Abstract
In tropical reservoirs, limnological factors are responsible for changes in plankton and vary at temporal and vertical scales. The aim of this study was to evaluate the effects of temporal and vertical variation of the water column on phytoplankton and zooplankton dynamics in two tropical reservoirs (mesotrophic and supereutrophic) in Northeastern Brazil. Monthly collections from three depths in the limnetic region of the reservoirs were performed to analyze the phytoplankton, zooplankton, and limnological variables. The temporal and vertical variation of the physical and chemical water variables, including their interactions, influenced the phytoplankton and zooplankton community. In the supereutrophic reservoir, decreased nitrogen and increased phosphorus and temperature contributed to the dominance of Microcystis panniformis Komárek, Komárková-Legnerová, Sant'Anna, M.T.P.Azevedo & P.A.C.Senna. Conversely, Planktothrix agardhii (Gomont) Anagnostidis & Komárek was dominant under high nitrogen concentrations and low temperatures. In the mesotrophic reservoir, the desmids were dominant and showed a positive relationship with nitrogen. Copepoda Calanoida was dominant and correlated to phytoplankton in both reservoirs. The results showed that nitrogen forms directly influenced phytoplankton, and the importance of nitrogen for management strategies of tropical reservoirs, as well as demonstrated the ability of Calanoida to adapt to different trophic conditions and phytoplankton compositions.
Highlights
Climate change and eutrophication have caused strong changes in aquatic ecosystems
The results showed that nitrogen forms directly influenced phytoplankton, and the importance of nitrogen for management strategies of tropical reservoirs, as well as demonstrated the ability of Calanoida to adapt to different trophic conditions and phytoplankton compositions
Our study showed that nutrients play an important role in structuring phytoplankton and zooplankton communities since nitrogen forms created two distinct scenarios in reservoirs: one with high phosphorus concentrations and another with high nitrogen concentrations
Summary
Climate change and eutrophication have caused strong changes in aquatic ecosystems. With the consequent increase in temperature, reduction of water levels, and nutrient enrichment (Van Zuiden et al 2016), many shallow reservoirs around the world have gone from a clear state dominated by aquatic macrophytes to a turbid state dominated by cyanobacteria blooms (Dong et al 2018). Increased temperature and nutrient concentrations are two factors responsible for increased cyanobacterial blooms (Lürling et al 2018). Long-term monitoring studies suggest that phosphorus (P) is the main nutrient responsible for cyanobacteria blooms in temperate and tropical regions (Downing et al 2001, Anneville et al 2005), according to Kosten et al (2012), high temperatures are important factors for algae growth.
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