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[Inter-annual Changes in Runoff Quality from Green Roofs with Different Vegetation]
Sun-Xun Zhang1, Shou-Hong Zhang1,2, De Ge1
1School of Soil and Water Conservation, Beijing Forestry University, Beijing 100083, China.
Huan Jing Ke Xue= Huanjing Kexue
|June 10, 2022
Summary
Green roofs effectively reduce ammonium-nitrogen runoff but increase phosphorus and heavy metal concentrations. Vegetation type and monitoring duration significantly impact nutrient and metal levels in runoff over time.
Area of Science:
- Environmental Science
- Urban Hydrology
- Green Infrastructure
Background:
- Green roofs are crucial components of sponge city initiatives, aimed at managing urban stormwater runoff.
- Understanding the long-term impact of different vegetation types on green roof runoff quality is essential for optimizing their performance.
- Previous research has highlighted the potential of green roofs to improve water quality, but inter-annual variations require further investigation.
Purpose of the Study:
- To investigate the inter-annual changes in runoff quality of green roofs with different vegetation types.
- To evaluate the influence of vegetation type (Sedum lineare, Portulaca grandiflora, and non-vegetated control) and monitoring period on runoff pollutant concentrations.
- To assess the role of green roofs as either sinks or sources for key nutrients and heavy metals in urban stormwater.
Main Methods:
- Field experiment established three green roofs with distinct vegetation covers in Beijing.
- Rainwater and runoff quality were monitored during the rainy seasons from 2017 to 2019.
- Plant growth characteristics and concentrations of ammonium-nitrogen (NH4+-N), nitrate-nitrogen (NO3--N), phosphate-phosphorus (PO43--P), and heavy metals (Cr, Cu, Ni) were analyzed.
Main Results:
- All green roofs acted as sinks for NH4+-N, reducing concentrations by 50.1%–79.2%.
- Green roofs were sources of PO43--P, Dichromate (DCr), Dicuprum (DCu), and Dinickel (DNi).
- Vegetation type and monitoring duration significantly affected NO3--N, PO43--P, DNi, and DCu concentrations (P<0.05).
- NO3--N runoff concentrations increased yearly in the non-vegetated control and S. lineare green roofs, while PO43--P increased in the P. grandiflora green roof.
- P. grandiflora showed superior NO3--N retention but potentially increased PO43--P, DNi, and DCu runoff concentrations.
Conclusions:
- Green roofs significantly alter stormwater runoff quality, with varying effects depending on vegetation type and time.
- While effective for NH4+-N removal, green roofs can contribute to nutrient and heavy metal pollution, necessitating careful plant selection and management.
- Long-term monitoring is crucial for understanding the dynamic performance of green roofs in urban water management.
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