Urban stormwater running o? streets, parking lots, driveways,and construction sites contains various pollutants such as sediment,oil and grease, heavy metals, toxic organic chemicals (e.g., pesticides),nutrients, and pathogens (Table 1) and needs to be treated beforedischarged to receiving waters [1,2]. Di?erent treatment structureshave been employed, including detention ponds, storm water wetlands,sand flters, bioretention cells, and level spreaders (e.g., vegetative flterstrips, swales, permeable pavements, and green roofs). Of these stormwater best management practices, bioretention is to collect storm waterinto a vegetated land depression and allow it to infltrate through theunderlying flter layer (typically a mixture of soil, sand, and compost)into the ground. Bioretention removes pollutants from storm water bysedimentation, fltration, sorption, microbial transformation, and plantuptake [3,4]. Te more or less constructed land depression is termed“bioretention area”, “bioretention cell”, or “rain garden.” If engineeredover?ow features such as a weir or under drain pipe are installed, thestructure is then called “bioretention basin” or “bioflter” [5].
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