145-4 Studying Long-Term Bioswale Effectiveness: Assessing the Progression of Heavy Metal Accumulation in Surface Materials.

Session: Dynamics of Natural and Built Environments (Posters)

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Bioswales are constructed to treat contaminated stormwater runoff by filtering the water and trapping pollutants in the bioswale plants and soils that would otherwise make their way into crucial groundwater or surface-water systems. This study seeks to understand how effective four bioswales, built by the Illinois Tollway along I-294 in northern Illinois in 2011, were at trapping common roadway metals within the bioswale soils over a 12-year period. Soil samples were collected from the upper 10 cm of soil within the four bioswales in 2011, 2015, and 2023, with 360 samples collected from the same locations along established transects in each year. The samples were analyzed in the lab for 30 different metals, however this study focused on zinc (Zn), copper (Cu), nickel (Ni), lead (Pb), chromium (Cr), and cadmium (Cd), heavy metals associated with automotive components and commonly found in roadway runoff. Concentrations of these metals were compared for each bioswale across all sampling years. Concentrations of Zn, Cu, Ni, and Cr generally increased during the 12-year period, with the highest overall percent increase observed in Zn. Concentrations of Cd and Pb generally decreased in three of the four bioswales, with the highest percent decrease observed in Cd. Percent differences in metal concentrations were generally positive and of higher magnitude as measured between 2015 and 2023 (8 years between sampling) versus 2011 and 2015 (four years between sampling). Changes in accumulation rates are possibly due to remobilization of heavy metals or changes in bioswale storage capacity over time. Differences in accumulation rates could also be due to changes in traffic density or precipitation levels over the course of this study. This study suggests that over the long term, the I-294 bioswales are capturing and trapping several roadway metals, some more effectively than others. Continued long-term monitoring and more consistent sampling periods are needed to better assess accumulation rates of metals in the bioswale soils and to track changes in bioswale effectiveness and heavy metal adsorption capacity over time.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9008

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