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Thesis advisor: Martha Carlson Mazur / Rivermouths are dynamic systems characterized by hydrologic mixing, where water, energy, sediment and nutrients from both river and receiving water unite to form a unique yet variable environment. Water levels in these environments are thus defined by, and subject to, streamflow from the river and lake-level fluctuations. Long-term fluctuations in water levels affect hydrogeomorphic structure, as well as wetland structure, distribution, and composition. A better understanding of these dynamics will help us to comprehend the processes that govern changes in wetland area and, thus, the breadth of the ecosystem services that estuarine wetlands provide. To this end, this study examined how wetland plant communities have changed through time in relation to long-term changes in water levels from both river and lake systems, using historic aerial photograph interpretation in three rivermouths on Lake Michigan. Additionally, the observed patterns of historic water levels and streamflows were used to inform our predictions for the future in light of climate changes. Results showed that higher water levels and peak streamflows led to less wetland area; average streamflow did not play a statistically detectable role in rivermouths that had lake-dominated morphologies but was significant in the rivermouth system that was riverine dominated. This suggests that varying rivermouth morphologies respond differently to lake and stream dynamics. Restoration decisions that take rivermouth morphology into account will be important as these systems continue to change both naturally and due to climate or other anthropogenic disturbances. It is important to realize not only the extent to which humans are affecting rivermouth systems, but also the interplay between water levels, streamflows, hydrogeomorphology, and wetland ecology within these systems themselves, so as to better understand the necessary steps for restoration. / Thesis (BS) — Boston College, 2013. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Geology & Geophysics Honors Program. / Discipline: Earth and Environmental Science.

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Made available in DSpace on 2016-12-23T14:20:38Z (GMT). No. of bitstreams: 1 Patricia Ramaldes Mendonca - Parte 1.pdf: 1399963 bytes, checksum: 23106a0020e621e1f75a8813e0ab1200 (MD5) Previous issue date: 2013-09-09 / Sedimentos gerados por erosão em bacias hidrográficas muitas vezes são carreados pelas chuvas para corpos hídricos comprometendo a qualidade da água. O objetivo do presente trabalho foi realizar uma avaliação comparativa das bacias hidrográficas dos rios Santa Maria do Rio Doce e Santa Joana quanto aos potenciais de geração de sedimentos, a partir de análises hidrogeomorfológicas, hidrosedimentológicas e mapeamento de fragilidade à erosão. A caracterização das bacias hidrográficas identificou os cenários ambientais existentes nas bacias hidrográficas, enfatizando os principais aspectos que interferem nos processos erosivos, como a declividade do terreno, o tipo de solo, o uso e cobertura da terra, entre outros. A análise hidrogeomorfológica foi realizada a partir da geração de dados morfométricos linear, areal e hipsográfico, buscando-se relacionar os resultados hidrosedimentológicos com os hidrogeomorfológicos. O mapeamento de fragilidade à erosão contribuiu para entender espacialmente os principais focos de erosão nas bacias hidrográficas. Com isso, foram sugeridas sub-bacias para intervenções de controle de erosão e monitoramento hidrosedimentológico. A média ponderada das classes de fragilidade à erosão permitiu uma comparação mais direta com os valores obtidos para outros parâmetros. Os resultados relativos aos parâmetros morfométricos e a média ponderada da fragilidade à erosão das bacias hidrográficas sugerem que a tendência à produção de sedimentos por unidade de área da bacia hidrográfica do rio Santa Maria do Rio Doce é ligeiramente superior à correspondente à bacia do Santa Joana. Os dados hidrosedimentológicos, apesar de limitados a alguns eventos de chuva, permitiram uma noção do transporte sólido nas calhas principais das duas bacias. Os métodos de análise utilizados na pesquisa demonstraram ser ferramentas importantes para o entendimento das dinâmicas erosivas nas bacias hidrográficas e, com isso, importantes instrumentos para futuros projetos de melhoria da qualidade da água dos cursos d água das bacias estudadas / Sediment generated by erosion in watersheds often are carried by rain to water bodies compromising water quality. The objective of this study was to perform a comparative assessment of the watersheds Santa Maria do Rio Doce and Santa Joana about the potential generation of sediment from hydrogeomorfophology analysis, hydrossedimentology analysis and mapping of erosion fragility on the watersheds. Characterization of watersheds identified existing environmental scenarios, emphasizing the main aspects that affect erosion processes, such as terrain slope, soil type, use and land cover, among others. Hydrogeomorphology analysis was performed from the morphometric drainage basin data of linear, areal and hypisographic parameters. it was also attempted to relate the results of hydrossedimentology with hydrogeomorfology analysis. The mapping of erosion fragility contributed to the spatial understanding of the main focus of erosion in river basins. Thus, sub-basins were suggested interventions for erosion control and hydrosedimentological monitoring. The weighted average of erosion fragility classes allowed a more direct comparison with the values obtained for other parameters analised. Results related with morphometric parameters and weighted average of erosion fragility classes suggest that the tendency of sediment yield per unit area of Santa Maria do Rio Doce river basin is slightly higher than the corresponding to the Santa Joana basin. Hydrosedimentological data, although limited to a few rain events, allowed a sense of solid transport in the river of the two main basins. Analysis methods used in the study proved to be important tools for understanding the erosive dynamics on watersheds and, therefore, important tools for future projects to improve the water quality of the studied watercourses

The contribution of this thesis is twofold: 1) the development of a hydrodynamic landscape evolution model for use on high-performance computing systems and 2) assessing the sensitivity of hydrogeomorphic processes to high-resolution rainfall input data and erosional parameterisation using the model. The thesis addresses a limitation in numerical landscape evolution models regarding how spatial variation in rainfall is represented or parameterised within such models. Typically, landscape evolution models forsake a realistic representation of rainfall patterns in favour of a simpler treatment of rainfall as being spatially homogeneous across the model domain. This simplification of rainfall spatial variability is still made despite the fact that many geomorphological processes are sensitive to thresholds of sediment entrainment and transport, driven by the distribution and movement of water within the landscape. The thesis starts by exploring current limitations in rainfall representation in landscape evolution models, and assesses various precipitation data sources that could be potentially used as more realistic rainfall inputs to landscape evolution models. A numerical model of landscape evolution is developed for deployment on high-performance parallel computing systems, based on the established CAESAR-Lisflood model (Coulthard et al., 2013). The new model code is benchmarked, showing performance benefits compared with the original CAESAR-Lisflood model it is based on. The model is applied to assessing the sensitivity of flood-inundation predictions, sediment flux, and erosion distribution within river catchments to spatial variation in rainfall during extreme storm events. Two real storm events that caused localised flash flooding in the UK are used as test cases: the Boscastle storm of 2004 and the North York Moors storm of 2005. Flood extent predictions and river discharges are found to be sensitive to the use of spatially variable input rainfall data, with high-resolution rainfall data leading to larger peak flood discharges. However, the differences are less pronounced in smaller catchments. The role of sediment erosion during large floods is also assessed, but it is found to play a minor role relative to spatially variable rainfall data. In contrast, the geomorphological response of catchments to single storm events is shown to be less sensitive to the spatial heterogeneity of rainfall input and controlled more strongly by the choice of erosional process parameterisation within the model. Nonetheless, spatial variability in rainfall data is shown to increase sediment yields during flash flood simulations.

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Cette thèse avait pour objectif principal d'approfondir nos connaissances sur l'écologie des différents types de milieux humides lacustres afin d'optimiser leur conservation. Pour ce faire, j’ai étudié la résilience, les fonctions et les services écologiques (FSE), ainsi que la biodiversité de trois types de milieux humides lacustres. Ces milieux humides sont riverains au lac Papineau, qui est situé dans la réserve naturelle de Kenauk Nature, entre les Laurentides et l’Outaouais. Cette thèse combine des approches globales, multifonctionnelles et ciblées, axées sur la conservation des milieux humides et de leur biodiversité. Dans mon premier chapitre, j'ai d’abord identifié les déterminants écologiques de la typologie des trois types de milieux humides étudiés : des tourbières, des aulnaies (marécages arbustifs) et des frênaies (marécages arborescents). À l’aide de données récoltées sur le terrain et de données cartographiques, j'ai quantifié 12 prédicteurs hydrogéomorphologiques (HGM) et j'ai pu identifier la pente et l'élévation comme étant les déterminants écologiques les plus importants. Mes résultats ont également apporté des nuances supplémentaires quant aux variables associées à chaque type de milieu humide. En utilisant ces 12 prédicteurs HGM, j'ai créé un modèle de forêts d’arbres décisionnels capable de prédire à la fois la présence des milieux humides lacustres et leur typologie. Ce modèle a permis de prédire avec une précision de 89 % la typologie des sites étudiés, ce qui en fait un outil intéressant pour étudier la répartition des milieux humides riverains à d'autres lacs. J'ai également utilisé ce modèle pour simuler différents scénarios de changements du niveau d'eau, mettant en évidence la résilience des tourbières et des aulnaies, ainsi que la vulnérabilité des frênaies, aux changements globaux. Dans mon second chapitre, j'ai quantifié huit FSE à l'aide de 25 indicateurs différents, dont 15 ont été quantifiés à partir de données terrain. J'ai ensuite développé une approche multifonctionnelle permettant d'étudier simultanément toutes les interactions de synergies et de compromis entre les indicateurs de FSE et les trois types de milieux humides. Mes résultats ont montré que chaque type de milieu humide maximise différentes FSE, mais que le choix des indicateurs influence considérablement les patrons de synergies et de compromis. Bien que certains types de milieux humides maximisent les mêmes FSE, ils le font à travers différents mécanismes écologiques. Enfin, la biodiversité floristique et faunique (plantes, oiseaux, poissons, zooplanctons et insectes chanteurs) présentait les patrons d'interaction les plus diversifiés, chaque type de milieu humide maximisant différents aspects de la biodiversité. Dans mon troisième chapitre, j'ai optimisé l'approche des espèces clés (keystone species) pour permettre son utilisation en conservation afin d’identifier les espèces indicatrices de la biodiversité. Pour cela, je me suis basée sur l’approche la plus récente proposée dans la littérature et j'ai identifié les éléments qui limitaient son utilisation pour les praticiens et les praticiennes. J'ai ensuite proposé des modifications pour surmonter ces limites. Ces modifications ont permis : 1) d'élargir l'utilisation de cette approche aux données d'inventaires terrain, 2) d'identifier les espèces ayant un impact négatif sur la biodiversité, et 3) de définir des seuils rigoureux pour identifier les espèces clés au sein d'une communauté. J'ai ensuite testé cette approche sur les communautés de plantes, d'oiseaux et de poissons des milieux humides échantillonnés dans le cadre de cette thèse. Mes résultats ont montré que cette approche permettait d'identifier des espèces possédant effectivement des caractéristiques écologiques expliquant leur importance dans l'augmentation ou la diminution de la biodiversité. Ensemble, les trois approches présentées dans cette thèse offrent une perspective intégratrice de la conservation des milieux humides lacustres. Les méthodes qui y sont proposées représentent des outils intéressants, qui ont le potentiel d’optimiser notre gestion du territoire à court et à long terme, mais aussi à petite et à grande échelle. / The main objective of this thesis was to deepen our understanding of the ecology of different types of lake-edge wetlands to optimize their conservation. To achieve this, I studied the resilience, the ecosystem functions and services (EFS), and the biodiversity of three types of lake-edge wetlands. All studies wetlands were riverine to Lake Papineau, which is located in a Kenauk Nature natural reserve, between the Laurentides and Outaouais regions. This thesis therefore combines a global, a multifunctional, and a targeted approach, all focused on wetland conservation. In my first chapter, I first identified the ecological determinants of the typology of the three types of wetlands studied: peatlands, alder swamps (shrub swamps), and ash swamps (trees swamps). Using both data collected on the field and map data, I quantified 12 hydrogeomorphological (HGM) predictors and identified slope and elevation as the most important ecological determinants. My results also provided additional nuances regarding the variables associated with each wetland type. Using these 12 HGM predictors, I then created a Random Forest model capable of predicting both the presence of lake-edge wetlands and their typology. This model predicted the typology of the studied sites with 89 % accuracy, making it an interesting tool to study the distribution of lake-edge wetlands along the shore of other lakes. I also used this model to simulate different scenarios of water level changes, highlighting the resilience of peatlands and alder swamps, as well as the vulnerability of ash swamps, to global changes. In my second chapter, I quantified eight EFS using 25 different indicators, with 15 indicators quantified using field data. I developed a multifunctional approach to simultaneously study all the synergies and trade-offs between the EFS indicators and the three wetland types. My results showed that each wetland type maximizes different EFS, and that the choice of indicators significantly influences the patterns of synergies and trade-offs. Although some wetland types maximized the same EFS, they do so through different ecological mechanisms. Finally, biodiversity exhibited the most diverse interaction patterns, with each wetland type maximizing different aspects of it. In my third chapter, I optimized the keystone species approach to allow its use in conservation to identify indicator species for biodiversity monitoring. To do so, I relied on the most recent approach proposed in the literature and identified the elements that limited its use for practitioners. I then proposed modifications to overcome these limitations. These modifications allowed 1) to expand the use of this approach to field inventory data, 2) to identify species that have a negative impact on biodiversity, and 3) to define rigorous thresholds to identify keystone species within a community. I then tested this approach on plant, bird, and fish communities in the wetlands sampled in this thesis. My results showed that this approach effectively identified species with ecological characteristics that explained their importance in increasing or decreasing biodiversity. Together, the three approaches presented in this thesis provide an integrative perspective on the conservation of lake-edge wetlands. The methods I propose represent interesting tools that have the potential to optimize land management in the short and long term, as well as at small and large scales.