Impact of a run-of-river dam in an Amazonian large river on the spatial and temporal patterns of phytoplankton beta diversity

Human activities degrade aquatic ecosystems and diminish biodiversity. Dams have a direct impact on river environments, notably affecting aquatic communities like phytoplankton. We investigated the impact of the damming of an Amazonian River on the composition and spatial and temporal beta diversity of phytoplankton, from October 2009 to July 2017. Also sought to understand how the contribution values for beta diversity (LCBD) changed over time. To achieve this, we performed a PERMANOVA to identify changes in phytoplankton composition between dam phases. Also calculated temporal beta diversity at local and regional scales and regressed these values over time to identify possible biotic homogenization and unidirectional changes in the community. Finally, we calculated the LCBD values of each site over time and regressed these values on species richness, environmental heterogeneity, and the site distance to the dam. We verified that the composition of the phytoplankton changed between the phases of the dam. The impact of time on both local and regional beta diversity was observable, particularly in the tributaries. This was attributed to shifts in community composition from the onset of the study to its conclusion, as well as to biotic homogenization detected in sites closest to the dam. These sites became similar over time, contributing less to beta diversity. This change was related to an increase in species richness. Therefore, it was possible to verify that the construction of the reservoir impacted the diversity of the community over time and that the tributaries backwaters were more affected than the main channel.