Functional diversity of freshwater phytoplankton under multiple environmental filters and seasonal variability in contrasting tropical ecosystems

Abstract The relationships between the functional diversity of phytoplankton and environmental conditions offer insights into phytoplankton community structure under environmental gradients in basins influenced by anthropogenic disturbances, including mining residues. Thus, we aimed to identify the main environmental drivers of the functional diversity of phytoplankton by considering three types of ecosystems and two distinct seasonal periods. We hypothesized that (1) ecosystems with higher hydrological stability and lower contamination—particularly deep lakes—support greater phytoplankton functional diversity, and (2) seasonal effects on functional diversity are more pronounced in rivers. Sampling was conducted between October 2018 and September 2021 in the Doce River and in shallow lakes and deep lakes of the floodplain. Functional diversity indices were measured based on seven functional traits comprising species volume, silica demand, heterocyst presence, mixotrophy potential, aerotope presence, flagella presence, and life form. Deep lakes exhibited higher functional diversity due to lower eutrophication conditions, metal contamination, and greater light availability. In the river, the increase in functional diversity during the dry season suggested an attenuation of anthropogenic pressures, considering the improvement in environmental conditions. Our results showed a dependence of the functional diversity of phytoplankton on the type of environment, and that the environments experienced distinct effects according to seasonality. Additionally, we demonstrated that resource availability, lower levels of metal contamination, and reduced grazing pressure resulted in greater functional diversity of the phytoplankton. We thus emphasize the importance of assessing functional aspects of phytoplankton in the biomonitoring of areas strongly impacted by anthropogenic activities.