The impacts of wildfire and rising temperatures on Spiny Mayfly (Ephemerellidae) diversity and abundance in the Pend Oreille watershed
In the western United States, aquatic macroinvertebrates are increasingly threatened by the dual pressures of rising temperatures and high-intensity wildfires. Spiny mayflies (Ephemerellidae) are critical components of river ecosystems, serving as sensitive bioindicators of water quality and food sources for salmonids. They process detritus and algae, contributing to nutrient cycling and improving water quality through their feeding and burrowing. This study investigates the distribution and diversity of spiny mayflies (Ephemerellidae) in the Pend Oreille watershed.
We hypothesize that wildfire-induced thermal spikes and post-fire sediment runoff would cause a decline in Ephemerellid abundance and diversity. Based on the known sensitivity of Ephemerellidae to temperature and physical habitat changes, we hypothesize that areas impacted by recent forest fires would exhibit lower population densities due to the synergistic effects of increased solar radiation (from canopy loss) and elevated levels of fine sediment runoff. We also hypothesize that water temperature alone would have a negative effect on Ephemerellid abundance and diversity.
We collected 4 benthic invertebrate samples from each of 7 tributaries in 2023 and 13 tributaries in 2024. Some tributaries were sampled in both years for a total of 17 independent sites. Ephemerellid nymphs are identified to the lowest practical taxonomic level, genus or species. Water temperature loggers were used to determine the 7-day maximum temperature for each site (maximum 7-DADMax). Fire records and GIS will be used to determine the proportion of watershed burned within the past 5 years for each site. Ephemerellid diversity in the watershed is high. We have observed 4 genera within the family (Drunella, Ephemerella, Matriella, and Serratella), and 3 species within the genus Drunella. Number of Ephemerellid taxa per site ranged from 0 to 4. Abundance and diversity of this sensitive and relatively well-characterized family may serve as indicators of the effects of global change within relatively undeveloped watersheds such as the Pend Oreille.