Dynamic Multi-year Performance of Bioretention Mesocosms—Patterns of Change

Bioretention systems are stormwater practices that are gaining popularity in urban settings as they offer hydrological, water quality, ecological, and aesthetic benefits. This research project investigated the performance of twenty-four bioretention mesocosms with different media, vegetation, and hydrologic loading over the period of four growing seasons since establishment. A total of 72 simulated storm events of varying magnitudes were applied to each mesocosm, allowing comparisons to be made across several design parameters and time. The importance of media and hydrologic regime were apparent early in the investigation. However, events with significant media effects decreased fivefold over the timespan. Vegetation effects were also subject to change, as in the case of reactive phosphorus, where their significance increased from 0 to 100% over the years. Overall, changes over time were observed in volumetric retention of runoff, infiltration, and pollutant concentrations in the effluent. This underscores that the performance of bioretention systems is not static and changes over time. To incorporate natural processes into engineering practice, a better understanding and appreciation of change is needed.