Le jardin : une clé de lecture du végétal en milieu urbain

Dans son livre L’Art du jardin et son histoire, recherchant une théorie sur l’art des jardins, John Dixon Hunt explicite la vision du jardin au XVIIe siècle. Reposant sur la théorie de l’imitation, le jardin jouait alors un rôle d’intermédiaire afin d’apporter à la société une meilleure compréhension de la nature. Cet objectif était atteint par un juste équilibre entre l’intervention humaine et l’élément naturel. L’article montre comment cette vision du jardin a pu être remise en cause, notamment dans le contexte de la modernité, mais aussi comment elle a pu se maintenir dans des courants parfois minoritaires. Aujourd’hui, elle semble se réaffirmer, même si les enjeux (les questions environnementales) et le contexte ont changé. Cette étude en déduit qu’il y a une certaine continuité dans cette façon de concevoir le jardin et avance l’idée que la notion de jardin serait l’une des approches possibles pour étudier le végétal dans les aménagements urbains.In his book, L’Art du jardin et son histoire, seeking a theory on garden design, Hunt explains the vision of the garden in the XVIIth century. Based on the theory of imitation, gardens used to play an intermediary role in giving society a better understanding of nature. This aim was achieved by a balance between human intervention and the natural element. The paper shows how this way of thinking of the garden has been reconsidered, especially in the context of modernity, but also how it has been maintained in a few minor currents. Today, though issues (environmental issues) and contexts are different, the concept of the garden as described by Hunt seems to reassert itself. Hence, this study infers that there is a continuity in this way of designing gardens and puts forward the idea that the notion of garden is one possible approach for studying the place of plants in urban development

Decoupling of arsenic and iron release from ferrihydrite suspension under reducing conditions: a biogeochemical model

High levels of arsenic in groundwater and drinking water are a major health problem. Although the processes controlling the release of As are still not well known, the reductive dissolution of As-rich Fe oxyhydroxides has so far been a favorite hypothesis. Decoupling between arsenic and iron redox transformations has been experimentally demonstrated, but not quantitatively interpreted. Here, we report on incubation batch experiments run with As(V) sorbed on, or co-precipitated with, 2-line ferrihydrite. The biotic and abiotic processes of As release were investigated by using wet chemistry, X-ray diffraction, X-ray absorption and genomic techniques. The incubation experiments were carried out with a phosphate-rich growth medium and a community of Fe(III)-reducing bacteria under strict anoxic conditions for two months. During the first month, the release of Fe(II) in the aqueous phase amounted to only 3% to 10% of the total initial solid Fe concentration, whilst the total aqueous As remained almost constant after an initial exchange with phosphate ions. During the second month, the aqueous Fe(II) concentration remained constant, or even decreased, whereas the total quantity of As released to the solution accounted for 14% to 45% of the total initial solid As concentration. At the end of the incubation, the aqueous-phase arsenic was present predominately as As(III) whilst X-ray absorption spectroscopy indicated that more than 70% of the solid-phase arsenic was present as As(V). X-ray diffraction revealed vivianite Fe(II)3(PO4)2.8H2O in some of the experiments. A biogeochemical model was then developed to simulate these aqueous- and solid-phase results. The two main conclusions drawn from the model are that (1) As(V) is not reduced during the first incubation month with high Eh values, but rather re-adsorbed onto the ferrihydrite surface, and this state remains until arsenic reduction is energetically more favorable than iron reduction, and (2) the release of As during the second month is due to its reduction to the more weakly adsorbed As(III) which cannot compete against carbonate ions for sorption onto ferrihydrite. The model was also successfully applied to recent experimental results on the release of arsenic from Bengal delta sediments

How to evaluate nature-based solutions performance for microclimate, water and soil management issues – Available tools and methods from Nature4Cities European project results

International audienceIn the context of climate change, Nature-Based Solutions (NBSs), a recently developed concept, are increasingly considered as part of the adaptation strategies of the cities. Studies using expert models and methods (EMM) receive a great deal of scientific attention. Considering EMM increasing use, this study aims to perform an analysis of the reported evaluation results, reflecting the capability of the EMM to accurately tackle urban challenges identified within the EU Nature4Cities project. Then, we propose a set of indicators and recommendations about sixteen EMM to be used by funders, researchers and practitioners when evaluating the performance of NBSs. The coupling of the different components (climate, water and soil) is not a simple matter. The analysis relies on the definition of the range of the reported metrics and on the investigation of the relationship between the various indices, applied for the EMM evaluation. Secondly, the study assesses the existing EMM, indicating the potential of NBSs: (i) to reduce urban heat island, (ii) to limit surface warming, (iii) to increase the thermal comfort of people, (iv) to limit the overheating and runoff of surfaces due to impervious areas, (v) to increase water retention during stormy episodes, (vi) to improve storm water quality at the outlet of the sustainable urban drainage systems, (vii) to promote the filtration and epuration of storm water runoff in soil and (viii) to be a support for vegetation. The analysis reveals that EMM can be considered as helpful tools for urban microclimate, urban soil and water management analysis, provided their limitations and characteristics are taken into account by the user when choosing tools and interpreting results (e.g. application scale). With regard to the performance of NBSs, the most commonly used indicators clearly depend on the scale of the project

Outil d'alerte pour identifier les périodes propices au rafraîchissement des parcs

International audienceAlert tool for identifying good periods to refresh parks. In the coolparks framework, mobile measurement campaigns will be performed to quantify the cooling induced by urban parks and the cool air diffusion within their surrounding urban areas. In order to identify the optimal conditions to implement these campaigns, fixed air temperature measurements performed during several years within parks (in Nantes, France) and their surrounding urban environment are utilized. Five interesting periods per season are identified for future campaigns : 3 are diurnal and 2 are nocturnal. For each of the {period, season} combinations, the meteorological conditions that allow to maximize the park cooling or the cool air diffusion within their close environment are investigated. Decision trees are constructed to facilitate the weather alert implementation allowing to identify the favorable days for future measurement campaigns taking place.Dans le cadre du projet CoolParks, des campagnes de mesures mobiles vont être menées pour mesurer le rafraîchissement occasionné par des parcs et la diffusion de cette fraîcheur dans leurs quartiers environnants. Afin d'identifier les conditions propices pour la mise en oeuvre de ces campagnes, des mesures fixes de température de l'air réalisées pendant plusieurs années dans des parcs nantais et leur environnement urbain sont utilisées. Cinq périodes intéressantes par saison sont identifiées pour les futures campagnes : 3 périodes diurnes et 2 périodes nocturnes. Pour chacune de ces combinaisons {période, saison}, les conditions météorologiques permettant de maximiser le rafraîchissement des parcs ou la diffusion de fraîcheur dans leur environnement proche sont étudiées. Des arbres de décision sont construits pour faciliter la mise en oeuvre d'alertes permettant d'identifier les journées propices à la tenue des futures campagnes de mesure

CoolParks : aide à la conception de parcs et de formes urbaines pour optimiser le rafraîchissement urbain

International audienceClimate projections for the next decades predict heat waves, which will be intensified in cities due to the Urban Heat Island (UHI) effect. To mitigate the UHI, new urban planning projects look forward to integrate more solutions based on vegetation and water. Thus, urban parks can generate cooled air but the amount of freshness created will depend on the park's constitution and proportion of each element and the urban environment surrounding the park. In addition, the cooled air will be spread differently in the surroundings depending on the urban district's morphology. The interaction between the urban morphology and the urban park will be considered in the CoolParks project. The aim of this project is to develop a tool for local communities to design urban parks and the surrounding districts with the aim to optimize urban cooling and reduce the buildings' energy consumption.Les projections climatiques des prochaines décennies prévoient des périodes de canicule plus longues et plus fréquentes qui seront exacerbées en ville par le phénomène d'Îlot de Chaleur Urbain (ICU). Un des enjeux des nouveaux aménagements urbains est d'intégrer des mesures pour atténuer l'intensité de l'ICU en ayant recours au végétal et à l'eau. Ainsi, les parcs urbains offrent une source importante de fraîcheur. Les effets de ces aménagements varient largement selon leur type, leur proportion, leur répartition, leur mode de gestion et l'environnement urbain dans lequel ils sont implantés. Aussi, la fraîcheur générée se diffuse différemment dans les alentours proches du parc selon la morphologie des quartiers qui l'environnent. Le projet de recherche Coolparks, présenté dans cet article, interroge ces problématiques. Son objectif est de concevoir un outil simple à mettre en oeuvre, permettant aux collectivités locales de concevoir conjointement les parcs et les quartiers environnants, en considérant leurs interactions réciproques, pour optimiser le rafraîchissement urbain et la réduction des consommations énergétiques dans les bâtiments

Le jardinage urbain : le défi de la qualité des sols urbains pour les collectivités

International audienceUrban gardening is a booming trend. Local authorities are actively taking part in this movement in response to the demand of inhabitants but also because they see it as a way of addressing many of the challenges of the sustainable city. As a result, they are confronted with the issue of soil quality. Urban soils, as an environmental component, are rarely highlighted yet they are subjected to many constraints such as loss of agronomic potential or pollution. Based on experiments in Nantes, the article explores the process by which municipalities establish a diagnosis and intervene on soil quality, addressing the questions regarding the tools employed and the interactions with community gardeners. The approach adopted based on the landscape makes it possible to simultaneously address and, if necessary, establish the interrelations between the many challenges faced by communities in understanding urban soils, the skills required, and the difficulties in addressing the technical and political dimensions.Le jardinage urbain est aujourd’hui en plein essor. Les collectivités prennent part à cette dynamique pour répondre à la demande des habitants mais aussi parce qu’elles y voient une solution à de nombreux enjeux de la ville durable. De ce fait, elles sont confrontées à celui de la qualité des sols. Compartiment de l’environnement rarement mis en avant, les sols urbains sont en effet soumis à de nombreuses contraintes : perte de potentialités agronomiques ou pollutions. Basé sur des expériences nantaises, l’article explore le processus par lequel les villes établissent un diagnostic puis interviennent sur la qualité des sols, abordant à la fois les outils et les interactions avec les habitants-jardiniers. L’approche paysagère adoptée permet d’aborder conjointement, et le cas échéant de relier, les nombreux défis de l’appréhension des sols par les collectivités à la fois par les inconnues qui persistent sur les sols urbains, les compétences et enfin la difficulté à articuler les dimensions technique et politique

Aqueous Fe (squares) and As (triangles) concentrations released during experiments AD1 (a), AD5 (b), CP1 (c), CP5 (d)

<p><b>Copyright information:</b></p><p>Taken from "Decoupling of arsenic and iron release from ferrihydrite suspension under reducing conditions: a biogeochemical model"</p><p>http://www.geochemicaltransactions.com/content/8/1/12</p><p>Geochemical Transactions 2007;8():12-12.</p><p>Published online 29 Nov 2007</p><p>PMCID:PMC2246110.</p><p></p> Empty symbols represent control experiments without bacteria. Proportions of released Fe and As are calculated by subtracting the concentration at the beginning of each experiment (Fig. 2) from the concentrations measured over time, and then dividing the differences by the initial solid content of Fe and As (Table 1), respectively. Error bars represent the standard deviation of duplicated measurements

Concentrations of aqueous Fe(II) in mg/L, of aqueous As(V) (black bars), As(III) (gray bars) and As(tot) (white bars) in mg/L, and of bacteria in million cells/mL

<p><b>Copyright information:</b></p><p>Taken from "Decoupling of arsenic and iron release from ferrihydrite suspension under reducing conditions: a biogeochemical model"</p><p>http://www.geochemicaltransactions.com/content/8/1/12</p><p>Geochemical Transactions 2007;8():12-12.</p><p>Published online 29 Nov 2007</p><p>PMCID:PMC2246110.</p><p></p> Each group of 3 bars includes data of experiments AD1, CP1, AD5, CP5 after 1 day, 28 days and 63 days of As-2LFh incubation. Error bars represent the standard deviation of duplicated measurements

How to use nature-based solutions in urban planning systems of Europe?

International audienceIn developed countries, the level of urbanization is still rising and expected to reach 83% in 2030 [United Nations, 2012]. As a result of rapid growing of urban areas and population, the urban planners several challenges. For example, risks of flooding due to overload of the drainage system, and pollution due to combined sewer overflows and diffuse pollution, consequently increase significantly. Questions about biodiversity promotion and urban heat islands are also emerging as major issues in the construction of sustainable cities [Berretta et al; 2014].European Commission, (2015) highlighted nature-based solutions in order to address the mentioned urban problems related to climatic, demographic and technological changes. The aim is to bring new solutions into urban planning and thus, to address those challenges and to improve the well-being sensation, quality of life of city dwellers.Nature-based solutions (NBS) are one of the newest concepts for tackling urban challenges. The concept of NBS was meant to reform the methodology of urban planning in EU countries and deliver multiple environmental, social and economic benefits through introducing and implementing a new toolkit based on natural resources. In the Horizon 2020 project, Nature4Cities besides multi-thematic and multi-scalar evaluation of nature-based solutions and their effectiveness in addressing different urban challenges we aim to deliver a platform used by urban planners. As an important step of producing the platform in this paper we analyse the possibilities of implementing nature-based solutions in the different planning systems of Europe. First, we give a short overview on similarities and differences between planning systems, and the different kind of plans (master plans, action plans, authorization plans, … etc.) Secondly, we describe Nature4Cities concept on NBS-typology, and thirdly we analyse the possibilities of inserting the particular nature-based solutions into the different kind of plans in different scales. As a result, we wish to establish a baseline of "business as usual" urban operations and how the mainstream "grey solutions" could be replaced by NBS. We also put emphasis on the social aspects of urban planning and that of NBS’: what are the alternative governance and participatory processes that enhance the implementation of NBS