From summer storms to winter freezing-thawing cycles: assessing treatment capacity and de-icing salt fate in bioretention systems

ABSTRACT

Bioretention systems are a sustainable solution for tackling stormwater management challenges. In northern countries, freezing-thawing cycles and the use of de-icing salts and abrasives during winter still cause uncertainties regarding bioretention efficiency. To better understand these issues, bioretention cells were monitored from the spring of 2022 to the spring of 2024 in a retrofitted parking lot in Victoriaville (Canada). In the warmer months, results showed a mean stormwater volume reduction of 78%, total suspended solids removal efficiency between 85 and 100%, and total phosphorous removal efficiency from 15 to 100%. Occasional release of total nitrogen was observed. Electrical conductivity downstream of the bio-retention system was always higher than upstream during the summer months. During winter, the sporadic rainy days caused short spikes in soil water content, even for rainfall events following very cold days, indicating water infiltration. The highest electrical conductivity peaks measured in the substrate were short and occurred due to the high mobility of salts with infiltrated runoff and snow melt. Results demonstrated that bioretention systems could perform adequately in a context of freezing-thawing cycles with the use of de-icing salts and abrasives, both in terms of runoff and pollutant reduction.