Wuhuan Zhang

Green infrastructure (GI) protects aquatic ecosystems from stormwater runoff caused by urban development. Bioretention (BR) is a typical GI system wherein stormwater runoff is routed to a soil basin planted with vegetation and has been shown to reduce deicing salt loads in surface runoff, but the removal mechanism of salt is poorly understood. This study explores the potential of different vegetation types to reduce deicing salt released from a BR by transpiration. Six engineered soil media columns were built in a laboratory greenhouse to simulate a 1012 m² BR basin along Lorton Road, Fairfax County, VA, USA. The effect of vegetation type (Blue Wild Indigo and Broadleaf Cattail) and influent salt concentration on flow volume and salt mass reduction were quantified for multiple storm events. For all storm events, chloride inflow concentrations, and vegetation types, Cl⁻ load reduction ranged from 26.1% to 33.5%, Na⁺ load reduction ranged from 38.2% to 47.4%, and volume reductions ranged from 11.4% to 41.9%. Different inflow salt concentrations yielded different removal rates of deicing salt, and for a given column, salt removal decreased over sequential storm events. For each influent salt concentration, columns planted with Broadleaf Cattail (BC) performed better for volume and salt mass reductions than columns planted with Blue Wild Indigo (BWI), which in turn performed better than the controls.

Green stormwater infrastructure (GI) imitates the hydrology of undeveloped land to mediate the impacts of stormwater runoff, but research is lacking that characterizes the performances of different types of independent GI systems in close proximity to each other in terms of runoff volume reduction. To address this gap, the runoff reduction by four GI systems was monitored for 48 rain events ranging in depth from 2.8 to 96.5 mm, with a total rain depth of 1,404.1 mm from June 2018 to July 2019, during their first full year of operation. The GI systems, located within 1 km of each other along Lorton Road in Fairfax County, Virginia, were a grass channel (GC), bioretention (BR), bioswale (BS), and compost-amended grass channel (CAGC). The GC, BR, and BS were on track to well exceed minimum requirements of the Virginia Department of Environmental Quality, with relative runoff reductions of 78%, 71%, and 56%, respectively, but the CAGC performed near its requirement at 43%. Contrary to expectations, the simply designed GC achieved the highest runoff reduction. The BR, with the second highest runoff reduction, had a small footprint relative to its contributing drainage area and demonstrated the least variation in performance in variable rainfall depths, intensities, and durations. The relatively small volume reductions of the BS and CAGC were attributed to their respective design elements: a sloping underdrain and close proximity to the road. This field study explored variations in runoff volume reductions of the four systems in various rainfall and seasonal conditions with respect to their design complexities, providing insights for future design and implementation of GI.

A novel sorbent material for Pb(ii) sorption was created by coating graphene oxide (GO) on a pretreated PDMS sponge.