Student Research Projects
Effectiveness of Amendments in Reducing nutrients and Mercury release from Green Roofs
Vegetated green roofs are effective in reducing storm water runoff. However, recent literature and experiments at Virginia Wesleyan College have found that green roofs leach higher concentrations of nutrients and mercury than typical gravel roofs due to added fertilizer or compost in the growing media, which can impact eutrophication and human health. Preliminary laboratory studies indicated that alum and Ultra-Phos Filter showed promise at reducing nutrient runoff. Fifteen experimental green roof plots and two real green roofs were used to evaluate 1) the difference in nutrient and mercury runoff from green versus traditional gravel roofs, and 2) the effectiveness of alum and Ultra-Phos Filter in reducing nutrients and mercury in the runoff. The experimental plots were divided among the following treatments: standard green roof, green roof plus alum, green roof plus Ultra-Phos Filter, and standard gravel roof. A dormitory roof was divided into four sections: green with slow release fertilizer, green with no fertilizer, green with fertilizer and Ultra-Phos Filter, and gravel. The roof of a commercial building in downtown Portsmouth, VA, was divided into two sections: green with Ultra-Phos Filter and gravel. Two to three rainstorms were sampled for each of the roof types. These initial results indicate that the green roofs continued to leach higher concentrations of nutrients than the gravel roofs, even three years after installation. The mean concentrations of nitrogen and phosphorus were not significantly lower in the treatments with added alum or Ultra-Phos Filter. Plans for ongoing studies to confirm these results will be discussed.
Virginia Water Research Conference, Oct 2009, Richmond, VA