Efeitos de distúrbios artificiais sobre o zooplâncton de açudes
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2020-02-17
Autores
Alves, Michael César
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Universidade Estadual Paulista (Unesp)
Resumo
A diversidade aquática está sendo drasticamente alterada pelo rápido aumento das atividades antrópicas, e uma das modificações mais comuns é a construção de reservatórios e açudes. Diversas espécies do zooplâncton exibem alta sensibilidade frente a mudanças ambientais, respondendo rapidamente com alterações nos atributos ecológicos como abundância e diversidade. Este estudo objetivou entender os efeitos causados pela ativação de pivôs de irrigação em 02 açudes sobre as assembleias de microcrustáceos (Cladocera e Copepoda). O uso da água pelos pivôs no período de estiagem ocasiona rebaixamento no nível da água, funcionando como um distúrbio induzido e frequente, e isso controla o tamanho de bancos de macrófitas submersas. Foram feitas coletas mensais nos dois açudes por um ano e a cada 05 dias no período de estiagem (julho) quando se detectou o rebaixamento o segundo lago. Os lagos foram homogêneos possivelmente pelos seus pequenos tamanhos comparados aos grandes reservatórios, e a variação sazonal foi mais importante para as variações das variáveis limnológicas. A composição do zooplâncton, a abundância de alguns táxons, a diversidade alfa com índice de Shannon-Wienner (H’) e a equitabilidade foram diferentes entre os lagos, sendo maiores no Lago 1, o com menor oscilação de nível da água, densos bancos de macrófitas submersas e pequena região pelágica (pouca coluna de água livre), embora seja levemente mais profundo que o Lago 2. Durante o rebaixamento, bastante intenso no Lago 2, houve redução da riqueza de espécies, da abundância total e da dominância, porém a diversidade alfa H’ se manteve estável, indicando a permanência das espécies raras, possivelmente refugiadas nas macrófitas submersas existentes em área reduzida no fundo do lago, controladas pelos rebaixamentos de nível recorrentes, e também ao abastecimento de água vindo dos lagos à montante. A presença das macrófitas seleciona a abundância e dominância de espécies litorâneas e planctônicas. Embora o distúrbio ocasione redução de diversidade e abundância, a recomposição é rápida, possivelmente atribuída a sistemas pequenos e conectados que fornecem novos indivíduos e ao refúgio oferecido pelos bancos de macrófitas.
Aquatic diversity is being drastically altered by the rapid increase in anthropogenic activities, and one of the most common modifications is the construction of reservoir and weirs. Several zooplankton species exhibit high sensitivity to environmental changes, responding rapidly with changes in ecological attributes. This project aimed to understand the effects caused by the activation of irrigation pivots in 02 weirs on the assemblages of micro crustaceans (Cladocera and Copepoda). The use of water by pivots during the drought period causes a drop in water level, functioning as a frequent and induced disturbance, and this controls the size of submerged macrophyte banks. Monthly collections were made in both dams and every 05 days during the dry season (July) when the lowering of the second lake was detected. The lakes were homogeneous possibly due to their small size compared to the large reservoirs, and seasonal variation was more important for variations of limnological variables. Zooplankton composition, abundance of some taxa, alpha diversity with Shannon-Wienner index (H') and equitability were different between lakes, being higher in Lake 1, the one with the lowest water level oscillation, dense banks of submerged macrophytes and small pelagic region (little column of free water), although slightly deeper than Lake 2. During the demotion, quite intense in Lake 2, there was a reduction in species richness, total abundance and dominance, but alpha H 'diversity remained stable, indicating the permanence of the rare species, possibly refugees in the submerged macrophytes in a reduced area at the bottom of the lake, controlled by recurrent downgrades, and also the supply of water from upstream lakes. The presence of macrophytes selects the abundance and dominance of coastal and planktonic species. Although the disturbance causes a reduction in diversity and abundance, recomposition is rapid, possibly attributed to small, connected systems that provide individuals and the refuge offered by macrophyte banks
Aquatic diversity is being drastically altered by the rapid increase in anthropogenic activities, and one of the most common modifications is the construction of reservoir and weirs. Several zooplankton species exhibit high sensitivity to environmental changes, responding rapidly with changes in ecological attributes. This project aimed to understand the effects caused by the activation of irrigation pivots in 02 weirs on the assemblages of micro crustaceans (Cladocera and Copepoda). The use of water by pivots during the drought period causes a drop in water level, functioning as a frequent and induced disturbance, and this controls the size of submerged macrophyte banks. Monthly collections were made in both dams and every 05 days during the dry season (July) when the lowering of the second lake was detected. The lakes were homogeneous possibly due to their small size compared to the large reservoirs, and seasonal variation was more important for variations of limnological variables. Zooplankton composition, abundance of some taxa, alpha diversity with Shannon-Wienner index (H') and equitability were different between lakes, being higher in Lake 1, the one with the lowest water level oscillation, dense banks of submerged macrophytes and small pelagic region (little column of free water), although slightly deeper than Lake 2. During the demotion, quite intense in Lake 2, there was a reduction in species richness, total abundance and dominance, but alpha H 'diversity remained stable, indicating the permanence of the rare species, possibly refugees in the submerged macrophytes in a reduced area at the bottom of the lake, controlled by recurrent downgrades, and also the supply of water from upstream lakes. The presence of macrophytes selects the abundance and dominance of coastal and planktonic species. Although the disturbance causes a reduction in diversity and abundance, recomposition is rapid, possibly attributed to small, connected systems that provide individuals and the refuge offered by macrophyte banks
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Copepoda, Cladocera, Agricultura, Impactos, Ecologia aquática, Rebaixamento artificial, Agriculture, Impacts, Aquatic ecology, Artificial drawdown