Do salt and low temperature impair metal treatment in stormwater bioretention cells with or without a submerged zone?

Reported removals of dissolved metals are fewer and contradictory, including both efficient removal and significant leaching.

“However, reported removals of dissolved metals are fewer and contradictory including both efficient removal and significant leaching (e.g. Muthanna et al., 2007; Søberg et al., 2017).”

Metals can negatively affect the ecological status of surface waters depending on their prevalence, toxicity and resistance to degradation and/or chemical transformation.

“Depending on their prevalence, toxicity and resistance to degradation and/or chemical transformation metals might negatively affect the ecological status of surface waters (Søberg et al., 2017).”

A large number of field and laboratory studies have shown efficient total metal removal for bioretention systems, often exceeding 80-90%.

“A large number of field and laboratory studies have shown efficient total metal removal for bioretention systems, often exceeding 80–90% (e.g. Hatt et al., 2008; Søberg et al., 2017).”

Several pilot-scale studies have shown LTU top-layer to be an efficient metal adsorbent.

“Several pilot-scale studies (Blecken et al., 2011; Søberg et al., 2017) have shown this material to be an efficient metal adsorbent.”

LTU-TOP efficiently removed metals in pilot-scale bioretention facilities under various ambient conditions, despite showing very low adsorption capacities in the present study.

“Although it showed very low adsorption capacities in the present study (Fig. 2), LTU-TOP efficiently removed metals in pilot-scale bioretention facilities under various ambient conditions (e.g. Blecken et al., 2009; Blecken et al., 2011; Søberg et al., 2017).”

It has been commonly observed that a majority of metal adsorption happens in the upper layers of bioretention.

“It has been commonly observed that a majority of metal adsorption happens in the upper layers of bioretention (e.g. Søberg et al., 2017) which would support the assumption of rather quick adsorption processes.”

Metals primarily accumulate in the top 5 cm of bioretention filter materials.

“The latter becomes evident considering that metals primarily accumulate in the top 5 cm of bioretention filter materials (e.g. Søberg et al., 2017).”