Aquatic insect faunal changes along Mill Creek (OR-WA): Insight into causative factors

Monday, November 11, 2024

8:12 AM – 8:24 AM MST

Location: Phoenix Convention Center, 226 B, PCC

Presenting Author(s)

Quinn Erik Miller (he/him/his)

Student
Whitman College
Portland, Oregon

Co-Author(s)

HD

Heidi Dobson

Whitman College
Walla Walla, Washington
LR

Lucien Rochelois

Whitman College
Walla Walla, Washington

In the Walla Walla Basin of southeast Washington state, substantial effort has been invested towards restoring fish populations, yet little is known about a critical aspect of their habitat: the aquatic insects! Mill Creek, which supports two threatened fish species (steelhead and bull trout), originates in the Blue Mountains (Oregon-Washington) then passes through agricultural and urban land before joining the Walla Walla River on its way to the Columbia River. In 2022 and 2023, two aquatic insect surveys were conducted in Mill Creek to identify and locate changes in the insect fauna. Aquatic insects were collected every two weeks (May-August) using D-nets and were identified as close to species level as possible; various environmental factors (e.g., temperature, nutrients, turbidity) were also measured at each site. The data indicated that insect richness and abundance decreased by approximately half between the watershed and the beginning of the city, associated with an 8°C increase in water temperature and a loss of river edge vegetation between those two sites. To determine the exact location of these changes and identify causes, in 2024, insect samples and environmental data were collected at six sites between the watershed and the city. Our data suggests that the temperature increase is gradual along this river stretch, but the drop in richness and abundance occurs at the start of the channelization, at the edge of the city. These findings can inform local river restorations by providing insight into the environmental variables impacting water habitat parameters and the aquatic insect fauna.