Student Research Projects
Mercury and nutrients in runoff from vegetated green roofs
Green roofs are a popular stormwater management strategy since they are effective in reducing runoff volume from buildings. While there are many studies on the quantity of runoff, little research has been conducted on the quality of rainwater runoff from green roofs. As part of an ongoing study, we have been evaluating the nutrients (nitrogen and phosphorus) and mercury in green roof runoff. These pollutants are of particular concern in our Chesapeake Bay watershed since nutrients can lead to eutrophication and “dead zones”, and mercury can bioaccumulate in fish threatening human health. Runoff from green and traditional gravel roofs was collected and compared from both experimental roof plots and real roofs. Chemical amendments were also investigated that could be added to roofs to reduce the nutrient runoff. Our results indicate that green roofs can leach higher concentrations of nutrients than gravel roofs. The chosen chemical amendments were not effective in lowering the nitrogen and phosphorus from the green roof runoff. Although mercury concentrations in runoff were sometimes higher from green roofs than gravel roofs, there was not a large difference in the total load of mercury coming off the roofs. Based on our nitrogen and phosphorus results, we recommend that fertilizer not be added during installation or maintenance of green roofs.
Mercury EXPO - William and Mary