2. Materials and methods
2.1. Site description
The study site and instrumentation have been described elsewhere (Borne et al., 2013a). Briefly, the experimental site is a stormwater retention pond located north of Auckland, New Zealand, and collects the runoff coming from a highway. The catchment is approximately 1.7 ha (75% impervious). The retention pond has been bifurcated into two straight-walled parallel sections (∼100 m2 each) with a permanent water depth of 0.75 m, in order to allow a side by side study. The accumulated sediments were dredged before refilling the pond, leaving a thick clay layer at the bottom. In one partition (FTW pond) an approximately 50 m2 FTW planted with Carex virgata (∼17 plants/m2) was installed in December 2010 (summer in the Southern Hemisphere) ( Fig. 1). The other partition remained as a conventional retention pond, to serve as a control (Control pond- Fig. 1).