COS 23-1 - Patterns of insect biodiversity in the highly urbanized Bronx River

Abstract: Aquatic insects are important components of stream food chains and are impacted by anthropogenic disturbances. Planning successful restoration projects of urban rivers is contingent on understanding the impact that urbanization has on aquatic communities, and while urbanization is a homogenizing process at the regional level, urban impacts could be heterogeneous at the local level. Therefore, lower local urban impacts some sites within highly urban rivers could support higher local biodiversity. The purpose of this study was to describe the richness and abundance of aquatic insect communities within the highly urbanized Bronx River and determine if those communities were homogeneous among sites. Furthermore, the potential impact of aquatic insect community composition on trophic dynamics within the river was explored. Insects were collected by kick netting in four equidistant sites once a month between May and August in 2021 and six sites between April and August 2022. Insect richness and abundance were recorded and compared between sites and months using generalized linear modeling. Due to the difference in the number of sites and sampling months between years, each year was analyzed separately. Additionally, the body length of Hydropsyche sp. (Trichoptera), the most common taxa in all sites, was measured as a proxy for body size.


A total of 1189 insects were collected in 2021 and 2022. Insect richness was low in all Bronx River sites, with a total of 10 unique insect taxa collected in 2021 and 2022 combined, representing nine families and four orders. While taxonomic richness was similar between sites, overall insect abundance and that of the dominant taxon, Hydropsyche sp., varied significantly between sites (5 – 60 individuals site^-1 month^-1). Furthermore, the size of individual Hydropsyche sp. varied significantly between sites (8 – 12 mm individual^-1 site^-1 month^-1). This suggests that there is heterogeneity of urban impacts within the highly urbanized Bronx River that may have important implications for biodiversity and trophic dynamics within the river. Understanding the heterogeneous nature of urbanization in urban rivers can help to inform conservation and restoration efforts within those ecosystems. This work has been the basis of numerous undergraduate independent studies and honors theses and has set the stage for further conservation projects in the Bronx River bringing together college students as well as local high school students as a part of the Bronx River Alliance Environmental Enrichment and Leadership for Students (EELS) program.