Use of a hydrotechnical infrastructure (Alqueva Dam) to regulate planktonic assemblages in the Guadiana estuary: Basis for sustainable water and ecosystem services management

Abstract: The phytoplankton and zooplankton assemblages in the Guadiana estuary (south Portugal) were compared in two contrasting hydrologic years, characterized by high and low freshwater discharges. Changes in salinity, nutrients and turbidity, which were mainly due to the changes in freshwater input, had an important influence on the structure of the planktonic assemblages. Nevertheless, coastal upwelling can also influence the productivity of the lower estuarine area during short periods both in winter and in summer. In 2000, a short-term freshwater pulse during May (average 126.46m3 s−1) was markedly beneficial; phytoplanktonic diversity increased, and this caused an increase in zooplanktonic diversity. As phyto-zooplankton coupling in these systems is an important regulator of processes in the trophic web, changes in the dominant groups can have consequences on water quality, especially on the occurrence of toxic plankton blooms. Modelling simulations indicate that a day discharge of 50m3 s−1, every week during critical periods, such as summer/autumn, could be enough to avoid cyanobacteria blooms. Since freshwater “pulses” can be managed by operating the freshwater release from hydrotechnical structures, understanding the relationships between the periodicity and magnitude of inflow pulse events and the estuarine ecosystem structure and healthy functioning is a crucial step towards the development of management modelling tools, as proposed in this study. [Copyright &y& Elsevier]