The ecological degradation of streams is primarily driven by human impacts such as agriculture and land cover change, which are linked to increases in nutrients and fine sediments, altered hydrology, changes to morphological and instream habitat, and disturbed or deforested riparian zones. These alterations simplify and degrade habitats and have caused widespread reductions in aquatic biodiversity. The area of intensive agriculture in the Brazilian Cerrado-Amazon region, known as “Arc of deforestation,” has greatly expanded in recent years. Our study took place in the headwaters of the Xingu River basin and focused on two questions: i) How does macroinvertebrate composition change among streams along a gradient of riparian forest degradation; and ii) How do macroinvertebrate functional traits shift with riparian degradation? To answer these questions, we sampled macroinvertebrates (Ephemeroptera, Plecoptera and Tricoptera- EPT), EPT functional traits, and environmental variables in nine streams with three classes of riparian forest degradation: preserved (within forested watersheds; three streams), degraded (within soy crop watersheds; three streams) and deforested (within soy crop watersheds; three streams). We used a PERMANOVA to compare EPT composition between streams and a GLMM approach to model the composition as a function of environmental variables and the trait-environment interaction.
Results/Conclusions
Community composition among streams with three classes of riparian forest degradation differed significantly (p=0.02). The genera that most contributed to this difference was Campylocia followed by Triplectides and Macronema. We found that the percentage of preserved forest in the watershed, percent canopy cover over the channel, and percentage of total vegetation cover (i.e. the sum of undergrowth, intermediary and canopy vegetation) were the environmental variables that best explained EPT community composition of streams. Three environment-trait interactions were significant: percent of forest in the watershed – size of adult individuals; percent channel canopy cover – abundance of filter collector; percent channel canopy cover- one cycle of reproduction per year. Our results show that environmental variables related to the structure of riparian forests are crucial to maintaining EPT communities in agricultural areas. Some traits related to morphology, ecology and feeding behavior modulated EPT abundance to different environmental conditions. EPT are known as bioindicators of stream health and a good way to measure the impact of human disturbance in this rapidly developing region. Our results highlight the importance of conserving riparian forests to maintain biodiversity and can be used to support future actions related to the Brazilian Forest Code.