Plankton relationships under small water level fluctuations in a subtropical reservoir |
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Authors: | María Elicia Mac Donagh María Adela Casco María Cristina Claps |
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Institution: | (1) CONICET, Buenos Aires, Argentina;(2) Division de Ficología, Museo de La Plata, Paseo del Bosque s/n., 1900 La Plata, Argentina;(3) ILPLA, Av. Calchaquí Km. 23,5, 1988 Florencio Varela, Argentina |
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Abstract: | In reservoirs, variations in water level may affect plankton biomass and species composition. Studies on the effect of water-level
fluctuations are scarce and restricted to Europe and Australia. In the Río Tercero Reservoir (Argentina), the management policies
of a nuclear-power plant require a minimum depth of 650 m. During periods of excessive rainfall, however, the input is such
that the excess passes over the spillway, thus causing a high turnover of water. Phytoplankton, zooplankton, and physicochemical
variables were monitored over 2 years at three sampling stations during a period with annual precipitation higher than the
historical annual mean. Different hydrological situations occurred based on precipitation, spillway outflow, and water-renewal
rate. At high renewal rates, phyto- and zoo-plankton diversities peaked. During high outflow periods phytoplankton biomass
peaked through the contribution of Ceratium hirundinella. Once the spillway outflow ceased, stable conditions (low renewal rates) were achieved, thus allowing the onset of biological
interactions. Maximum phytoplankton density (mainly Actinocyclus normanii) was reached at such times, and efficient grazers (Daphnia laevis) with long life cycles dominated in terms of biomass. The structure and dynamics of the plankton community could be altered
by changes in hydrological conditions (renewal rate and spillway outflow) that act to compromise the apparent stability imposed
by steady water levels. These variables must be considered to identify disturbance conditions and improve knowledge of reservoir
environments, so as to implement appropriate management practices. |
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Keywords: | Phytoplankton Zooplankton Reservoir management Spillway outflow Water-level stability |
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