Nutrient leaching in extensive green roof substrate layers with different configurations

Component design optimization of green roof substrate layer based on the assessment of multifunctional performance

A high-quality substrate layer is the cornerstone of supporting that green roofs (GRs) can become an efficient and sustainable nature-based solution to urban environmental problems. In the present study, three lightweight substrate materials commonly used in GRs of peat soil, vermiculite and pumice with four appropriate proportions of the nutrient substrate and the mineral substrates were selected to install twelve substrate modules. The lightweight property, water-holding, nutrient retention and rainwater reduction performance of the substrate modules were investigated by the laboratory determination methods and the simulated rainfall experiment. An assessment model based on the multifunctional performance established by analytic hierarchy process (AHP) was used for the component design optimization of GR substrate layer. The results showed that the substrate modules based on peat soil and vermiculite (PV) as the mineral substrate, which the dry volumetric weights and the average water content were 1.40-1.70 kN m-3 and 47.80%-49.06%, always exhibited better lightweight properties and water-holding performance compared to those composed of pumice. PV-40 had the highest value of the multifunction index even while none of its functional performance was optimal among all the substrate modules. The present study emphasizes the necessity of optimizing the GR substrate layer component based on the assessment of multifunctional performance to better promote the sustainable development of GRs in urban areas.

Biochar Benefits Green Infrastructure: Global Meta-Analysis and Synthesis

Urbanization has degraded ecosystem services on a global scale, and cities are vulnerable to long-term stresses and risks exacerbated by climate change. Green infrastructure (GI) has been increasingly implemented in cities to improve ecosystem functions and enhance city resilience, yet GI degradation or failure is common. Biochar has been recently suggested as an ideal substrate additive for a range of GI types due to its favorable properties; however, the generality of biochar benefits the GI ecosystem function, and the underlying mechanisms remain unclear. Here, we present a global meta-analysis and synthesis and demonstrate that biochar additions pervasively benefit a wide range of ecosystem functions on GI. Biochar applications were found to improve substrate water retention capacity by 23% and enhance substrate nutrients by 12-31%, contributing to a 33% increase in plant total biomass. Improved substrate physicochemical properties and plant growth together reduce discharge water volume and improve discharge water quality from GI. In addition, biochar increases microbial biomass on GI by ∼150% due to the presence of biochar pores and enhanced microbial growth conditions, while also reducing CO2 and N2O emissions. Overall results suggest that biochar has great potential to enhance GI ecosystem functions as well as urban sustainability and resilience.

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.