoplankton community was represented by 198 taxa distributed among Bacillariophyceae, Coscinodiscophyceae, Cyanophyceae, Fragilariophyceae, Chlorophyceae, Euglenophyceae, Dinophyceae, Cryptophyceae, Chrysophyceae and Xantophyceae. Geitlerinema amphibium (C. Agardh) Anagnostidis, Planktothrix agardhii (Gom.) Anagnostidis and Komárek, Pleurosira laevis (Ehrenberg) Compère and Ulnaria ulna (Nitzsch) P. Compère occurred in all samples. The majority of species (n = 111; 56.06% of the taxa) were classified as rare in the Contas River, as these organisms were only recorded during one or two months.

The installation of dams causes changes to the integrity of rivers and to the water cycle, performing an instrumental role in the organization of biological communities, including that of phytoplankton. In the present study, we analyzed the taxonomic composition of phytoplankton in two hydroelectric reservoirs on the São Francisco River, Itaparica and Xingó reservoirs. Samples were collected at quarterly intervals between December 2007 and September 2009, at 12 sampling stations in each reservoir, totaling 92 samples. We identified 110 species in the Itaparica reservoir and 136 in the Xingó reservoir, of which diatoms followed by green algae, played a major contribution to both reservoirs. Most of the species is rare and/or occasional. In the Itaparica reservoir, there were no very frequent species, although in the Xingó this category was represented by the diatoms Aulacoseira granulata (Ehrenberg) Simonsen and Fragilaria crotonensis Kitton. These results show that, despite the similarity in the composition of phytoplankton, the reservoirs studied certainly differed regarding their environmental conditions.