RESUMO -(Variação temporal da comunidade fitoplanctônica em curtos intervalos amostrais no reservatório de Mundaú, Nordeste brasileiro). O objetivo deste estudo foi detectar a influência dos fatores abióticos sobre a comunidade fitoplanctônica em um reservatório de abastecimento, em curtos intervalos amostrais. As amostras foram coletadas na subsuperfície (0,1 m) e fundo das regiões pelágica (8 m) e litorânea (2 m), durante dois períodos sazonais, estações seca e chuvosa. As variáveis abióticas analisadas foram: temperatura da água, oxigênio dissolvido, condutividade elétrica, sólidos totais dissolvidos, turbidez, pH, nitrogênio total, nitrito, nitrato, fósforo total, fósforo total dissolvido e ortofosfato. A biomassa fitoplanctônica foi determinada a partir de valores de biovolume. A influência das variáveis abióticas na dinâmica das espécies fitoplanctônicas foi determinada através da Análise de Correspondência Canônica. A biomassa algal variou de 1,17×10 4 a 9,21×10 4 µg.L -1 , sendo que as cianobactérias apresentaram valores de biomassa entre 1,07×10 4 e 8,21×10 4 µg.L -1 . A mais alta disponibilidade de fósforo, limitação de nitrogênio, pH alcalino e estabilidade térmica favoreceram florações de cianobactérias, especialmente durante o período seco. As diferenças entre os horários e as estações amostrais na distribuição da comunidade fitoplanctônica foram determinadas pelos valores de temperatura, pH, fósforo total e turbidez. As associações fitoplanctônicas que mais se destacaram foram do grupo funcional Sn, formado por Cylindrospermopsis raciborskii, que predominou no sistema em ambos períodos sazonais. Concluiu-se que o fitoplâncton apresentou uma forte influência das variáveis abióticas especialmente no estabelecimento de padrões sazonais de distribuição. Palavras-chave: Cylindrospermopsis raciborskii, eutrofização, nutrientes, reservatório de abastecimentoABSTRACT -(Temporal variation of the phytoplankton community at short sampling intervals in the Mundaú reservoir, Northeastern Brazil). The aim of this study was to determine how abiotic factors drive the phytoplankton community in a water supply reservoir within short sampling intervals. Samples were collected at the subsurface (0.1 m) and bottom of limnetic (8 m) and littoral (2 m) zones in both the dry and rainy seasons. The following abiotic variables were analyzed: water temperature, dissolved oxygen, electrical conductivity, total dissolved solids, turbidity, pH, total nitrogen, nitrite, nitrate, total phosphorus, total dissolved phosphorus and orthophosphate. Phytoplankton biomass was determined from biovolume values. The role abiotic variables play in the dynamics of phytoplankton species was determined by means of Canonical Correspondence Analysis. Algae biomass ranged from 1.17×10 4 to 9.21×10 4 µg.L -1 ; cyanobacteria had biomass values ranging from 1.07×10 4 to 8.21×10 4 µg.L -1 . High availability of phosphorous, nitrogen limitation, alkaline pH and thermal stability all favored cyanobacteria blooms, particularly during the dry season. Tem...
Cyanobacterial blooms are a frequent occurrence in northeastern Brazil and constitute a serious public health problem. Using the polymerase chain reaction (PCR) method, eleven environmental samples with cyanobacteria from seven reservoirs were used to determine the presence of the gene involved in microcystin biosynthesis (mcyB). Two sets of oligonucleotide primers were designed from the sequencing of Brazilian populations of microcystin producing cyanobacteria (mcyB-F/R and mcyB-F/R-A). The presence of the mcyB gene involved in microcystin biosynthesis was found in all samples, indicating the potential of this gene for producing the toxin. The PCR method proved sensitive and appropriate for the detection of potential producers of microcystins in environmental samples. Its ability to reveal potentially toxic cyanobacteria demonstrates that it can be a valuable tool in the monitoring of blooms.
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