Contribution of zooplankton as a biological element in the assessment of reservoir water quality (original) (raw)

Contribution of zooplankton as a biological element in the assessment of reservoir water quality European water policies aim to achieve a good ecological status in all water bodies. The Water Framework Directive (WFD) defined a group of biological elements to assess water quality. In reservoirs and lakes, phytoplankton is the only biological element used for water quality evaluation. However, zooplankton is an important link in the trophic web, since it is able to control the phytoplankton community and was already described as a good bioindicator, with high sensitivity to different environmental stresses. The main goal of this work is to demonstrate the ability of zooplankton communities to be used in the evaluation of water quality in reservoirs. A group of four reservoirs in the north of Portugal (Paradela, Alto Cávado, Alto Rabagão, and Venda Nova) were sampled every three months, during one year, to assess the water quality. Physical and chemical parameters, as well as phytoplankton communities, were studied according to the metrics proposed by the WFD for this typology of water bodies. Additionally, zooplankton communities were also sampled in each reservoir, to understand if their seasonal dynamics are influenced by alterations of the water quality in the reservoirs. Results show that the reservoirs present a good ecological potential, according to WFD reference values for physical and chemical parameters and phytoplankton communities, with occasional drops to moderate ecological potential due to variations in the dissolved O 2 and total phosphorus values. The results observed in the dynamics of zooplankton communities show that this biological element is sensitive to changes in the reservoirs and provides a more detailed image of the state of the ecosystem. Zooplankton communities responded to alterations in the water level in the reservoir, to shifts in the trophic status and in the water quality, both at the taxonomic level and on a functional perspective. Therefore, the metrics proposed by WFD to evaluate water quality in reservoirs seem to be insufficient to understand all the alterations that occur in these aquatic ecosystems.