Impacts of Runoff Water Quality from Extensive Green Roofs

摘要

Green roofs are well-documented for mitigating volume and flow rate of stormwater runoff.However, impacts associated with nutrients in green roof runoff are less well-known. This studycompares water quality of green roof runoff with precipitation and runoff from a traditionalshingle membrane roof. A demonstration-scale extensive green roof reduced overall runoffvolume and served as a sink for nitrate and ammonium but was a source for phosphate, sulfate,dissolved organic carbon, and organic nitrogen, particularly notable during large storms (>0.5inches rainfall). Zinc and lead data suggested higher mass loads in traditional roof runoff than inprecipitation and green roof runoff, although results were not statistically significant. Life CycleAssessment software was used to map pollutant mass loads to environmental impacts, taking intoaccount runoff volume reduction by the green roof. As a source of phosphorous and a sink fornitrogen, LCA results show negligible or reduced impacts from the green roof in all categoriesexcept freshwater eutrophication. Therefore, impacts of fertilization should be considered wheninstalling and maintaining green roofs, especially near inland freshwaters where phosphorus isthe limiting nutrient.