Abstract
Reis Lake is located in the municipality of Caracaraí, state of Roraima (Brazil) and is subject to fluctuations in water level. The aim of this study was to analyze the structure of the phytoplankton community on the nictemeral and seasonal scales and determined the influence of limnological variables. Sampling was performed in the rainy season (June/2006) and dry season (November/2006), considering two nictemeral cycles. The phytoplankton community was assessed with regard to composition and density, abiotic variables were analyzed simultaneously. The lake had low concentrations of oxygen, clinograde profile and water stratified during the day and homogenous at night, with low concentrations of nutrients and waters ranging from slightly acidic to alkaline. The phytoplankton was represented by 43 taxa, 35 species in the dry season and 29 species in the rainy season. Low densities of phytoplankton occurred in both nictemeral cycles, with accentuated vertical gradient. The highest densities were recorded in the dry season. Reis Lake exhibits characteristics that classify it as a polymythic and oligotrophic environment. The variability in the data was more important seasonally than on the nictemeral scale, supporting the hypothesis of the influence of the hydrological cycle on the dynamics of phytoplankton communities in floodplain lakes.
Highlights
Brazilian Amazon has a hydrographic basin with a large variety of aquatic systems distinguished by their combination of physical, chemical and biological characteristics
Based on the hypothesis that spatial and temporal patterns of phytoplankton in floodplain lakes are influenced by fluctuations in abiotic variables as a result of variation in the water level in these environments, this study aimed to characterize a lake ecosystem of the floodplain of the Branco River, in the Brazilian Amazon, with regard to the composition and dynamics of the phytoplankton community and the influence of environmental variables on this community during the period of high waters and low waters
The minimum value was found during the dry season (Zmax 1.8 m) and the maximum value occurred during the rainy season (Zmax 8.0 m)
Summary
Brazilian Amazon has a hydrographic basin with a large variety of aquatic systems distinguished by their combination of physical, chemical and biological characteristics. Some lakes located in depressions of the Boa Vista Formation are generally small and isolated from large and medium-sized rivers (Silva et al 2010). In these areas, lakes generally have clear waters that may. The area drained by the Branco River basin creates numerous lakes that are characterized by remaining connected to the river during the flood period and becoming isolated in the dry season. These lakes are used by the surrounding population, mainly for fishing or for recreation. Hydrographic and hydrological characteristics are suggested as being the factors that determine the behavior of the phytoplankton of these lakes
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