The influence of extensive vegetated roofs on runoff water pollution load

The influence of extensive sedum-moss vegetated roofs on runoff water pollution loads was studied for four full scale installations located in southern Sweden. The aim of the study was to ascertain whether the vegetated roof behaves as a sink or a source of pollutants on annual basis. The pollution loads from vegetated roofs was also compared with the pollution loads from two non-vegetated roofs located in the study areas. The annual pollution loads were calculated based on the measured water quality and the volumes of annual precipitation and the annual roof runoff. Concentrations were measured during four precipitation events in November-December 2003. The following metals and nutrients were investigated: Cd, Cr, Cu, Fe, K, Mn, Pb, Zn, NO3-N, Tot-N, PO4-P, and Tot-P. The results show that, on the annual basis when total loads are considered, vegetated roofs behave as sink of nitrogen and source of potassium and phosphorus, the last with the exception of the oldest vegetated roof. The influence of vegetated roofs on annual heavy metals loads in runoff is less significant.