L’intérêt pour le sujet prend comme point de départ la médiatisation internationale du concept de « servicesécosystémiques », par le rapport onusien du Millenium Ecosystems Assessment, paru en 2005. Cette étude postule quel'homme dépend du bon état des écosystèmes, au travers des services qu'il en retire pour la satisfaction de son bien-être etde ses besoins élémentaires. Concomitamment, la directive européenne du 21 avril 2004 sur la responsabilitéenvironnementale intègre les services écologiques au champ des éléments de l’environnement, réparables en cas dedommages accidentels. Sa transposition par la loi du 1er avril 2008 introduit les services écologiques au droit français,alors définis comme les fonctions assurées par les sols, les eaux, et les espèces et les habitats protégés au bénéfice d’uneressource naturelle ou au bénéfice du public. Si le concept est a priori inédit pour le droit interne, on observe pourtantque les services se coulent dans une approche fonctionnelle de la nature, qui elle, ne lui est pas inconnue. Des législationssectorielles, applicables à certains systèmes écologiques exploités ou protégés, se sont déjà dotées de principes et d'outilsvisant à organiser la multifonctionnalité, le multi-usage, voire le multi-services. Mais alors que les services écologiquesse diffusent insidieusement, et sont en voie d'intégrer le rang des principes généraux, ce sont les concepts, lesinstruments, et les valeurs véhiculées par le droit qui se trouvent réinterrogés. A travers le prisme des services, nousassistons aujourd'hui à une mutation, à la fois douce et profonde, vers un droit des systèmes complexes. / The interest for the subject starts with the international media coverage of the "ecosystem services" concept, as stated inthe 2005, United Nations report, Millenium Ecosystems Assessment. This study postulates that human beings depend onhealthy ecosystems, through services they receive to benefit their well-being and basic needs. Concomitantly, on April21, 2004, the European directive on environmental liability, integrated ecological services in the field of repairable itemsof environment, in the case of accidental damages. The implementation, by the April 1st, 2008, law, introducedecological services in the French law, defined as functions performed by protected species and natural habitats, land andwater for the benefit of another natural resource or the public. If the concept is, a priori, unique for domestic law, theservices fit into a functional approach of nature, which conversely, is not unknown to it. Sectoral legislations, applicableto certain exploited or protected ecological systems, are already equipped with principles and tools to organize themultifunctional, the multi-usage or the multi-services. While ecological services are spreading insidiously, and are on theverge of integrating general principles, these concepts, instruments, and values conveyed by the law are being questionedonce again. Through the prism of services, we witness today the soft and profound change towards a law of complexsystems.

Dentre as variáveis que procuram mensurar a qualidade ambiental, a vegetação ganha destaque pela diversidade de serviços ecológicos prestados ao sistema urbano. Neste sentido, a análise das áreas verdes deve ser contextualizada em função do arranjo espacial dos principais elementos que exercem pressão sobre o ambiente. Por isto, trabalhamos com um índice de qualidade ambiental que integra variáveis clássicas como a proporção de cobertura vegetal, com outros elementos significativos da paisagem urbana como a extensão das áreas construídas e o adensamento vertical. Para o desenvolvimento deste índice aplicamos uma metodologia de Sensoriamento Remoto (SR) baseada na integração de ortofotos digitais e atributos altimétricos derivados do LIDAR (ALS) que permitiu mensurar a dimensão vertical da paisagem urbana tornando mais realística a modelagem dos efeitos das áreas construídas na qualidade ambiental. / Given the diversity of its ecological services, vegetation is among the main indicators of environmental quality in urban systems. For that, green areas must be analyzed in the context of the spatial distribution of the main elements putting pressure on the environment. In order to do that, we have worked with an index of environmental quality that integrates traditional variables, such as the proportion of vegetation cover, with other significant elements of the urban landscape, such as the extension of built areas and vertical densification. For the development of the index we applied a Remote Sensing (RS) methodology combining digital orthophotos and altimetric parameters based on LIDAR (ALS), which allowed to measure the vertical dimension of the urban landscape becoming more realistic modeling of the effects of the built environment on environmental quality.

Dentre as variáveis que procuram mensurar a qualidade ambiental, a vegetação ganha destaque pela diversidade de serviços ecológicos prestados ao sistema urbano. Neste sentido, a análise das áreas verdes deve ser contextualizada em função do arranjo espacial dos principais elementos que exercem pressão sobre o ambiente. Por isto, trabalhamos com um índice de qualidade ambiental que integra variáveis clássicas como a proporção de cobertura vegetal, com outros elementos significativos da paisagem urbana como a extensão das áreas construídas e o adensamento vertical. Para o desenvolvimento deste índice aplicamos uma metodologia de Sensoriamento Remoto (SR) baseada na integração de ortofotos digitais e atributos altimétricos derivados do LIDAR (ALS) que permitiu mensurar a dimensão vertical da paisagem urbana tornando mais realística a modelagem dos efeitos das áreas construídas na qualidade ambiental. / Given the diversity of its ecological services, vegetation is among the main indicators of environmental quality in urban systems. For that, green areas must be analyzed in the context of the spatial distribution of the main elements putting pressure on the environment. In order to do that, we have worked with an index of environmental quality that integrates traditional variables, such as the proportion of vegetation cover, with other significant elements of the urban landscape, such as the extension of built areas and vertical densification. For the development of the index we applied a Remote Sensing (RS) methodology combining digital orthophotos and altimetric parameters based on LIDAR (ALS), which allowed to measure the vertical dimension of the urban landscape becoming more realistic modeling of the effects of the built environment on environmental quality.

BiG

The valuation of ecosystem services requires first and foremost, that the current level or stock of a service first be estimated. Here, I investigate the relationship between the fields of environmental science and ecological economics in their research effort of ecosystem services and the implications this may have on the ecosystem valuation research program. I investigate two ecological functions described as ecosystem services within specific ecosystem types: the flood control provisioning services of wetlands and pollination service provisioning by pollinator populations in agroecosystems. I examined the environmental literature to provide quantitative estimates of a) the distribution of the level of service delivered as well as b) the ability of environmental scientists to predict this level of service. The results presented here suggest a moderately strong correlation between research efforts in environmental science and ecological economics at the pooled level of ecosystem types and services. I suggest however, an integrated research enterprise between social and environmental scientists may provide greater efficiency by means of a global ecosystem service research network and repository. I found that, on average, consistent with conventional wisdom, wetlands do indeed have a positive effect by reducing the frequency and magnitude of floods, increasing low flows, and increasing water storage. In the same vein, I found on average and consistent with conventional wisdom, there is a consistent and comparatively strong association between pollinator abundance and agroecosystem productivity as inferred from measures of plant fertilization success. In both investigations however, metaregression analysis indicated that our current ability to predict either pollination or flood control services is poor to modest at best. The low predictive power combined with the observed heterogeneity in effect size in both investigations suggest that flood control service delivered by wetlands or pollination services delivered by natural pollinator populations in agroecosystems and the expected changes in the level of services delivered under a candidate management scenario, will have a large uncertainty. Such uncertainty should be explicitly incorporated into estimates of both the current economic value of ecosystem services, as well as estimates of how these values are likely to change under alternative management scenarios. Given these, I suggest that the implications for the development of Market-based instruments (MBIs) or any payment of ecosystem services to conserve ecosystem services: that the associated ecological function(s) must be few and well characterized, and we must agree on what endpoints ought to properly be used to characterize these functions. If this condition is not met, an ordinal ranking is the best we can do and in the absence of obvious enthusiasm for more detailed scientific research which leads to the conclusion that perhaps alternate strategies like command and control may be the better alternative to protect ecosystem services.

The valuation of ecosystem services requires first and foremost, that the current level or stock of a service first be estimated. Here, I investigate the relationship between the fields of environmental science and ecological economics in their research effort of ecosystem services and the implications this may have on the ecosystem valuation research program. I investigate two ecological functions described as ecosystem services within specific ecosystem types: the flood control provisioning services of wetlands and pollination service provisioning by pollinator populations in agroecosystems. I examined the environmental literature to provide quantitative estimates of a) the distribution of the level of service delivered as well as b) the ability of environmental scientists to predict this level of service. The results presented here suggest a moderately strong correlation between research efforts in environmental science and ecological economics at the pooled level of ecosystem types and services. I suggest however, an integrated research enterprise between social and environmental scientists may provide greater efficiency by means of a global ecosystem service research network and repository. I found that, on average, consistent with conventional wisdom, wetlands do indeed have a positive effect by reducing the frequency and magnitude of floods, increasing low flows, and increasing water storage. In the same vein, I found on average and consistent with conventional wisdom, there is a consistent and comparatively strong association between pollinator abundance and agroecosystem productivity as inferred from measures of plant fertilization success. In both investigations however, metaregression analysis indicated that our current ability to predict either pollination or flood control services is poor to modest at best. The low predictive power combined with the observed heterogeneity in effect size in both investigations suggest that flood control service delivered by wetlands or pollination services delivered by natural pollinator populations in agroecosystems and the expected changes in the level of services delivered under a candidate management scenario, will have a large uncertainty. Such uncertainty should be explicitly incorporated into estimates of both the current economic value of ecosystem services, as well as estimates of how these values are likely to change under alternative management scenarios. Given these, I suggest that the implications for the development of Market-based instruments (MBIs) or any payment of ecosystem services to conserve ecosystem services: that the associated ecological function(s) must be few and well characterized, and we must agree on what endpoints ought to properly be used to characterize these functions. If this condition is not met, an ordinal ranking is the best we can do and in the absence of obvious enthusiasm for more detailed scientific research which leads to the conclusion that perhaps alternate strategies like command and control may be the better alternative to protect ecosystem services.

El suelo es uno de los componentes principales de los agro-ecosistemas (capital natural), que junto a las demás formas de capital, brindan servicios ecológicos (SE) destinados a las necesidades y bienestar humanos. La Región Semiárida Pampeana (RCP), en la Provincia de La Pampa, posee suelos poco desarrollados, recibe escasas lluvias y vientos de moderados a fuertes. Estas condiciones son propicias para el proceso de erosión eólica potencial, es decir la pérdida de suelo por acción del viento. Esta pérdida implica la reducción de la fertilidad física y química, con la consecuente reducción en el flujo de los SE. Las condiciones de manejo del suelo, definen la erosión eólica actual, la cual puede cuantificarse experimentalmente. Adicionalmente, se puede determinar la composición química de estos residuos. El avance de la agricultura, la intensificación de los sistemas productivos y prácticas de laboreo tradicionales inapropiados, hacen de este fenómeno un proceso irreversible, cuando se supera valores umbrales considerados moderados. Se expresa en toneladas por hectárea (t/ha). El productor no considera entre sus costos de producción, los SE del suelo que esta utilizando, los que toma de un stock inicial y sobre los que tampoco existe un precio de mercado de referencia. Una de las hipótesis de trabajo fue que las pérdidas por erosión actual, en rotaciones y en el ciclo de los cultivos agrícolas, pueden alcanzar niveles moderados a severos. La incorporación en los costos directos de cultivos agrícolas, del nitrógeno (N) y fósforo (P) involucrados en el material erosionado, por su magnitud puede causar niveles de quebranto en el margen bruto (MB) final. El costo de reemplazo de estos nutrientes se lo denominó Indicador Ambiental (IA) y se estimó, monetariamente, a través de su equivalente en nutrientes de fertilizantes. Otra hipótesis planteada, sugiere que es posible plantear actividades tecnológicamente superadoras, que reduzcan los niveles de erosión, mejoren el balance de algunos nutrientes esenciales y que se integren en un sistema productivo ambiental y económicamente sustentable. Para estimar la tasa de erosión eólica, se utilizó el modelo empírico identificado en castellano con las siglas EWEQ (Wind Erosion Equation), el cual fue cargado con secuencias de cultivos reales (rotaciones), con longitud de tiempo variables y para 6 sitios de la estepa pampeana: 3 sitios de la denominada Subzona Castex (Castex Norte, Castex Sur-Santa Rosa y Castex Sur-Anguil); 2 sitios de la Subzona Pico (Pico Norte y Pico Sur) y 1 sitio de la Subzona Guatrache. El modelo devuelve la tasa de erosión promedio anual de toda la rotación, como también la tasa de erosión del ciclo de cada cultivo agrícola (t/ha ciclo), aprovechando el detalle en las fecha precisas entre operaciones. Con estos registros, se estimaron los costos directos de todos los ciclos disponibles de trigo, girasol, soja y maíz. Utilizando los precios de insumos y productos de Febrero de 2008, se calculó la incidencia del IA, en los costos directos y sus efectos en el MB final. El plan de optimización se realizó para las condiciones agroclimáticas, dimensiones y caracterización de sistemas productivos del Sitio Castex Norte (Subzona Castex), a través de una matriz de programación lineal (PL). Se diseñaron previamente los planteos técnicos basados en tecnologías disponibles, los resultados económicos (MB) y el balance de N, P y carbono orgánico (CO) de cada actividad. La tasa de erosión eólica estimada para cultivos en siembra convencional (SC) en la primera parte, fue un insumo directo de la matriz, utilizada como restricción ambiental. Las pérdidas de N y P involucradas por esta vía, formaron parte de los egresos, dentro del balance de nutrientes. Fue necesario simular en el EWEQ, aquellas alternativas tecnológicamente mejoradas, no disponibles entre los registros reales y donde predominó la siembra directa (SD) y estrategias de fertilización. También se estimaron los índices para algunos de los recursos forrajeros de la actividad ganadera (invernada). Se puso énfasis en las restricciones ambientales, mientras que desde lo técnico-agronómico no hubo limitaciones en las restricciones de capital de trabajo ni diferenciación en el tipo de suelo. Para esta segunda etapa, se utilizaron precios de insumos de 2006 y las cotizaciones del disponible 2007 para los productos. Se detectaron menores tasas de erosión eólica en SD que en SC. En el Sitio Guatraché se redujo de 10,0 t/ha en una rotaciones en SC a 5,6 t/ha en SD (44% menos). También se redujo en más de un 50% entre ciclos de cultivos, dentro de una misma rotación, al utilizar SD. En todos los casos, significó un pasaje del grado de erosión de moderado/severo a erosión ligera. El costo de reemplazo del IA, fue variable entre cultivos, entre sistema de siembra (SD vs SC) e influenciado por el nivel de costos directos totales. En los cultivos conducidos en SC, con tasas de erosión eólica cercanas y levemente superiores a 8 t/ha ciclo, la participación del IA fue de 20 a 40 % en trigo; 15 a 25% en maíz; 20 a 35% en girasol y de 20 a 30% en soja. Con tasas de erosión 4 a 6 t/ha ciclo en SD, el IA tuvo una participación del 8% en maíz; del 8 a 16 % en trigo y del 8 a 21% en girasol. Respecto al efecto sobre el MB inicial, solo se produjeron quebrantos cuando los rendimientos de trigo fueron inferiores a 1t/ha y un caso de maíz, con una producción de 1,4 t/ha. Las actividades propuestas en la matriz de PL permitieron detectar déficits generalizados en el balance de nutrientes, en aquellos cultivos conducidos con esquemas tradicionales de manejo tecnológico y/o de escaso nivel de fertilización. Por el contrario, la actividad ganadera mostró todos los índices positivos. Sobre una explotación de 506 ha, la mejor solución de la matriz de PL quedo integrada por 143 ha de trigo en SC con aplicación de fertilizante apuntando a máximo rendimiento (TrSCDMR); 170 ha de maíz en SD y de alta producción (MaSDAP) y 193 ha de girasol en SD con fertilización de máxima respuesta (GiSDFER). Este sistema agrícola alcanzó el máximo margen bruto total (MBT) con una erosión eólica promedio anual de 4,9 t/ha. Los beneficios ambientales de la ganadería no se aprovecharon frente a un precio promedio de 2,70 $/kg de carne. Sin embargo, los costos de sustitución indicaban que la invernada podía participar con un precio de 3,46 $/kg de carne (+28%). Siendo un valor esperable dentro de la volatilidad de precios de la serie 2007/2008, se simuló un escenario mixto, donde la invernada participó con 245 ha, la misma alternativa de girasol en SD con 153 ha, y el mismo maíz de alta producción con 143 ha. Entre el sistema agrícola y el mixto, el MBT se redujo solo el 1% ($ 390.660 vs. $386.795 respectivamente). Palabras clave: erosión eólica, servicios ecológicos, programación lineal, balance de nutrientes, nitrógeno, fósforo. / Soil is one of the main components of agro-ecosystems (natural capital). Together with other forms of capital, provides ecological services (ES) for human needs and welfare. The Semi-Arid Pampas Region (SPR) has poorly developed soils, receives little rain and moderate to strong winds. These conditions are favourable for the process known as potential wind erosion, namely the loss of soil by wind action. This loss implies a reduction of both physical and chemical fertility, with consequent reduction in the flow of those ES, mentioned above. The conditions of soil management, define the current wind erosion, which can be quantified experimentally. Additionally, chemical composition of these residues can be determined. It is expressed in tons per hectare (t/ha).The advancement of agriculture, the intensification of production systems and traditional inappropriate tillage practices, generates an irreversible phenomenon, when it exceeds threshold values, considered moderate. Farmers do not consider among their production costs, the ES they are using, which they take from an initial stock. In addition, there is no price market reference. One of the working hypothesis was that losses caused by current wind erosion, in both rotations and crops cycle, can achieve moderate to severe levels. The incorporation into crops direct costs of nitrogen (N) and phosphorus (P) involved in the eroded material might produce actual gross margin (GM) losses. The replacement cost of these nutrients was named in this research as Environmental Index (EI) and it was considered, in money terms, through its equivalent in nutrients from fertilizer. Another hypothesis suggests that it is possible to raise productive activities technologically enhanced that reduces the levels of erosion, improve the balance of some essential nutrients and can be integrated into a production system, environmentally and economically sustainable. The empirical model Wind Erosion Equation (EWEQ) was used to estimate wind erosion rate. Its inputs were farmers real data, including crops seasonal sequences (rotations). Records varied in lengths of time and came from six places in the Pampas Steppe: three places in the so-called Sub-Zone "Castex" (North Castex site, South-Castex- Santa Rosa site and South Castex-Anguil site), two in the Sub-Zone "Pico" (North Pico site and South Pico site) and one site of Sub-Zone "Guatraché". The model returns the average annual erosion rate of the entire rotation, and the cycle crop erosion rate (t/ha cycle). This last rate takes advantage of the detail in the precise date information between machinery operations, within the model. These records, also allowed estimating direct costs of all the available crops cycles of: wheat, sunflower, soybeans and corn. Using inputs and commodities prices of February 2008, the incidence of EI in direct costs and its impact on the final GM, was calculated. The optimization plan was carried out for agro-climatic conditions, farm size and production systems patterns of North Castex Site (Sub-Zone "Castex"), through a matrix of linear programming (LP). Previously, technical set up approaches were designed, based on available technology, also the economic performance (GM) and the balance of N, P and organic carbon (OC) of each activity. The estimated wind erosion rate estimated for crops in the first part of the study and involving conventional tillage (CT) sowing system was a direct input for the matrix, used as environmental constraints. The concentration of N and P involved in this losses, were part of discharges within the balance of nutrients. It was necessary to use the EWEQ, to simulate those alternatives technologically enhanced, witch no records were available, and where no-tillage (NT) and fertilization strategies have been used. It was also estimated rates for some of the forage resources of livestock activity (fattening steers). Emphasis was placed on the environmental constraints, while no limitations were set from those technical-agronomic constraints such as working capital or differentiation in the type of soil. For this second stage is used pricing of inputs, 2006 and 2007 current prices of commodities. Wind erosion rates resulted lower in NT than in CT. In Site Guatraché the index varied from 10.0 t/ha year-1 in a CT rotation, to 5.6 t/ha year-1 in NT rotation (44% less). It also declined by over 50% between cycles of crops, within a single rotation, by using NT. In all cases, it was an overtaking from a moderate/severe degree of erosion to light erosion rate. The replacement cost of EI, varied between crops, between sowing system (NT vs CT) and highly influenced by the level of total direct costs. Those crops conducted in CT, with wind erosion rates nearby and slightly higher than 8 t/ha cycle-1, the EI share in costs was 20 to 40% in wheat, 15 to 25% in corn, 20 to 35% in sunflower and 20 to 30% in soybeans. With erosion rates of 4 to 6 t/ha cycle-1, in NT cycle, the EI had an 8% share of corn costs, from 8 to 16% in wheat and from 8 to 21% in sunflower. Concerning to the effect on initial GM, economic losses occurred only when the yields of wheat were lower than 1t/ha and in the case of corn, one case was found when production reached 1,4 t/ha. The proposed activities in the matrix of LP helped to detect widespread deficits in the balance of nutrients in crops those conducted with traditional patterns of technological management and/or low levels of fertilization. By contrast, livestock activity showed all positive indexes. On a farm of 506 hectares, the best solution of the matrix of LP resulted in 143 ha of CT wheat with fertilizer application aimed at maximum performance (TrSCDMR); 170 ha of NT corn and high production (MaSDAP) and 193 ha of NT sunflower with the highest expected fertilization response (GiSDFER). This "grain cropping system reached a maximum total gross margin (TGM) with an average annual wind erosion rate of 4.9 t/ha year-1. The environmental benefits of livestock are not exploited, facing an average price of 2,70 $/kg of live weight. However, the "shadow price" indicated that livestock activity might take part of the solution with a price of 3,46 $/ kg of live weight (+28%). Since this was an expected value along 2007/2008 meat market prices series, it was simulated a "crop and beefs mixed system where livestock participated with 245 ha, along with 153 ha of former NT sunflower alternative, and 143 ha of the same high production corn. When comparing the "grain cropping and "crop and beefs mixed systems, TGM decreased only 1% ($ 390,660 vs. $ 386,795, respectively).

Cities are facing environmental crises like never before, with problems of excess water runoff, degraded water quality, air pollution, and energy use reaching critical levels. The development of urban areas and the built environment is the primary cause of these problems and the built environment needs to be a part of the solution. This design thesis project produces a prototype design for the Urban EcoHousing development on a city block in Alexandria, Virginia. Design goals for the project connect the "Ecological Services of the Urban Landscape" to the "Rights of the Urban EcoHousing Resident" to create livable green spaces that can serve ecological functions and give the residents spaces to use. A comparison study with a conventional housing development at the same location illustrates that ecohousing can meet the requirements of the conventional development while providing superior results for the residents and the environment. / Master of Landscape Architecture

Les marais filtrants artificiels sont des écosystèmes recréés par l’homme dans le but d’optimiser l’épuration des eaux usées. Lors de la sélection d’espèces végétales pour la mise en place de ces marais filtrants, l’utilisation d’une polyculture ainsi que d’espèces indigènes non invasives est de plus en plus recommandée. Néanmoins, la plupart des marais filtrants existants sont des monocultures utilisant des plantes envahissantes, probablement à cause du manque d’évidences scientifiques sur les avantages de la diversité végétale et de la performance des espèces locales. Ainsi, les questions de recherche autour desquelles s’oriente ma thèse sont: Les polycultures présentent-elles un potentiel épuratoire aussi ou plus grand que les monocultures, et une espèce indigène est-elle aussi efficace et performante qu’une espèce exotique envahissante dans des marais filtrants ? Trois expériences ont été conduites afin de répondre à ces questions. J’ai d’abord testé l’influence de la richesse végétale sur l’élimination des polluants en deux dispositifs expérimentaux: 1) comparant deux espèces de plantes émergentes en monoculture ou combinées séquentiellement, et 2) évaluant la performance de quatre espèces flottantes plantées en monoculture par rapport à des associations de deux (avec toutes les combinaisons possibles) et de quatre espèces. Une troisième expérience a été réalisée afin de comparer l’efficacité épuratoire de l’haplotype européen envahissant du roseau commun (Phragmites australis) et de la sous-espèce locale non-invasive (P. australis subsp. americanus). La composition en espèces végétales a produit un effet notable sur la performance des marais filtrants. La comparaison des performances en mono- et en polyculture n’a pas permis de démontrer clairement les avantages de la diversité végétale pour l’élimination des polluants dans les marais filtrants. Toutefois, les marais filtrants plantés avec une combinaison d’espèces étaient aussi efficaces que les monocultures des espèces les plus performantes. La comparaison entre les deux sous-espèces de P. australis indiquent que la sous-espèce indigène pourrait remplacer le roseau exotique envahissant, évitant ainsi les potentiels risques environnementaux sans toutefois compromettre l’efficacité du traitement. Les résultats prometteurs de la sous-espèce indigène de P. australis doivent encore être testés dans des expériences à grande échelle avant d’utiliser largement cette espèce dans les marais filtrants. Nos résultats suggèrent que, dans des conditions où la performance des macrophytes disponibles est inconnue ou ne peut être déterminée, l’utilisation d’une combinaison d’espèces présente les meilleures chances d’accomplir le plus haut niveau possible d’élimination de polluants. De plus, même si la diversité végétale ne présente pas un avantage mesurable en termes d’efficacité épuratoire, celle-ci améliore la résilience des marais filtrants et leur résistance aux stress et aux maladies. / Treatment wetlands (TWs) are complex engineered ecosystems designed to remove pollutants from wastewater. In selecting plant species for TWs, the use of polycultures as well as the choice of local non-invasive species is increasingly recommended. However, to date, the majority of TWs have been planted in monoculture using invasive species, probably because the performance of native species and the possible advantages associated with plant diversity have not been clearly demonstrated. The research questions of my thesis are: Are polycultures as good as or better than monocultures for pollutant removal, and could a native species be as efficient as an exotic invasive species in TWs? Three experiments were performed to answer this question. The influence of plant richness on pollutant removal was tested in two mesocosm experiments: 1) comparing two emergent plant species in monoculture and planted in sequence, and 2) evaluating four free-floating species, each in monoculture versus pairs of species (all possible combinations) and the four species planted together. A third experiment was carried out to compare the removal efficiency of the invasive European haplotype of common reed (Phragmites australis) and the native non-invasive subspecies (P. australis subsp. americanus). Plant species composition influenced the performance of TWs. The comparison of the performance of monocultures versus polycultures showed that, overall, TWs planted with a combination of species were as efficient as monocultures of the best performing species. Comparing the performance of native and invasive P. australis strongly suggests that the native could replace the invasive species in TWs, thereby avoiding possible environmental risks without compromising treatment efficiency. The promising results of the native P. australis subspecies need to be further tested in full-scale experiments in order to encourage the use of this species in TWs. The results obtained comparing plant species combinations suggest that under circumstances in which the performance of available macrophytes is unknown or cannot be determined, using a mixture of species offers the best chances of achieving the highest possible level of pollutant removal. Furthermore, it has been suggested that plant diversity contributes to TWs in terms of their resilience to stress and disease.

No description available.