Bioretention: assessing effects of winter salt and aggregate application on plant health, media clogging and effluent quality

Bioretention offers the potential to better match pre-development water balances while improving stormwater quality. The now extensive body of research shows bioretention to be a viable and effective option in the management of stormwater, however there continues to be a demand for information related to cold climate design and performance. To study the impact of winter road salting on bioretention functions, a salt and aggregate mixture was applied to outdoor, bioretention mesocosms with soil, mulch and vegetation layers. Freezing of the media within mesocosms was found to increase the infiltration rates. Smaller increases in infiltration rates occurred for mesocosms exposed to the salt and aggregate mixture, suggesting that media clogging due to high suspended solids loading may be counteracting the effects of expansion due to freezing. Sodium and chloride were temporarily retained in the bioretention media, but were subsequently flushed by infiltrating water. Plant species, Aster nova angliae 'Red Shades' and Panicum virgatum were shown to be capable of withstanding high salt exposure. The exposure of the bioretention soils to de-icing materials did not alter the media's ability of the media to remove contaminants. No evidence of increased heavy metal mobility during this study was observed. Overall, results support the potential for application of bioretention facilities in cold climate regions.