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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Phytoplankton seasonal variation in a shallow stratified eutrophic reservoir (Garcas Pond, Brazil)
Auteurs :	Barbara M. Fonseca, Auteur ; Carlos E. de M. Bicudo, Auteur
Type de document :	Article
Dans :	Hydrobiologia (600 MAR 2008)
Article en page(s) :	267-282
Résumé :	This study aimed at describing the phytoplankton dynamics and structure in a shallow eutrophic reservoir, the Garcas Pond, located in the Parque Estadual das Fontes do Ipiranga (23 degrees 38'40.6 '' S, 46 degrees 37'28.0 '' W), in the Municipality of Sauo Paulo, southeast Brazil. Samples were collected monthly from January to December 1997 in five depths (subsurface, 1 m, 2 m, 3 m, and 20 cm above the bottom) in the pelagic zone (Z(max) = 4.7 m). Abiotic variables studied were: water temperature, turbidity, transparency, conductivity, pH, dissolved oxygen, alkalinity, inorganic carbon, and N and P dissolved and total forms. Altogether 236 phytoplankton taxa distributed among 10 classes were identified. Phytoplankton seasonal and vertical variation was related to shifts in the water chemical features as a consequence of a warm-wet season with stratified water column (phase 1, January-March and September-December) alternating with a cool-dry season with mixed water column (phase 2, April-August). There were shifts in cyanobacterial dominance over the entire year. During phase 1, Raphidiopsis/Cylindrospermopsis was one of the most important taxon. During phase 2, Raphidiopsis/Cylindrospermopsis biomass decreased, whereas richness and diversity increased and diatoms were relatively abundant. In September, when the water column was markedly stratified, a cyanobacterial bloom (Sphaerocavum brasiliense) occurred. Changes in water chemical variables caused by the bloom allowed recognition of a phase 3, in which pH and chlorophyll a, TP and CO32- concentration reached their highest values. According to Reynolds and collaborators' functional groups approach, phase 1 was marked by groups S/W1/W2/H1/Y, phase 2 by groups K/L-M/L-O/D/P/X1/F, and phase 3 by group M. This sequence was corroborated by canonical correspondence analysis (CCA) results.

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