Nature-based Systems (NbS) for mitigation of stormwater and air pollution in urban areas: A review

In recent years, increasing attention has been given to the application of Nature-based systems (NbS) for mitigation of environmental pollution in cities. NbS namely bioretention systems, green roofs and constructed wetlands are widely adopted in urban environments for stormwater hydrology management and treatment, while roadside vegetation is utilized for mitigating air pollution of local traffic origin. Both bioretention systems and wetlands are capable of removing diverse pollutants such as total suspended solids, nutrients (nitrogen and phosphorous) and potentially toxic elements from runoff. Green roofs can act as a sink, or a source of pollutants to roof runoff outflow depending on the composition of engineered media used in support of vegetation growth. A holistic understanding of NbS in terms of their wide range of ecosystem services, multi-functionality nature, and contribution to circularity in cities is currently lacking. NbS can improve public health by providing clean air to breathe and natural waters of better quality for various purposes, but this application is not fully elucidated with an integrated approach involving both air and water quality assessments. For effective use of NbS, fundamental laboratory studies on the relative importance of phytoremediation versus bioremediation, laboratory studies to assess their actual performance under diverse weather conditions, and numerical simulations of hydrology and airflow should be conducted in tandem. Furthermore, it is important to develop guidelines for the design, installation, operation and maintenance of NbS for effective removal of environmental pollutants in the context of sustainable urban development.