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.

Located in Giles County, Virginia, Mountain Lake has a documented history of dramatic water level fluctuations. Previous water balance studies have documented that the main cause of water loss is outflow to groundwater. However, the flow paths of water exiting the lake are unknown. This study applied hydrologic, geophysical, and dye tracer methods to examine the pathways for water loss and the possible geologic controls on these flow paths. Continuous lake level monitoring data show seasonal trends of draining and filling over a three year period. Electrical resistivity profiles suggest the presence of a large low-resistivity zone beneath the northern end of the lake. A dye tracer study yielded limited positive results, but dye detection in one stream and within the lake suggest complex flow dynamics. The most likely reasons for the lack of dye recovery include dilution of the dye during lake recovery, seepage of water below monitoring site locations, or formation of a temporary seal in the depressions created by influx of sediment during periods of lake bed exposure. / Master of Science

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal. / Thèse de doctorat effectuée en cotutelle au Département de Géographie Université de Montréal et à l'Institut Méditerranéen d'Écologie et de Paléoécologie Université de Droit, d'Économie et de Sciences d'Aix-Marseille 111 / La tourbière de Mirabel (basses terres du St-Laurent, Québec méridional) a été étudiée dans le but de préciser l'influence exercée par les différents paramètres autogènes et allogènes sur l'accumulation postglaciaire du carbone. (l) Les dynamiques végétales régionales révèlent un contrôle climatique général, modulé localement par le contexte paléogéographique, la physiographie et les processus écologiques. (2) L'histoire postglaciaire du climat régional fut reconstituée par la méthode des analogues modernes, contrainte par les fluctuations du niveau du lac Hertel (Mont St-Hilaire). Les résultats obtenus témoignent d'un important réchauffement entre 13 000 et 11 000 cal. BP, d'un optimum thermique autour de 8000 cal. BP, et de deux périodes sèches (10 000-6500 et 5000-3000 cal. BP). (3) Les dynamiques postglaciaires internes de la tourbière furent indépendamment reconstituées en trois dimensions par l'analyse pluridisciplinaire de sept profils. Ces derniers montrent des successions végétales similaires, conformes au modèle de terrestrialisation, mais asynchrones. Ils témoignent en outre de conditions de surface très humides avant 6700 cal. BP, suivies de nombreuses fluctuations asynchrones sur l'ensemble du site. L'accumulation du carbone présente en revanche des tendances similaires dans tous les profils, caractérisées par de fortes accumulations avant 6200 cal. BP (moyennes de 7.1 à 19.1 gC.m .an'1) et de faibles accumulations depuis (moyennes de 2.7 à 6.3 gC.m'2.an ). (4) Les différentes conditions postglaciaires du développement de la tourbière sont confrontées. L'accumulation du carbone paraît avoir été essentiellement contrôlée par les interrelations entre la physiographie (alimentation minérotrophe initiale) et les processus autogènes, qui ont progressivement isolé la végétation tourbigène de la nappe phréatique. Notamment, ni le climat, ni les feux ne semblent avoir joué de rôle significatif. / Mirabel bog (St. Lawrence lowlands, southern Quebec) was studied with the aim to specify the influences exerted by the different autogenic and allogenic parameters on postglacial carbon accumulation. (1) Regional vegetation dynamics reveal a general climatic control, locally modified by the palaeogeographical context, physiography and ecological processes. (2) The postglacial history of the regional climate was reconstructed by the modem analogues method, constrained by the water level fluctuations of Lac Hertel (Mont St- Hilaire). Obtained results provide evidence for an important climate improvement between 13 000 and 11 000 cal. BP, a thermal optimum around 8000 cal. BP and two dry periods (10000-6500 and 5000-3000 cal. BP). (3) Postglacial internal dynamics were independently reconstmcted in three dimensions by the multidisciplinary analysis of seven profiles. They show similar plant successions, conforming to the terrestrialisation model but were asynchronous. They moreover attest the occurrence of very humid conditions prior to 6700 cal. BP, followed by numerous asynchronous fluctuations throughout the site. By contrast, carbon accumulation presents similar trends in all proiïles, characterised by high accumulation rates prior to 6200 cal. BP (averages from 7.1 to 19.1 gC.m .year ) and low rates since this date (averages from 2.7 to 6.3 gC.m'2.year-l). (4) The different postglacial conditions of peatland development arc coirfronted. Carbon accumulation appears to have been essentially controlled by the interplay between physiography (initial minerotrophic supply) and autogenic processes, which progressively isolated the peat-forming vegetation from groundwater. Notably, neither climate nor fire seem to have played a significant role.