Urban agriculture as a keystone contribution towards securing sustainable and healthy development for cities in the future

Urban agriculture as a keystone contribution towards securing sustainable and healthy development for cities in the future S. L. G. Skara,*, R. Pineda-Martosb, A. Timpec, B. Pöllingd, K. Bohne, M. Külvikf, C. Delgadog, C. M.G. Pedrash, T. A. Paçoi, M. Cujicj, N. Tzortzakisk, A. Chrysargyrisk, A. Peticilal, G. Alencikienem, H. Monseesnand R. Junge o a Division of Food Production and Society, Dept. of Horticulture, Norwegian Institute of Bioeconomic Research (NIBIO), P.O. BOX 115, 1431 Aas/Reddalsveien 215, 4886 Grimstad, Norway b School of Agricultural Engineering, University of Sevilla, Sevilla, Spain c RWTH Aachen University (Rheinisch-Westfälische Technische Hochschule Aachen), Germany d South-Westphalia University of Applied Sciences, Soest, Germany e School of Architecture and Design, University of Brighton, UK f Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Friedrich Reinhold Kreutzwaldi 1, Tartu 51006, Estonia g Faculdade de Ciências Sociais e Humanas –Interdisciplinary Center of Social Sciences –CICS.NOVA, Universidade Nova de Lisboa, Av. de Berna, 26-C, 1069-061 Lisboa, Portugal h Faculdade de Ciências e Tecnologia, University of Algarve, Faro, Portugal i LEAF, Linking Landscape, Environment, Agriculture and Food, Instituto Superior de Agronomia, Universidade de Lisboa, Lisboa, Portugal j Vinca Institute of Nuclear Sciences, University of Belgrade, Mice Petrovica Alasa, Belgrade, Serbia k Department of Agricultural Sciences, Biotechnology and Food Science, Cyprus University of Technology, Anexartisias 33, P.O. BOX 50329, 3603, Limassol, Cyprus l USAMV Bucharest, Marasti Blv 59, Bucharest, Romania m Kaunas University of Technology, Food Institute, K. Donelaicio St. 73, 44249 Kaunas, Lithuania n Dpt. Ecophysiology and Aquaculture, Leibniz Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany o IUNR Institute of Natural Resource Sciences, ZHAW Zurich University of Applied Sciences, P.O. Box, CH-8820 Wädenswil, Switzerland *Corresponding author. E-mail: [email protected] Abstract Research and practice during the last 20 years has shown that urban agriculture can contribute to minimising the effects of climate change by, at the same time, improving quality of life in urban areas. In order to do so most effectively, land use and spatial planning are crucial so as to obtain and maintain a supportive green infrastructure and to secure citizens’healthy living conditions. As people today trend more towards living in green and This is an Open Access article distributed under the terms of the Creative Commons Attribution Licence (CC BY 4.0), which permits copying, adaptation and redistribution, provided the original work is properly cited (http://creativecommons.org/licenses/by/4.0/). © 2020 The Authors Blue-Green Systems Vol 2 No 1 1 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user sustainable city centres that can offer fresh and locally produced food, cities become again places for growing food. The scope of urban agriculture thereby is to establish food production sites within the city’s sphere; for example, through building-integrated agriculture including concepts such as aquaponics, indoor agriculture, vertical farming, rooftop production, edible walls, as well as through urban farms, edible landscapes, school gardens and community gardens. Embedded in changing urban food systems, the contribution of urban agriculture to creating sustainable and climate-friendly cities is pivotal as it has the capacity to integrate other resource streams such as water, waste and energy. This article describes some of the current aspects of the circular city debate where urban agriculture is pushing forward the development of material and resource cycling in cities. Key words: agriculture, circular city, ecosystem services, infrastructure, recirculation, urban farming INTRODUCTION Humans today face a plethora of environmental challenges. Some of them are aggravated by concentration of the populations in the cities, all of which constitute a complex set of future challenges; transport of people and goods (i.e. excessive carbon emissions), need for substantial rainfall absorption, high levels of air pollution, urban heat island effect, drinking water supply, waste management, lack of biodiversity. All these challenges result in illness and stress syndromes in the population. Urban agriculture has the potential to contribute towards minimising several of these adverse effects and thus improve the liveability of cities. This review aims to address and clarify some of these aspects, in order to facilitate the implementation of urban agriculture within the context of nature-based solutions (NBS) in circular cities of the future. Currently, the majority of the world population growth is in the cities, especially in developing countries. Urban areas worldwide are expected to absorb all the population growth expected over the next four decades and continue to draw in the rural population (United Nations 2018). While cities today cover about 2–3% of all land area, they consume approximately 75% of the world’s energy and generate 80% of the CO 2 emissions (UN 2018). The cities also utilise large quatities of water, create an enormous quantity of waste and pollute the air. Climate changes are predicted to cause more environmental stressors in the future, while we need to intensify food production (Junge & Graber 2014). The required transition will need increased exibility of the urban environment, more sustainable use and re-use of natural resources as well as the adaptation of infrastructure systems (Herrera-Gomez et al. 2017). All this requires future city development to be smart and to integrate innovative solutions. One key to a more sustainable and healthy city development in the future might be in a relocalisation of the food system and a narrowing of the cities’foodsheds. This idea perfectly coincides with the idea of a circular city, where organic disposals are reused as resources to produce new agricultural products. The contemporary linear understanding of a city, where most independent entities consume, metabolise and dispose of resources, urgently needs –not only but especially in the eld of food –a more systematic perspective to solve existing challenges. In contrast to other infrastructures like water and electricity, the food production, and provisioning system did not get much attention in city planning and are still a neglected eld (Pothukuchi & Kaufman 1999). It needs to be considered that in the process of building the modern city historical ties and links to the localised food system have been disrupted. During expansion, cities lost large areas of their surrounding fertile farmland and have mostly beneted from access to a globalised food system. The consequences of the globalisation of the food system can be seen in an abundance of food but also in the creation of a not sustainable industrialised system that overproduces, pollutes natural resources, declines biodiversity and stimulate obesity and malnourishment (Kennedy et al. 2004;IPBES 2019). It has also favoured massive path dependencies (Moragues-Faus et al. 2017) that can have a signicant impact on food security and that needs to be identied and overcome to shape localised, circular economy-based food systems for the circular city. Blue-Green Systems Vol 2 No 1 2 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user Urban environment conditions, such as air quality, solar radiation and climate are inherently different from rural environments, and these differences may have an impact on crop growth (Eriksen- Hamel & Danso 2010). One of the risks for urban farming that stems from air pollution is decreased irradiance, caused by solar dimming, which is caused by increased reectance of radiation away from the ground, due to air pollutants and aerosols over urban areas. Polluted urban areas can receive 8% less solar radiation than rural areas (Eriksen-Hamel & Danso 2010). This article summarises major aspects related to urban agriculture in order to implement circular agriculture-based schemes in urban settings. What resources exist in an urban biosphere to bring into the context of urban agriculture? The main purpose of urban farming is to produce food within a city, but we also want to pay closer attention to other resources available from urban farming systems, which are usually considered to be waste. URBAN AGRICULTURE AND CIRCULAR CITIES Urban food systems: urban agriculture and urban farming As an increasingly popular phenomenon in different domains during the last twenty years, Urban Agriculture (Table 1) is discussed in science, policy-making, media and society and its denition is context-dependent (Delgado 2018). Because of the rapid development of the eld, several interpretations of the term ‘urban agriculture’exist, capturing nuances within different contexts. Amongst those, two denitions stand out: one from the seminal publication of the United Nations Development Program (UNDP) (Smit 1996); and the other from Mougeot (2001) which provides an extension of the former stressing that it is ‘its integration into the urban economic and ecological system’that distinguishes urban from rural agriculture rather than its urban location only. Smit’s and Mougeot’s denitions are nowadays the most commonly used ones and are valued for their simplicity, openness and implicit inclusion of a circular-city approach. Urban agriculture spans all actors, communities, activities, places, and economies which focus on primary production in a spatial context categorised as ‘urban’(Vejre et al. 2015), it can be structured into two sub-groups; urban food gardening and urban farming (Table 1). The common denominator of both is the bio-based output of products, which are harvested and consumed while other effects of urban agriculture on environment and society can be classied as by-products, externalities or co-benets. These benets can be classied into four dimensions: food security, economic, social and environmental (McEldowney 2017), and include contributing to employment, improved education and health, to social inclusion through integrating those at risk of social exclusion. The business-as-usual farming operation, as well as non-urban adapted farming, also exist in urban areas (Deelstra & Girardet 2000;Simon-Rojo et al. 2015). The key benets include contributing to employment and the development of small-scale rural entrepreneurs; improved education and health; and to social inclusion, through integrating those at risk of social exclusion, such as migrants. A food system encompasses the full value chain of producing food for human consumption, from agricultural activities and other means, through transportation, handling, processing, storage, distribution and consumption, to organic –including human –waste management and disposal/ reintroduction into productive use (Ericksen 2008). A food system gathers all the elements: people, environment, infrastructures, inputs, processes, institutions and activities that relate to the production, processing, distribution, preparation and consumption of food, and the outputs of these activities, including socio-economic and environmental outcomes (Figure 1). Blue-Green Systems Vol 2 No 1 3 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user Continuous productive urban landscapes (CPUL) and growing space typologies Agriculture is space and time-bound: plants and animals grow in a certain place and at a certain pace. Thus nding space in cities and city-regions is a prerequisite for urban farming. While some of these spaces are well known, such as traditional farming land, allotment gardens or family gardens, other spaces might offer the potential for urban farming in a permanent or a temporar way (Table 2). The Continuous Productive Urban Landscapes (CPUL City) concept (Viljoen et al. 2005) describes an urban future based on the planned and designed introduction interconnected urban landscapes dened by urban agriculture into existing and emerging cities. It follows a systemic approach using quantiable and qualitative arguments to propose that urban agriculture contributes to more sustainable and resilient food systems while also adding benecially to the spatial and social quality of the urban realm (Bohn 2016). A CPUL aims to interconnect urban food-producing landscapes within a city and to the citizens on the one hand and to connect these landscapes to the rural hinterland on the other and thereby facilitates activities across all parts of the urban food system. This was illustrated also by the outcomes of the studies that evaluated the stakeholder perceptions of rooftop agriculture in Berlin and Barcelona (Sanyé-Mengual et al. 2015a;Specht et al. 2015a, 2015b) and concluded that even if there are a number of potential risks assossiated with the urban Table 1 |Denitions of urban agriculture, urban farming and urban gardening Denition Source Urban and peri-urban agriculture (UPA) can be dened as the growing of plants and the raising of animals within and around cities. Urban and peri-urban agriculture provides food products from different types of crops (grains, root crops, vegetables, mushrooms, fruits), animals (poultry, rabbits, goats, sheep, cattle, pigs, guinea pigs, sh, etc.) as well as non-food products (e.g. aromatic and medicinal herbs, ornamental plants, tree products). UPA includes trees managed for producing fruit and fuelwood, as well as tree systems integrated and managed with crops (agroforestry) and small-scale aquaculture. FAO (2019) Urban and peri-urban agriculture can be dened as the growing, processing and distribution of food and other products through plant cultivation and (seldom) raising livestock in and around cities for feeding local populations Game & Primus (2015) Urban agriculture spans all actors, communities, activities, places and economies that focus on biological production in a spatial context which –according to local standards –is categorised as ‘urban’. Urban agriculture takes place in intra- and peri-urban areas and one of its key characteristics is that it is more deeply integrated into the urban system compared to other agriculture. Urban agriculture is structurally embedded in the urban fabric; it is integrated into the social and cultural life, economics and the metabolism of the city. Vejre et al. (2015) Urban agriculture is growing, processing and distribution of food or livestock within and around urban centres with the goal of generating income. McEldowney (2017); Roggema (2016) Urban agriculture is an industry that produces, processes and markets food and fuel, largely in response to the daily demand of consumers within a town, city or metropolis, on land and water dispersed throughout the urban and peri-urban area, applying intensive production methods, using and reusing natural resources and urban wastes, to yield a diversity of crops and livestock. Smit (1996) Urban agriculture is an industry located within (intra-urban) or on the fringe (peri-urban) of a town, a city or a metropolis, which grows and raises, processes and distributes a diversity of food and nonfood products, (re-)using largely human and material resources, products and services found in and around that urban area, and in turn supplying human and material resources, products and services largely to that urban area. Mougeot (2001) Urban food gardening encompasses agricultural activities with generally low economic dependence on the material outputs while using food production for achieving other, mostly social, goals. Simon-Rojo et al. (2015) Urban farming refers to intentional business models taking advantage of proximity to the city by offering local or regional agricultural products or services. The importance of the production in proportion to the other societal benets can vary strongly (…), both, the production-oriented side or the co-benet-oriented side may prevail depending on the individual practices of an urban farming operation. Pölling et al. (2015) Blue-Green Systems Vol 2 No 1 4 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user farming system, stakeholders establish new market structures (e.g., short supply-chains) to overcome barriers and to ensure a socially accepted development of this new form of urban agriculture. Relationship between urban agriculture and green infrastructure The signicance of urban agriculture has been highlighted by a set of UN-Habitat reports on how cities can work with nature. In these reports, it is argued that to achieve environmental and economic resilience; biodiversity needs to be reinstated in urbanised areas (UN Habitat 2012). One of the major co-benets of urban agriculture lies in its contribution to the urban environment, green infrastructure and the related ecosystem services (Viljoen et al. 2005;Santo et al. 2016;McEldowney 2017;Samson et al. 2017;Golden & Hoghooghi 2018;Piorr et al. 2018). Green infrastructure is a signicant element in European planning policies on all scale levels. It is one of the primary tools for achieving the EU Biodiversity Strategy 2020 (European Commission 2011) as well as smart, sustainable and inclusive growth dened by the Europe 2020 Strategy (European Commission 2010). Urban agriculture contributes to the ecosystem services of green infrastructure as a provisioning service for food, energy and raw materials, as well as through a range of other ecosystem services (Table 3). Figure 1 |This diagram shows the many links food, and the food system has with most aspects of urban life. It gives weight to spatial aspects related to urban food, including those related to urban agriculture. Blue-Green Systems Vol 2 No 1 5 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user Tóth & Timpe (2017) have shown the quantitative importance of urban agriculture in the green infrastructure networks of four differently structured European urban regions (Dublin/Ireland, Soa/Bulgaria, Ruhr Metropolis/Germany and Geneva/Switzerland). The regional green infrastructure systems of urban regions, which form a continuous system of open spaces often described as spatially coherent gures (green corridors, green wedges or green belts), can, in most cases, only achieve this claim of continuity if they include the semi-natural areas used for urban agriculture. Urban agriculture is an indispensable component of green urban systems. Biodiversity and ecosystem services Due to their population density, urban areas have a very high demand for multiple ecosystem services. Moreover, cities play an essential role in climate change mitigation and is increasingly vulnerable to climate change impacts (Rosenzweig et al. 2010). To achieve well-functioning circular cities that ensure good quality of life for their residents, it is urgent to safeguard biodiversity and improve the supply of regulating, cultural and supporting ecosystem services (McPhearson et al. 2015). Environmental benets associated with urban agriculture include increased biodiversity, mitigation of the ‘urban heat-island effect’and a reduced risk of ooding (McEldowney 2017). Urban agriculture has enormous potential to provide multiple ecosystem services in addition to food production, signicantly contribute to the functioning of green/blue infrastructure and mitigate climate change (Lwasa et al. 2014). However, to maximise multiple benets that can arise from urban food production, urban agriculture has to adopt sustainable farming practices (for instance organic farming, use of agroecological approaches), ensure functional integration to the urban fabric, and Table 2 |A typology of growing spaces for urban farming (adapted after Santo et al. 2016;Simon-Rojo et al. 2015) Typology of the city area Urban farming spaces in cities Examples and references Soil-bound spaces Arable land Allotment gardens Individual gardening (commune patch) Family gardens Individual gardening (private patch) Squatter gardens Community gardens Parks and other public green spaces Van Leeuwen et al. (2010) Urban derelict land Guerrilla gardening Brown et al. (2016) Manchester, UK* Mobile and soil-independent systems Growing boxes and bags Mobile containers e.g. PAFF Box (Delaide et al. 2017) Building bound spaces Rooftops: Buehler & Junge (2016) Glasshouses –Open rooftops –Covered rooftops –Flat roof –Roof with inclination Facades: Glasshouse –Open facades –Covered facades Building extensions: –Balconies –Window sills Indoor spaces with/without articial lighting Water bound spaces Urban streams Urban stagnant waters e.g. ponds, lakes Amphibia systems e.g. oating islands *http://www.urbanallotments.eu/leadmin/uag/media/STSM/Binder_shortreportSTSM_nal.pdf. Blue-Green Systems Vol 2 No 1 6 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user safeguard biodiversity key areas (IPBES 2019). This applies to both small-scale food production for personal or community use (urban food gardening) as well as commercial farming in urban areas (urban farming). Table 3 shows the contributions of urban agriculture as this is what the green infrastructure is based on. Air pollution risk and agronomic considerations on urban farming Pollution risks of urban food farming, understanding food production outsides in open city spaces, can be combined with risk for food safety and content of pollutants in the food products. There are a few articles on this topic but more research is needed to fully understand the risks. There are three primary risks of gardening in cities and urban environment: soil, water and air pollution. For air pollution, there are three categories: (1) not accumulated in plants, (2) transport-vectors of pollutants and (3) pollutants that are taken up in plants. Within a city, many sources of pollution are present: e.g. trafc, industries, heating (Ortolo 2017). Fruit trees are most affected by air pollution. The air pollution in China has caused damage to fruit trees by delaying sprouting, shortening the owering period, accelerating senescence and reducing CO 2 assimilation. This resulted in a reduction of fruit numbers and premature dropping of fruit (Zheng & Chen 1991). High ozone concentrations cause chlorotic spotting, necrotic lesions and premature senescence in trees, vegetable crops and cereals (Rich 1964;Krupa et al. 2001). The ambient air pollutants (SO 2 , NO x , SPM and RSPM) caused a signicant reduction in total chlorophyll, carotenoid, ascorbic acid, plant height, shoot fresh weight, root fresh weight and yield of wheat and mustard crops grown at polluted sites (Chauhan & Joshi 2010). The elevation of CO 2 concentration has been shown to increase the yield of crops under laboratory conditions, but in reality the degree of growth stimulation is dampered in the environment due to high temperatures and increasing Table 3 |Contributions of urban agriculture as green infrastructure (GI) based on Timpe et al. (2015) Ecosystem Services TEEB (2015) a : ES Benets Group European Commission (2013a, 2013b): GI Benets Possible contribution of urban agriculture Provisioning services Multifunctional resilient agriculture and forestry Providing food, bre and biomass and enhancing pollination. Investment and employment Employment in agriculture, investment in agricultural enterprises and buildings, productive and maintained land as contributions to a better local image. Cultural services Tourism and recreation A broad range of recreational activities proposed on farms and in gardening associations, farms and gardens as a destination. Education Agriculture as a teaching resource and ‘natural laboratory’. Health and wellbeing Farm work and gardening as activities for physical and mental health, access to healthy local food. Regulation services Enhanced efciency of natural resources Maintenance of agricultural soil fertility, pollination through urban beekeeping. Climate change mitigation and adaptation The cooling effect of agricultural areas, carbon storage in soils. Water management Groundwater recharge and purication under agricultural soils, stormwater retention. Land and soil management Reduction of soil erosion, maintaining/enhancing soil’s organic matter, increasing soil fertility and productivity, mitigating land consumption, fragmentation and soil sealing. Disaster prevention Flood hazard reduction through stormwater retention and agricultural polders, erosion control. Habitat Conservation benets Maintenance of agrobiodiversity, maintenance of agricultural habitats. Low-carbon Short-chain food provision, local bioenergy from agriculture. a The Economics of Ecosystems and Biodiversity –TEEB. Blue-Green Systems Vol 2 No 1 7 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user tropospheric O 3 (Ainsworth 2008). A case study in Varanasi, India concluded that gaseous pollutants such as SO 2 , NO 2 and O 3 have damaging effects on the yield of wheat, mustard, mung and palak plants (Agrawal et al. 2003). Apart from ozone, it can be difcult to identify the causal link between a specic gas and damage to crops, which is why there are few studies made on this topic (Hamel & Danso 2011). A study in Greece used a combined air quality and GIS modelling approach to estimate crop damages from photochemical air pollution (O 3 ) and depict the corresponding economic damages. Total economic damage to crops turned out to be signicant and estimated to be approximately 43 M€for the reference year (Vlachokostas et al. 2010). Suspended particulate matter has the most signicant effect on crop yields and the quality of the crops. Atmospheric pollutant deposition has been noted as the most common pathway for lead contamination of leafy greens in Uganda (Nabulo et al. 2006). A study in Nigeria of the correlation between trafc emissions of Cd, Cu, Cr, Ni, Pb and Zn near a highway and the concentration of heavy metals in the vegetation and soil samples near the highway has been conducted. The study showed that roads have a signicant effect on heavy metal accumulation in vegetation (Ndiokwere 1984). MATERIAL AND RESOURCE MANAGEMENT Resource management Resources such as water, food and energy are what cities need to function (Figure 2). The entirety of resource streams and their interactions with each other, citizens and urban space are incredibly complex. Despite some of these resources being nature-based, most resources ows are linear: they are used and then disposed of. This linear urban metabolism (Rogers 1997;Daigger 2009) dominates in contemporary towns and cities all over the world, and it is causing a plethora of problems. The Figure 2 |Resource streams in urban metabolism. This diagram shows how food and the food system are located as part of other resource streams into and out of the city (Source:Bohn 2016). Blue-Green Systems Vol 2 No 1 8 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user circular approach explores how to manage resources by reducing, reusing and recycling. As a consequence, this leads to redesign of the urban, peri-urban and rural space, and to a new conceptualisation of their interlinkages. One of the critical elements in the development of closed-loop designs is a localised food systems approach, which also links to a broader understanding of a (peri-)urban water– energy–food nexus (Figure 2). Growing media Soil is the ‘default’growing substrate for plants, however urban soils are often degraded (De Kimpe & Morel 2000) and do not enable healthy plant growth. Therefore, replacing the soil with other substrates in urban environments, can contribute towards healthy produce. Based on chemical properties, growing media can be split into organic and inorganic (Table 4). The most important physical property is particle size, which affects the physical characteristics (e.g. porosity, water holding capacity, air space). Well-balanced physical and chemical properties of the growing media induce the plant growth and also promote biological activity (Maucieri et al. 2019). Also, it should be free of weeds, pathogens and toxins. In circular cities of the future, it is important to focus on renewable materials from agricultural, industrial and municipal waste streams to identify benecial and environmentally sustainable materials as growing media (European Commission 2019). It is environmentally benecial to reuse and recycle renewable materials, and contributing to the circular economy (CE) which is, together with bioeconomy, supporting concepts in order to facilitate the transition to a sustainable society. Deposition of pollutants in soil Particulate air pollutants are usually settleable by gravity and are deposited on the ground through wet and dry deposition. They cause acidication, salinisation and high heavy metals concentrations. To assess the inuence of air pollution on soil composition, a study of heavy metals concentrations (Cd, Pb, Ni, Sb and Bi) in the settleable particulate matter in two locations in Spain has been performed. The study showed signicant seasonal variability for heavy metal content and a strong dependence on rainfall in the area. The maximum values of heavy metals were measured in spring or autumn when there was the highest rainfall (Soriano et al. 2012). Werkenthin et al. (2014) reviewed studies of metals in European roadside soils and concluded that the highest levels of Cr, Cu, Ni, Pb and Zn, were determined in the topsoil layer, and located in the rst 5 m beside the road. Generally, the inuence of trafc on soil contamination decreased with increasing soil depth and distance to the road. Based on these ndings, there are some concerns about the quality of food produced in the urban environment. The suitability of food produced in close proximity of urban trafc or other sources of pollution, should be closely examined. Available water resources Treated domestic or municipal wastewater, also designated as reclaimed water, is used worldwide as an alternative water source. In some countries is even used as a water source for drinking water, such as in Singapore and Texas-USA (Yi et al. 2011). In California-USA, in full-scale large dimension projects, reclaimed water is being used for irrigation. In the near future, when the health and social objections existing presently in Europe, are overcome by the overwhelming current efciency of advanced wastewater and water treatment technology, reclaimed water will become one of the most important sources of urban water (Norton-Brandão et al. 2013). Blue-Green Systems Vol 2 No 1 9 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user ANALYSIS OF CURRENT EUROPEAN PROJECTS Methods The publications and projects were analysed regarding the potential contribution of the elements of urban farming systems to circular economy approach for a resourceful, resilient and sustainable city. This study was based on the literature available from various bibliographic reference databases (namely Google Scholar, Research Gate, Web of Science, Scopus) and the work of CA17133 members. The systematic literature review process was applied to select the latest and the most relevant studies on this particular topic. Specic terms were used, like ‘nature-based solutions in cities and vegetable production’and synonyms for ‘urban agriculture’,‘urban farming’,‘closed circular systems’, ‘business models’. The article’s relevance was discussed and grouped into three to six persons (authors) per groups, dealing with each topic related to urban agriculture as a keystone contribution towards securing sustainable and healthy development for cities in the future. Dening all the terms, from urban agriculture to the contribution of elements of urban farming systems –specially developed for dense urban areas (e.g. underground, vertical and rooftop farming) –in a circular economy approach, helping to understand the status of a circular city based on project-data- base of COST Action CA17133. Two surveys were developed to the COST members concerning the: (1) projects participating in the COST Action; and (2) water sources, treatment, storage and irrigation systems. In the rst survey, we combined expertise in food systems governance (Moragues-Faus et al. 2017), innovative production systems and business models, food safety, food waste, water consumption, irrigation systems, knowledge transfer, education, participation, alternative protein sources for feed and urban–rural nexus analysis. It was screened through the project-database and added peerreviewed publications which we identied as key-articles for our eld of research. It was also ident- ied research gaps and extracted research questions which need to be answered to proceed into the design of a circular city. No quantitative information on current water sources, treatment, storage and operating irrigation system are available for current urban farming projects. To ll up this gap, the second survey was carried out within the 250 participants of the COST Action CA17133 Circular City, in February 2019 on water resources of urban farming research projects. (To nd the nine questions, the list of surveyed research projects and their geographical distribution, please see the supplemental material.) The case of green roofs in Lisbon with native species study of urban landscape area, allows enhancing water use and sustainability in Mediterranean conditions. CIRCULAR CITIES: A SURVEY OF PROJECTS PARTICIPATING IN THE COST ACTION CA17133 The relevant projects based on a keyword search through the COST Project collection are shown in Table 5. Fourteen keywords were selected based on the denitions of Food Systems (Table 1) de- nition and are listed on the table (see columns D to R). About our 14 words searched, several gaps where identied with signicant absence: Food transportation and distribution, Food processing and transformation, Food storage, Consumption and Compost. Few references were found related to governance, consumers, citizens, and authorities. We analysed 13 projects (Table 5). However, some of them need to be seen as extremes. Project 9 (Pyrolysis of faecal wastes) is listed due to its potential to close the loop of the system. The research areas addressed were: food policies, food systems, stakeholders engagement and awareness, urban and peri-urban agriculture for sustainable local development. The survey includes also answers from COST members on the following questions: 1. What are the critical questions from a members point of view? 2. Critical points (gaps) enabling the contribution of urban farming to circular cities? Blue-Green Systems Vol 2 No 1 16 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user 3. Why is the understanding of urban farming within the food system critical to circular cities? 4. Why the understanding of urban farming within the food system is a critical shift from linear cities to circular cities? The topics presented in the thirteen projects were (Table 6): stakeholders, food, production, transportation and distribution, storage, processing and transformation, food policy(-ies), food system, governance and authorities, consumers and citizens, farmers, urban farming, compost and the Table 5 |Relevant projects identied by searching project-database of the COST Action on Circular Cities and publications A B C No. Project Website if applicable Location 1 Integrating Edible City Solutions for social resilient and sustainably productive cities –EdiCitNet https://cordis.europa.eu/project/rcn/ 216082/factsheet/en Tygron and other world cities 2 Urban and Peri-Urban Agriculture for sustainable local development: The Multi-stakeholder Policy Action Planning as a tool for reconciling sectorial policies http://bit.ly/ UPAforSustainableDevelopmentMuiti- StakeholderPolicyAction Portugal 3 CITYFOOD –Smart integrated multitrophic city food production systems –water and energy-saving approach for global urbanisation (2018–2021) https://www.igb-berlin.de/en/project/ cityfood Norway, Sweden, Germany, the Netherlands, Brazil and the USA 4 Continuous Productive Urban Landscape: Designing urban agriculture for sustainable cities http://www.foodurbanism.org/cpulscontinuous-productive-urban- landscapes/ Worldwide (sustainable urban design concept) 5 GEOFOOD (2018–2021) https://geofoodproject.eu/ Iceland, Slovenia and the Netherlands 6 Living from the Earth –OTKA 116219 and OTKA 100682 (2016–2019) dealing with rural-urban divide and to make rural life attractive in Hungary, the changing role of the local small-scale agri-food production https://www.aur.edu Hungary 7 NACHWUCHS –Nachhaltiges Agri- Urbanes zusammenWachsen (Sustainable AgriUrban Growth) https://urbact.eu/agri-urban Germany 8 Plattform ‘Produktive Stadt’ [Platform ‘Productive City’] http://blogs.brighton.ac.uk/pulr/2019/06/ 10/platform-productive-city-holds-its- 2nd-participatory-workshop-germany/ Berlin (Germany) 9 Pyrolysis of faecal wastes https://www.zhaw.ch/de/lsfm/institutezentren/iunr/ecological-engineering/ oekotechnologie/biochar-sanitation/ Waedenswil (Switzerland) 10 Productive Green Infrastructure for post-industrial urban regeneration (proGIreg) http://www.progireg.eu/ Aachen (Germany) 11 Urban Allotment Gardens in European Cities: Future, Challenges and Lessons Learned https://www.cost.eu/actions/TU1201 Riga (Latvia) 12 Characterisation of nutrient recycling processes of a model aquaponic system https://www.zhaw.ch/de/lsfm/institutezentren/iunr/ecological-engineering/ oekotechnologie/aquaponic/ Waedenswil (Switzerland) 13 The smart and sustainable city district of the future https://www.balticurbanlab.eu/ goodpractices/hiedanranta-smart-and- sustainable-city-district-future-tampere Häme (Finland) The search keywords were: circular cities. Blue-Green Systems Vol 2 No 1 17 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user circular city. Most projects covered topics related to food (11 out of 13), production (8 out of 13) and stakeholders (6 out of 13). Water sources, treatment, storage and irrigation systems The survey yielded 22 research projects, which geographically covered most of Europe. Water sources used by the projects were very diverse (Figure 4). Interestingly tap water, as the only water source was used by only 23% of the projects, while most projects (45%) used a mixture of sources. The use of wastewater, greywater or stored rainwater was rare –one project relied to 100% on natural rain. Table 6 |The goals of relevant projects identied by searching project-database of the COST action on circular cities and publications Project number Topic 1 2 3 4 5 6 7 8 9 10 11 12 13 Stakeholders x x x x x x Food x x x x x x x x x x x no Production x x x x x x x x Transportation/Distribution x Storage x Processing/Transformation x Food Policy(-ies) x x x x Food System x x x x x Governance/Authorities x x x Consumers/Citizens x x x x Farmers x x Urban Farming x x x Compost x Circular city x x The numbers 1–13 denote the projects listed in Table 5. Figure 4 |Sources of water supply for 22 recent urban agriculture research projects participating in the COST Action CA17133, February 2019. Blue-Green Systems Vol 2 No 1 18 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user Regarding prior water treatment, 59% of the projects did not use any treatment of their water. The remaining used a variety of treatments including mechanical lters, plant-based, bio-reactor, sedimentation or disinfection systems. Only two of the ten hydroponic systems used greywater as a source. The survey showed that (i) rainwater management or reuse infrastructures are often not readily in place to be used for urban agriculture projects, (ii) farming projects rely heavily on tap water and (iii) circular usage of water is not yet common except in the hydroponic projects. CONCLUSIONS The development of future cities is now advancing into smart and sustainable cities with a global understanding of how vital food production, supporting the circular economy, is. In 2050 about 50% of all people on earth are living in cities and will need clean water, food, energy, social space, meeting points, relax areas and knowledge pools. Land use and planning It is visible that municipalities around the world are beginning to consider food issues in their city planning proactively, most evident perhaps in the Food Policy Pact signed by more than 180 cities since its foundation in 2015 during the Milan World Expo. This rapid development has followed the mainly practice-based, citizen-led experiences with urban agriculture that emerged, as a conscious movement, in cities and at their edges for nearly 20 years. It is now of great importance to integrate urban food production and other food system activities into urban planning, thereby linking sustainable food provision and circular resource processes to infrastructural productive urban landscape development. Water systems Assessment of underlying spatial and temporal variability in water use decisions at a landscape scale regarding the water demand and irrigation water requirements in response to climate change and different urban farming location. Some projects (e.g. URBAN GreenUP; NativeScapeGR, Nature4- Cities, CITYFOOD) focus on mitigation the effects and risks of climate change and improving the water management cities. Other projects contribute to a better understanding of ecosystem services through evaluation and mapping the urban environments (TUNESinURB, Nedkov et al. 2017). A better understanding how irrigation is used in the urban farming is needed to reduce pressures on limited freshwater resources, based on the knowledge how to use it efciently based on economics, yield, environmental and social issues, aesthetics and safety for human health criteria. Assessment of underlying spatial and temporal variability in water use decisions at a landscape scale regarding the water demand and irrigation water requirements in response to climate change and different urban farming location. What appears to be missing in most projects are concepts and experiences of water storage, rainwater harvesting and optimised usage of water with state-of-the-art irrigation systems. Very few long-term experiences exist at the moment for combining urban agriculture and any wastewater usage –as would t within the concept of the circular city. As many current projects are using hydroponic systems, more research into a combination of hydroponic systems and wastewater reuse could be benecial. Air pollution The economic growth, industrialisation and urbanisation has caused increased concentrations of pollutants such as ozone (O 3 ), nitrous oxides (NOx), sulphur dioxide (SO 2 ) and suspended particulate matter (SPM) in urban areas. These gases can cause signicant damage to crops. Blue-Green Systems Vol 2 No 1 19 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user Suspended particulate matter has the most signicant effect on crop yields and the quality of the crops. Several studies ascertained the correlation between the atmospheric pollutant deposition originating from trafc emissions (e.g. Cd, Cu, Cr, Ni, Pb and Zn) and the concentration of heavy metals in the vegetation and soil samples. Therefore it is necessary to assess the suitability of produce grown near pollution sources for human consumption and also identify causal links between a specic pollutant and damage to crops. Education and knowledge transfer Combined circular food systems –aquaculture and plant production together in the same system –are entirely new in the perspective of food production techniques and can also be implemented widely in education and knowledge transfer (Junge et al. 2019). In Norway, researchers have focused on the development of recirculating aquaculture systems (RAS) during the past 30 years, and the production of the most salmonids ngerlings grow in land-based RAS. In NIBIO Landvik, an aquaponics facility is operated with salmonids (brown Salmo trutta, rainbow trout Oncorhynchus mykiss and a relict salmon species called ‘bleke’Salmo salar (Barlaup 2011), together with a wide range of plant species, such as wild herbs, Asian greens, edible owers, leafy plants and several lettuce varieties (Skar et al. 2015). The system is used for research and education, and works as a showcase for an innovative approach to a more sustainable food production. The latest development is to apply the system to prisons, to create jobs, build skills and build prisoners’social acceptance in city communities by producing local and healthy food for the surrounding community (Skar 2018). Together with the system in Norway, further aquaponic systems were constructed for educational and knowledge transfer purposes, e.g. within the CITYFOOD project in Brazil and Germany and within the AQU@TEACH project in the United Kingdom, Slovenia, Spain and Switzerland. These so-called ‘living labs’are serving as perceptible demonstration sites and are a central part of a diverse communication and dissemination agenda. Knowledge gaps and further research question in urban agriculture Consolidating the current knowledge on urban agriculture in green urban systems is needed. More knowledge is needed on multifunctionality and the relation to green infrastructure and food-pro- ductive urban landscapes, circular city debates and discussions of the possible adverse effect of air pollution on urban agriculture products’quality. Improved sustainability in the cities by integrating with buildings and waste conversion sites. To encourage more holistic solutions to the problem, we present a comprehensive overview of European projects and examples which consider circular city approaches on urban farming. Examples of solutions from our expertise and database COST Action is found here: http://www.circular-city.eu/ images/pdf_download/Proceedings_COST_WS_13-15Feb.pdf. Due to the mainstreamed globalisation of urban food systems, the entire production and marketing schemes have shifted to comfort the needs of globalised value chains. Changes like these in the built environment and the socio-cultural practice create path dependencies. A signicant gap of research on what a change in food production, processing, distribution and consumption can and will do to the cities, especially in the area of transportation/logistics, green infrastructure, resource streams and all the physical requirements on which they are based (streets, shops, pipes, wires, channels and more). We also identied a gap in food governance research and realised an almost complete absence of the social dimension meaning the analysis of socio-cultural patterns and practices in the food preparation and consumption. Blue-Green Systems Vol 2 No 1 20 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user ACKNOWLEDGEMENTS The work is funded within the COST Action CA17133 Circular City (‘Implementing nature-based solutions for creating a resourceful circular city’,http://www.circular-city.eu, duration 22 Oct 2018–21 Oct 2022). COST Actions are funded within the EU Horizon 2020 Programme. The authors are grateful for the support and very early contribution of this article: T. Schvartz, Z. Heuschel, A. Helm, E. Paton, H. Paulenz, L. Straigyte and A. Canet-Martí. SUPPLEMENTARY MATERIAL The Supplementary Material for this paper is available at http://dx.doi.org/10.2166/bgs.2019.931. REFERENCES Agha Rokh, A. 2008 Evaluation of ornamental owers and shes breeding in Bushehr urban wastewater using a pilot-scale aquaponic system. Water and Wastewater 19 (65), 47–53. Agrawal, M., Singh, B., Rajput, M., Marshall, F. & Bell, J. N. B. 2003 Effect of air pollution on peri-urban agriculture: a case study. Environmental Pollution 126 (3), 323–329. https://www.sciencedirect.com/science/article/pii/S0269749103002458# aep-section-id24. Ainsworth, A. E. 2008 Rice production in a changing climate: a meta-analysis of responses to elevated carbon dioxide and elevated ozone concentration.Globe Change Biology. https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2486.2008. 01594.x,10.9.2019. Aubry, C. & Kebir, L. 2013 Shortening food supply chains: a means for maintaining agriculture close to urban areas? The case of the French metropolitan area of Paris.Journal of Food Policy 41, 85–93. Aubry, C., Kebir, L. & Pasquier, C. 2012 Le raccourcissement des circuits alimentaires: une nouvelle ruralité en périphérie des villes? (étude de cas en île-de-France). In: Nouveaux Rapports à la Nature Dans Lescampagnes (Papy, F., Mathieu, N. & Férault, C. eds). Editions Quae, Paris, pp. 55–69. Bachman, G. R. & Metzger, J. D. 2008 Growth of bedding plants in commercial potting substrate amended with vermicompost. Bioresource Technology 99 (8), 3155–3161. Bailey, A., Williams, N., Palmer, M. & Geering, R. 2000 The farmer as a service provider: the demand for agricultural commodities and equine services.Journal of Agricultural Systems 66, 191–204. doi:10.1016/S0308-521X(00)00047-0. Barbieri, C. & Mahoney, E. 2009 Why is diversication an attractive farm adjustment strategy? Insights from Texas farmers and ranchers.Journal of Rural Studies 25, 58–66. doi: 10.1016/j.jrurstud.2008.06.001. Barlaup, B. T. 2011 Byglandsbleke Salmo Salar. Fact sheet: Artsdatabankens faktaark no. 175. http://www2.artsdatabanken.no/ faktaark/Faktaark175.pdf. Barrett, G. E., Alexander, P. D., Robinson, J. S. & Bragg, N. C. 2016 Achieving environmentally sustainable growing media for soilless plant cultivation systems –A review.Scientia Horticulturae 212, 220–234. Beauchesne, A. & Bryant, C. R. 1999 Organic farming: combining economic, social and environmental objectives in metropolitan regions. In: Progress in Research on Sustainable Rural Systems (Bowler, I., Bryant, C. R. & Firmino, A. eds). Série Estudos, No. 2, Universidade Nova de Lisboa, Centro de Estudos de Geograa e Planeamento Regional. https:// www.researchgate.net/publication/268872462_Organic_farming_combining_economic_social_and_environmental_ objectives_in_metropolitan_regions/stats. Bohn, K. 2016 PHVision: Development Vision for Patrick-Henry-Village Heidelberg. University of Brighton. https://iba. heidelberg.de/de/projekte/landwirtschaftspark. Boons, F. & Lüdeke-Freund, F. 2013 Business models for sustainable innovation: state-of-the-art and steps towards a research agenda.Journal of Cleaner Production 45, 9–19. Brown, S. L., Chaney, R. L. & Hettiarachchi, G. M. 2016 Lead in urban soils: a real or perceived concern for urban agriculture? Journal of Environmental Quality 45 (1), 26–36. Bruun, E. W., Ambus, P., Egsgaard, H. & Hauggaard-Nielsen, H. 2012 Effects of slow and fast pyrolysis biochar on soil C and N turnover dynamics.Soil Biology and Biochemistry 46, 73–79. Buehler, D. & Junge, R. 2016 Global trends and current status of commercial urban rooftop farming.Sustainability 8(11), 1108. Chauhan, A. & Joshi, C. P. 2010 Effect of ambient air pollutants on wheat and mustard crops growing in the vicinity of an urban and industrial area.New York Science Journal 3(2), 52–60. https://pdfs.semanticscholar.org/0af3/ d227dda90d61f4c7e9cc62b1d1f5383cf20c.pdf. Chen, Z., Ngo, H. H. & Guo, W. 2013 A critical review on the end use of recycled water.Journal of Environmental Science and Technology 43 (14), 1446–1516. doi:10.1080/10643389.2011.647788. Blue-Green Systems Vol 2 No 1 21 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user Clarke, L. W., Jenerette, G. D. & Bain, D. J. 2015 Urban legacies and soil management affect the concentration and speciation of trace metals in Los Angeles community garden soils.Environmental Pollution 197, 1–12. doi: 10.1016/j.envpol.2014.11.015. Corcoran, M. P. & Calvin, J. S. 2015 Introduction. In: Urban Agriculture Europe (Lohrberg, F., Licka, L., Scazzosi, L. & Timpe, A. eds). Jovis, Berlin, pp. 56–57. Daigger, G. 2009 Evolving urban water and residual management paradigms: water reclamation and reuse, decentralization, resource recovery.Water Environment Research 81 (8), 809–823. Deelstra, T. & Girardet, H. 2000 Urban agriculture and sustainable cities. In: Growing Cities, Growing Food: Urban Agriculture on the Policy Agenda. A Reader on Urban Agriculture (Bakker, N., Dubbeling, M., Gündel, S., Sabel-Koschella, U. & de Zeeuw, H. eds). Deutsche Stiftung für Internationale Entwicklung (DSE), Zentralstelle für Ernährung und Landwirtschaft, pp. 43–65. Available from: https://www.researchgate.net/publication/284992045_Urban_agriculture_and_sustainable_ cities. De Kimpe, C. R. & Morel, J. L. 2000 Urban soil management: a growing concern.Journal of Soil Science 165 (1), 31–40. Delaide, B., Delhaye, G., Dermience, M., Gott, J., Soyeurt, H. & Jijakli, M. H. 2017 Plant and sh production performance, nutrient mass balances, energy and water use of the PAFF Box, a small-scale aquaponic system.Aquacultural Engineering 78, 130–139. Delgado, C. 2018 Contrasting practices and perceptions of urban agriculture in Portugal.International Journal of Urban Sustainable Development 10, 170–185. doi: 10.1080/19463138.2018.1481069. Despommier, D. 2010 The Vertical Farm: Feeding the World in the 21st Century. Picador, New York. Drechsel, P., Keraita, B., Coe, O. O. & Nikiema, J. 2015 Productive and safe use of urban organic wastes and wastewater in urban food production systems in low-income countries. In: Cities and Agriculture –Developing Resilient Urban Food Systems (de Zeeuw, H. & Drechsel, P. eds). RUAF Foundation, International Water Management Institute, Leusden, The Netherlands, pp. 162–191. Available from: https://www.ruaf.org/sites/default/les/7.%20Productive%20and%20safe% 20use-min.pdf. Ecosystem Services –TEEB 2015, available at http://www.teebweb.org/resources/ecosystem-services/ (accessed 20 May 2015). Elgåker, H. & Wilton, B. 2008 Horse farms as a factor for development and innovation in the urban-rural fringe with examples from Europe and Northern America. 10th annual conference. In: Nordic-Scottish University for Rural and Regional Development, 2007 03 08–2007 03 10, Vejle, Denmark. Innovation systems and rural development, pp. 43–55. Ericksen, P. J. 2008 Conceptualizing food systems for global environmental change research.Global Environmental Change 18 (1), 234–245. doi:10.1016/j.gloenvcha.2007.09.002. Eriksen-Hamel, N. & Danso, G. 2010 Agronomic considerations forurban agriculture in southern cities.International Journal of Agricultural Sustainability 8(1–2), 86–93. doi:10.3763/ijas.2009.0452. https://www.tandfonline.com/doi/pdf/10.3763/ ijas.2009.0452. Escala, M., Zumbuhl, T., Koller, C., Junge, R. & Krebs, R. 2012 Hydrothermal carbonization as an energy-efcient alternative to established drying technologies for sewage sludge: a feasibility study on a laboratory scale.Energy & Fuels 27 (1), 454–460. European Commission 2010 A Strategy for Smart, Sustainable and Inclusive Growth. No. COM(2010) 2020 Final. https://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=COM:2010:2020:FIN:EN:PDF. European Commission 2011 The EU Biodiversity Strategy to 2020, Environment. Publ. Off. of the Europ. Union, Luxembourg. http://ec.europa.eu/environment/nature/info/pubs/docs/brochures/2020%20Biod%20brochure%20nal%20lowres.pdf. European Commission 2013a Green Infrastructure (GI) - Enhancing Europe’s Natural Capital, Communication from the Commission No. COM(2013) 249 nal. http://ec.europa.eu/environment/nature/ecosystems/docs/green_infrastructures/ 1_EN_ACT_part1_v5.pdf. European Commission 2013b Technical Information on Green Infrastructure (GI). Commission Staff Working Document No. SWD(2013) 155 nal. http://ec.europa.eu/environment/nature/ecosystems/docs/green_infrastructures/1_EN_autre_ document_travail_service_part1_v2.pdf. European Commission 2019 Implementation of the Circular Economy Action Plan. Report from the commission to the European parliament, the council, the European economic and social committee and the committee of the regions. https:// ec.europa.eu/environment/circular-economy/pdf/report_implementation_circular_economy_action_plan.pdf. FAO 2019 Urban Agriculture: FAO’s Role in Urban Agriculture. Available online: fao.org/urban-agriculture/en/ (accessed on 10.09.2019). Fletcher, T. D., Andrieu, H. & Hamel, P. 2013 Understanding, management and modelling of urban hydrology and its consequences for receiving waters: a state of the art.Advances in Water Resources 51, 261–279. doi: 10.1016/j.advwatres. 2012.09.001. Game, I. & Primus, R. 2015 Global Sustainable Development. Report, 2015 Edition. Advance Unedited Version. Economic and Social Affairs, United Nations, p. 198. Gardner, B. L. 1994 Commercial agriculture in metropolitan areas: economics and regulatory issues.Cambridge Journal of Agricultural and Resource Economics Review 23 (1), 100–109. doi: https://doi.org/10.1017/S1068280500000460. Gold, M., Cunningham, M., Bleuler, M., Arnheiter, R., Schönborn, A., Niwagaba, C. & Strande, L. 2018 Operating parameters for three resource recovery options from slow-pyrolysis of faecal sludge.Journal of Water, Sanitation and Hygiene for Development 8(4), 707–717. https://doi.org/10.2166/washdev.2018.009. Golden, H. E. & Hoghooghi, N. 2018 Green infrastructure and its catchment-scale effects: an emerging science.WIRES Water 5(1), 14. doi: 10.1002/wat2.1254. Blue-Green Systems Vol 2 No 1 22 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user Graber, A. & Junge, R. 2009 Aquaponic systems: nutrient recycling from sh wastewater by vegetable production.Desalination 246 (1–3), 147–156. doi:10.1016/j.desal.2008.03.048. Gruda, N. & Schnitzler, W. H. 2006 Wood bres as a peat alternative substrate for vegetable production.Eur. J. Wood Prod. 64 (5), 347–350. https://doi.org/10.1007/s00107-005-0067-7. Hamel, E. N. & Danso, G. 2011 Agronomic considerations for urban agriculture in southern cities.International Journal of Agricultural Sustainability 8, 1–2. Source: https://doi.org/10.3763/ijas.2009.0452. Harland, I., Lane, S. & Price, D. 1999 Further experiences with recycled zeolite as a substrate for the sweet pepper crop.Acta Horticulturae 481, 187–194. doi:10.17660/ActaHortic.1999.481.19. Heimlich, R. E. & Barnard, C. H. 1992 Agricultural adaptation to urbanization: farm types in northeast metropolitan areas. Northeastern Journal of Agricultural and Resource Economics 21 (1), 50–60. Herrera-Gomez, S. S., Quevedo-Nolasco, A. & Pérez-Urrestarazu, L. 2017 The role of green roofs in climate change mitigation. A case study in Seville (Spain).Building and Environment 123, 575–584. doi:10.1016/j.buildenv.2017.07.036. Houston, P. 2005 Re-valuing the fringe: some ndings on the value of agricultural production in Australia’s peri-urban regions. Journal of Geographical Research 43 (2), 209–223. https://doi.org/10.1111/j.1745-5871.2005.00314.x. Inwood, S. M. & Sharp, J. S. 2012 Farm persistence and adaptation at the rural-urban interface: succession and farm adjustment.Journal of Rural Studies 28, 107–117. IPBES 2019 Summary for Policymakers of the Global Assessment Report on Biodiversity and Ecosystem Services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services.https://www.ipbes.net/system/tdf/ spm_global_unedited_advance.pdf?le=1&type=node&id=35245. Jean-Soro, L., Le Guern, C., Béchet, B., Lebeau, T. & Ringeard, M.-F. 2015 Origin of trace elements in an urban garden in Nantes, France.Journal of Soils and Sediments. 15 (8), 1802–1812. doi:10.1007/s11368-014-0952-y. Jensen, M. H. 2010 Controlled Environment Agriculture in Deserts, Tropics, and Temperate Regions –A World Review. Supported by CEAC, the Controlled Environment Agricultural Center, College of Agriculture and Life Sciences, and The University of Arizona, USA, p. 9. Junge, R. & Graber, A. 2014 The Potential of Aquaponics for Food Production in the Cities of the Future. Publication, ZHAW/ University of Ljubljana. https://pd.zhaw.ch/publikation/upload/207531.pdf. Junge, R., Griessler Bulc, T., Anseeuw, D., Yavuzcan Yildiz, H. & Milliken, S. 2019 Aquaponics as an educational tool. In: Aquaponics Food Production Systems: Combined Aquaculture and Hydroponic Production Technologies for the Future (Goddek, S., Joyce, A., Kotzen, B. & Burnell, G. M. eds). Springer Nature Switzerland, pp. 561–595. https://link.springer. com/chapter/10.1007/978-3-030-15943-6_22. Kennedy, G., Nantel, G. & Shetty, P. 2004 Globalization of Food Systems in Developing Countries: A Synthesis of Country Case Studies. Globalization of Food Systems in Developing Countries: Impact on Food Security and Nutrition. FAO Food and Nutrition Paper 83, pp. 1–26. Available from: http://www.fao.org/3/a-y5736e.pdf. Khalil, S. & Kakar, M. K. 2011 Agricultural use of untreated urban wastewater in Pakistan.Asian Journal of Agriculture and Rural Development 1(1), 21–26. Khan, F., Khan, M. J., Samad, A., Noor, Y., Rashid, M. & Jan, B. 2015 In-situ stabilization of heavy metals in agricultural soils irrigated with untreated wastewater.Journal of Geochemical Exploration 159, 1–7. doi:10.1016/j.gexplo.2015.07.002. Krucker, M., Hummel, R. L. & Cogger, C. 2010 Chrysanthemum production in composted and non composted organic waste substrates fertilized with nitrogen at two rates using surface and sub-irrigation.HortScience 45 (11), 1695–1701. doi:10. 21273/HORTSCI.45.11.1695. Krupa, S., McGrath, M. T., Andersen, C. P., Booker, F. L., Burkey, K. O., Chappelka, A. H., Chevone, B. I., Pell, E. J. & Zilinskas, B. A. 2001 Ambient ozone and plant health.Plant Disease 85, 4–12. Lennard, W. A. & Leonard, B. V. 2006 A comparison of three different hydroponic sub-systems (gravel bed, oating and nutrient lm technique) in an aquaponic test system.Aquaculture International 14 (6), 539–550. Lwasa, S., Mugagga, F., Wahab, B., Simon, D., Connors, J. & Grifth, C. 2014 Urban and peri-urban agriculture and forestry: transcending poverty alleviation to climate change mitigation and adaptation.Urban Climate 7, 92–106. doi:10.1016/j. uclim.2013.10.007. Maher, M., Prasad, M. & Raviv, M. 2008 Organic soilless media components. In: Soilless Culture: Theory and Practice (Raviv, M. & Lieth, J. H. eds). Elsevier, Amsterdam, pp. 459–504. Maucieri, C., Nicoletto, S., Sambo, Z., Komives, P., Borin M, T. & Junge, R. 2017 Vegetable intercropping in a small-scale aquaponic system.Agronomy 7(4), 63. doi: 10.3390/agronomy7040063. Maucieri, C., Forchino, A. A., Nicoletto, C., Junge, R., Pastres, R., Sambo, P. & Borin, M. 2018a Life cycle assessment of an aquaponic system built using recovered material for learning purposes.Journal of Cleaner Production 172, 3119–3127. doi. org/10.1016/j.jclepro.2017.11.097. Maucieri, C., Nicoletto, C., Junge, R., Schmautz, Z., Sambo, P. & Borin, M. 2018b Hydroponic systems and water management in aquaponics: a review. Italian Journal of Agronomy 13, 1012. Available from: https://www.agronomy.it/index.php/agro/ article/view/1012,https://doi.org/10.4081/ija.2017.1012. Maucieri, C., Nicoletto, C., van Os, E., Anseeuw, D., Van Havermaet, R. & Junge, R. 2019 Hydroponic Technologies. In: Aquaponics Food Production Systems: Combined Aquaculture and Hydroponic Production Technologies for the Future (Goddek, S., Joyce, A., Kotzen, B. & Burnell, G. M. eds). Springer Nature Switzerland AG, pp. 77–110. https://doi.org/10. 1007/978-3-030-15943-6_4. Blue-Green Systems Vol 2 No 1 23 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user McClintock, N. 2010 Why farm the city? Theorizing urban agriculture through a lens of metabolic rift.Cambridge Journal of Regions Economy and Society 3(2), 191–207. doi: 10.1093/cjres/rsq005. McEldowney, J. 2017 Urban Agriculture in Europe: Patterns, Challenges and Policies. In-Depth Analysis. Report European Parliament, EPRS (European Parliamentary Research Service), Brussels. PE 614.641. doi:10.2861/413185. McPhearson, T., Andersson, E., Elmqvist, T. & Frantzeskaki, N. 2015 Resilience of and through urban ecosystem services. Ecosystem Services 12, 152–156. doi:10.1016/j.ecoser.2014.07.012. Michel, J. C. 2010 The physical properties of peat: a key factor for modern growing media. Mires and Peat 6. HAL Id: Hal-00729716. https://hal-agrocampus-ouest.archives-ouvertes.fr/hal-00729716. Million, A., Bürgow, G. & Steglich, A. 2016 Urban waters for urban agriculture –ROOF WATER-FARMs as participatory and multifunctional infrastructure. In: Sustainable Urban Agriculture and Food Planning (Roggema, R. ed.). Routledge, New York, pp. 142–165. Ming, D. W. & Mumpton, F. A. 1989 Zeolites in soils. In: Minerals in Soil Environments (2nd edn, Dixon, J. B. & Weed, S. B. eds). SSSA Book Series, no. 1. Soil Science Society of America, pp. 73–911. https://dl.sciencesocieties.org/publications/ books/abstracts/sssabookseries/mineralsinsoile/873/preview/pdf. Monsees, H., Kloas, W. & Wuertz, S. 2017 Decoupled systems on trial: eliminating bottlenecks to improve aquaponic processes. PloS ONE 12 (9), e0183056. https://doi.org/10.1371/journal.pone.0183056. Monsees, H., Suhl, J., Paul, M., Kloas, W., Dannehl, D. & Würtz, S. 2019 Lettuce (Lactuca sativa, variety Salanova) production in decoupled aquaponic systems: same yield and similar quality as in conventional hydroponic systems but drastically reduced greenhouse gas emissions by saving inorganic fertilizer.PLoS ONE 14 (6), e0218368. https://doi.org/10.1371/ journal.pone.0218368. Moragues-Faus, A., Sonnino, R. & Marsden, T. 2017 Exploring European food system vulnerabilities: towards integrated food security governance.Environmental Science & Policy 75, 184–215. doi:10.1016/j.envsci.2017.05.015. Mougeot, L. J. A. 2000 Urban Agriculture: Denition, Presence, Potentials and Risks, and Policy Challenges. Cities Feeding People Series, Report 31, p. 62. https://idl-bnc-idrc.dspacedirect.org/bitstream/handle/10625/26429/117785.pdf? sequence=12. Mougeot, L. J. A. 2001 Urban agriculture: Denitions, presence, potentials and risks. In: Growing Cities, Growing Food, Thematic Paper 1: Urban Agriculture on the Policy Agenda: A Reader on Urban Agriculture (Bakker, N. et al. eds). German Foundation for International Development (DSE), Feldang, Germany, pp. 1–42. https://www.ruaf.org/sites/default/les/ Theme1_1_1.PDF. Mumenthaler, C. 2015 Developing A Methodology to Analyse and Compare Governance of Urban Agriculture. STSM report COST Action Urban Agriculture Europe, p. 23. http://www.urban-agriculture-europe.org/les/stsm_report_mumenthaler. pdf (accessed on 15/08/2019). Murray, A. & Buckley, C. 2010 Designing reuse-oriented sanitation infrastructure: the design for service planning approach. In: Wastewater Irrigation and Health –Assessing and Mitigating Risks in low-Income Countries (Drechsel, P., Scott, C. A., Raschid-Sally, L., Redwood, M. & Bahri, A. eds). Earthscan, International Water Management Institute (IWMI), International Development Research Centre (IDRC), pp. 303–318. http://publications.iwmi.org/pdf/H042615.pdf. Nabulo, G., Oryem-Origa, H. & Diamond, M. 2006 Assessment of lead, cadmium and zinc contamination of roadside soils, surface lms, and vegetables in Kampala City, Uganda.Environmental Research 101, 42–52. doi: 10.1016/j.envres.2005.12. 016. Nair, R., Varghese, S. H., Nair, B. G., Maekawa, T., Yoshida, Y. & Kumar, D. S. 2010 Nanoparticulate material delivery to plants.Plant Sci 179 (3), 154–163. doi: 10.1016/j.plantsci.2010.04.012. Ndiokwere, C. L. 1984 A study of heavy metal pollution from motor vehicle emissions and its effect on roadside soil, vegetation and crops in Nigeria.Environmental Pollution Series B, Chemical and Physical 7(1), 35–42. https://doi.org/10.1016/0143- 148X(84)90035-1. Nedkov, S., Zhiyanski, M., Dimitrov, S., Borisova, B., Popov, A., Ihtimanski, I., Yaneva, R., Nikolov, P. & Bratanova-Doncheva, S. 2017 Mapping and assessment of urban ecosystem condition and services using integrated index of spatial structure. Research Article in One Ecosystem 2, e14499. doi: 10.3897/oneeco.2.e14499. Némethy, S., Bittsánszky, A., Schmautz, Z., Junge, R. & Komíves, T. 2016 Protecting plants from pests and diseases in aquaponic systems. In: Ecological Footprint in Central Europe. Multiauthorial Monograph (Łabaj, M. & Sobczuk, J. eds). The University College of Tourism and Ecology Press, Sucha Beskidzka, Poland, pp. 166–179. Available from: https://pbn. nauka.gov.pl/sedno-webapp/works/780004#. NiChualain, D., Carlile, W., Hynes, C., Phelan, G., O’Haire, R. & Doyle, O. P. E. 2011 Nutrient status of co-composted indigenous Irish wastes, and their use in growing media.Acta Horticulturae 891, 85–92. doi:10.17660/ActaHortic.2011.891.8. Norton-Brandão, D., Scherrenberg, S. M. & van Lier, J. B. 2013 Reclamation of used urban waters for irrigation purposes – A review of treatment technologies.Journal of Environmental Management 122 (15), 85–98. https://doi.org/10.1016/j. jenvman.2013.03.012. Nozzi, V., Graber, A., Schmautz, Z., Mathis, A. & Junge, R. 2018 Nutrient management in aquaponics: comparison of three approaches for cultivating lettuce, mint and mushroom herb.Agronomy 8(3), 27. https://doi.org/10.3390/ agronomy8030027. Okorogbona, A. O. M., Denner, F. D. N., Managa, L. R., Khosa, T. B., Maduwa, K., Adebola, P. O., Okorogbona, A. O. M., Denner, F. D. N., Managa, R. L., Khosa, B. T., Maduwa, K., Adebola, P. O., Amoo, S. O., Ngobeni, H. M. & Macevele, S. Blue-Green Systems Vol 2 No 1 24 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user 2018 Water quality impacts on agricultural productivity and environment. In: Sustainable Agriculture Reviews 27 (Lichtfouse, E. ed.). Springer, Cham, pp. 1–35. Ortolo, M. 2017 Air Pollution Risk Assessment on Urban Agriculture. Master thesis, WUR, NL. https://www.wur.nl/ upload_mm/7/c/2/f753d12f-e73d-4a88-b4ac-8988b661283f_MSc_thesis_Ortolo%20%28nal%29.pdf. Oteng-Peprah, M., Acheampong, M. A. & deVries, N. K. 2018 Greywater characteristics, treatment systems, reuse strategies and user perception –a review.Water Air & Soil Pollution 229, 255. doi:10.1007/s11270-018-3909-8. Paço, T. A., Cruz de Carvalho, R., Arsénio, P. & Martins, D. 2019 Green roof design techniques to improve water use under Mediterranean conditions.Urban Sci. 3, 14. doi:10.3390/urbansci3010014. Perez-Murcia, M. D., Moral, R., Moreno-Caselles, J., Perez-Espinosa, A. & Paredes, C. 2006 Use of composted sewage sludge in growth media for broccoli.Bioresource Technology 97 (1), 123–130. https://doi.org/10.1016/j.biortech.2005.02.005. Pérez-Urrestarazu, L., Fernández-Cañero, R., Franco-Salas, A. & Egea, G. 2015 Vertical greening systems and sustainable cities. Journal of Urban Technology 22 (4), 65–85. doi:10.1080/10630732.2015.1073900. Piorr, A., Zasada, I., Doernberg, A., Zoll, F. & Ramme, W. 2018 Research for AGRI Committee: Urban and Peri-Urban Agriculture in the EU –A Study Requested by the AGRI Committee. Policy Department for Structural and Cohesion Policies, Directorate General for Internal Policies of the Union, Brussels. PE 617.468. doi:10.2861/953859. Pölling, B., Alfranca, Ó., Alves, E., Andersson, G., Branduini, P., Egloff, L. D., Giacchè, G., Heller, A., Herkströter, K., Kemper, D., Koleva, G., Lorleberg, W., Mendes-Moreira, P., Miguel, A., Neves, L., Paulen, O., Pickard, D., Prados, M. J., Recasens, X., Ronchi, B., Spornberger, A., Timpe, A. G., Torquati, B., van der Schans, J. W., Weissinger, H. & Wydler, H. 2015 Creating Added Value Societal Benets of Urban Agriculture. In: Urban Agriculture Europe (Lohrberg, F., Licka, L., Scazzosi, L. & Timpe, A. eds). Jovis, Berlin, pp. 92–100. Pothukuchi, K. & Kaufman, J. L. 1999 Placing the food system on the urban agenda: The role of municipal institutions in food systems planning. In: Agriculture and Human Values, Vol. 16. Kluwer Academic Publishers, Printed in the Netherlands, pp. 213–224. doi:10.1023/A:1007558805953. Prain, G. & de Zeeuw, H. 2007 Enhancing technical, organisational and institutional innovation in urban agriculture. Urban Agriculture Magazine 19, 9–15. Pratt, T., Allen, L. N., Rosenberg, D. E., Keller, A. A. & Kopp, K. 2019 Urban agriculture and small farm water use: case studies and trends from Cache Valley, Utah.Agricultural Water Management 213 (C), 24–35. doi:10.1016/j.agwat.2018.09.034. Prové, C., Kemper, D., Loudiyi, S., Mumenthaler, C. & Nikolaidou, S. 2015 Governance of Urban Agriculture Initiatives: Insights drawn from European case studies. In: Urban Agriculture Europe (Lohrberg, F., Licka, L., Scazzosi, L. & Timpe, A. eds). Jovis, Berlin, pp. 64–69. Qadir, M., Wichelns, D., Raschid-Sally, L., Singh Minhas, P., Drechsel, P., Bahri, A. & McCornick, P. 2007 Agricultural use of marginal-quality water –opportunities and challenges. In: Water for Food Water for Life –A Comprehensive Assessment of Water Management in Agriculture (Molden, D. ed.). Earthscan, International Water Management Institute (IWMI), pp. 425–457. Available from: https://www.researchgate.net/publication/237526608_Agricultural_use_of_marginal- quality_water-_opportunities_and_challenges. Rakocy, J. E. 2012 Aquaponics –Integrating Fish and Plant Culture. In: Aquaculture Production Systems (Tidwell, J. ed.). John Wiley & Sons, Inc., pp. 343–386. Available from: https://onlinelibrary.wiley.com/doi/abs/10.1002/9781118250105.ch14. Raviv, M. 2013 Composts in growing media: what’s new and what’s next? Acta Horticulturae 982, 39–47. Rich, S. 1964 Ozone damage to plants.Annual Review of Phytopathology 2, 253–266. Rogers, R. 1997 Cities for A Small Planet. Faber & Faber Limited, London, p. 180 Roggema, R. 2016 Sustainable Urban Agriculture and Food Planning, Routledge Studies in Food. In: Society and the Environment (Roggema, R. ed.). Taylor and Francis, Milton, pp. 286. Available from: https://doi.org/10.4324/ 9781315646039. Rosenzweig, C., Solecki, W., Hammer, S. A. & Mehrotra, S. 2010 Cities lead the way in climate–change action. Nature – International Journal of Science 467 (7318), 909–911. https://www.nature.com/articles/467909a.pdf. Samson, R., Ningal, T. F., Tiwary, A., Grote, R., Fares, S., Saaroni, H., Hiemstra, J. A., Zhiyanski, M., Vilhar, U., Carinanos, P., Järvi, L., Przybysz, A., Moretti, M. & Zürcher, N. 2017 Species-Specic Information for Enhancing Ecosystem Services. In: The Urban Forest, Future City 7 (Pearlmutter, D. et al. eds). Springer International Publishing, pp. 111–144. doi:10.1007/ 978-3-319-50280-9_12. Santo, R., Palmer, A. & Brent, K. 2016 Vacant Lots to Vibrant Plots: A Review of the Benets and Limitations of Urban Agriculture. Baltimore. doi:10.13140/RG.2.2.25283.91682. Sanyé-Mengual, E., Anguelovski, I., Oliver-Solà, J., Montero, J. I. & Rieradevall, J. 2015a Resolving differing stakeholder perceptions of urban rooftop farming in Mediterranean cities: promoting food production as a driver for innovative forms of urban agriculture.Agriculture and Human Values. 3–22. doi: 10.1007/s10460-015-9594-y. Savvas, D. & Passam, H. 2002 Hydroponic Production of Vegetables and Ornamentals. Embryo publications, Athens, Greece, p. 463. Schmautz, Z., Loeu, F., Liebisch, F., Graber, A., Mathis, A., Griessler Bulc, T. & Junge, R. 2016 Tomato productivity and quality in aquaponics: comparison of three hydroponic methods.Water 8(11), 533. https://doi.org/10.3390/w8110533. Schmilewski, G. 2008 The role of peat in assuring the quality of growing media. Mires & Peat 3, 1–8. Available from: https:// pdfs.semanticscholar.org/bcdf/aa9ba59ef6c39c52a4cb1e81962f2cf33171.pdf. Schwarz, K., Pickett, S. T. A., Lathrop, R. G., Weathers, K. C., Pouyat, R. V. & Cadenasso, M. L. 2012 The effects of the urban built environment on the spatial distribution of lead in residential soils.Environmental Pollution 163, 32–39. Blue-Green Systems Vol 2 No 1 25 doi: 10.2166/bgs.2019.931 Downloaded from http://iwaponline.com/bgs/article-pdf/2/1/1/868208/bgs0020001.pdf by Universidad da Sevilla user