Study on bioretention for stormwater management in cold climate, part II: Water quality

Abstract

Typical continental, cold climate conditions were applied to four large, laboratory columns to simulate temperatures ranging from −20 to +20 °C over summer, winter, and spring runoff. The goal of this research was to assess the seasonal effectiveness of bioretention application in cold climate regions that are currently experiencing the impacts of climate change. 1.6 years’ worth of equivalent Edmonton precipitation volume was applied over a 10-month period to evaluate the water quality improvement through two soil types (i.e., loam and sandy loam) with and without amendments intended to enhance nutrient removal. During summer, excellent removal of total suspended solids (TSS), phosphate, and ammonium (i.e., ≥90% average concentration reduction) was observed in both the loam and sandy loam columns without the nutrient removal amendments. The columns containing the amendments also reduced TSS, ammonium, and phosphate, but not as effective as the non-amended columns for TSS and ammonium. During winter and spring runoff, if infiltration occurs, physical removal of TSS, phosphate, and ammonium was still achieved, only days after the complete freezing (and subsequent thawing) of bioretention media at −20 °C. After an initial maturation and leaching period, nitrate was well removed (≥65.2% average concentration reduction) via denitrification in the columns with the nutrient removal amendments and submerged zone.