Macroinvertebrate functional traits differed with land use practices at Patagonian streams

The analysis of functional trait composition in aquatic macroinvertebrate communities is a valuable tool for assessing the impacts of environmental changes on fluvial ecosystems. We investigated Patagonian watercourses subjected to different land use practices (natural, agricultural, and urban) and predicted that disturbances would decrease trait diversity while favoring certain trait modalities over others. RLQ and fourth corner analysis were utilized to explore potential relationships between species, traits, and environmental gradients. Differences in macroinvertebrate taxonomic and functional diversity metrics among land uses was also tested. Our results showed that land use had a significant impact on macroinvertebrate communities, with water pollution and riparian condition being the most important factors shaping their functional structure. The RLQ ordination grouped sites according to a disturbance gradient and revealed that traits positively associated with urbanization included deposit feeding, aquatic reproductive stage, non-flyer dispersion mode, cylindrical form, low body armoring, and adhesive secretions as adaptation to the flow. In contrast, natural sites favored respiration through gills, streamlined body, low flexibility, moderate body armoring, crawlers, and species with terrestrial reproductive stage, among others. The agricultural sites displayed moderate disturbance, and no specific trait modalities were associated with this particular land use. Functional diversity metrics mirrored the patterns observed in taxonomic diversity indexes, but only functional evenness showed the expected decline with increased disturbance. The trait-based approach complemented traditional methods for assessing land use impacts, providing insights into the mechanisms by which environmental stressors affect macroinvertebrates. This approach has emerged as a valuable tool for river management and land use policy.