Des Technosols construits à partir de produits résiduaires urbains : services écosystémiques fournis et évolution

Abstract : Cities are becoming denser at the expense of nature spaces that are correspondingly decreasing, as are the ecosystem services associated with them. Faced with this observation, the greening of buildings appears as a valuable alternative. Nowadays, green roofs have become a planning tool in urban planning. These roofs take different forms, adapting to urban constraints and challenges. In recent years, a new form of green roof has emerged: productive green roofs (i.e. of edible biomass). Despite a growing interest, rooftop farming is still poorly developed and known. Their design, their development and especially, the ecosystem services they could deliver are still poorly understood and need to be known. Keystone to green roofs, the soil in place directly and indirectly influences the provided ecosystem services. Despite, it’s key role, soil is still poorly studied. Furthermore, non-renewable products such as pozzolan or expanded clay or peat are today mostly used in their composition. In this work we have studied constructed soils, named Technosols, for productive roofs made only of urban wastes. The objectives of this thesis were: (i) to achieve a quantitative assessment of delivered ecosystem services (ii) analyze the first stages of Technosol pedogenesis. In order to do so, three experimental devices were implemented on the “Bertrand Ney” rooftop of the technical University AgroParisTech in Paris. The experimental devices consist of multiple plots filled with different disposal of five urban wastes: green waste compost, shredded woods, crushed tiles and bricks, spent coffee grounds used to grow mushroom and a biowaste compost. The impact of the different Technosols on (i) ecosystem services, (ii) food production (quality and quantity), (iii) fertility) and (iv) temporal evolution, were assessed. Constructed Technosol are fertile and allow a consistent food production over one to five years. The level of food production was equivalent to that of a professional producer and food quality regarding trace metal element was below existing norms. The quantitative assessment of ecosystem services (food production, urban waste recycling, rainwater retention and overflow quality (C and N)), highlighted the multifunctional nature of productive green roofs. However, we identified an ecosystem disservice which is an alteration in the quality of the leachates due to carbon leaching and presumably other elements. A first phase of rapid and strong pedogenesis was observed marked by an intense biodegradation and lixiviation of the Technosols. Our works identified two trade-offs in the design of a productive Technosol: between (i) the biodegradation or organic materials (ensuring the supply of mineral nutrient to plants) and the maintenance of the structure and porosity of the Technosol (i.e. its physical fertility) and (ii) the supply of nutrients by biodegradation and leaching, resulting in a loss of these elements and an alteration of the quality of percolation waters on the other hand. Knowledge of the properties of the materials used to build Technosols and on their link with the expected ecosystem services already makes it possible to design multifunctional productive rooftop based on urban waste and manage them sustainably.
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Baptiste Grard. Des Technosols construits à partir de produits résiduaires urbains : services écosystémiques fournis et évolution. Ecologie, Environnement. Université Paris-Saclay, 2017. Français. ⟨NNT : 2017SACLA043⟩. ⟨tel-01779723⟩

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