Harnessing Vegetation For Pollutant Capture In Sustainable Urban Drainage Systems

Janine Robinson from Portsmouth University embarked on a research project to explore how grasses and wildflowers could improve the performance of Sustainable Urban Drainage Systems (SuDs). Her study aimed to address urban surface water pollution and erosion by investigating the potential of vegetation to slow water flow and absorb pollutants. A key focus of the research was on Polycyclic Aromatic Hydrocarbons (PAHs), harmful pollutants found in road runoff, primarily from vehicle emissions, brake dust, and oil. Understanding how plants can trap or break down these pollutants was central to her investigation.

In late 2015, a 32-foot-long model swale was constructed, utilizing sod supplied by our sister company, Wildflower Turf Ltd. The swale was installed on nearly one foot of soil, allowing sediment samples to be collected for in-depth analysis. To simulate storm events, 264 gallons of water were introduced over a 30-minute period, with half of the water containing PAH pollutants. These storm simulations were conducted regularly, and sediment samples were collected biweekly to monitor pollution levels within the soil. Runoff water was also analyzed to measure water quality output. Additionally, mesocosms were developed to further explore the role of plants in reducing pollutant levels.

Early results indicate that vegetated swales can significantly enhance water quality in urban drainage systems. The study found that the plants demonstrated resilience, with no observable decline in growth, despite frequent exposure to high levels of pollution. PAH retention was highest in the top two inches of soil, highlighting the importance of plant roots in capturing and retaining pollutants. The significant reduction of PAHs in deeper soil layers suggests that the vegetated layer effectively traps pollutants before they can penetrate further. As Janine Robinson notes, "evidence so far shows that vegetated swales significantly improve water quality," reinforcing the value of integrating vegetation into SuDs for urban water management.