Stream ecosystem resilience following extreme high-frequency summer floods in Glacier Bay, Alaska

The frequency and magnitude of extreme hydrological disturbance events are increasing under climate change in all regions of the world. These disturbances act as significant drivers of change in ecosystems. This research sought to explore how disturbances, in particular high-frequency flooding, directly and indirectly effect stream ecosystems. Further, it sought to consider the resilience of ecological communities following the floods. High-frequency floods significantly altered ecosystems at four streams of varying geomorphological complexities, driving homogenisation of benthic macroinvertebrate community composition both within and between streams, predominantly through the processes of community reassembly. Juvenile salmon community size structure, condition and trophic linkages were significantly altered by the floods leading to a decoupling of terrestrial resources and an increasing reliance upon the selection of Chironomidae prey post-flood. The floods drove a decoupling of metrics of community stability with an increasing role of invasions observed during community reassembly. This thesis further demonstrated the capacity of multiple and linked disturbance events to sequentially degrade the resilience and decouple the metrics of stability in ecosystems. Finally, the importance of more explicitly exploring the processes which govern biological response to disturbance is highlighted. A novel conceptual perturbation pathway approach is proposed, which enables intermediary processes, which govern biological response, to be more easily and consistently defined and thus incorporated into our theoretical understanding of disturbance in ecology.