Efeitos experimentais de estressores múltiplos na composição e estrutura de tamanho de macroinvertebrados bentônicos em clima tropical

Abstract

Agriculture has increased exponentially in recent years, changing land use. Among the stressors related to agricultural activities that affect lotic ecosystems, the deposition of fine sediments, changes in flow and increased concentrations of hydrating nutrients stand out. In addition to taxonomic composition, changes in body size spectra (size-biomass relationships) can provide important information about ecosystem functioning. Our general objective in this work was to associate the size structure and composition in benthic communities with the impacts associated with intensification in land use, such as increased nitrogen concentration, reduced water flow and sedimentation, in mesocosm experiments simulating streams (system ExStream). Furthermore, we expected that multiple impacts would cause negative and less pronounced slopes in size spectra with environmental impact, due to the simplification of the food network and the presence of only resistant and efficient organisms that transfer more energy along the food chain. Contrary to expectations, size spectra showed a positive relationship between species abundance and size, changing systematically in relation to sedimentation and flow velocity. According to the size structure results, we observed changes in the composition of communities exposed to reduced water flow, and the interaction of this stressor with sedimentation was also significant. This interaction interferes with the abundance of many taxa of Chironomidae (Diptera), and rare genera were not presented in this treatment. These results provide new insights into the responses that macroinvertebrate communities can present to different stressors related to agriculture.