Sustainable development is a ubiquitously used concept referring to a vision of society centred on the principles of global responsibility, integration, inter- and intra-generational equity, precaution, participation and a long-term time horizon. It is a contested concept that regroups various sub-discourses which embody its constructive ambiguity. For sustainable development to become a decision-guiding strategy in pubic decision-making, adequate decision-supporting processes are required. This thesis reflects on the theory and on the practice of ‘sustainability assessment’ in various contexts by combining discourse analysis with a case-study approach. <p>The thesis builds on three case studies, undertaken in different –institutional, geographical, thematic and research- contexts. The three cases (situated respectively in the realm of sub-national policies; development co-operation and energy policy) allow for different approaches to sustainability assessment to be applied and analyzed. The relative novelty of sustainability assessment created room for experimental participatory approaches and provided opportunities for policy-relevant learning. Understanding how sustainability assessment contributes to a shared interpretation of sustainability, to an enhanced structuring of information and to influencing policy decisions is key to develop and apply the approach in the future. Research findings indicate that: sustainability assessment should act as a forum giving sense to the interpretational challenge of sustainability, within the boundaries set by essential sustainability principles. Participatory approaches are key in performing sustainability assessment, for both intrinsic and pragmatic reasons. Stakeholder knowledge should be combined with scientific information in real-life ‘science for sustainability’ experiments. There is no blueprint approach for developing and applying sustainability assessment. The discursive-institutional interplay determines how sustainability assessment is conceptualized and applied. Windows of opportunity for introducing and applying sustainability assessment may arise unexpectedly due to discursive and institutional convergences facilitated by the interpretational width of the sustainability concept, and these should be taken up. Sustainability assessment should be designed as a de-polarizing process, bringing the co-production of knowledge and decisions into practice. <p>The capacity of sustainable development to grasp the complexity of current societal challenges by providing a decision-guiding framework can be operationalized by sustainability assessment, which entails an increased awareness of the overlap between different areas of public policy. If sustainability assessment is to actually support decision-makers, scientifically and participatory designed beacons are needed. This is a challenge where scientists act as analysts and facilitators to help translate the intrinsically dynamic meaning of sustainability into actions. This thesis wishes to contribute to this endeavour. <p><p><p><p><p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Au cours des dernières décennies, un type de marais filtrant, généralement planté de saules, a été développé pour opérer un système de traitement d’eau sans effluent, par évapotranspiration. Ces marais à effluent sont généralement utilisés pour le traitement d’eau usée domestique, mais pourraient aussi présenter une alternative intéressante pour d’autres applications, comme le traitement de lixiviat contaminé. Les guides de conception actuellement disponibles ne permettent toutefois pas de concevoir un système flexible qui permettrait de gérer les grandes variations de volume à traiter liées à la nature même des lixiviats (i.e. résultent entièrement des précipitations) et ne tiennent pas compte de la variation inter et intra-annuelle de l’évapotranspiration (ET) du saule. Cette thèse présente d’abord une revue de littérature de ET du genre Salix et de ses facteurs de variation les plus importants. Il apparaît que les conditions de croissance ont plus d’importance que l’identité spécifique et que la disponibilité en eau, la fertilisation et la contamination sont les principaux facteurs dictant l’ET des saules. L’effet de l’âge, du contexte expérimental, de la densité de plant et du type de sol n’a pas pu être clairement démontrés par cette revue. Ensuite, une étude portant sur le potentiel d’ET de S. miyabeana ‘SX67’ est présentée. Il est démontré qu’un modèle basé sur des paramètres foliaires et sur le déficit de pression de vapeur d’eau dans l’air permet de prédire l’ET de S. miyabeana en condition de marais filtrant. Cette étude permettra entre autres d’améliorer les plans de conception d’un éventuel marais de saules à effluent nul. Pour continuer, la réponse de S. miyabeana ‘SX67’ à différentes concentrations de lixiviat et à différents types de substrats a été étudiée. Ce cultivar s’est montré tolérant aux concentrations du lixiviat brut retrouvées sur un site d’entreposage de poteaux de bois traité. Le type de substrat a influencé la réponse du saule et ses performances écophysiologiques, en plus d’affecter la dynamique des contaminants. Finalement, la modélisation hydrologique d’un système à effluent nul par marais de saules permet de proposer une méthode de dimensionnement des différents compartiments du système pour atteindre un objectif d’effluent nul sur une période de 20 ans, ainsi que de proposer des solutions de conception et d’opération optimale. L’application du modèle au cas spécifique d’un site d’entreposage de poteaux de bois traité a permis d’évaluer la faisabilité, d’un point de vue hydrologique, de cette technologie dans le contexte climatique du sud du Québec. Sur la base de cette étude, la principale limite pour l’application des marais à effluent nul au Québec sont la surface de marais et le volume de stockage requis. Dans le cas où une étape de prétraitement efficace précède le marais de saule, la durée de vie du marais ne devrait pas être limitante et dépendra principalement de la durée de vie des végétaux. Cependant, le destin des contaminants dans le système, qu’il s’agisse de la disposition des contaminants accumulés à l’étape de prétraitement ou d’une éventuelle translocation de contaminants dans les parties aériennes des végétaux, devrait être considéré avant d’établir un système à effluent nul. Les résultats de cette recherche permettent, entre autres, de proposer les marais de saules à effluent nul comme une alternative intéressante pour le traitement d’eau contaminée au Québec. / During the last decades, a type of constructed wetlands, usually planted with willows, was developed to operate a water treatment system with zero effluent, by evapotranspiration. These zero liquid discharge wetlands are typically used for domestic wastewater treatment, but could also be an attractive alternative for other applications, such as contaminated leachate treatment. However, the design guidelines currently available do not allow for the design of a flexible system that would manage the large variations of volume to be treated related to the very nature of leachates (i.e. produced entirely from precipitation) and do not take into account inter and intra-annual variation of willows evapotranspiration (ET). This thesis first presents a literature review of ET for the genus Salix and its most important driving factors. It appears that growing conditions are more important than species identity and that water availability, fertilization and contamination are the main factors dictating ET in willow. The effect of age, experimental context, planting density, and soil type could not be clearly demonstrated by this review. Then, a study on the potential ET of S. miyabeana 'SX67' is presented. It is shown that a model based on foliar parameters and on the water vapor pressure deficit in the air makes it possible to predict the ET of S. miyabeana under wetland conditions. This study will, among other things, improve the design plans for a potential zero effluent willow wetland. To continue, the response of S. miyabeana 'SX67' to different leachate concentrations and different types of substrates was studied. This cultivar has been tolerant of raw leachate concentrations found at a treated wood pole storage site. The type of substrate influenced the willow response and ecophysiological performance, and affected the dynamics of the contaminants. Finally, the hydrological modelling of a system with zero effluent by willow bed makes it possible to propose a method of dimensioning for the different compartments of the system in order to reach a zero effluent objective over a period of 20 years, as well as to propose solutions for optimal design and operation. The application of the model to the specific case of a treated wood pole storage site made it possible to assess the hydrological feasibility of this technology in the climate context of southern Quebec. On the basis of this study, the main limit for the application of zero effluent willow bed in Quebec is the wetland area and the storage volume required. In the case where an effective pre-treatment step precedes the willow bed, the life of the wetland should not be limiting and will depend mainly on the lifespan of the plants. However, the fate of the contaminants in the system, be it the disposition of the accumulated contaminants at the pre-treatment stage or a possible translocation of contaminants into the aerial parts of the plants, should be considered before establishing a system with zero effluent. The results of this research make it possible, among other things, to propose zero-effluent willow wetlands as an interesting alternative for the treatment of contaminated water in Quebec.

Doctorat en environnement, Orientation urbanisme et aménagement du territoire / info:eu-repo/semantics/nonPublished