Nonpoint sources are responsible fo

Nonpoint sources are responsible for a significant amount of
water quality impairments in the United States (USEPA, 2009). In
urban areas, roof surfaces contribute excess nutrients and toxic
metals to receiving waters (Bannerman et al., 1993; Egodawatta
et al., 2009; Förster, 1996; Van Metre and Mahler, 2003). These surfaces
can cover from 12% in residential areas to 21% in commercial
areas (Bannerman et al., 1993; Boulanger and Nikolaidis, 2003).
Green roofs are becoming more common in North America as a
means to control runoff and nonpoint source pollution from urban
areas, and for their aesthetic value, insulation and noise reduction,
and wildlife habitat (Getter and Rowe, 2006; Teemusk and Mander,
2006; USEPA, 2005b). Green roofs are classified as either extensive
or intensive and are often added to an existing roof. The difference
between the two types is based primarily on the thickness of the
growing media and the vegetation present. Extensive green roofs
typically have thin (≤10 cm) media and drought tolerant vegetation,
whereas intensive green roofs have thicker growing media
and may include trees and shrubs (Berndtsson, 2010; Carter and
Fowler, 2008; Getter and Rowe, 2006). All green roof construction
∗ Corresponding author. Tel.: +1 860 486 0139; fax: +1 860 486 5408.
E-mail addresses: bruce.gregoire@uconn.edu (B.G. Gregoire),
john.clausen@uconn.edu (J.C. Clausen). 1 Tel.: +1 860 486 1874; fax: +1 860 486 5408.
typically consists of a root barrier, drainagematerial layer, filter fabric,
growing media, and vegetation (Berndtsson, 2010; Clark et al.,
2008; Getter and Rowe, 2006).