Engineered and Environmental Controls of Microbial Denitrification in Established Bioretention Cells

Area of Science:

• Environmental Science
• Microbiology
• Water Quality Management

Background:

• Bioretention cells (BRCs) are crucial for urban stormwater treatment.
• Nitrogen removal efficiency in BRCs is highly variable and not fully understood.
• Quantifying denitrifying microorganisms and their control by BRC design is lacking.

Purpose of the Study:

• To analyze denitrifier abundance and activity in BRCs.
• To determine the influence of BRC design characteristics on denitrifier populations.
• To identify factors controlling nitrogen removal in BRCs.

Main Methods:

• Studied 23 BRCs across Maryland, Virginia, and North Carolina.
• Quantified bacterial denitrification genes (nirK and nosZ).
• Measured potential enzymatic denitrification rates in soil media.

Main Results:

• BRC design factors, not local environment, most affected denitrifier abundance and activity.
• Denitrifier populations increased with soil organic carbon and inorganic nitrogen.
• Grass vegetation and bottom BRC layers showed lower denitrifier activity compared to other conditions.

Conclusions:

• BRC design significantly influences nitrogen removal potential.
• Optimizing soil media composition and vegetation can enhance denitrification.
• Further design improvements are possible to mitigate nitrogen export from urban stormwater.