CT - DCIV - Artigos publicados em periódicos

URI Permanente para esta coleçãohttps://repositorio.ufrn.br/handle/1/168

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Agora exibindo 1 - 20 de 201

Use of sewage sludge as raw material in the manufacture of roofs
(Anais da 2ª Conferência Internacional de Ciências Civis, Materiais e Ambientais Série: Avanços na Pesquisa de Engenharia, 2015) Nascimento, Rubens Maribondo do; Ingunza, Maria Del Pilar Durante; Lima, Andressa Dantas
The present study verifiesthe possibility of incorporating sewage sludgein the production ofceramic massfor ceramicroof tiles. Domestic sewage sludge and clay from ceramic industries of the northeastregion of Brazil were used. The raw materials were chemically and mineralogically characterized. Seven hundred and fifty tiles were manufactured using different concentrations of sludge (2%, 4%, 6%, 8% and 10% of sludge dry mass). The high amount of organic material (71%) from the sludge shows itself as being main factor onaffecting the quality of roof tiles. The increaseddosage of sludge implies a linear tendency of increased absorption and decreasedload rupture on flexion.Results haveshown the possibility of using nearly 4% of sludge (dry matter) on ceramic mass to manufacture roof tiles with no interferencein itsfinal product properties,in compliancewith current international standards.
Avaliação de resíduos de mineração de rochas cristalinas para uso como agregado em concreto segundo sua petrografia, índices físicos e resistência mecânica
(FapUNIFESP (SciELO)., 2020) Nascimento, Rubens Maribondo do; Medeiros, Ana Beatriz Azevedo de; Ingunza, Maria del Pilar Durante; Galindo, Antônio Carlos
Na atualidade, os resíduos de mineração vem sendo considerados como matéria prima nos programas de sustentabilidade ambiental, com o objetivo de minimizar os impactos decorrentes da atividade mineradora. Diante disso, o presente trabalho propõe analisar os resíduos de mineração de pegmatito para uso em agregado para concretos. As amostras foram caracterizadas petrograficamente, segundo seu potencial reativo à Reação Álcali-Agregado sob a norma ABNT 15577-3 e foram realizados ensaios para avaliação dos índices físicos e da resistência mecânica. Verificou-se entre as amostras de pegmatitos que duas delas obtiveram inocuidade para a reação álcali-agregado, por conter teores de fases deletéreas à RAA abaixo do limite aceitável pela norma. Entretanto, as demais amostras apresentaram potencial reatividade à RAA, por conter ora quartzo deformado, ora ambas as fases deletéras identificadas de acordo com a norma utilizada: quartzo deformado e microgranular. Os valores de resistência mecânica assumiram valores abaixo dos valores médios apresentados pela literatura consultada. Esse fato se justifica pelo grau de alteração observado nas amostras estudadas. Comprovou-se que os resíduos de lavra foram submetidos às ações intempéricas, tendo como resultado uma queda nos valores de resistência mecânica esperados. Considerando os índices físicos, as amostras apresentaram bons resultados no que diz respeito à capacidade de absorção de umidade
A mixed formulation for general triangular isoparametric shell elements based on the degenerated solid approach
(Elsevier, 2000-11) Bucalem, Miguel Luiz; Nóbrega, Selma Hissae Shimura da
A mixed formulation to construct general shell elements based on the degenerated solid approach is presented. This mixed formulation can be understood as a modification of the discrete potential energy of the shell in which the membrane and shear energy terms are obtained as a combination of the usual terms, i.e., directly obtained from the displacement and geometry interpolation assumptions, and membrane and shear terms obtained from assumed strain fields. This energy splitting idea was first introduced in the context of the Naghdi shell theory by Arnold and Brezzi. This mixed formulation is used to study quadratic general triangular shell elements based on the degenerated solid approach. Although considerable success has been achieved in the formulation of reliable, free of locking, general quadrilateral shell elements, the attempts of formulating general triangular shell elements have not yet produced an element that satisfies the locking free requirements. Therefore, there is a great interest in investigating new approaches, as the one discussed in this paper, that can lead to triangular elements that do not suffer from locking difficulties. We present in this paper the formulation of specific elements and their numerical assessment through the use of well established benchmark shell problems
Study of tension in the periodontal ligament using the finite elements method
(Dental Press International, 2012) Cossetin, Eliziane; Nóbrega, Selma Hissae Shimura da; Carvalho, Maria Goretti Freire de
Orthodontic movement is process of transformation of a physical stimulation into a force applied to a tooth, with a biological response identified as bone remodelling. Although it is possible to measure the force applied on a tooth, its distribution around the root is irregular forming areas of higher concentration of tensions, which do not correspond to the force initially applied. To evaluate the behavior of the periodontal ligament after the application of an external action and to prove which would be the areas of higher tension generated in the periodontium, the Finite Elements Method (FEM) was used in comparison to the results obtained in vivo on experimental models in rat. To test the error susceptibility of the technique used in the experimental model, the force application was simulated in three different heights on the mesial surface of the molar. The resulting histological analysis was compared with the result obtained for the computational code and disclosed that the greater focus of osteoclasts in activity had coincided with the compressed areas of the periodontal ligament. The alteration of points of force application generated areas of more extensive deformations in the periodontal ligament, as the point of application was more distant of the initial point, the horizontal force vector became bigger. These results demonstrate that the FEM is an adequate tool to study the distribution of orthodontic forces. The sensitivity of the experimental model used was also observed in relation to the installation of the dental movement device, which should be considered depending on the objective of the research
The new rigid element for laminated cylindrical shell
(David Publishing Company, 2014-11-25) Lovón, Oscar Bayardo Ramos; Ramos, Ana Paula Ferreira; Nóbrega, Selma Hissae Shimura da
Thermal effects are incorporated into developed discrete layer mechanics for two-dimensional cylindrical shells structures. Finite element equations are developed according to layerwise theory of laminated structure. Following the layerwise theory, a variable kinematic model that incorporates mechanics and thermal conditions is also presented. The new element has a field of displacement compatible with the cylindrical shell element or plate and it can be used as a rigid element for this structural element.In the laminate model construction, adjacent layers are arranged as bonded layers. The layer has a unique constant thickness that can be different to each layer. The fiber reinforced is used and the fibers in a laminate may be oriented arbitrarily. The shear stress is adopted equal to zero because the thin thickness, on the other hand, the normal stress is maintained in order to ensure the compatibility of stress in material. The previously authors of this methods neglect the implications of thermal effects on cylindrical shells structures. Thermal effects become important when the structure has to operate in either extremely hot or cold temperature environments. These extreme conditions may severely affect the response of structure in two distinct ways: (1) induction of thermal stresses due to differences in the coefficients of thermal expansion between the various composite plies and layers and (2) temperature dependence of the elastic properties. Only a limited amount of work has been reported concerning this topic. All in all, the main contribution of this work is the consideration of this kinematic for cylindrical shells that incorporate mechanics and thermal conditions. In addition, numerical results are presented to demonstrate the capability of the current formulation to represent the behavior of cylindrical shells with these characteristics
Perigo sísmico no Brasil e a responsabilidade da engenharia de estruturas
(Instituto Federal de Educação, Ciência e Tecnologia do Rio Grande do Norte, 2016) Nóbrega, Petrus Gorgonio Bulhões; Nóbrega, Selma Hissae Shimura da
No Brasil os terremotos são relativamente raros, especialmente os de maior magnitude, sendo a probabilidade de desastres e mortes relativamente pequena a ponto de muitos projetos de engenharia não a levarem em conta, a despeito do que está estabelecido na norma brasileira de projetos de estruturas resistentes a sismo (NBR 15421). Todavia, a sismicidade do Brasil não é nula; especialmente para algumas áreas, como a borda passiva, cuja média é superior a 70% da registrada na região continental estável. Os terremotos são imprevisíveis, mas a boa engenharia não deve ser. Este artigo discute a importância da consideração das ações sísmicas nas análises das estruturas civis, fazendo uma avaliação do mapa de perigo sísmico trazido pela NBR 15421, indicando procedimentos e condutas que devem ser tomados para o adequado projeto. Embora os projetos de algumas edificações, em algumas áreas do país, possam realmente desprezar a ação sísmica, tem-se a necessidade de discutir os procedimentos adequados para os prédios de operação especial e uso coletivo, exatamente aqueles que deveriam funcionar em caso de sinistro. Se não é possível eliminar o perigo sísmico, o objetivo é diminuir a vulnerabilidade a fim de se ter um risco sísmico aceitável, com um custo econômico e social admissíveis
Anisotropy and holes in epoxy composite reinforced by carbon/glass and carbon/aramid hybrid fabrics: experimental and analytical results
(Elsevier, 2017-09-15) Batista, Ana Cláudia Melo Caldas; Tinô, Sérgio Renan Lopes; Fontes, Raphael Siqueira; Nóbrega, Selma Hissae Shimura da; Aquino, Eve Maria Freire de
This study is based on research into the effect of anisotropy and the presence of holes on mechanical properties and final fracture characteristics in uniaxial tensile testing of two laminates, one using a carbon/glass fiber hybrid fabric and the other a carbon/aramid fiber hybrid fabric in loading directions at 0°, 90° and ±45°. Both laminates were impregnated with epoxy vinyl ester thermosetting resin (Derakane Momentum™ 411-350). An analytical study assesses stress concentration using the Point Stress Criterion (PSC) and Average Stress Criterion (ASC). The results show the direct influence of anisotropy, holes and residual properties on all the parameters studied. With respect to failure theories, both PSC and ASC showed good agreement when the geometric K value was used
Analytical, experimental and finite element analysis of the width/diameter hole ratio effect in vinylester/carbon hybrid twill weave composites
(Elsevier, 2020-10) Batista, Ana Cláudia Melo Caldas; Tinô, Sérgio Renan Lopes; Fontes, Raphael Siqueira; Nóbrega, Selma Hissae Shimura da Nóbrega; Aquino, Eve Maria Freire de
This study analyzes the influence of hybridization type and the presence of open holes in two bidirectional hybrid twill fabric-reinforced (glass/carbon fibers and carbon/aramid fibers) polymer composite laminates. Stress concentration based on the variation of the w/D ratio (specimen width/hole diameter) is studied. Analytical and numerical studies were based on the Point Stress Criterion (PSC) and Average Stress Criterion (ASC), in addition to the Finite Element Method (FEM). An experimental study based in tensile testing was conducted and the results showed that analytical and numerical modeling associated with experimental data generally exhibit good agreement with those reported in the literature for polymer composite laminates.
Application of failure criteria in aeronautical sandwich structure composites with a central hole subjected to bending testing
(ABM, ABC, ABPol, 2020-06-01) Silva, Franciélio Gomes da; Freire Júnior, Raimundo Carlos Silverio; Nóbrega, Selma Hissae Shimura da; Dias, Avelino Manuel da Silva
This study aimeds at investigating the mechanical behavior of an E-glass fiber-reinforced epoxy resin of a laminated composite sandwich with honeycomb core and a central hole, used in the aeronautics industry submitted to bending loading. Three analytical failure models applied to laminated composites were compared in order to study the influence of stress concentration due to a central hole. The following criteria were assessed: Average Stress Criterion (ASC), Point Stress Criterion (PSC) and the Inherent Flaw Model (IFM). These models were applied to experimental data obtained in a four-point bending test in samples of the sandwich laminate. Finally, modifications on failure prediction models were proposed and appied in sandwich laminates with a central hole. The results obtained showed the applicability of the proposed formulation and that the suggested changes to the model more adequately fit it to the experimental data
Classificação de espécies de mangue no Nordeste do Brasil com base em imagens híbridas de sensoriamento remoto
(Anuário do Instituto de Geociências, 2017) Costa, Bruno Cesar Pereira da; Amaro, Venerando Eustáquio; Ferreira, Anderson Targino da Silva
As imagens de satélites têm sido utilizadas para mapear, monitorar e quantificar a qualidade dos recursos naturais. O mapeamento detalhado da vegetação de mangue é uma demanda crescente por se tratar de um importante instrumento de gestão, manutenção e conhecimento do ecossistema manguezal frente às modificações provocadas pelas atuações antrópicas e/ou naturais. Este trabalho combinou dados multiespectrais da região do visível e infravermelho do satélite LANDSAT-8 com imagem da faixa espectral das micro-ondas do satélite RADARSAT-2 na segmentação e classificação de manguezais no Rio Grande do Norte, Nordeste do Brasil. A composição híbrida entre o sistema óptico e de micro-ondas mostraram excelente desempenho na identificação desta unidade geoambiental e permitiram maior realce das propriedades estruturais e florísticas das espécies de mangue. Os resultados permitiram delimitar a área geral de ocupação dos manguezais em aproximadamente 5.538 ha e revelaram a ocorrência de quatro principais condições estruturais de espécies: Rhizophora mangle (porte alto e adensamento convencional), Rhizophora mangle (porte baixo e adensado), Avicennia schaueriana e regiões de espécies mistas. R. mangle é a espécie de mangue mais abundante na área estudada, ocupando área de aproximadamente 3.513 ha, cerca de 63% de todo o manguezal da área estudada. Regiões mistas de espécies ocupam área de 1.142 ha, representando 21% do total. A. schaueriana ocupa área de 882 ha, cerca de 16% do total. Os resultados ainda mostraram que a diferença na reflectância das áreas de mangue ocupadas pelas espécies ocorrentes não se dá apenas influenciada pelo teor de clorofila das espécies, pela prevalecente condição ambiental, do solo e da água de fundo, mas principalmente pelo espaçamento das copas e densidade do dossel para cada espécie ocorrente. Este estudo buscou atender às expectativas de maior eficiência em levantamentos espaço-temporais com alta acurácia para o monitoramento da qualidade dos ecossistemas manguezais, altamente sensíveis às alterações ambientais e como subsídio à sua preservação
Spatial and temporal variations of Dinophyceae in subtropical reservoirs in southern Brazil
(Springer, 2010-08-08) Becker, Vanessa; Cardoso, Luciana de Souza; Fagundes, Paula Braga
Knowledge of dinoflagellate diversity in Brazilian reservoirs is limited, especially in subtropical environments. We investigated as to how nutrients and other environmental variables influenced the biomass of Dinophyceae species in three subtropical ecosystems. The reservoirs Samuara, Faxinal, and Sa˜o Miguel were sampled fortnightly from 2002 to 2006, and eight dinoflagellate taxa were identified. High temperature was a determining factor for the occurrence of Peridinium africanum Lemmermann. Peridinium umbonatum Stein and P. willei HuitfeldKass required high concentrations of nutrients. P. willei was inversely related to temperature and directly related to nutrients. P. umbonatum Stein var. umbonatum Stein showed the largest range of tolerance toward resources. Durinskia baltica Carty & Cox and Peridinium gatunense Nygaard could be opportunistic, since they did not show any spatial or temporal pattern
Driving factors of the phytoplankton functional groups in a deep Mediterranean reservoir
(Elsevier, 2010-03-20) Becker, Vanessa; Caputo, Luciano; Ordóñez, Jaime; Marcé, Rafael; Armengol, Joan; Crossetti, Luciane O.; Huszar, Vera L. M.
The control of phytoplankton growth is mainly related to the availability of light and nutrients. Both may select phytoplankton species, but only if they occur in limiting amounts. During the last decade, the functional groups approach, based on the physiological, morphological and ecological attributes of the species, has proved to be a more efficient way to analyze seasonal changes in phytoplankton biomass. We analysed the dynamics of the phytoplankton functional groups sensu Reynolds, recognising the driving forces (light, mixing regime, and nutrients) in the Sau Reservoir, based on a oneeyear cycle (monthly surface-water sampling). The Sau Reservoir is a Mediterranean water-supply reservoir with a canyon-shaped basin and a clear and mixed epilimnion layer. The long stratification period and high light availability led to high phytoplankton biomass (110.8 fresh-weight mg L 1) in the epilimnion during summer. The reservoir showed P-limitation for phytoplankton growth in this period. All functional groups included one or more species (X2-Rhodomonas spp.; Y-Cryptomonas spp.; F-Oocystis lacustris; K-Aphanocapsa spp.) selected by resources, especially phosphorus. Species of Cryptomonas (group Y) dominated during the mixing period (winter season) in conditions of low light and relatively high availability of dissolved nutrients. Increases in water-column stability during spring stratification led to phytoplankton biomass increases due to the dominance of small flagellate functional groups (X2 and X3, chrysophyceans). The colonial chlorophycean O. lacustris (group F) peaked during the mid-summer stratification, when the mixed epilimnion was clearly depleted in nutrients, especially SRP. High temperature and increases in nutrient concentration during the end-summer and mid-autumn resulted in a decrease of green algae (group F) and increase of Aphanocapsa spp. (cyanobacteria, group K) and dinoflagellates (group Lo). The study also revealed the important role of physical processes in the seasonal gradient, in selecting phytoplankton functional groups, and consequently in the assessment of ecological status. The Q index (assemblage index) based on functional groups indicated the overall good ecological status of the Sau Reservoir, which varied as a function of the mixing regime. This is the first application of the Assemblage Index to a European water-supply reservoir
Occurrence of anatoxin-a(s) during a bloom of Anabaena crassa in a water-supply reservoir in southern Brazil
(Springer, 2009-06-09) Becker, Vanessa; Ihara, Priscila; Yunes, João Sarkis; Huszar, Vera Lúcia M.
Cyanobacterial blooms and the accompanying production of cyanotoxins are a serious global problem. Toxic blooms of Anabaena species are common in lagoons and reservoirs of southern Brazil. Worldwide, species of the genus Anabaena produce the majority of the known hepatotoxins (microcystins) and neurotoxins [anatoxin-a, anatoxin-a(s), and saxitoxins]. This report links a bloom of Anabaena crassa in the Faxinal Reservoir, the main water supply for the city of Caxias do Sul (400,000 inhabitants) in southern Brazil, to the occurrence of anatoxin-a(s) in the water. During the bloom period, the reservoir was strongly stratified, with higher temperatures and a deep anoxic hypolimnion. Two methods for sample concentration (direct and complete extraction) were tested, and direct extraction of samples proved to be more efficient. Water samples collected during the bloom showed 9% acetylcholinesterase inhibition at 50 mg mL−1, corresponding to 0.61μg of anatoxin-a(s) per gram of lyophilized powder. At these concentrations, symptoms of neurotoxicity and mortality were not observed in tests with Swiss albino mice. Although the concentrations of anatoxin-a(s) in the Faxinal Reservoir were low, these results are important because this is the first record of the toxin for A. crassa. Furthermore, this cyanotoxin is not yet included in Brazilian legislation for drinking-water monitoring, because of the lack of information about toxicity levels and risk calculation for oral doses. The data presented here contribute to the basis for the future inclusion of this toxin in Brazilian legislation for drinking-water quality control, and for the development of analytical methods for this toxin
Dynamics of plankton and fish in a subtropical temporary wetland: Rice fields
(Academic Journals, 2011-05-18) Becker, Vanessa; Rodrigues, Lúcia Helena Ribeiro; Canterle, Eliete Bertazzo; Gazulha, Vanessa; Hamester, Ângela; Marques, David da Motta
Rice fields are temporary wetlands that harbor many of the same species that breed in natural temporary ponds. These systems have a complex limnology, characterized by rapid physical, chemical, and biological changes. The goal of this study was to evaluate the role of nutrients in the plankton and fish dynamics during a production cycle, based on the auto-ecology of the species related to their adaptations to environmental temporal changes in an irrigated rice field in Southern Brazil. The principal components analysis (PCA) indicated a temporal gradient driven by nutrient availability, grouping sampling periods according to the production cycle. ANOVA indicated temporal differences in the limnological variables during the development of the rice field production cycle. Linear regression showed a positive relationship between chlorophyll a, nutrients and biomass of small and medium filter-feeders. In contrast, planktivorous fish biomass was inversely related to chlorophyll a. This study showed both top down and bottom up processes simultaneously regulating the primary production in the rice field wetland along a temporal gradient the rice production cycle
Is phytoplankton functional classification a suitable tool to investigate spatial heterogeneity in a subtropical shallow lake?
(Elsevier BV, 2012-11-27) Becker, Vanessa; Crossetti, Luciane Oliveira; Cardoso, Luciana de Souza; Rodrigues, Lúcia Ribeiro; Costa, Luciana Silva da; Motta-Marques, David da
Functional groups of phytoplankton are widely recognized to vary in response to certain environmental variables, according to their niche preferences. The aim of this study was to evaluate the strength of the relationship between functional traits of phytoplankton and environmental predictors in a spatially heterogeneous large subtropical shallow lake (Mangueira Lake, southern Brazil), analyzing whether phytoplankton functional approach is a suitable tool to investigate spatial heterogeneity. Samples were taken twice a year (summer and winter), for six years (2001–2006) in the subsurface water at north, center and south sampling stations in that large system (90 km long). This biannual frequency enabled us to evaluate the seasonal and spatial changes of functional groups in relation to environmental variations, by means of ordination analysis (PCA and CCA). The integrated analysis of phytoplankton functional groups and abiotic variables evidenced clear and significant spatial and seasonal gradients (Monte Carlo test, p = 0.01). The seasonal gradient was related to temperature, water-level fluctuations and wind action, leading to spatial heterogeneity of the phytoplankton. The northern part of the lake proved to be dissimilar, with greater availability of soluble reactive phosphorus and higher biomass of phytoplankton. Functional groups related to turbid and mixed environments, such as MP, S1 and J were important. Hydrodynamics-related features were the driving forces for structuring the phytoplankton functional groups, which appropriately showed the main tendencies observed in this ecosystem, proving to be and adequate tool to access spatial heterogeneity
Balanço de Massa de Fósforo Total e o Estado Trófico em Reservatórios do Semiárido Brasileiro
(Associação Brasileira de Recursos Hídricos, 2014-04) Becker, Vanessa; Bezerra, Anderson Felipe de Medeiros; Mattos, Arthur
O aumento do impacto antrópico sobre os ecossistemas aquáticos vem acelerando o processo de eutrofização, comprometendo os usos múltiplos de água dos lagos e reservatórios no Brasil e no mundo. Este fato faz parte da realidade dos reservatórios do semiárido do Estado do Rio Grande do Norte. O objetivo deste trabalho foi realizar o balanço de massa de fósforo durante um ciclo hidrológico e compreender a relação com o estado trófico em dois reservatórios tropicais localizados na região do semiárido do Rio Grande do Norte. Foram realizadas amostragens mensais, durante o período de seca (de junho a dezembro de 2010) e o período chuvoso (de janeiro a março de 2011). Em cada reservatório foram amostrados 3 pontos ao longo do eixo longitudinal, além dos rios contribuintes e da água de chuva durante o período chuvoso. As cargas de fósforo total e sólidos suspensos, recebidas pelos reservatórios através dos rios afluentes foram elevadas. Os afluentes podem estar atuando na manutenção do estado trófico dos reservatórios, e estes, como acumuladores de sólidos e nutrientes da bacia de drenagem, o que se relaciona com o uso e ocupação na área da bacia e com a qualidade da água
Diel dynamic of phytoplankton functional groups in a tropical water supply, Extremoz Lake, northeastern Brazil
(Associação Brasileira de Limnologia, 2014-10) Becker, Vanessa; Pinto, Thársia da Silva
Aim: This study analyzed - the diel and vertical dynamics of phytoplankton functional groups in a natural tropical lake (Extremoz Lake, northeast Brazil), to investigate and understand the driver factors of the community during a severe drought period. Methods: Sampling of the abiotic variables and phytoplankton was performed at intervals of 6 hours over 24 hours in vertical profiles, in dry and rainy seasons (according to the historical average). The phytoplankton species were grouped according to the functional groups’ approach sensu Reynolds et al. (2002). Results: October/12 was considered as a dry period (18.4 mm), while March/13, due to the historical average, as a rainy season, due to the low rainfall during the study period (15.7 mm), it was called severe drought. The lake showed thermal and chemical destratification in both periods. Phytoplankton biomass was higher in the dry season and their vertical distribution was stratified in both periods. In both samplings there were less algal biomass during the night. Phytoplankton functional groups of mixed and shallow systems (S1, L0 and K) were descriptors throughout the study period with higher biomass always registered in the group S1, represented by Planktolyngbya limnetica (Cyanobacteria) Conclusion: The lack of seasonality observed in this study, due to prolonged drought, may have influenced the pattern of homogeneous behavior in both samplings. This pattern strongly influenced the vertical distribution of phytoplankton in the two periods, with a constancy of dominance of functional descriptors groups
Is the future blue-green or brown? The effects of extreme events on phytoplankton dynamics in a semi-arid man-made lake
(Springer, 2015-06-03) Becker, Vanessa; Medeiros, Luciana de Castro; Mattos, Arthur; Lurling, Miquel
In arid and semi-arid regions, a hydrological regime characterized by an annual cycle of drought and rainy seasons changes the volume and retention time of reservoirs. Such changes affect the limnological characteristics and lead to changes on phytoplankton community. Phytoplankton seasonal succession was studied in a Brazilian eutrophic semiarid water supply reservoir (Cruzeta). In this study, the changes in the biomass and species composition of phytoplankton during two annual hydrological cycles were analyzed, and the driving factors were evaluated.The composition of phytoplankton alternated between filamentous cyanobacteria, such as Cylindrospermopsis raciborskii, under conditions of mixing, and colonial species, such as Microcystis panniformis and Sphaerocavum brasiliensis, under conditions of high water column stability. The lower water level during a severe drought favored adaptive phytoplankton species with low requirement for resources, such as diatoms and cryptomonads. Extreme events, i.e., torrential rains and severe droughts, governed by the hydrological regime of the semi-arid region led to strong altered availability of resources in the watershed, directing the spatial and temporal dynamics of the phytoplankton in the Cruzeta man-made lake. The results showed an unusual behavior of the phytoplankton community contradicting the expectations about the climatic change scenario. Instead of an expected increase in cyanobacteria, the severe drought led to low biomass and resources, favoring diatoms and cryptomonads
Influence of extended drought on water quality in tropical reservoirs in a semiarid region
(Associação Brasileira de Limnologia, 2015-06-03) Becker, Vanessa; Braga, Gustavo Girão; Oliveira, José Neuciano Pinheiro de; Mendonça Junior, Jurandir Rodrigues de; Bezerra, Anderson Felipe de Medeiros; Torres, Laíssa Macêdo; Galvão, Ângela Marília Freitas; Mattos, Arthur
Aim: Drought periods often occur in Brazilian semiarid region and are supposed to induce water quality degradation by changes in physical, chemical and biological properties of freshwater ecosystems. Reservoirs in this region are used as drinking-water supplies and are exposed to wide volume fluctuations during drought periods due to lack of precipitation and high evaporation rates. This study aimed to identify patterns on water quality of two reservoirs during a long drought period. It was expected that more arid and shallower conditions would favor algal growth by enhancing nutrient availability, causing a decrease on water quality. Methods: The study was based on monthly sampling over 20 months (May 2011 to December 2012) at two tropical reservoirs on Brazilian semiarid region. Precipitation and volume data were obtained from environmental agencies. Transparency was measured on field using a Secchi disk and conductivity, nutrients, suspended solids and chlorophyll-a were analyzed on laboratory. Temporal changes in all environmental variables were analyzed in each reservoir using two-way cluster analysis and also principal component analysis (PCA). Results: The volume of both reservoirs decreased considerably over the study because of low or shortage of precipitation. It was possible to detect two opposite patterns of chlorophyll-a in each reservoir throughout the drought season: in the first one phytoplankton growth was favored, while in the second one chlorophyll-a decreased by high inorganic turbidity. Both reservoirs tended to increase their turbidity and conductivity during the drought period due to shallow conditions, which probably contributed to sediment resuspension. Conclusions: Water level reduction during the extended drought period, contributed for water quality degradation due to high algal biomass and also high turbidity found during drought period. Local factors, as the nature of suspended solids, play an important role on predicting water quality
Effects of water level reduction on the dynamics of phytoplankton functional groups in tropical semi-arid shallow lakes
(Springer, 2015-12-15) Becker, Vanessa; Costa, Mariana Rodrigues Amaral da; Attayde, José Luiz
Droughts are large-scale perturbations that affect freshwater ecosystems worldwide. A water level reduction caused by drought is an important driving factor of phytoplankton dynamics. It has been suggested that a water level reduction alters the light and mixing regime and increases nutrient concentrations and phytoplankton biomass favoring cyanobacterial blooms. We took advantage of two exceptionally dry years in the Brazilian semi-arid region to investigate the effects of the water level reduction on the water quality and phytoplankton communities of two shallow man-made lakes. In both lakes, the water level was reduced by half, while the water turbidity, conductivity, and nutrient concentrations increased.In the deeper lake, the phytoplankton biomass increased and was dominated by a cyanobacteria group as expected, but it decreased in the shallower lake and was dominated by mixotrophic flagellate groups. This was because of sediment resuspension by wind and fish facilitated by a water level reduction and increased the water turbidity more strongly in the shallower than in the deeper lake. Therefore, a water level reduction caused by a drought may either increase or decrease the phytoplankton biomass and cyanobacteria dominance in tropical shallow lakes depending on the lake depth and the concentration of inorganic suspended sediments

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