Disturbance plays a critical role in shaping stream ecosystems, with floods being a key driver of
abiotic and biotic dynamics. However, the unpredictable nature of large floods limits
opportunities for studying their ecological effects, resulting in relatively sparse case studies. In
August 2021, a major 900 cubic meter per second (m³/s) flood swept through
Sycamore Creek in the Sycamore Canyon Wilderness, Arizona, USA, dramatically altering the
channel, toppling riparian vegetation, and depositing substantial woody debris.
This study leverages a unique opportunity to examine the effects of this flood on aquatic
macroinvertebrate communities, with pre-flood samples collected in spring 2021 and post-flood
samples in fall 2021, spring 2022, and fall 2022. During each sampling event, replicate samples
were taken from both pool and riffle habitats across two reaches of the creek. Physical stream
characteristics, including water velocity, depth, substrate size, water chemistry, and canopy
cover, were recorded for each habitat.
PERMANOVA results indicated significant shifts in stream-wide aquatic macroinvertebrate
communities across sampling events. Mean taxonomic richness declined following the flood,
dropping from 27.25 in spring 2021 to 21.83 in fall 2021, before rebounding to 28.00 by fall
2022. While mean Shannon diversity also followed a similar pattern, there was no significant
difference in macroinvertebrate density or biomass between sampling events, despite these
compositional changes. These results likely reflect successional dynamics, where fast-life cycle
taxa quickly recolonized post-flood, while slow-life cycle taxa showed delayed recovery in the
system. We aim to clarify these shifts in community composition by examining population
dynamics of key taxa driving post-flood recovery identified through indicator species analysis.
Our findings will contribute to understanding the ecological role of large floods in stream
ecosystems, offering insights into macroinvertebrate community resilience, and informing
conservation strategies for arid, highland wilderness streams.