UC Riverside

Urbanization is rapidly changing the structure and function of freshwater ecosystems across the planet. Southern California is currently experiencing an advanced urban stream syndrome regime due to the dense human population. Urban alterations have resulted in changes to rivers and streams that include physical alterations, effluent discharge that changes hydrology and water chemistry, the introduction of non-native and invasive species that alter biotic filters, and management of these systems to preserve threatened and endangered species. This suite of changes results in a patchwork landscape for species within a city. I examine the heterogeneity that exists within a highly urbanized river to better understand urban heterogeneity, its impacts on freshwater trophic structure, and species foraging preference. In chapter one I present the results of monthly habitat and benthic community surveys across an urban gradient containing three wastewater treatment plants. I found that these impacts did not have consistent impacts on habitat or freshwater benthic communities across the studied gradient and that certain habitat variables had strong impacts on diatom and macroinvertebrate species richness and density. My second chapter investigates the role of wastewater treatment plants on community trophic structure and invasive species diets across three wastewater discharge channels and the main stem of an urban river. I found that wastewater facilities had different impacts on nutrient enrichment, community trophic structure, and invasive species diets. These changes were not consistent between wastewater and main stem channels with trophic compression occurring in each. Chapter three examines how wastewater facilities impact a federally threatened species foraging preference within an urban river. We found that this species had a clear preference for the forage below one of the three wastewater discharge points and for forage in the main stem of the river away from wastewater inputs. This preference did not overlap with the species current distribution in the river. Throughout this dissertation, I demonstrate the level of urban heterogeneity that exists within this system, how the impacts of alterations had different impacts, and present opportunities to improve management of urban freshwater ecosystems.