Data for: Climate change is poised to alter mountain stream ecosystem processes via organismal phenological shifts

Climate change is affecting the phenology of organisms and ecosystem processes across a wide range of environments. However, the mechanisms linking organismal to ecosystem process change in complex communities are uncertain. Here we examined how earlier snowmelt will alter the phenology of stream organisms and ecosystem processes, via a large-scale field experiment in outdoor stream channels. Extended low flows increased water temperature, reducing production-to-respiration ratios by 32%. The stream invertebrate community shifted due to phenological shifts in two-thirds of the taxa, and emergent flux pulses of the dominant insect group (Chironomidae) almost doubled, benefitting a generalist riparian predator. Our study shows that climate change in mountain streams is poised to alter the dynamics of stream food webs via fine-scale changes in phenology—leading to novel predator-prey ‘matches’ or 'mismatches’ even when community structure and ecosystem processes appear stable at the annual scale.