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Publication Date

3-18-2026

It is well-documented that dams can have negative effects on fish diversity. What is less known is the impact of urban dams on other aquatic organisms, specifically macroinvertebrates. Dams might create a mosaic of habitat patches in which above dam habitats exhibit differences in water chemistry and physical properties compared to below dam habitats, resulting in differences in macroinvertebrate diversity between these two habitats. Alternatively, the impacts of urbanization might overwhelm the impacts of dams resulting in biotic homogenization where both above dam and below dam habitats are dominated by a few of the same pollution-sensitive taxa or invasive species. One place to test these ideas is in New York City’s only freshwater river: the Bronx River. In this investigation, our objectives were to conduct a biological assessment profile of the Bronx River and to assess differences in macroinvertebrate diversity, water chemistry, and physical properties of habitats situated immediately above and below the nine dams located on the Bronx River. The study yielded several key results. First, above dam habitats exhibited greater river depth, smaller substrate size, lower water velocity, and lower pH than below dam habitats. Second, consistent with historical studies, biological assessment profiles of the Bronx River ranged from severely impacted to moderately impacted. Third, regression analyses revealed that habitats immediately downstream of a dam exhibited higher biological assessment profile scores, macroinvertebrate family richness, macroinvertebrate abundance, and EPT (Ephemeroptera, Plecoptera, and Trichoptera) abundance than habitats immediately upstream of a dam. Finally, two invasive species, the Asian clam (Corbicula fluminea) and the rusty crayfish (Faxonius rusticus), were abundant throughout the Bronx River. Our results suggest that the dams of the Bronx River create a mosaic of habitat patches comprised of lentic, pond-like ecosystems above dams and lotic, free-flowing ecosystems below dams with higher richness and abundance in sampling locations below dams.

DOI

10.15365/1932-7048.1404

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