Phytoplankton seasonal and vertical variations in a tropical shallow reservoir with abundant macrophytes (Ninféias Pond,Brazil) |
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Authors: | Bárbara M Fonseca Carlos E de Mattos Bicudo |
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Institution: | 1.Universidade Católica de Brasília, Curso de Ciências Biológicas (Sala E-10),Brasília,Brazil;2.Instituto de Botanica, Núcleo de Pesquisa em Ecologia,S?o Paulo,Brazil |
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Abstract: | This study aimed at analyzing the environmental factors which determine the structure and dynamic of phytoplankton in a shallow
reservoir with abundant macrophyte flora, Ninféias Pond (Brazil). It is hypothesized that, although its shallowness, periodic
stratifications play an important role on its phytoplankton community. Water samples were collected monthly, from January
to December 1997, in four depths (sub-surface, 1 m, 2 m, and bottom) of pelagic zone (Z
max = 3.6 m). Community seasonal and vertical variations followed a hot-rainy season with water column stratification (phase
1; Q index: medium), alternating with a cool-dry season with water column mixing (phase 2: Q index: excellent). Nanoplanktonic flagellates dominated, mainly mixotrophic species. During phase 1, Chlamydomonas sp. (G) was the main species, dominating at the anoxic and nutrient-rich hypolimnion. At the same time, richness and diversity were
relatively lower. During phase 2, lower water temperatures and higher dissolved oxygen concentrations favoured the prymnesiophyte
Chrysochromulina cf. breviturrita (X2). Sequence of functional groups over phases 1 and 2 was: phase 1 = G → transition = Y/P/E/D/F/W2/X3 → phase 2 = X2/Lo/X1; most of these groups have been associated to oligo-mesotrophic systems. Seasonal stratifications played a decisive role
in determining the structure and dynamic of phytoplankton in the Ninféias Pond. However, in such a complex and heterogeneous
system, other compartments of the food web (macrophytes, zooplankton, fishes) may also act as relevant driving forces, in
synergy with the physical and chemical environment. |
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