Green stormwater infrastructure (GSI), or low impact development, encompasses a diverse and expanding
portfolio of strategies to reduce the impacts of stormwater runoff on natural systems. Benchmarks for
GSI success are usually framed in terms of hydrology and water chemistry, with reduced flow and loadings
of toxic chemical contaminants as primary metrics. Despite the central goal of protecting aquatic
species abundance and diversity, the effectiveness of GSI treatments in maintaining diverse assemblages
of sensitive aquatic taxa has not been widely evaluated. In the present study we characterized the baseline
toxicity of untreated urban runoff from a highway in Seattle, WA, across six storm events. For all
storms, first flush runoff was toxic to the daphniid Ceriodaphnia dubia, causing up to 100% mortality or
impairing reproduction among survivors. We then evaluated whether soil media used in bioretention,
a conventional GSI method, could reduce or eliminate toxicity to juvenile coho salmon (Oncorhynchus kisutch)
as well as their macroinvertebrate prey, including cultured C. dubia and wild-collected mayfly
nymphs (Baetis spp.). Untreated highway runoff was generally lethal to salmon and invertebrates, and
this acute mortality was eliminated when the runoff was filtered through soil media in bioretention columns.
Soil treatment also protected against sublethal reproductive toxicity in C. dubia. Thus, a relatively
inexpensive GSI technology can be highly effective at reversing the acutely lethal and sublethal effects of
urban runoff on multiple aquatic species.