A comparison of the growth status, rainfall retention and purification effects of four green roof plant species

Improved efficiency of Sedum lineare (Crassulaceae) in remediation of arsenic-contaminated soil by phosphate-dissolving strain P-1 in association with phosphate rock

The selection of appropriate plants and growth strategies is a key factor in improving the efficiency and universal applicability of phytoremediation. Sedum lineare grows rapidly and tolerates multiple adversities. The effects of inoculation of Acinetobacter sp. phosphate solubilizing bacteria P-1 and application of phosphate rock (PR) as additives on the remediation efficiency of As-contaminated soil by S. lineare were investigated. Compared with the control, both the single treatment and the combination of inoculation with strain P-1 and application of PR improved the biomass by 30.7-395.5%, chlorophyll content by 48.1-134.8%, total protein content by 12.5-92.4% and total As accumulation by 45.1-177.5%, and reduced the As-induced oxidative damage. Inoculation with strain P-1 increased the activities of superoxide dismutases and catalases of S. lineare under As stress, decreased the accumulation of reactive oxygen species in plant tissues and promoted the accumulation of As in roots. In contrast, simultaneous application of PR decreased As concentration in S. lineare tissues, attenuated As-induced lipid peroxidation and improved As transport to shoots. In addition, the combined application showed the best performance in improving resistance and biomass, which significantly increased root length by 149.1%, shoot length by 33%, fresh weight by 395.5% and total arsenic accumulation by 159.2%, but decreased the malondialdehyde content by 89.1%. Our results indicate that the combined application of strain P-1 and PR with S. lineare is a promising bioremediation strategy to accelerate phytoremediation of As-contaminated soils.

Sustainable green roofs: a comprehensive review of influential factors

Green roofs have gained much attention as a modern roofing surface due to their potential to deliver many environmental and social benefits. Studies have indicated that different GR designs deliver different ecosystem services, and there are important factors that affect GR performance. This article reviewed significant factors that influence GR performance and sustainability. Substrate and drainage layer material choice significantly affects stormwater retention potential, leachate quality, plant survival, and determines GR environmental footprints. Subsequently, type of plants, their form, and kinds used on GRs impact GR ecosystem function. Leaf area is the most studied trait due to its influence on the cooling potential and energy performance. In order to achieve a sustainable GR, it is essential to select the type of plants that have a high survival rate. Perennial herbs, particularly forbs and grass as dominant groups, are heat and drought tolerant, which make them suitable in GR experiment. Furthermore, selecting a suitable irrigation system is as important as two other factors for having a sustainable GR. Irrigation is essential for plant survival, and due to the current pressure on valuable water sources, it is important to select a sustainable irrigation system. This review presents three sustainable irrigation methods: (i) employing alternative water sources such as rainwater, greywater, and atmospheric water; (ii) smart irrigation and monitoring; and (iii) using adaptive materials and additives that improve GR water use. This review sheds new insights on the design of high-performance, sustainable GRs and provides guidance for the legislation of sustainable GR.

Stormwater retention performance of green roofs with various configurations in different climatic zones

Green roof stormwater retention performance is fundamentally related to design configurations and climates. Efficient tools for assessing stormwater retention performance of green roofs with various configurations in different climates are highly desirable for practical applications. In this study, a hydrological model which can be used to simulate dynamic changes in moisture content and evapotranspiration of green roofs is developed and tested (with average Nash-Sutcliffe Efficiency of 0.8197 for calibration and 0.8252 for verification) using monitoring data (2018-2019) of four green roofs with various configurations. The model is applied to simulate long-term (1970-2018) moisture content, actual evapotranspiration, and retention performance of green roofs in eight cities across different climates of China. Green roofs built with engineered soil and Portulaca grandiflora show the largest evapotranspiration and thus provide the largest stormwater retention rates (R_r), while green roofs with light growing medium and Sedum lineare show the lowest evapotranspiration and R_r. R_r of green roofs increases as climate changes from humid to arid. Green roofs at Guangzhou (humid climate) provide the lowest R_r (28% ± 3%) caused by plenty of rainfall (1827 mm), while green roofs at Urumqi (desert climate) show the lowest mean annual actual evapotranspiration (167-269 mm) but provide the largest R_r (84% ± 5%) as a result of the lowest annual rainfall (282 mm). The results highlight that stormwater retention performance of green roofs could be enhanced through configuration optimization. However, a limiting factor in improving green roofs water retention rates may be the peculiarity of local climatic conditions.

Growth and development of succulent mixtures for extensive green roofs in a Mediterranean climate

Green roof systems, aimed at reducing anthropic impact on the environment, are considered environmental mitigation technologies and adopted by many countries across the world to strengthen urban ecosystem services. This study evaluates two mixtures of succulent: one of Crassulaceae and the other of Aizoaceae, used in the creation of a continuous and homogenous plant groundcover in Mediterranean environments. To assess the species mixtures, the parameters plant height, growth index, cover percentage and flowering were observed. Hydrological observations were also carried out to evaluate the rainfall retained by the test system in any given month. All data were subjected to analysis of variance. Growth indicators in the study showed trends characteristic of xeric plants, which tend to slow down in dry, summer climate conditions to the point of halting plant vertical growth and ground cover development completely. The Aizocaeae mix, during the initial stage, showed prevalent horizontal growth, confirmed by greater a greater growth index (13,21) and cover percentage (45%) compared to Sedum (Growth index: 3,61; Cover: 36%). In contrast, the Sedum mix recorded greater vertical growth at the beginning (Sedum mixture: 7.53 cm; Aizoaceae mixture: 6,11 cm). During the final stages of observations, however, greater vertical growth in the Aizoaceae (7,88 cm) became apparent together with a recovery in horizontal growth in the Sedum (79%), albeit not sufficient to outperform the Aizoaceae mixture (87%). Flowering in the two mixtures occurred between late spring and late summer. The Sedum mixture guaranteed a longer flowering period (130 days) compared to the Aizoaceae (93 days), with a gradual start followed by steady flower emission. Regarding rainfall water retention, a comparison of the mixtures in late winter/early spring revealed that the Sedum performed best (44.9 L m²vs 37.4 L m²), whilst the Aizoaceae outperformed the Sedum in Autumn (63 L m²vs 55 L m²), in conjunction with favorable growth rates in both species mixtures. Both mixtures demonstrated satisfying results and are considered suited to a Mediterranean environment. Furthermore, based on the different growth rates of the species in the two test mixtures, this study suggests that new combinations of Sedum and Aizoaceae together might prove more resilient in Mediterranean environments.

Experimental evaluation of the rainfall retention and inorganic pollutant mitigation effect by dual-layer and polyacrylamide-modified green roofs

Research on substrate layer modification and filler configuration is an important direction for improving the retention and interception efficiency of green roofs. In this study, four green roof modules were established using peat soil, vermiculite, and zeolite as the main substrate layer. In addition, a polyacrylamide (PAM) modifier was added and mixed with these substrates. By simulating seven rainfall events, this study calculated and analyzed the outflow of each green roof as well as the average event mean concentration (EMC) and cumulative outflow quantity (COQ) of turbidity, ammonia nitrogen ([Formula: see text]), nitrate nitrogen ([Formula: see text]), total nitrogen (TN), and total phosphorus (TP). At the same time, the nitrogen mass balance of each green roof was analyzed. The experimental results showed that the interception capacity of the LP module was higher than the unmodified green roofs under heavy rain conditions. The modules also showed an improved capacity to inhibit the leaching of [Formula: see text]; therefore, TN was effectively suppressed. However, suppression of [Formula: see text] did not significantly improve. The outflow turbidity from the MP and LP modules was low and stable, and the TP concentration showed no apparent change. After the simulated rainfall experiment with the rainfall of 426.3 mm, the proportion of TN leaching out of the LP module was at its lowest (0.85%), and the residual proportion of TN reached 80.7%. Overall, the addition of PAM to the dual-substrate layer can better form the soil aggregate structure, to improve the retention and purification effect of the extensive green roofs.

Stormwater retention and detention performance of green roofs with different substrates: Observational data and hydrological simulations

Green roofs are widely considered as a promising nature-based solution for urban stormwater management. In this study, the stormwater retention and detention performance of 6 green roof modules with different types and depth of substrates at Beijing, China was investigated through 3-year continuous monitoring. The Hydrus-1D was applied to further explore the stormwater management performance of green roofs under extreme storms. The average event-based stormwater retention and detention rates of the green roofs with 10 cm substrates ranged between 81% and 87%, and 83%-87%, respectively; and the average time delays in runoff generation and peak discharge ranged between 82 and 210 min, and 63-131 min, respectively. Green roofs with 15 cm depth of substrates offered higher stormwater retention and peak runoff attenuation rates than those with 10 cm substrates. However, due to the high frequency (55 out of total 92) of light rainfall events (<10 mm) and short antecedent dry weather periods (3.8 days in average), no significant difference was found on stormwater control performance of those green roofs. The Hydrus-1D simulations revealed that green roof stormwater retention rate decreases exponentially with return periods of extreme storms but increases with substrate depth. There exists a critical depth of substrates and further increases in substrate depth beyond this critical value could not bring much improvement in stormwater retention performance of green roofs. The application of extensive green roofs with 10-15 cm substrates provides promising stormwater retention and detention performance in highly urbanized area of Beijing.