Environmental filters influencing phytoplankton taxonomic structure in cascade reservoirs

Abstract

In this study we analyzed the dynamics of the phytoplankton community in two cascade reservoirs in six sampling periods, to investigate the infuence of environmental flters on phytoplankton, and the community concordance with the environ‑ mental variability. We addressed several questions, and from phytoplankton biomass data and abiotic variables sampled at the Salto Osório and Salto Santiago reservoirs, Paraná, Brazil, we obtained the answers. A total of 136 taxa distributed in cyanobacteria, diatoms, green algae and mixotrophic fagellates were recorded. Diatoms and mixotrophic fagellated algae contributed most of the phytoplankton biomass in both reservoirs. Environmental flters such as nutrient concentrations, light, pH, depth and temperature had the greatest infuence on phytoplankton taxonomic structure, being the community in concordance with the environmental conditions. Although some environmental diferences between reservoirs were recorded, the phytoplankton community was similar, probably associated with environmental connectivity, but with diferences in biomass, which is possibly associated with seston retention in upstream regions. Our results revealed important drivers that infuence the phytoplankton structure and dynamics in reservoirs, and this understanding is of interest, due to the maintenance of ecosystem functions and services.