Land use intensification has led to conspicuous changes in plant and animal communities across the world. Shifts in trait-based functional composition has recently been hypothesized to manifest well before any changes in species-based taxonomic composition; however, little is known about commonality in these responses across taxonomic groups and geographic regions. We investigated this hypothesis by testing for taxonomic and geographic similarities in the composition of riverine fish and invertebrate communities across sharp gradients of land use in the conterminous United States. Our results demonstrate abrupt threshold changes in both taxonomic and functional community composition due to land use conversion. Functional composition consistently demonstrated lower threshold responses compared to taxonomic composition, with predominantly lower thresholds for urban versus agricultural land use for both fish and aquatic invertebrates. Threshold responses of functional composition to both urban and agricultural land use change were also more geographically consistent than those of taxonomic composition. Traits contributing the most to overall functional composition change differed along urban and agricultural land gradients, and conformed to predicted ecological mechanisms of community change. This study points to reliable early-warning thresholds that accurately forecast compositional shifts in riverine communities to land use conversion, and highlight the importance of considering trait-based indicators of community change to inform large scale land use management strategies and policies.