Use of phytoplankton functional groups as a model of spatial and temporal patterns in reservoirs: a case study in a reservoir of central Brazil

We analyzed the temporal (dry and rainy periods) and spatial (zones) phytoplankton biomass variation (FGs-functional groups) in a tropical reservoir, and determined the main drivers. We hypothesized that water flow negatively affects the FG-environment relationship because high flow promotes dispersal stochasticity. Our results indicated that the FG-environment relationship was affected mainly by the rainfall regime. Periods with intermediate precipitation showed greater predictability than periods with extreme precipitation. This suggests that the effect of stochastic processes on the phytoplankton community is more important in both the highest and lowest water flow, and deterministic processes are more important at intermediate flow. The longitudinal gradient of nutrients, light, and water-column mixing influenced the distribution of the FG biomass. The riverine zone showed high nutrient concentrations, low light availability, and a high biomass of organisms related to highly enriched systems (FG J-chlorophyceans) and shade-adapted taxa (FG S1-cyanobacteria). The lacustrine zone showed high light availability and a high biomass of heterocytous cyanobacteria (FGs S (N) and H1) and meroplanktonic diatoms (FG MP). The functional approach can be applied to understand the processes responsible for species coexistence and for the organization of aquatic ecosystems.