Fitoplâncton em três lagoas marginais ao Rio Paranapanema e em sua desembocadura no Reservatório de Jurumirim (São Paulo, Brasil) durante um período prolongado de seca
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Data
2006-09-01
Autores
Henry, Raoul [UNESP]
Ushinohama, Érika [UNESP]
Ferreira, Rosa M.R. [UNESP]
Título da Revista
ISSN da Revista
Título de Volume
Editor
Sociedade Botânica de São Paulo
Resumo
Durante um período de desconexão (de outubro de 1999 a dezembro de 2000) entre lagoas laterais e o Rio Paranapanema, a estrutura da comunidade fitoplanctônica e suas alterações foram examinadas em amostras coletadas trimestralmente nas zonas litoral e pelágica. Um total de 183 táxons de algas foi encontrado, sendo a comunidade predominante constituída por Chlorophyceae e Bacillariophyceae no Rio Paranapanema e em um ambiente lacustre permanentemente isolado, e por Bacillariophyceae e Chlorophyceae em duas outras lagoas. Ao longo do ano, diminuição na riqueza de espécies foi encontrada somente no ambiente lêntico com maior perda de conectividade. Cryptophyceae foi abundante (densidades maior que a densidade média do fitoplâncton) nas três lagoas, zonas e épocas do ano, exceto na zona litoral da lagoa com maior perda de conectividade em novembro de 1999. No Rio Paranapanema, Cryptophyceae predominou em mês chuvoso (fevereiro), sendo os índices de diversidade mais elevados nos demais períodos. A seca severa acarretou redução significativa do volume e área de superfície das lagoas, uma delas, a lagoa isolada, sendo extinta no último período de amostragem. Somente, nesta última, um efeito de concentração na abundância do fitoplâncton foi evidente. O predomínio em densidade de Cryptomonas brasiliensis Castro, C. Bic. & D. Bic., Chroomonas spp. e Chlamydomonas spp. nas três lagoas foi atribuído às condições adversas para o desenvolvimento das demais algas. A baixa profundidade, a grande quantidade de sedimentos suspensos na água após episódios de ventos fortes e, em conseqüência, a extinção acentuada da luz, foram fatores limitantes para as algas não adaptadas a essas condições, a despeito das concentrações favoráveis de nutrientes. No Rio Paranapanema, as alterações temporais na estrutura da comunidade fitoplanctônica parecem estar associadas a flutuações de velocidade e fluxo de água bem como ao nível hidrológico.
During a disconnection period (from October 1999 to December 2000) between lateral lakes and the Paranapanema River, the temporal changes on structure of phytoplankton community were examined in samples collected every three months, at the littoral and pelagic zones. A total of 183 algae species was found, being the community predominantly constituted by Chlorophyceae and Bacillariophyceae in the Paranapanema River and in an unique continuously isolated lake; and by Bacillariophyceae and Chlorophyceae in the other two lakes. During the year, a decrease on species richness was only found in the lentic ecosystem with higher connectivity loss. The algae Cryptophyceae were abundant (density higher than mean abundance of phytoplankton) in the three lakes, at both zones and during all the year, except at the littoral zone of the lake with higher loss connectivity in November 1999. In the Paranapanema River, Cryptophyceae predominated during a rainy month (February), being the diversity indexes lower than in the other sampling periods. The severe drought conducted to a significant reduction of volume and surface area of the lakes and, one of them, the isolated lake, was completely extinct in the last study period. Only in this lentic ecosystem, a concentration effect on the abundance of phytoplankton was recorded. The predominance of Cryptomonas brasiliensis Castro, C. Bic. & D. Bic., Chroomonas spp. and Chlamydomonas spp., in the three lakes was attributed to the adverse conditions for the development of other algae. Low depth, great amount of sediments in water ressuspended after windy episodes and, in a consequence, high light extinction were the limiting factors for the algae unadapted to these conditions, despite the adequate nutrient contents. In the Paranapanema River, the temporal alterations on the structure of phytoplankton community appear to be linked to water velocity and flux together with hydrological level.
During a disconnection period (from October 1999 to December 2000) between lateral lakes and the Paranapanema River, the temporal changes on structure of phytoplankton community were examined in samples collected every three months, at the littoral and pelagic zones. A total of 183 algae species was found, being the community predominantly constituted by Chlorophyceae and Bacillariophyceae in the Paranapanema River and in an unique continuously isolated lake; and by Bacillariophyceae and Chlorophyceae in the other two lakes. During the year, a decrease on species richness was only found in the lentic ecosystem with higher connectivity loss. The algae Cryptophyceae were abundant (density higher than mean abundance of phytoplankton) in the three lakes, at both zones and during all the year, except at the littoral zone of the lake with higher loss connectivity in November 1999. In the Paranapanema River, Cryptophyceae predominated during a rainy month (February), being the diversity indexes lower than in the other sampling periods. The severe drought conducted to a significant reduction of volume and surface area of the lakes and, one of them, the isolated lake, was completely extinct in the last study period. Only in this lentic ecosystem, a concentration effect on the abundance of phytoplankton was recorded. The predominance of Cryptomonas brasiliensis Castro, C. Bic. & D. Bic., Chroomonas spp. and Chlamydomonas spp., in the three lakes was attributed to the adverse conditions for the development of other algae. Low depth, great amount of sediments in water ressuspended after windy episodes and, in a consequence, high light extinction were the limiting factors for the algae unadapted to these conditions, despite the adequate nutrient contents. In the Paranapanema River, the temporal alterations on the structure of phytoplankton community appear to be linked to water velocity and flux together with hydrological level.
Descrição
Palavras-chave
composição, conectividade, fitoplâncton, seca, composition, connectivity, drought, phytoplankton
Como citar
Brazilian Journal of Botany. Sociedade Botânica de São Paulo, v. 29, n. 3, p. 399-414, 2006.