**Abstract Text**
Bioretention cells are an increasingly popular green infrastructure stormwater control measure (SCM) which rely on an engineered sandy soil media, vegetation, and microbes to treat stormwater. Stemming from nutrient leaching observed from organic-rich media blends used in early installations, today’s bioretention cells often feature nutrient deficient soils (i.e., low organic content, low P content) designed to limit pollutant export. Sedimentation, filtration, and biogeochemical transformations in these systems contribute to long-term, sustainable removal of particulate-bound and dissolved pollutants. However, the capacity to adsorb dissolved pollutants such as P to bioretention media is finite; pollutant accumulation over the lifespan of these systems (i.e., 20-25 years) may introduce challenges and questions regarding maintenance intervals required to prevent pollutant breakthrough. There is a need to understand the evolution of bioretention media over time and the patterns and influential factors which impact pollutant accumulation to inform the long-term management of these systems. To that end, soils of 47 bioretention cells in Ohio, Kentucky, and Michigan were sampled between 7-19 years after their construction. Despite a lack of spatial variation in P accumulation, P concentrations were significantly higher in the organic-laden upper 5 cm of the filter material compared with soils 10-15 cm and 35-50 cm below the surface, which more closely resembled the original media blends. Results from this study can be used to better understand P concentrations in bioretention cells over time and the frequency at which maintenance measures targeting pollutant accumulation (e.g., media replacement) are needed to prevent media saturation and export.



Investigating Phosphorus Retention in Mature Bioretention Cells in the Midwestern US (Room 301 C, Monday 7th, 1:30pm-3:00pm)

The International Low Impact Development Conference highlights interdisciplinary practice, research, and implementation of Low Impact Development (LID), Green Infrastructure (GI), Sustainable Urban Drainage Systems (SUDS) and Water Sensitive Urban Designs (WSUD). The focus will be on using our past and present understanding of LID to tune management programs, design practice, and operation and maintenance into the future.