LAUSR

Usage of green roofs is a major technique for urban stormwater management. In this study, layered and mixed substrate green roof platforms, using perlite or vermiculite as adsorption substrates, were established to investigate rainwater retention and pollutant leaching. The platforms were subjected to 12 simulated rainfall events. The average rainwater retention of layered substrate with perlite (30.95% ± 17.20%) was significantly higher than mixed substrate with perlite (21.66% ± 12.91%). However, there was no significant difference in rainwater retention between layered and mixed substrates with vermiculite (p > 0.05). The layered substrate effectively controlled total phosphorus (TP), phosphate (PO4–P) and ammonia (NH4–N) leaching and layered substrate with perlite also exhibited better chemical oxygen demand (COD), total nitrogen (TN) and nitrate (NO3–N) leaching control than the mixed substrate with perlite. The cumulative leaching masses of layered substrate with perlite were lower (COD: 44.77%, TN: 19.60%, TP: 45.51%, NH4–N: 20.27%, NO3–N: 21.47%) than mixed substrate; the TP and NH4. +–N cumulative leaching masses of layered substrate with vermiculite decreased by 51.49% and 25.34% compared with mixed substrate. Moreover, layered and mixed substrates with vermiculite showed better TP, NH4–N and PO4–P leaching control than perlite. The layered substrate improved pollutant leaching overall, but the selection of adsorption substrate plays an important role in the leaching control of green roofs.