Missisquoi Bay, Lake Champlain is a eutrophic, northern shallow freshwater bay that experiences toxic cyanobacteria blooms during the summer months, largely as result of high nutrient (P and N) loading from the agricultural watershed. The sediments, which contain minerals that readily sorb P, can act as a sink or source of water column nutrients. Phosphorus, both inorganic and some organic forms, sorbs to metal oxides at neutral pH in the sediment, thus P release into overlying and pore water can be significantly affected by the reduction and subsequent solubilization of these oxides. This study addresses novel aspects of nutrient cycling in lake sediments as part of a larger study to better understand the link between phosphorus forms, mobility, and cyanobacteria blooms. These aspects include: 1) diel and seasonal sediment redox fluctuations and 2) the role of organic P (Porg) in overall P mobility within sediments as a function of depth and time. Missisquoi Bay sediment porewater redox chemistry was monitored across diel and seasonal cycles over the course of two summers (May-October, 2007 and 2008) by using in-situ voltammetry. Redox chemistry was monitored at the sediment-water interface (SWI) continuously over diel cycles, and the vertical concentration profiles of several key redox species (O2, Mn2+, Fe2+, and FeS(aq)) were obtained from cores collected at different times. The sediments were then analyzed for Total P (TP), Reactive P (RP), Porg, Mn, Fe, Ca, Al, Total Organic C and N. A bloom did not occur in Missisquoi Bay during the summer of 2007, but did in summer of 2008, providing an opportunity to compare the sediment chemistry between non-bloom and bloom conditions. Increasingly anoxic SWI conditions across summer 2008 were observed but the SWI remained oxic for the duration of summer 2007. Significant changes in diel cycle redox chemistry at the SWI were also detected in both summers. Reactive P in the surface sediments decreased across the 2008 season but not in 2007. A strong correlation found between RP and RFe (operationally defined as Fe(III)OOH) suggests that a significant portion of sediment P (30-40%) is closely associated with Fe(III)OOHs, which are susceptible to reduction in anoxic conditions. Phosphorus mobility from the sediment into the water column can be limited by the amount of Fe(III)OOH at the surface, thus P flux from the sediments would be greatest when reducing conditions promote solubilization of these minerals. Completely anoxic surface sediments were only observed during the presence of a bloom, explaining the loss of RP in the surface sediments in 2008 in the late summer. Organic P species represent 18-26% of the P in sediments and the lack of a definite, consistent trend of Porg fractionation across the season suggests that there is variable mobility and degradation of these complex organic compounds on small timescales. The loss of RP from the sediment in 2008 could have contributed to an estimated water column P increase on the order of thousands of μg/L, which in addition to measured increases in NH4+ gradients and subsequent N flux estimates in the upper sediment, could have sustained the bloom for an extended period of time. The relationship between the bloom and reducing sediment conditions suggest that bloom dynamics enhance nutrient release from the sediments, allowing for proliferation and sustainability of the bloom.

For several decades, grassland bird populations have been facing consistent declines throughout North America with population declines >1.5% per year in the past 40 years in the eastern United States. If this current rate persists, the populations will be reduced to half their current size in less than 50 years. Multiple causes have been proposed to explain the decline of grassland birds, but loss of available habitat and declining habitat quality are recognized as key elements in the decline of this guild. The Champlain Valley has the potential to be an important area for the conservation of grassland birds due to large acreage of grassland habitat; however, management practices are not always compatible with grassland bird habitat requirements. Therefore, there is a need to focus conservation efforts in areas that will have the greatest probability of maintaining populations of grassland birds. This project was designed to identify priority areas for implementing conservation programs for grassland birds in the Champlain Valley of Vermont. Using ArcGis, I created detailed layers that included landscape level factors (forest, grassland, development and roads) and patch level factors (size, management and conservation) important in grassland bird habitat selection. Integrating the GIS dataset into a multicriteria decision analysis framework, I produced maps in which grassland patches were ranked on the basis of their quality for grassland birds. The Analytic Hierarchy Process was the decision rule used to identify priority conservation areas. The use of a hierarchical structure distributed the relative weights of different factors deemed important by grassland bird experts, allowing a greater number of criteria to be included while keeping the methodology manageable. These procedures resulted in a series of habitat quality maps that federal, state, and non-governmental land managers will be able to use as a baseline to focus conservation efforts on areas that will have the greatest probability of maintaining viable populations of grassland birds. The maps emphasize the protection of grassland patches larger than 5-10 ha that are 2 km away from roads with high traffic, and the selection of blocks of > 50 ha of protected or bird-friendly grassland habitat. The Analytic Hierarchy Process is a flexible method that can be applied to conservation decisions across a variety of ecosystems and species.

Au Québec, la transition glaciaire-interglaciaire a été caractérisée par la Mer de Champlain. L'invasion marine postglaciaire a débuté vers Il 100 ± 100 ans ¹⁴C dans les Basses-Terres du St-Laurent durant une période de 1500 ans ¹⁴C. La Mer de Champlain a abrité une faune riche et diversifiée incluant des kystes de dinoflagellés, foraminifères, pélécypodes, ainsi que des os d'oiseaux, de poissons et de mammifères, dont un béluga (Delphinapterus leucas), qui a été trouvé dans les dépôts marins de St-Félix-de-Valois. L'échantillonnage de différentes coupes sédimentaires de la Mer de Champlain (St-Nicolas, St-Félix-de-Valois, St-Césaire, Ste-Monique-de-Nicolet, Lac Hertel et Casselman) a permis l'analyse des palynomorphes terrestres et marins à des fins de reconstitutions paléoenvironnementales des conditions hydrologiques de surface. Les analyses polliniques ont permis de retracer l'évolution du couvert végétal, passant d'une végétation de type toundra, suivie d'une phase d'afforestation pour terminer par une phase arboréenne. Les assemblages de foraminifères des sites de St-Nicolas et du Lac Hertel permettent de déterminer le type d'environnement de ces sites, soit un environnement profond (>100m) à St-Nicolas dominé par Islandiella helenae et Cassidulina reniforme et un environnement peu profond (<30m) dominé par Elphidium excavatum au Lac Hertel. L'analyse des kystes de dinoflagellés a permis l'établissement d'une écostratigraphie en 4 zones d'assemblage, toutes dominées par des taxons ubiquistes tels Brigantedinium spp. et Operculodinium centrocarpum. Ces assemblages ont servi à des reconstitutions des conditions hydrographiques, à partir de fonctions de transfert. Les conditions de surface reconstituées présentent des températures estivales et des salinités de surface variant entre 0 et 5°C et entre 26 et 34 psu respectivement et la présence d'un couvert de glace de mer de 8 à 12 mois par année.

Road salt and other products used for winter maintenance in the Northeastern United States and Canada can impact ecosystems, pose risks to aquatic life, and create human health concerns. In response to these impacts and rising cost of materials, many municipalities have adopted preventative best management practices (BMPs) that reduce the amount of application materials used, save money, and/or provide a similar level of service and safety. Private companies that maintain parking lots and private roadways also contribute to the increasing chloride concentrations seen in the northeastern United States and Canada, but the practices of these companies have largely not been previously assessed. This mixed-methods study focused on private contractors in the Lake Champlain Basin in Vermont and New York who maintain parking lots, driveways, and roadways. A census and interviews were used to characterize practices used by private contractors and to identify key factors that drive their decision-making processes. A literature review was conducted to understand winter maintenance practices including recommended BMPs, potential environmental impacts and ways that contractors may be incentivized to adopt reduced-salt practices. The literature review informed the development of a census of winter maintenance companies in the Lake Champlain Basin. Contractors most often reported maintaining parking lots and roadways, and most commonly applying sand and salt. Physical snow removal techniques and adjustable material application rates were commonly adopted BMPs. Other BMPs including proactive applications, calibrating equipment, and using brine were infrequently adopted. In addition, the study examined the motivations and barriers contractors have to adopt recommended BMPs through qualitative and quantitative methods. Commonly reported motivations included perceived liability or safety concerns, customer request or expectations, and cost. Commonly reported barriers included cost, time, and customer requests or expectations. Across census and interview results, companies that focus on commercial lots and individuals who learn management practices through in-person trainings or online resources were found to use more recommended BMPs than other groups. Results of the study informed the development of outreach recommendations to increase private contractors’ adoption of BMPs and to lessen road salt use. These included: developing online resources, annual conferences, and reoccurring in-person trainings.

Les études récentes ont montré qu'il y aurait une forte influence de la matière organique dissoute (MOD) sur la dynamique des écosystèmes aquatiques. En particulier, certaines catégories de MOD ont des propriétés antialgues, susceptibles de réduire la biomasse des espèces de cyanobactéries. Nous avons testé les effets de différentes catégories de matières organiques dissoutes, ainsi que leurs interactions avec la lumière et les nutriments, sur la composition des communautés de phytoplancton lors d'incubations in situ (7 jours). La composition initiale en phytoplancton et les caractéristiques de la matière organique dissoute ont été des facteurs déterminants pour les modifications de la structure des communautés de phytoplancton, lors des incubations. Les résultats de notre étude montrent que la croissance du phytoplancton était fortement dépendante de la disponibilité en nutriments dans la baie Missisquoi en 2007, et que les concentrés d'extrait d'orge et de matière organique naturelle peuvent inhiber la croissance du phytoplancton, particulièrement des espèces de cyanobactéries. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : Matière organique dissoute (MOD), Cyanobactérie, Phytoplancton, Incubations, Lac Champlain.

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The geology, hydrogeology, and groundwater geochemistry are described for an interface aquifer in Eastern Ontario exhibiting anomalously high proportions of iodine (I) as iodide (I-) and dissolved methane (CH4). The studied area is unique in that it shows a significant marine influence, attributed to the most recent Champlain Sea incursion 10 – 12 ka BP, which has implications for I and CH4 enrichment. I and CH4 in groundwater are found in high proportions in reducing fossil seawaters, which are typically observed in depressions in the bedrock surface that are overlain by thick layers of glaciomarine muds. I is released via microbial decomposition of marine phytoplankton into mud porewaters, where it is then leached to underlying groundwaters. 129I and 14C isotopic signatures of I and C compounds highlight the importance of allochthonous I and C sources in the Champlain Sea basin derived from glacial abrasion of the surrounding terrain and imported via glacial meltwater. CH4 is microbial in origin, with marine phytoplankton from the Champlain Sea incursion and ancient terrestrial organic matter from an Early Wisconsinian interstadial period (60 – 75 ka BP) as the dominant substrates. A thermogenic CH4 component was observed for areas underlain by the Billings shale unit. Both I and CH4 originate at least partially from the same marine phytoplankton source within the muds, demonstrate similar controls on enrichment, and have a Spearman’s rank coefficient of 0.62, indicating that the correlation between I and CH4 in groundwater in the studied area is significant.

In shallow lake systems, phosphorus (P) availability to cyanobacteria populations is often controlled by the release (internal loading) or sequestration of sediment P. This study provides novel insight into the feedbacks between the water column and benthic P pools across multiple time scales and explain how these dynamics influence chemical partitioning of P in lake sediment. Phosphorus partitioning in seasonal sediment core time series collected from a shallow eutrophic bay of Lake Champlain were quantified with SEDEX and enzyme hydrolysis selective extraction schemes. Time series extraction data were interpreted with concurrent water column physical and biogeochemical monitoring data to examine the relationship between water column dynamics and P partitioning of near-surface sediments in this intensively monitored system. Nonmetric multidimensional scaling analysis (NMDS) indicates that both sediment and water column time series cluster seasonally, linking water column variables such as pH, thermal stratification, and dissolved oxygen concentrations to the behavior of sediment P pools over the course of a year. Iron (FeP), exchangeable (Ex-P), calcium carbonate bound P (Ca-P) pools, and enzyme labile P were highly dynamic, especially in spring and summer. The SEDEX concentration data indicated that the sediment was mainly composed of inorganic bound P (De-P), but FeP and Ex-P pools proportionally varied most between sampling dates. Remarkably, while highly dynamic on an intra-annual timescale, the sediment ultimately returned to similar P concentration and chemical partitioning by late fall. The hysteretic nature of this interaction between water column dynamics and sediment P inventory/partitioning was clearly driven by systematic seasonal changes in water column physical, chemical, and ecological conditions governed by northern Vermont’s climate and the physical configuration of the bay and its watershed. This study provides novel insight into the unique challenges associated with improving water quality in lake systems impacted by internal loading of legacy P.

Les sédiments contenus dans les fjords offrent un excellent potentiel de reconstitution paléoenvironnementale, et ce, à haute résolution, puisque ces anciennes vallées glaciaires généralement situées à la confluence du domaine continental et marin sont caractérisées par de hauts taux de sédimentation. Les fjords sont formés de longues vallées étroites et profondes ayant été modelées à plusieurs reprises au cours de cycles glaciaires et interglaciaires. Ils contiennent typiquement des dépôts et formes de terrain qui témoignent des variations des anciennes marges glaciaires. Certains fjords peuvent aussi appartenir au domaine lacustre, et ce, en milieux alpins ou en périphérie d'anciennes zones recouvertes par un glacier où les vallées ont été ennoyées par les eaux de fonte et/ou les eaux marines, mais que le relèvement glacio-isostatique combiné à la régression marine postglaciaire les a émergés et isolés. Plusieurs fjords-lacustres sont présents au Québec et au Labrador, mais leur évolution depuis la dernière glaciation reste peu documentée puisque la plupart de leurs analogues lacustres dans d'autres régions du monde ont encore aujourd'hui des langues glaciaires dans leur bassin versant, ou sont situés en milieux alpin où aucune transgression marine n'a jamais eu lieu. Une approche combinant les technologies hydro-acoustiques telle que la bathymétrie multifaisceaux et les profils de sous-surface permet de visualiser à haute résolution la morpho-stratigraphie de bassins subaquatiques afin d'analyser les processus majeurs ayant modelé leur bassin et de mieux comprendre leur dynamique sédimentaire passée et récente. Une telle approche appliquée dans des fjords-lacustres situés à des endroits stratégiques permettrait d'ailleurs de raffiner l'histoire de la déglaciation tardi-quaternaire dans certaines régions où les reconstitutions paléoenvironnementales sont peu nombreuses. Cette thèse présente et analyse les données bathymétriques et sismo-stratigraphiques à haute résolution de huit fjords-lacustres du Québec (lacs Mékinac, Jacques-Cartier, Pohénégamook, Témiscouata, Pentecôte, Walker et Pasteur) et du Labrador (Lac Grand), ainsi que les modèles numériques de terrain (MNT) de leur vallée et environs. L'analyse géomorphologique et sismo-stratigraphique des huit lacs a permis de 1) reconstituer la séquence de déglaciation en Mauricie et dans l'est du Labrador; 2) raffiner la position du complexe morainique Mars-Batiscan ainsi que la limite de la mer de Champlain sur la rive nord du Saint-Laurent; 3) mieux comprendre la dynamique du retrait glaciaire dans les fjords de Mékinac et Grand durant les périodes de refroidissements climatiques du Dryas récent et de l'événement de 8.2 ka BP; et 4) construire un modèle d'évolution morpho-stratigraphique des fjords-lacustres du Québec et du Labrador, de la déglaciation à aujourd'hui. / Sediments contained in fjords have a high potential to reconstruct paleoenvironmental changes since these glacial valleys located at the interface of continent and ocean are generally characterized by high sedimentation rates. Fjords are long narrow valleys that were deeply incised during successive glaciations and interglacial periods. They typically contain glacial deposits and landforms that inform on past variations of ice margins. Fjords can also exist in lacustrine environments, such as in alpine area or formerly glaciated regions, where the glacio-isostatic rebound combined with the postglacial marine regression isolated the fjord from the sea. Many fjord-lakes are found in Québec and Labrador, but the evolution of these lacustrine basins since deglaciation is poorly documented, as many worldwide analogues of these type of lakes are still glaciated today, or are located in alpine regions where no marine transgression ever occurred. Hydroacoustic technologies such as multibeam bathymetry and sub-bottom profiles allow visualizing at a high resolution the morpho-stratigraphy of subaquatic basins in order to interpret the major events that modeled their basins and lead to a better understanding of their past and modern sedimentary dynamics. Using such an approach in fjord-lakes located at key locations would also allow refining history of last glaciation in areas where only few paleoenvironmental studies exist. This thesis reports and describes multibeam bathymetry data and sub-bottom profiles collected in eight fjord-lakes of Québec (lakes Mékinac, Jacques-Cartier, Pohénégamook, Témiscouata, Pentecôte, Walker & Pasteur) and Labrador (Grand Lake), as well as Digital Elevation Model (DEM) of their valleys and surrounding areas. The analysis that combine geomorphology and sismo-stratigraphy allow: 1) reconstructing the sequence of deglaciation in Mauricie (Southern Québec) and eastern Labrador; 2) refining the location of the Mars-Batiscan morainic belt as well as the transgression limit of the deglacial Champlain Sea on the north shore of the St. Lawrence River; 3) a better understanding of the dynamics of ice retreat in the fjords of Mékinac and Grand during climatic cold episodes (Younger Dryas and 8.2 ka BP event, respectively); and 4) establishing a model of morpho-stratigraphic evolution for fjord-lakes of Québec-Labrador, from deglaciation to the postglacial period.