STABLE ISOTOPES AND ACOUSTIC TELEMETRY ELUCIDATE FOOD WEB ECOLOGY, MOVEMENT PATTERNS, AND HABITAT SELECTION OF LARGEMOUTH BASS (MICROPTERUS NIGRICANS) IN AN URBAN RIVER

Urbanization degrades rivers, leading to biodiversity loss and diminished ecosystem services. To inform urban river environmental management and improve ecosystem function, we conducted two studies to understand how urbanization affects food web production and fish habitat use. In chapter one, we analyzed the stable isotope ratios (δ¹⁵N, δ¹³C, δ²H, and δ¹⁸O) of food web members in the Chicago Area Waterway System (CAWS), a severely altered urban river where flow is primarily driven by effluent. We found that organisms in effluent-receiving areas had enriched δ¹⁵N values, indicating that effluent is supporting food web production. Additionally, ambient water isotope values resembled those of nearshore Lake Michigan, reflecting municipal water use and direct diversions. However, unexplained site-specific differences in δ¹³C, δ²H, and δ¹⁸O suggests complex production pathways beyond effluent and Lake Michigan inputs. In chapter two, we deployed an acoustic telemetry array spanning 40km of the CAWS to track largemouth bass (Micropterus nigricans) movement and assess habitat selection. We visualized habitat use over time to identify high occupancy river segments, and we used random forest algorithms and mixed effects modeling to investigate factors affecting habitat selection. We found that bass generally preferred off-channel areas, which have greater habitat complexity and less vessel traffic than main channel areas. Additionally, habitat occupancy was influenced by temperature differences between connected segments and the sudden onset of hypoxia. These findings highlight how effluent release and habitat alteration affect aquatic communities in the CAWS. Enhancing off-channel habitat could provide crucial spawning, overwintering, and foraging sites for largemouth bass and other species while supporting nutrient cycling and reducing reliance on effluent. This research underscores the importance of combining multiple approaches and analyses to better understand urban river ecosystems and inform management strategies.