In a joint project between two agencies in Singapore, the National Parks Board and the National University of Singapore—Singapore Delft Water Alliance, more than 30 plants species were screened and tested to select those that are suitable for application as vegetation in bioretention systems. The research project investigated the remediation capacity of the plants and their associated rhizosphere microbial communities. Of the numerous stormwater pollutants, the phytoremediation study focused on nitrogen.
The experiments were set up and conducted from September 2010 through June 2011 at a site in Singapore, with an average day time temperature of 32 ± 1.87 °C and night time temperature of 25 ± 1.28 °C.
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The bioretention system comprised of three distinct layers: filtration layer, transition layer and drainage layer. The top filter media composed of 50 % Singapore’s Approved Soil Mix (ASM) and 50 % medium to coarse sand. The transition media is made up of coarse sand and the bottom drainage media is made up of fine gravel. The filter media had a hydraulic conductivity of ca. 136 mm h−1, which was compliant with the 50–200 mm h−1 range proposed in the bioretention design guidelines (PUB 2009).
Layer | Substrate | Particle size (mm) | Depth (mm) |
|---|---|---|---|
Filter media | Mixture of 50 % ASM and 50 % medium to coarse sand | Varied | 600 |
Transition layer | Coarse sand | 0.7–1.0 | 100 |
Drainage layer | Fine gravel | 1.0–5.0 | 200 |
To test the remediation capabilities of the plants for nutrients, irrigation water was chemically spiked to give a final concentration of 10 mg L−1 nitrate and 2 mg L−1 phosphate. These nutrient concentrations were above the levels commonly detected in urban stormwater runoffs, particularly in Singapore (Chua et al. 2009).
At the end of the experiment, the bioretention setups exhibited 100 % efficiency in removing phosphate. However, phosphate was also completely removed in the unplanted control, indicating that the remediation of phosphate was primarily attributable to the bioretention substrate.
Eleven plant species demonstrated high efficiency in nitrate uptake, removing more than 85 %. The plant information of the 24 species with more than 50 % nitrate uptake level is presented below.
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Acalypha wilkesiana
cultivar
Family name: Euphorbiaceae Common names: Copperleaf, Joseph’s Coat Plant growth form: Shrub Maximum height: 3.6 m Maximum plant spread/crown width: 3 m Origin: South Pacific Islands Landscape uses: Hedge; border; mass planting; container or aboveground planter; screen; Accent Desirable plant features: Ornamental foliage Light preference: Full sun Water preference: Moderate Water Percentage of Nitrate Removal: 79 % |
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Arundo donax
var. versicolor
Family name: Poaceae (Gramineae) Common names: Carrizo, Variegated Giant Reed, Spanish Reed Plant growth form: Shrub, Grass and Grass-like Plant Maximum height: 6.1 m Origin: Asia Landscape uses: Architectural accent/Screen Desirable plant features: Ornamental Foliage Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 96 % |
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Bougainvillea
‘Sakura Variegata’
Family name: Nyctaginaceae Common names: Bougainvillea Plant growth form: Scandent shrub Origin : South America Landscape uses: Shrubs, Bushes, Groundcover, Trellis, Accent Desirable plant features: Ornamental Flowers Light preference: Full Sun Water preference: Little Water Percentage of Nitrate Removal: 96 % |
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Bulbine frutescens (L.) Willd.
‘Hallmark’
Family name: Asphodelaceae Common names: Orange Bulbine, Orange-stalked Bulbine Plant growth form: Shrub (Herbaceous; Creeper) Maximum height: 0.3–0.6 m Origin: Southern Africa Landscape uses: Flowerbed/Border Desirable plant features: Ornamental Flowers Light preference: Full Sun Water preference: Little Water Percentage of Nitrate Removal: 68 % |
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Chrysopogon zizanioides (L.) Roberty
Family name: Poaceae (Gramineae) Common names: Vetiver Grass Plant growth form: Shrub, Grass and Grass-like Plant Maximum height: 1.5 m Origin: Tropical India Landscape uses: Hedge, Screening, Accent Plant, Borders Desirable plant features: Strong, deep roots for soil stabilisation Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 93 % |
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Codiaeum variegatum (L.) Rumph. ex A.Juss. Synonyms: Croton pictus, Croton variegatus, Codiaeum variegatum var. pictum
Family name: Euphorbiaceae Common names: Croton, Garden Croton, Puding, Joseph’s Coat, Variegated Croton, Variegated Laurel, Joseph’s Coat, Puding, Codiaeum Plant growth form: Shrub Maximum height: 3 m Origin: South India, Ceylon and Malaya Landscape uses: Indoor, General Desirable plant features: Ornamental Foliage Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 67 % |
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Complaya trilobata
Family name: Asteraceae (Compositae) Synonyms: Wedelia trilobata, Wedelia carnosa, Silphium trilobatum, Thelechitonia
trilobata, Sphagneticola trilobata (L.) Pruski Common names: Yellow Creeping Daisy, Singapore Daisy, Creeping Oxeye, Trailing Daisy, Rabbit’s Paw Plant growth form: Shrub Maximum height: 0.15–0.70 m Maximum plant spread/crown width: 2 m Origin: Central America, South America Desirable plant features: Ornamental flowers, ornamental foliage Landscape uses: General, coastal, flowerbed/border, container planting Light preference: Full sun, semi-shade Water preference: Moderate water Percentage of Nitrate Removal: 95 % |
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Cymbopogon citratus (DC.) Stapf
Synonyms: Andropogon citriodorum, Andropogon citratus
Family name: Poaceae (Gramineae) Common names: Serai, Lemon Grass, West Indian Lemon Grass, Oil Grass, Fever Grass, Serai Makan, Sereh Makan Plant growth form: Shrub, Grass and Grass-like Plant Maximum height: 1.2–1.8 m Maximum plant spread/crown width: 1.2 m Origin: Southeast Asia Landscape uses: General, Flowerbed/Border, Container Planting Desirable plant features: Ornamental Foliage, Fragrant (Flowers: Time Independent; Foliage) Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 95 % |
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Dracaenaceae reflexa ‘Song of India’
Family name: Dracaenaceae Synonyms: Pleomele reflexa ‘Variegata’ Common names: Song of India Plant growth form: Shrub Origin: South India, Ceylon Desirable plant features: Ornamental Foliage Landscape uses: General Light preference: Full Sun, Semi-Shade Water preference: Moderate Water Percentage of Nitrate Removal: 64 % |
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Ficus microcarpa ‘Golden’
Synonyms: Ficus nitida ‘Golden’ Family name: Moraceae Common names: Indian Laurel Fig Plant growth form: Tree Maximum height: 10 m Origin: India, Malaysia Landscape uses: House plantings, Hedge, Roadside Plantings, Bonsai Desirable plant features: Ornamental Foliage Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 68 % |
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Galphimia glauca Cav.
Synonyms: Thryallis glauca Family name: Malpighiaceae Common names: Shower of Gold, Rain of Gold Plant growth form: Shrub (Woody) Maximum height: 1.0 m Origin: Mexico to Guatemala Landscape uses: Hedge/Screening, Groundcover, Container planting Desirable plant features: Ornamental Flowers Light preference: Full Sun Water preference: Little Water Percentage of Nitrate Removal: 65 % |
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Ipomoea pes-caprae
Family name: Convolvulaceae Synonyms: Ipomoea pes-caprae ssp. Brasiliensis, Ipomoea biloba Common names: Beach Morning Glory, Railroad Vine, Sea Morning Glory, Tapak Kuda, Goat’s Foot Plant growth form: Groundcover Origin: Native to Singapore Desirable plant features: Ornamental flowers, ornamental foliage Landscape uses: Coastal Light preference: Full sun Water preference: Lots of water Flower Colour(s): Purple Percentage of Nitrate Removal: 95 % |
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Leucophyllum frutescens (Berland.) I.M. Johnst.
Family name: Scrophulariaceae Common names: Barometer Bush, Ash Plant, Cenizo, Texas Ranger, Texas Silver Leaf, Purple Sage Plant growth form: Shrub (Woody) Maximum height: 1.2–2.4 m Maximum plant spread/crown width: 1.5 m Origin: Rio Grande Valley (Texas, New Mexico), northern Mexico Landscape uses: General, Coastal, Hedge/Screening, Flowerbed/Border, Container Planting Desirable plant features: Ornamental Flowers, Ornamental Foliage, Ornamental Stems, Fragrant (Flowers: Day; [Remarks]: Peppery/spicy scent, reminiscent of carnations) Light preference: Full Sun Water preference: Little Water Percentage of Nitrate Removal: 87 % |
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Loropetalum chinense (R. Br.) Oliv. Family name: Hamamelidaceae Common names: Chinese Loropetalum Plant growth form: Shrub Maximum height: 1.5 m Origin: China Landscape uses: Hedge, Garden Plant Desirable plant features: Ornamental Flowers, Ornamental Foliage Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 71 % |
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Melastoma malabathricum L. Family name: Melastomataceae Common names: Common Sendudok, Singapore Rhododendron, Indian Rhododendron, Sesenduk, Malabar Gooseberry, Straits Rhododendron, Sendudok, Senduduk Plant growth form: Shrub (Herbaceous) Maximum height: 1–3 m Origin: Mauritius, Seychelles, Taiwan, Indian subcontinent, Indo-China, Malesia, Australia Landscape uses: Invasive/Potentially Invasive, [Remarks] (Considered weedy. May form thick thickets) Desirable plant features: Ornamental Flowers Light preference: Full Sun, Semi-Shade Water preference: Moderate Water Percentage of Nitrate Removal: 68 % |
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Nerium oleander ‘Pink’
Family name: Apocynaceae Common names: Oleander Plant growth form: Shrub Maximum height: 6–7 m Origin: Unknown, probably South-west Asia Landscape uses: Interiorscape/ Indoor Plant, Hedges, Borders Desirable plant features: Ornamental Flowers, Fragrant Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 88 % |
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Ophiopogon jaburan
Family name: Convallariaceae Common names: Lilyturf, Mondo-grass Plant growth form: Groundcover Origin: Japan Landscape uses: Ornamental plants in gardening, houseplants Desirable plant features: Ornamental foliage Light preference: Full sun, semi-shade Water preference: Moderate water Percentage of Nitrate Removal: 77 % |
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Osmoxylon lineare (Merr.) Philipson
Synonyms: Boerlagiodendron lineare Family name: Araliaceae Common names: Green Aralia, Miagos Bush Plant growth form: Shrub (Herbaceous) Maximum height: 3 m Origin: South-east Asia Landscape uses: This species is used in Japanese-style gardens for its fine leaf texture Desirable plant features: Ornamental Foliage Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 66 % |
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Pennisetum alopecuroides (L.) Spreng.
Synonyms: Panicum alopecuroides, Alopecurus hordeiformis, Pennisetum hordeiforme, Pennisetum compressum, Pennisetum japonicum Family name: Poaceae (Gramineae) Common names: Chinese Fountain Grass, Swamp Foxtail Grass, Swamp Foxtail, Chinese Pennisetum Plant growth form: Shrub (Herbaceous), Grass and Grass-like Plant Maximum height: 0.6–1.5 m Maximum plant spread/crown width: 0.5–0.6 m Origin: India, China, Japan, Myanmar, Philippines, Indonesia, Australia Landscape uses: General, Coastal, Flowerbed/Border, Container Planting Desirable plant features: Ornamental Flowers Light preference: Full Sun Water preference: Lots of Water, Moderate Water Percentage of Nitrate Removal: 93 % |
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Pennisetum x advena ‘Rubrum’ Synonyms: Pennisetum setaceum ‘Cupreum’, Pennisetum setaceum ‘Rubrum’ Family name: Poaceae (Gramineae) Common names: Purple Fountain Grass, Red Fountain Grass, Rose Fountain Grass Plant growth form: Shrub (Herbaceous; Creeper) Maximum height: 1.2–1.5 m Maximum plant spread/crown width: 0.5–1.2 m Origin: Central Africa Landscape uses: General, Coastal, Green Roof, Vertical Greenery/Green Wall, Flowerbed/Border, Focal Plant, Container Planting Desirable plant features: Ornamental Flowers, Ornamental Foliage Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 70 % |
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Phyllanthus myrtifolius Müll.Arg.
Family name: Euphorbiaceae Common names: Ceylon Myrtle, Mousetail Plant Plant growth form: Shrub Maximum height: 0.5 m Origin: India, Sri Lanka Landscape uses: Flowerbed/Border, Bonsai Desirable plant features: Ornamental Foliage Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 55 % |
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Sanchezia oblonga Ruiz & Pav. Synonyms: Sanchezia speciosa, Sanchezia nobilis Family name: Acanthaceae Common names: Zebra Plant, Yellow Sanchezia, Shrubby Whitevein, Gold Vein Plant Plant growth form: Shrub (Herbaceous) Maximum height: 1–3 m Origin: Eucador, Northeastern Peru Landscape uses: Hedge/Screening, Flowerbed/Border, Interiorscape/ Indoor Plant, Container Planting Desirable plant features: Ornamental Flowers, Ornamental Foliage Light preference: Full Sun, Semi-Shade Water preference: Moderate Water Percentage of Nitrate Removal: 87 % |
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Serissa japonica (Thunb.) Thunb.
Synonyms: Serissa foetida Family name: Rubiaceae Common names: Japanese Serissa, Snowrose, Tree of a Thousand Stars, Japanese Boxthorn Plant growth form: Shrub (Woody) Maximum height: 0.45–0.60 m Origin: India, China, Japan Landscape uses: General, Coastal, Container Planting, Bonsai Desirable plant features: Ornamental Flowers, Ornamental Foliage, Ornamental Stems, Fragrant (Flowers: Time Independent; Foliage; Stems) Light preference: Full Sun, Semi-Shade Water preference: Moderate Water Percentage of Nitrate Removal: 71 % |
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Scaevola taccada (Gaertn.) Roxb. Synonyms: Scaevola sericea, Lobelia taccada, Scaevola frutescens Family name: Goodeniaceae Common names: Ambung-ambung, Merambung, Pelampung, Sea Lettuce, Sea Lettuce Tree Plant growth form: Tree, Shrub (Herbaceous; Creeper) Maximum height: 10 m Origin: S.E.A. to tropical Australia, Micronesia, Melanesia, Hawaii and Madagascar Landscape uses: Coastal Desirable plant features: Ornamental Foliage Light preference: Full Sun Water preference: Moderate Water Percentage of Nitrate Removal: 88 % |
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