Stormwater runoff from paved surfaces, which contains high levels of heavy metals, suspended solids and organic contaminants, has been identified as one of the major causes of pollution in receiving waters. Recent studies have indicated that the use of ecologically-based methods for stormwater treatment, including bioretention systems, may provide increased pollutant removal and protection of downstream receiving waters. However, there is little data addressing the long-term performance of these systems in the field or the effects of contaminant accumulation over time on treatment effectiveness. In this study, we present results from a three year study of a bioretention site in northeastern Kansas. The field study was conducted in Lenexa, KS at a bioretention cell treating stormwater runoff from a 4-lane roadway. A sediment mesh trap was installed in the sewer entrance to filter large particles in the runoff. Samples were collected and analyzed after each storm event for suspended solids (TSS), heavy metals (Cu and Zn) and nutrients (nitrogen and phosphorus). Study results showed that 90% of TSS had been reduced by the bioretention system, while reductions of 50% and 70% for total Cu and total Zn, respectively, were found. Moderate removal rates were observed for total nitrogen and total phosphorus. Accumulation and fate of nutrients in the bioretention cell are analyzed to aid in the design and planning of bioretention systems for better performance under climate and soil conditions found in the Great Plains region. Advisors/Committee Members: Peltier, Edward (advisor), Young, Bryan (cmtemember), Kindscher, Kelly (cmtemember).