Taxonomic and functional spatial distribution model of phytoplankton in tropical cascading reservoirs

We assessed the impact of cascaded reservoirs on the phytoplankton’s functional and taxonomic structure. We tested whether functional traits in these communities were selected by the chemical and physical changes that occur in reservoirs downstream in a cascade. Functional diversity and composition were assessed based on eight functional phytoplankton traits and the Simpson taxonomic diversity index. To identify the impact of cascades on functional and taxonomic diversity, we used multiple regression models with environmental variables and variables that indicate cascade interference as predictors and diversity metrics as a response. We fitted simple regression models with physiological and chemical variables in response to the number of reservoirs upstream. Functional and taxonomic diversity and richness decreased with an increasing number of upstream reservoirs. Downstream reservoirs represented by the largest number of upstream reservoirs contained higher proportions of unicellular algae and lower densities of colonial and mucilaginous algae. They also showed higher functional similarity and greater flagellated and unicellular algae density. Both the number of upstream reservoirs and the distance between cascaded reservoirs affected the taxonomic and functional diversity and selection of phytoplankton traits. The increasing distance from upstream dams may help the ecosystem recover, since the larger distance between the dams favored a more uniform traits distribution. These results provide information that is useful for future reservoir management. Graphical Abstract