Title: INITAIL INVERTEBRATE COMMUNITY DEVELOPMENT OF AN ARTIFICALLY CONSTRUCTED SIDE CHANNEL OF THE BOISE RIVER

Program: Biology MS

Committee Chair: Peter Koetsier

Committee: Peter Koetsier, Ian Robertson, Allison Simler-Williamson

Abstract: Riverine landscapes are increasingly modified through projects that include the creation of new aquatic habitats, such as engineered side channels, to enhance ecological diversity and complexity within larger river systems. However, the initial biological succession and development of these human-created lotic ecosystems are not well documented. This study investigated the first two years of habitat formation and invertebrate colonization within a newly engineered side channel of the Boise River, Idaho. I compared the establishment of invertebrate communities, key energy sources (periphyton and detritus), and substrate composition in the constructed channel to the adjacent main Boise River, which served as the primary source of colonists and a reference for ecological development. Seasonal samples of invertebrates, periphyton, benthic organic matter, and substrate were collected from multiple sites in both the channel and river for two years post-channel inundation.

My findings revealed that the engineered channel rapidly developed distinct characteristics. Substrate in the channel was finer than the cobble-dominated river, a difference likely due to inputs from bank erosion and the channel's design. Detrital concentrations in the channel quickly became comparable to the river, whereas periphyton abundance was initially higher in the channel before declining to levels similar to the river by the second year. Invertebrate communities in the channel achieved richness and density levels similar to the main river within the two-year study period, although total biomass remained lower. Functional feeding group structure in the channel largely mirrored the source river community, whereas invertebrate habitat preferences in the constructed channel diverged with the source river over time. Specifically, the channel supported a higher proportion of invertebrates adapted to depositional environments. Invertebrate richness, density, and biomass increased with detritus in both the channel and the source river, whereas periphyton showed a negative association. Julian date (time) did not have a clear effect on the invertebrate community after accounting for periphyton and detrital energy sources.

My research suggests that engineered side channels can quickly support diverse invertebrate assemblages, comparable in some respects to established riverine habitats, fueled by the rapid establishment and utilization of detrital resources. However, the development of unique substrate conditions and shifts in invertebrate habitat use indicate a distinct early successional trajectory. These insights underscore the importance of detrital pathways and predictable substrate composition in the early development of newly created stream ecosystems. Observing and characterizing these initial colonization dynamics and driving factors are crucial for designing effective habitat creation projects and setting realistic ecological expectations for newly formed lotic environments.