Biofilms, Bugs, and the Built Environment: Exploring Local and Landscape Drivers of Diatom and Macroinvertebrate Assemblages in Urban Stormwater Ponds.

Stormwater management ponds (SWPs) are engineered systems designed primarily for flood control and sediment capture in urban landscapes. Despite their intended function, these ponds are often colonized by aquatic biota and can contribute to urban biodiversity. We investigated the ecological condition of 21 SWPs in a highly urbanized city in southern Ontario, Canada, by assessing the composition of periphytic diatom and aquatic macroinvertebrate assemblages and relating these to water quality, pesticide contamination, physical habitat features, and surrounding land use. Assemblages were dominated by pollution-tolerant taxa. Water quality parameters were good predictors of variation in community composition for both assemblages, whereas pesticide contamination was associated with diatom relative abundances, and local vegetation cover was associated with macroinvertebrate relative abundances. Landscape variables within a 300-m buffer surrounding the SWPs were not associated with community composition or taxonomic richness for either assemblage, suggesting that site-level conditions exert stronger ecological influence. These findings highlight the importance of using multiple biological assemblages to capture different aspects of ecological condition and the value of integrating biological monitoring into stormwater infrastructure planning. Enhancing emergent and riparian vegetation, reducing pollutant inputs, and managing contaminant pathways may improve biodiversity potential in urban SWPs.