Estrutura e dinâmica da comunidade fitoplanctônica em um reservatório paraense

Abstract

The present study had as objective to characterize the phytoplankton community of the reservoir of the Tucuruí Hydroelectric Plant, since these water bodies are constructions for various exploratory purposes such as public water supply, aquaculture, leisure and power generation. The biological samples were collected in seven georeferenced points, four upstream and three in the lake region along the reservoir, in two seasonal periods (rainy and not rainy) in the months of March, June, September and December of 2011, and March and June 2012 in horizontal trawls in the subsurface of the water during five minutes, using conical plankton and cylindrical mesh (20μm opening mesh). In real time, physical and chemical parameters (temperature, pH and dissolved oxygen) were recorded on the surface of the water, which were within the normal range for the Amazon region. A total of 86 species were identified, distributed in 29 genera, 18 families and eight classes. In relation to the composition and distribution of the phytoplankton community, Zignematophyceae Chlorophyceae were the most representative groups, as well as the most abundant ones. Regarding the frequency of occurrence, the values followed the same pattern of relative abundance, presenting very frequent species (100% occurrence) according to the most abundant groups. The phytoplankton density was higher in the months of lower rainfall, due to the increase of the euphotic zone and consequent increase of the phytoplankton density. The diversity and equitability indices did not show different values between sample points and the study period. Species richness presented values below that expected by Jacknife 1 and Jacknife 2 demonstrating that the occurrence of species did not reach the desired asymptote for the study area. In general, the floristic composition, relative abundance, frequency of occurrence, density, diversity, equitability and species richness in the reservoir of the Tucuruí Hydroelectric Plant suggest that the river dynamics is still able to disperse pollutants from anthropic actions, ecosystem remains in good condition for the aquatic community and public use.