Runoff water quality from intensive and extensive vegetated roofs

Vegetated roofs are becoming a trend in urban design, among others as a tool for city greening, mitigating urban heat island effect, and lowering urban storm runoff. Additionally, pollutant removal within vegetated roofs is often expected; however, it is commonly riot a design feature. This study investigated influence on runoff water quality from two fullscale vegetated roofs (an intensive from Japan and an extensive from Sweden). Results show that both extensive and intensive vegetated roofs are a sink of nitrate nitrogen and ammonium. nitrogen with similar performance. The intensive vegetated roof is also a sink of total nitrogen in contrast to the extensive roof. Phosphorus release is observed from the extensive vegetated roof but not from the intensive vegetated roof;, release of dissolved organic carbon and potassium is observed from both roofs. The vegetated roofs, if not retaining the metal pollutants, were generally not a significant source. The increase of average pH during rainwater passage through the intensive vegetated roof indicated rapid neutralization of the acid depositions. (C) 2008 Elsevier B.V. All rights reserved.