Design and Development of Low P-Emission Substrate for the Protection of Urban Water Bodies Collecting Green Roof Runoff

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/cm 3 , 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.

Phosphate Leaching from Green Roof Substrates—Can Green Roofs Pollute Urban Water Bodies?

“…Most green roof substrates are a mixtures of mineral and organic compounds. The most popular mineral components are: clay, sand, volcanic materials, crushed brick, and expanded lightweight materials, and among organic components, the most popular are: compost and peat [4]. Compost typically has very high P content.…”

“…Compost typically has very high P content. Buffam and Mitchell [5] obtained the value of leachable phosphate of above 200 mg•P-PO 4 3− /kg in deionized water extract. Toland et al [6] reported that SRP concentrations in runoff from green roofs with compost were more than 10 times greater than SRP concentrations without compost added.…”

Phosphorus and Metals Leaching from Green Roof Substrates and Aggregates Used in Their Composition

“…Only one sample (SM1) of 13 tested substrates was within this limit ( Figure 5). SM1 is the mineral substrate developed as a "low P emission substrate" [32]. Mineral-organic substrates (SMO 1-7) were characterized by high P content (37.68-713.23 mg/kg), as well as second mineral substrate SM2 (554.16 mg/kg) and Sedum mates Ma1-4 (24.79-917.09 mg/kg).…”

“…Based on the review given in [32], the most popular mineral components of green roof substrates are stated as clay, sand, volcanic materials, crushed brick, and expanded lightweight materials, while the most popular organic components are compost and peat. For the purpose of this study, tested mineral substrate compounds were characterized as natural origin (17 samples) and man-made (12 samples).…”

Green-Roof: The Role of Community in the Substitution of Green-Space toward Sustainable Development

“…The benefits of green-roof contribute to some environmental aspects, including increasing biodiversity, reducing the effects of urban heat island [1][2][3][4][5], decreasing the thermal temperature of buildings [6][7][8]; on the economic aspect, including reducing maintenance costs and lowering operational costs [9][10][11]; and on aspects of social space, where people have access to green areas [12][13][14]. Economically, green-roof initiatives are feasible under certain conditions, but consideration needs to be paid to the construction costs of green-roof for the entire roofs of the buildings [9].…”