Fine sediments produce tipping points in the taxonomic and functional structure of benthic macroinvertebrates in neotropical streams

The influence of substrate homogenization on the taxonomic structure of benthic macroinvertebrate assemblages is well known worldwide. However, understanding the response thresholds of macroinvertebrate assemblages to a fine sediment deposition gradient is rarely reported for neotropical regions. Furthermore, most studies focus on taxonomic indicators, without considering the functional aspects of benthic macroinvertebrates. Therefore, we used taxonomic and functional analyses to assess the threshold responses of macroinvertebrate assemblages to fine sediments in 40 neotropical savanna streams in the hydrological unit of the Furnas hydropower reservoir. We found that stream locations with increased fine sediment supported lower taxonomic and functional composition, negatively selecting for the functional traits of gill respiration and flattened and streamlined body shape. In contrast, integument respiration and spherical body characterized macroinvertebrates positively associated with fine sediments. We also found that taxonomic (Shannon and Simpson indices) and functional (functional richness and functional evenness) indicators were sensitive to habitat homogenization resulting from increased fine sediments. We strongly recommend that energy companies monitor hydropower basins by identifying areas with accumulations of fine sediments, using the taxonomic and functional components of macroinvertebrates in the biomonitoring of neotropical streams. This information is of critical importance for future rehabilitation efforts to avoid siltation of tropical hydropower dams. Besides intense unplanned urbanization and agriculture, the climate crisis is predicted to increase intense tropical rains and sediment transport in headwater streams. Benthic structure and functional composition are early warning signals of environmental degradation and important indicators for long-term monitoring and rehabilitation investments worldwide.