Phytoplankton community of Reis lake in the Brazilian Amazon

Abstract

<p id="para1">Reis Lake is located in the municipality of Caracara&#237;, 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.</p><br><p id="para2">O lago dos Reis est&#225; localizado no munic&#237;pio de Caracara&#237;, no estado de Roraima (Brasil) e est&#225; sujeito a flutua&#231;&#245;es no n&#237;vel da &#225;gua. O objetivo do estudo foi analisar a estrutura da comunidade fitoplanct&#244;nica nas escalas nictemeral e sazonal e determinar a influ&#234;ncia de vari&#225;veis limnol&#243;gicas nesta comunidade. As amostragens foram realizadas nos periodos chuvoso e seco, considerando dois ciclos nictemeral. A comunidade fitoplanct&#244;nica foi avaliada no que diz respeito &#224; composi&#231;&#227;o e densidade, simultaneamente, vari&#225;veis abi&#243;ticas foram analisadas. O lago apresentou baixas concentra&#231;&#245;es de oxig&#234;nio, perfil clinogrado, coluna d' &#225;gua estratificada durante o dia e homog&#234;nea &#224; noite, com baixas concentra&#231;&#245;es de nutrientes e pH variarando de levemente &#225;cido a alcalino. Baixas densidades fitoplanct&#244;nicas ocorreram em ambos os ciclos nictemeral, com um gradiente vertical acentuado. As maiores densidades foram registradas durante a esta&#231;&#227;o seca e a menor foi registrada durante a esta&#231;&#227;o chuvosa. Lago dos Reis apresenta caracter&#237;sticas que o classificam como um ambiente polim&#237;tico e oligotr&#243;fico. A variabilidade dos dados foi mais importante sazonalmente do que na escala nictemeral, refor&#231;ando a hip&#243;tese da influ&#234;ncia do ciclo hidrol&#243;gico sobre a din&#226;mica das comunidades fitoplanct&#244;nicas em lagos de v&#225;rzea.</p