Constructed wetlands as nature-based solutions

Accordingly to The United Nations World Water Development Report 2018 "Nature-based solutions (NBS) are inspired and supported by nature and use, or mimic, natural processes to contribute to the improved management of water". In general, if NBS are incorporated in a multipurpose green infrastructure, the network can perform better or equally to a grey alternative. Designed and inspired in processes that occur in natural wetlands, constructed wetlands are good examples of cost-effective NBS for water treatment (e.g., domestic, industrial, water runoff), providing adequate water quality suitable for a range of non-potable uses, including irrigation. This is based mainly on functions played by their components, including plants, microbial populations and the growing substrate. They are valuable biotopes representing highly productive ecosystems, dependent on the climate zone and type of plant species used. Also, they are multifunctional systems that besides water treatment provide a series of ecosystem services at the level of provisioning, regulatiing, supporting and cultural. Constructed wetlands are usually considered within decentralized approaches for water treatment, for example houses with limited access to a sewage network, small populations, runoff schemes or industrial application, although they may have a significant relevance to the New Urban Agenda (NUA), as they can contribute to water availability, water quality and flood reduction, augmenting resilience, both locally and at larger scales. They also have a great potential to contribute to water quality-related Sustainable Development Goals (SDGs). With the present chapter authors intent to give an overview of the functions of constructed wetlands as NBS, emphasising their vegetation and associated microorganisms.