Field Study of the Ability of Two Grassed Bioretention Cells to Reduce Storm-Water Runoff Pollution

• Published in: Journal of irrigation and drainage engineering 2009-08, Vol.135 (4), p.505-510
• Main Authors: Passeport, Elodie, Hunt, William F, Line, Daniel E, Smith, Ryan A, Brown, Robert A
• Format: Article
• Language: English
• Subjects: Agricultural and forest climatology and meteorology. Irrigation. Drainage; Agronomy. Soil science and plant productions; Asphalt; autumn; Biological and medical sciences; coliform bacteria; Contact; denitrification; Drainage; Effluents; feces; Fluid dynamics; Fluid flow; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; grasses; Hydraulics; Inflow; Inlets; Irrigation; Irrigation. Drainage; Media; nitrate nitrogen; nitrogen; North Carolina; Nutrients; Outflow; Outlets; Parking; Phosphorus; Pollution abatement; pollution control; pollution load; Reduction; Runoff; Seasons; shrubs; Storms; stormwater; Stormwater management; Surface area; Sustainable development; TECHNICAL NOTES; Trees; Vegetation; Water pollution; Winter
• ISSN: 0733-9437; 1943-4774
• DOI: 10.1061/(ASCE)IR.1943-4774.0000006

Two grassed bioretention cells including internal storage zones (ISZs) were monitored for 16 months in central North Carolina. Each cell had a surface area of 106 m2 and fill media depths were 0.75 and 1.05 m for the north (North) and the south (South) cells, respectively. Asphalt parking lot inflow and outflows were analyzed for nitrogen and phosphorus forms and fecal coliform (FC). Outflow volumes and peak flows for individual storms were generally less than those of inflow. Overall, except for N O2,3 –N , effluent nitrogen species event mean concentrations (EMCs) and loads were significantly (α=0.05) lower than those of the inflow, and nitrogen species load reductions ranged from 47 to 88%. Apart from fall and winter, during which a longer hydraulic contact time seemed to be needed, the ISZs appeared to improve denitrification. Total phosphorus (TP) and OP O4 -P EMCs were significantly lower than those of the inlet. Reductions were 58% (South) and 63% (North) for TP and 78% (North) and 74% (South) for OP O4 –P . There was no significant difference in TP and OP O4 –P loads between the inlet and the two outlets. Moreover, effluent concentrations for both phosphorus species were low, relative to other studies. The best nutrient EMC and load reductions occurred during the warm and humid seasons. When considering effluent concentrations in addition to removal rates, the grassed cells showed promising results for FC and nutrient pollution abatement when compared to conventionally vegetated bioretention (trees, shrubs, and mulch) previously studied in North Carolina.