Maria Rosélia Marques Lopes

Short term spatial and temporal variation of phytoplankton in a shallow tropical oligotrophic reservoir, southeast Brazil

Locally called IAG pond, system is a small, oligotrophic, shallow, urban reservoir located in the Parque Estadual das Fontes do Ipiranga Biological Reserve, south of Sao Paulo municipality, southeastern Brazil. Study was carried out in two phases to cover the two climatic periods (dry and rainy) that characterize the area. Daily samples were collected on seven consecutive days (dry = 20–26 August 1996; rainy = 22–28 January 1997), three times a day (07:00 h, 13:00 h, and 19:00 h), following the water column vertical profile at reservoir’s deepest site (Zmax = 4.7 m). The phytoplankton’s community structure’s diurnal variation was compared with environmental variables (thermal structure of the water column, pH, CO2, dissolved oxygen, total phosphorus, and NH4). Analysis of variance (ANOVA) showed significant variation among sampling hours and days but not among depths for most species, thus revealing a tendency towards a homogeneous vertical distribution of phytoplankton in the reservoir. Canonical Correspondence Analysis (CCA) showed a significant relationship between distribution of phytoplankton species and environmental variables used for ordination. Water temperature was the environmental variable that best explained distribution of sample units. Atelomixis was the only possible explanation for how a non-motile alga as, for example, the chlorococcal Oocystis lacustris Chodat and the diatom Cyclotella stelligera Cleve & Grunow, can be so widespread and abundant in the IAG pond during the stratified period.

Desmidioflórula de um Lago da Planície de Inundação do Rio Acre, Estado do Amazonas, Brasil

This paper presents a taxonomic survey of the desmid flora of a marginal oxbowl lake on the River Acre - Lago Novo Andira (AM), northern Brazil. The study is based on 52 samples collected over 13 consecutive months (May 1988 to June 1989). Ninety-eight taxa of desmids were identified and described, classified in 10 genera and 3 families. Of the 98 taxa, 38 are variation of the corresponding typical forma. The genera Cosmarium, Closterium and Staurastrum were qualitatively the best-represented in the lake, with 29, 19, and 16 species respectively. The least represented were Gonatozygon, Octacanthium, and Xanthidium, each one with a single species. Geographical distribution was based on all data in the literature published up to December 1998 including publications in which there are morphological descriptions and/ or illustrations of the algae, as well as those in which mere check lists were considered. Taxonomic problems involved were directly related to the morphological variation observed within the populations, and the genera Staurastrum displayed the greatest number of taxonomic difficulties in conflict with data in the literature. Morphological variation observed at population level made the infraspecific identification of Euastrum verrucosum Ehrenberg ex Ralfs impossible.

Structural and successional variability of periphytic algal community in a Amazonian lake during the dry and rainy season (Rio Branco, Acre)

The colonization process and successional patterns of a periphytic algal community were evaluated in a Amazonian Viveiro Lake (Rio Branco, Acre, Brazil). Sampling was performed over a period of 35 days; at four-day intervals for 20 days, and then at five-day intervals. Water sampling for physical, chemical and biological analyses was done during the dry and rainy season. Glass slides were used as artificial substrates for periphyton colonization. The structural community was evaluated through population density, algae class, diversity indices and descriptive species. Species richness, diversity and evenness increased as succession progressed. While density of Bacillariophyceae, Euglenophyceae and Zygnemaphyceae increased with succession, Cyanobacteria remained dominant. Synechocystis aquatilis, Synechocystis diplococcus and Navicula pseudolanceolata were the main descriptive species in both the dry and rainy season. Cymbela tumida, Frustulia rhomboides, Trachelomonas lacustris and Closterium acicularis was correlated with an increase in hydrologic level during the rainy season. Conversely, the density of Chlamydomonas sp., Chroomonas nordstedtii, Trachelomonas volvocinopsis, Trachelomonas volvocina and Synechococcus linearis was correlated with an increase in water transparency during the dry season. In general, the periphytic algal community showed high diversity and species richness independent of season. Season also had little influence on representation of algae class and main descriptive species. However, successional patterns varied by season, and changes in hydrologic levels acted directly on the succession path of periphytic algae. More research on periphyton dynamics is needed to improve our understanding of tropical lake ecosystems, especially in Amazonian.

Diel responses of phytoplankton of an Amazon floodplain lake at the two main hydrological phases

OBJETIVO: O objetivo deste estudo foi avaliar mudancas em curto prazo da comunidade fitoplanctonica em um lago da planicie de inundacao do Rio Acre, Amazonia, Brasil. METODOS: As amostras foram coletadas com garrafa de Van Dorn, em tres profundidades (superficie, meio e fundo), durante as estacoes climaticas (seca e chuvosa), durante sete dias consecutivos, em dois horarios, manha e noite. RESULTADOS: A comunidade fitoplanctonica foi representada por 198 taxons e a classe Euglenophyceae foi a mais bem representada em ambos os periodos. Ocorreram mudancas abruptas na comunidade durante a estacao chuvosa (potamofase). Durante este periodo, em condicoes de atelomixia parcial, foram registrados os mais elevados valores de biovolume do fitoplâncton e dominância de Gonyostomum semen (Ehr.) Dies. (Raphidophyceae). CONCLUSOES: No periodo seco (limnophase), as condicoes do lago foram mais estaveis, a diversidade e a taxa de mudanca da comunidade foi mais baixa, e os frequentes periodos de estratificacao e mistura foram responsaveis pela dominância de Geitlerinema sp. (Cyanobacteria).