Seasonal variation of zooplankton community structure between two subtropical reservoirs of contrasting hydraulic retention time

Reservoirs significantly influence aquatic ecosystems by modifying river flows and forming artificial lakes. This study examines the zooplankton communities in two Uruguayan connected reservoirs, Bonete and Baygorria, focusing on the impact of different water residence times. Upstream Bonete has a long retention time of 140 days, whereas Baygorria has a short retention time of 3 days. The investigation was conducted over 2019–2020, involving ten sampling events at three depths. Physical and chemical variables, including temperature, dissolved oxygen, pH, turbidity, chl-a, total nitrogen, total phosphorus, and organic matter concentrations were measured. Zooplankton biomass and community structure were analyzed through Redundancy Analysis (RDA). Results indicated higher zooplankton biomass in Bonete, with significant seasonal and vertical variations linked to environmental factors. Temperature, chl-a concentration, and water residence time were identified as key determinants. The study highlights the role of water residence time in shaping zooplankton communities. The findings underscore the need for tailored management strategies to address the ecological dynamics of reservoirs.