Zooplankton diversity in highly urbanized ponds: The role of road salt is not reflected by watershed impervious cover

Abstract Urban ecosystems are structured by multiple anthropogenic stressors, yet despite the increasing extent and rate of urbanization worldwide, the ecological consequences of excessive road salt application and other urban phenomena remain poorly resolved. To advance understanding of these drivers and their effects on aquatic ecosystems, we collected zooplankton and associated environmental data from 50 permanent stormwater management ponds in Brampton, Canada. Generalized linear regression analysis revealed that zooplankton richness and diversity were strongly influenced by chloride and nitrate, with chloride having a strong negative effect. Community uniqueness was greatest in ponds with elevated calcium, while the presence of fish and higher pH levels promoted community homogeneity. Redundancy analysis showed that zooplankton beta‐diversity was mainly impacted by water chemistry, which explained the most variation in zooplankton composition (9.2%), whereas watershed impervious cover explained none (0%). Surprisingly, despite strong negative impacts of chloride from road salts on multiple dimensions of zooplankton diversity, structural equation models failed to detect any direct or indirect effects of impervious land cover on zooplankton diversity mediated by its influence of water quality on other biotic factors (e.g., fish presence). These findings highlight the limitations of using impervious surfaces as a proxy for the impacts of urbanization on aquatic ecosystem condition but also suggest that reducing salinization may offer meaningful benefits to biodiversity even in densely populated areas.