Variação espacial e temporal da comunidade fitoplanctônica da Lagoa Bonita, DF

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

The Distrito Federal has few natural lagoons. Between them distinguishes the Lagoa Bonita located in Estação Ecológica de Águas Emendadas (15 32 to 15 38 S and 47 33 to 47 37 W). The objective of this work was to analyse the structure and dynamics of the phytoplankton community of Lagoa Bonita considering its spatial and temporal variation. The phytoplankton community was investigated in three sample stations, two in the littoral zone (1 and 2) and one in the pelagic zone (3), between April/2005 and March/2006. The following physical and chemical variables were analysed: water temperature, pH, electrical conductivity, dissolved oxygen, depth, as well total Nitrogen and Phosphorus and dissolved Phosphorus. After phytoplankton counting through Utermöhl method, the celular volume was calculated from cell dimensions of each species taking into comparison their forms with geometric solids, isolated and in combination. The water of Lagoa Bonita showed acid pH in all sampled points, varying from 5.1 (July/2005, point 1) and 6.9 (April/2005, point 3). The electrical conductivity varied from 3.1 μS.cm-1 (August/2005, point 3) to 12.8 μS.cm-1 (October/2005, point 1), with values up the highest average registered through the whole study period : 5.2 2.1 μS.cm-1 (point 1). The dissolved oxygen concentrations varied from 4.4 mg.L-1 April/2005, point 2) to 9.1 mg.L-1 (May/2005, point 2). The Total Nitrogen (TN) showed highest concentrations (0.235 mg.L-1 in point 2 to 0.757 mg.L-1 in point 1), with no significant difference among the three sampled points (ANOVA, P = 0.073). Total phosphorus (TP) varied from values under the limit of the detection method (<0.002 mg.L-1 in points 2 and 3), to 0.066 mg.L-1 in point 1, with no significant differences among points (ANOVA, P = 0,394). The Principal Component Analysis (PCA) indicated low sazonal variation of physical and chemical data during the study period. The total of 121 taxa were registered, distributed into eight classes: Zygnemaphyceae (69%), Chlorophyceae (11%), Bacillariophyceae (10%), Cyanophyceae (5%), Dinophyceae (2%), Chrysophyceae (1%), Cryptophyceae (1%) and Xanthophyceae (1%). The maximum algal density occurred in the rainy period of 2005 with higher values in both litoral zones 1 (2365 ind.mL-1 in November) and 3 (2235 ind.mL-1 in October). The biovolume was higher in points 1 and 3: 11.4 7.2 mm3.L-1 e 11.0 17.5 mm3.L-1, respectively. In the pelagic region it varied uniformelly through the investigated months (2.6 1.5 mm3.L-1), never up to 6.0 mm3.L-1. The species that contributed with 5% of the total biovolume of each sampled unit were represented by seven functional groups, according to sensu Reynolds (N, P, Lo, T, A, F, J). During the investigation period Zygnemaphyceae functional groups predominated (N e P), with the abundance of the algae Actnotaenium wollei and dinoflagelates (Lo, Peridinium umbonatum). The predominant functional groups were according to the aquatic environmental conditions: low nutrient concentrations, mainly phosphorus, acid pH, low ionic concentrations and low biomass, due to the lagoon shalowness, with favor water circulation. Total water transparency and abundant subaquatic macrophyte also contributed to the phytoplankton dynamics of Lagoa Bonita.

ASSUNTO(S)

lagoa tropical rasa functional groups grupos funcionais oligotrophic lake fitoplâncton phytoplankton distrito federal distrito federal ecologia shallow tropical lake lagoa oligotrófica

ACESSO AO ARTIGO

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