INDIVIDUAL AND COMBINED EFFECTS OF AGRICULTURAL STRESSORS AND CLIMATE CHANGE ON BENTHIC MACROINVERTEBRATES IN TROPICAL STREAMS
Agricultural activities cause changes in land use and affect the ecological integrity of streams, where the main impacts are related to increased nutrient and sediment input, as well as changes in water flow dynamics. Generally, stressors simultaneously affect aquatic ecosystems, but the combined effects of these multiple stressors on streams are still poorly understood. Therefore, we tested the singular and combined effects of three agricultural stressors (nutrient enrichment, sediment deposition, reduced flow velocity) on the richness and abundance of the benthic macroinvertebrate community in tropical streams using the ExStream system. The ExStream system consists of 128 mesocosms that simulate streams, with the same physical and chemical characteristics as natural streams. The results showed that both for richness and abundance, the singular effect of nitrate enrichment was not as harmful as the effects of the combination of stressors. The combination that presented the highest harmfulness to the benthic macroinvertebrate community was the combination of increased nitrate, reduced flow, and increased sedimentation, which showed lower richness and abundance values than the singular effects of nitrate. Therefore, the results indicate that streams impacted by nutrient enrichment can be further degraded when subjected to sediment deposition and reduced flow, which are commonly observed in agricultural streams.