Abstract
Zooplankton are widely recognised as being regulated primarily by predators and food availability. In reservoirs, the quantity and quality of food resources are generally affected by the characteristics of the water, which in turn are controlled by the flow pulse generated by operation of the dams. In this study, we investigated the relationship between zooplankton, water quality and food availability (phytoplankton) in eight hydroelectric reservoirs located in Brazil. Samples were collected during the rainy and dry periods between 2008 and 2009. In general, the reservoirs exhibited mesotrophic conditions and Cyanobacteria were the predominant phytoplankton. The results showed that the rotifers Kellicottia bostoniensis, Hexarthra mira, Keratella spp., and Polyarthra vulgaris were present, indicating nutrient-rich environments. In addition, the copepod Thermocyclops decipiens occurred in eutrophic environments. In contrast, the cladoceran Daphnia gessneri and copepod Notodiaptomus henseni were considered indicators of more desirable water quality, owing to their relationship with waters with lower levels of nutrients and suspended solids. The results support the use of these organisms as a useful tool for understanding changes in water quality and in the ecosystem processes involved.
Highlights
Reservoirs are inseparable components of the Brazilian landscape and are present in all the main hydrographic basins as a result of the choice made by the country to generate hydroelectricity (Takahashi et al, 2009; Simões et al, 2015)
Most of the reservoirs studied exhibited mesotrophic conditions, with the exception of the FUN and MAR reservoirs, which were experiencing eutrophication at the time of study. These reservoirs differ in many morphofunctional parameters, such as size, water residence time (WRT), and depth
Great occurrences and abundances of cladocerans and juvenile copepods can be an important indicator of the beginning of the eutrophication process in these reservoirs
Summary
Reservoirs are inseparable components of the Brazilian landscape and are present in all the main hydrographic basins as a result of the choice made by the country to generate hydroelectricity (Takahashi et al, 2009; Simões et al, 2015). There has been an increased proliferation of these engineering works, which are important for the national energy matrix (Agostinho et al, 2007). They are considered of extreme importance for regional socio-economic development due to their multiple uses, including water supply, irrigation, aquaculture, and recreation, which increases the importance of studying these systems (Soares et al, 2008). Dams significantly alters riverside ecosystems because the creating of a reservoir blocks the free flow of the river and creates a semi-lentic or lentic habitat Important factors such as the quantity and quality of water, habitats, and nutrient transport can change dramatically (Baumgartner et al, 2017; Loken et al, 2018). Artificial variations in the water level can directly and indirectly affect zooplankton communities
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