Amphibian use of urban stormwater wetlands: The role of natural habitat features

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Urbanization is recognized as a major driver of amphibian declines globally. To maintain urban biodiversity, features that promote local amphibian populations must be identified. The construction of stormwater ponds is a useful tool for mitigating wetland loss and retaining water runoff from impermeable urban surfaces, yet their value as breeding habitat for amphibians that require both terrestrial and aquatic habitat to persist remains poorly known. Within the City of Edmonton, Canada, we surveyed 75 urban wetlands (stormwater, natural upland and river valley) using call surveys and trapping for amphibian species. We related amphibian occurrence to 14 within-wetland parameters (reflecting water chemistry and aquatic vegetation) and four landscape features. We used an information-theoretic approach to identify predictors of anuran occurrence. Three of the five amphibian species known to occur regionally (wood frog, boreal chorus frog, and western tiger salamander) were found at all wetland types. Overall, natural wetlands had higher levels of occurrence and abundance of calling wood and boreal chorus frogs than stormwater wetlands; however, constructed stormwater wetlands did frequently serve as breeding habitat for amphibians. Total nitrogen concentrations and aquatic vegetation were the best within-wetland predictors of frog occurrence whereas the nature of terrestrial habitat and amount of wetlands surrounding breeding habitats were the best landscape predictors. Within-wetland habitat could be improved if stormwater wetlands were designed to promote the growth of emergent and submerged aquatic plants. Urban amphibian populations would benefit if managers preserved or restored terrestrial habitat surrounding stormwater sites.