Short-term taxonomic and functional responses of zooplankton to the Floc and Sink technique: implications for non-target ecological effects

Abstract Geoengineering techniques have been applied to control phosphorus and cyanobacteria, showing promising outcomes for the restoration of eutrophic aquatic ecosystems worldwide. However, the effects of the materials used in these techniques on non-target organisms, like zooplankton communities, are not well understood. This study evaluated the impacts of the materials used in the Floc and Sink geoengineering technique—specifically aluminum sulfate and polyaluminum chloride coagulants, alone or in combination with lanthanum-modified bentonite—on the taxonomic and functional diversity of zooplankton, identifying the functional traits associated with species sensitivity and tolerance. To achieve this, we conducted a 192-h bench-scale experiment using water from a eutrophic reservoir. We monitored biomass, taxonomic (richness, Shannon, and evenness) and functional (functional richness, evenness, and divergence) diversity, and functional traits related to mobility and feeding mode. Significant reductions in zooplankton biomass and diversity were observed, particularly in the treatments containing bentonite. Small-bodied, low-mobility filter feeders (e.g., rotifers and nauplii) were the most sensitive, while larger, more mobile raptorial copepods were more tolerant. These findings demonstrate that functional traits can predict species sensitivity or tolerance to geoengineering materials and highlight the importance of considering non-target impacts when applying the Floc and Sink technique for eutrophication management.