Abstract
Urbanization leads to higher phosphorus (P) concentration in urban catchments. Among different stormwater retention measures, green roofs are the least efficient in phosphorus retention. Moreover, much research has shown that green roofs act as sources of phosphorus, and they can emit P in significant loads. In this study low P emission green roof substrate was developed based on the proposed step by step procedure for the selection of materials including laboratory tests, column experiments, and the monitoring of the open air green roof model. Developed substrate is the mixture of crushed red brick (35% of volume), crushed limestone (20% of volume), and sand (45% of volume), and is characterized by a bulk density of 1.52 g/cm3, water permeability of 9 mm/min, water capacity of 24.6% of volume, and granulometric composition that meets the Landscaping and Landscape Development Research Society (FLL) guidelines. Limestone was added to limit the potential P leaching from crushed red brick and vegetated mate consisted of Sedum album, Sedum acre, Sedum kamtschaticum, Sedum spurium, Sedum reflexum, Sedum sexangulare, Dianthus deltoides, Dianthus carthusianorum, and Thymus vulgaris. The open air model experiment was run for 319 days, from March 2015 to February 2016. The total water runoff from the green roof model amounted to 43.3% of runoff from the reference roof. The only one runoff event polluted with phosphorus was connected with the outflow of melted snow from an unfreezing green roof model.
Highlights
Urban waters are known to be phosphorus (P) rich environments [1]
As was stated by [18] in their review, research gaps still exists for factors affecting green roof runoff quality
Most of the previous studies concentrate on the monitoring of green roof runoff quality [7,9,10,11,14], not on substrate chemical composition
Summary
Urban waters are known to be phosphorus (P) rich environments [1]. Sources of phosphorus (P) in stormwater runoff originate from lawn fertilizers, atmospheric deposition, soil erosion, animal wastes, grass litter, soil microbial communities, vegetative detritus, and detergents [1,2,3]. Among different stormwater measures e.g., retention soil filters, sedimentation basins, trench infiltration, or swale infiltration; green roofs are the least efficient in phosphorus retention [6]. Much research has shown that green roofs act as sources of phosphorus, and they can emit P in significant loads. In different studies, observed phosphates concentration in leachate amounted: 0.27–0.40 mg/L for Rooflite® drain extensive growth media [7], 2.7 mg/L for extensive mix with 20% of compost and woodchips [8], 1.8 mg/L for GaiaSoil [8], 19.8 mg/Lfor Pro-Gro extensive mix, and 11.2 mg/L for Pro-Gro extensive mix amended with biochar [9], 1.0–3.4 mg/L for Tremco’s aggregate-base extensive substrate [10], 0.4–1.9 mg/L for commercial soil substrate type STT [11], 0.003–0.079 mg/L for GreenGrid® substrate with lightweight expanded shale, composted biosolids and perlite [12], 5.64 mg/L for 6 cm substrate made of pouzzolane, bark and peat [13], 0.23 and 0.18 mg/L for LWA-based green roofs, and sod roofs, respectively [14], 0.16–0.36 mg/L for substrate made of volcanic rock, compost, blonde peat, cooked clay, and washed sand [15], 2.35–3.58 mg/L for extensive green roof models [16], 19.8–40.0 mg/L for substrate made of white peat, black peat, and clay, and 20 mg/L for substrate from volcanic material and compost mixed with mineral and organic fertilizers [17]
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