Impacts of types and depth of substrates on quantity and quality of runoff from green roofs
ZHANG Sunxun1, ZHANG Shouhong1,2
1. School of Soil and Water Conservation, Beijing Forestry University, 100083, Beijing, China; 2. Beijing Engineering Research Center of Soil and Water Conservation, 100083, Beijing, China
Abstract:[Background] As an important measure of sponge city, green roofs have been wildly adopted in urban water resource management in recent years. However, few researches focus on both water quantity and quality of green roof runoff in North China. Substrate is one of the key components of green roofs, thus it is important to clarify how substrate influences runoff quantity and quality from green roof. [Methods] We set up 6 extensive green roofs with 3 types (i. e., local planting soil, engineered soil, and light growing medium) and 2 depths (15 cm and 10 cm) of substrates in Beijing. In order to analyze the influences of type and depth of substrates on the water quantity and quality of green roof runoff, we used a weather station (HOBO U30) and rain gauges to monitor the rainfall and runoff processes of green roofs under natural rainfall conditions during the rainy season in 2017. The nutrients (NH4+-N, NO3--N, NO2--N and PO43--P) and dissolved heavy metals (DCr, DCd, DCu, and DNi) in the rainwater and runoff were analyzed by Automatic Discrete Analyzer (SmartChem 200) and ICP-MS. [Results] 1) The average runoff reduction rates of green roofs with local planting soil and engineered soil were significantly higher than the that of green roofs with light growing medium (P<0.05). The local planting soil, engineered soil and light growing medium green roofs with a substrate thickness of 15 cm provided higher runoff reduction rates (67.8%, 60.3%, and 46.6%, respectively) than the those with a substrate thickness of 10 cm (55.6%, 53.0%, and 41.5%, respectively). 2) The experimental green roofs were the sinks of NH4+-N, NO3--N and NO2--N, the mean pollution load reduction rates were (86.8±15.6)%, (69.4±17.1)% and (58.5±24.1)%, respectively. The engineered soil green roof with a substrate thickness of 15 cm and the light growing medium green roof with a substrate thickness of 10 cm were the sinks of PO43--P, the reduction rates of pollution loads were 21.8% and 7.8%, respectively, but the other green roofs were all the sources of PO43--P. 3) The experimental green roofs were the sinks of DCd, and the mean reduction rate of pollution load was (52.4±8.8)%. Except for the engineered soil green roof with a substrate thickness of 15 cm was the sink of DCr (the reduction rate of pollution load was 18.6%), the other 5 green roofs were all the sources of DCr, and all of the 6 experimental green roofs were the sources of DCu and DNi. [Conculsions] The runoff reduction rates of local planting soil and engineered soil green roofs are significantly higher than that of the light growing medium green roofs. Green roofs with 15 cm depth have better performance in runoff management than green roofs with 10 cm depth. The substrate type and depth also affect pollution loads in runoff from green roofs, and all the 6 experimental green roofs were the sinks of NH4+-N, NO3--N, NO2--N, and DCd, but were the sources of DCu and DNi. The results of this experiment provide scientific reference for the water quality evaluation and hydrologic design of green roofs in North China.
章孙逊, 张守红. 基质类型及厚度对绿色屋顶径流量和水质影响[J]. 中国水土保持科学, 2021, 19(2): 117-126.
ZHANG Sunxun, ZHANG Shouhong. Impacts of types and depth of substrates on quantity and quality of runoff from green roofs. SSWC, 2021, 19(2): 117-126.
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