Patterns of Aquatic Insect Biodiversity in the Highly Urbanized Bronx River, NY

Abstract - Aquatic insects are important components of stream food webs and are greatly impacted by anthropogenic disturbances, including urbanization. Successful restoration of urban rivers is contingent on the growth of aquatic insect populations from colonizers from local, less-disturbed streams. However, rivers in highly urbanized watersheds may not have nearby source populations, and therefore must rely only on individuals already surviving in the river. At the regional level, urbanization is a homogenizing process, but the impacts could be heterogeneous at the local level. Therefore, some sites within highly urban rivers might support higher local biodiversity and provide source populations for restoration projects focused on other sites in the river. In this study, we collected aquatic insects from sites within the Bronx River, a highly urbanized river in the New York City metropolitan area, NY, in the summers of 2021 and 2022. We found that while taxonomic richness was similar among sites, insect abundance and dominant taxa, particularly members of Hydropsychidae (Trichoptera), varied significantly among sites. These findings suggest sites within the Bronx River are not homogenous and that some sites within the river harbor larger populations of aquatic insects and may be integral to the success of future conservation projects. This pattern of within-river heterogeneity may exist in other urban rivers and deserves consideration in determining conservation goals and the planning of stream-restoration projects.