Phytoplanktonic Structure and Chemistry of the Water in the Monjolinho Reservoir (SP, Brazil) During a Cyanobacterial Bloom Episode

The composition of the phytoplankton and parameters of the water quality were studied in a tropical reservoir during cyanobacterial bloom episode. Samples were collected at two sites during October 2004. The phytoplankton community consisted of 69 taxa, distributed into 9 classes. Most taxa belonged to Cyanobacteria (17), Chlorophyceae (21), Bacillariophyceae (8), Conjugatophyceae (7), Dinophyceae (1), Chrysophyceae (4), Euglenophyceae (9), Cryptophyceae (1) and Xanthophyceae (1). Anabaena circinalis Rabenhorst ex Bornet et Flahault e Anabaena spiroides Klebahn were the dominant species. Statistical analyses revealed significant spatial variation (p < 0.05) between sampling points only for N compounds and chlorophyll a. Most limnological variables analyzed showed no significant temporal variation (p > 0.05). Cyanobacteria bloom was concomitant with the following environmental conditions, warm water temperatures (19 to 22 oC), periods of water column stability and high concentrations of N (724.9 μg.L-1) and P (90.9 μg.L-1) in the reservoir and NH4 as being the predominant nitrogen compounds. It is speculated that those conditions could play a role in the dominance of cyanobacteria

Structure of the phytoplankton in a water supply system in the State of Pernambuco - Brazil

The aim of this work was to study the phytoplankton community composition at limnetic environment in Pernambuco, Brazil. Samplings were carried out from April/2001 to March/2002. Samples to analyses the biotic variables were taken using a recipient with a large overture, at the subsurface and with a Van Dorn bottle at the bottom. The rainfall data were recorded and the water transparency was used to calculate the light attenuation coefficient, photic zone and the determination of trophic state index. The concentrations of total phosphorus and total nitrogen were determined in a typical dry and rainy month. Equitability, also the, similarity and diversity indexes and the densities and correlation of total densities among depths were calculated. Forty-five taxa were identified in Chlorophyta (21spp), Cyanophyta (17spp) and Bacillariophyta (7spp), while flagellates were quantified in groups without identification. Cyanophyta presented highest diversity at both the depths and Planktothrix agardhii was the highest density species. Significant differences were not observed between subsurface and bottom densities. Results showed that the reservoir was eutrophicated and presented high densities of Cyanophyta.<br>O objetivo deste trabalho foi o estudo da comunidade fitoplanctônica em ambiente limnético de Pernambuco, Brasil. As amostras foram coletadas de abril/2001 a março/2002. As amostras para análises abióticas foram coletadas na superfície da água e destinadas às análises bióticas foram coletadas na subsuperfície e no fundo, sendo fixadas com solução de lugol e quantificadas usando microscópio invertido. Equitatividade, índices de similaridade e diversidade foram calculados, bem como correlação entre as profundidades. 45 táxons foram identificados, pertencentes as Chlorophyta (21spp), Cyanophyta (17spp) e Bacillariophyta (7spp). Os flagelados foram apenas quantificados, mas não foram identificados. Cyanophyta apresentou a mais alta diversidade em ambas as profundidades e Planktothrix agardhii foi a espécie que apresentou a maior densidade. Diferenças significativas quanto às densidades não foram observadas entre subsuperfície e fundo. O reservatório encontra-se eutrofizado, sendo encontradas altas densidades de Cyanophyta durante todo o período de estudo

Limnological characteristics and seasonal changes in density and diversity of the phytoplanktonic community at the Caçó pond, Maranhão State, Brazil

Seasonal changes of the phytoplanktonic community and limnological abiotic characteristics of Caçó pond (Maranhão State, Brazil) was evaluated from two field researches during the rainy (April 1999) and dry (November 1999) seasons. Measurements of twelve chemical and physical variables and phytoplankton collections were carried out at eight sampling stations. The Chlorophyceae and Cyanobacteria groups were in highest fractions during the rainy and dry seasons, respectively. The limnological abiotic variables showed a homogenous spatial distribution. The cluster analysis, using Bray-Curtis distance, distinguished two major groups, represented by the most common and abundant species in both the periods. The results showed that the climate regime, due to the seasonal changes in pluviosity, was a determinant over the phytoplanktonic community structure at Caçó pond.<br>Mudanças sazonais na comunidade fitoplanctônica e nas características limnológicas abióticas da lagoa do Caçó, Estado do Maranhão, Brasil, foram avaliadas a partir de duas coletas, nos períodos de chuva (Abril/1999) e seca (Novembro/1999). Medidas de quatorze variáveis físicas e químicas e coletas do fitoplâncton foram realizadas em oito estações de amostragem. Quantitativamente, os grupos Chlorophyceae e Cyanobacteria apresentaram maior contribuição nos períodos de chuva e seca, respectivamente. As variáveis limnológicas abióticas mostraram uma distribuição espacial homogênea em relação aos dois períodos amostrados. A análise de agrupamento a partir da distância de Bray-Curtis para comunidade fitoplanctônica distinguiu dois grandes grupos (estação seca e chuvosa), representados pelas espécies mais comuns e abundantes em ambos períodos. Os resultados deste estudo permitiram concluir que o regime climatológico foi determinante sobre a dinâmica e a estrutura da comunidade fitoplanctônica da lagoa do Caçó