[Urban Runoff Phosphorus Removal Pathways in Bioretention Systems].

Area of Science:

• Environmental Science
• Water Resources Management
• Soil Science

Background:

• Stormwater runoff is a significant source of phosphorus pollution.
• Bioretention systems are engineered systems designed to treat stormwater runoff.
• Understanding phosphorus removal mechanisms in bioretention is crucial for effective water quality management.

Purpose of the Study:

• To investigate the role of vegetation and saturated zones in removing dissolved phosphorus (PO43--P) from stormwater using bioretention microcosms.
• To evaluate the effectiveness of different bioretention configurations under varying hydrological and phosphorus loading conditions.

Main Methods:

• Nine bioretention columns with mixed filter media (sand and local soil) were used.
• Columns were dosed with synthetic stormwater under varied hydrological conditions and phosphorus loading rates.
• Monitoring was conducted over a 12-month period to assess phosphorus removal.

Main Results:

• Bioretention systems achieved remarkable phosphorus removal (>90%), with or without vegetation.
• Planting *P. alopecuroides* significantly enhanced PO43--P removal.
• Saturated zones reduced effluent PO43--P but did not significantly impact total phosphorus removal.
• Phosphorus retained in the top 0-22.5 cm of filter media was available for plant uptake.
• 57.1% to 76.1% of total phosphorus input was stored in above-ground plant shoots.

Conclusions:

• Bioretention systems utilizing sand and local soil are highly effective for stormwater phosphorus removal.
• Vegetation, particularly *P. alopecuroides*, enhances dissolved phosphorus removal.
• Periodic harvesting of plant shoots presents a sustainable strategy for phosphorus management in bioretention systems.