Metcalfe, Robert

Muskrat populations are declining across North America. In recent decades, hybrid cattail Typha x glauca has been invading wetlands in North America. This invasion is degrading wetland habitat, leading to reduced interspersion of water and vegetation. Muskrats are wetland-obligates and their populations are positively linked to marsh interspersion. Therefore, muskrat populations may be declining due to the invasion of T. x glauca and subsequent reduction in interspersion. To test this hypothesis, I first sampled marshes across south-central Ontario, comparing muskrat densities with the relative frequency of T. x glauca and the degree of interspersion. Second, I measured intensity of use by muskrats in a large wetland along a gradient of interspersion. My findings suggest that reduced interspersion may be contributing to muskrat population declines, but it is unclear to what degree T. x glauca is responsible. Further research is needed to understand the effects of wetland invasions on muskrat populations.

Author Keywords: invasive species, Ondatra zibethicus, Southern Ontario, Typha x glauca, wetlands, wildlife conservation

The fine-scale controls of active layer dynamics in the subarctic at the southern edge of continuous permafrost are currently poorly understood. The goal of this thesis was to understand how environmental conditions associated with upland tundra heath, open graminoid fen, and palsas/peat plateaus affected active layer thermal regime in a subarctic peatland in northern Canada. Indices of active layer thermal regime were derived from in-situ measurements of ground temperature and related to local measurements of air temperature, snow depth, and surface soil moisture. Active layer thaw patterns differed among landforms, with palsas and tundra heath having the least and greatest amount of thaw, respectively. Tundra heath thaw patterns were influenced by the presence of gravel and sandy soils, which had higher thermal conductivity than the mineral and organic soils of fens and palsas. Vegetation also influenced thaw patterns; the lichen cover of palsas better protected the landform from incoming solar radiation than the moss, lichen, and low-lying shrub cover of upland tundra heath, thus allowing for cooler ground temperatures. Air temperature was the most significant predictor of active layer thermal regime. Surface soil moisture varied among landforms and greater surface soil moisture reduced the amount of active layer thaw. These findings improved understanding of how landform and climate can interact to affect the active layer.

Author Keywords: Active layer thermal regime, Active layer thickness, Climate change, Peatland, Permafrost, Subarctic

Water storage is a fundamental component of drainage basins, controlling the synchronization between precipitation input and streamflow output. The ability of a drainage basin to store water and regulate streamflow may mediate sensitivity to climate and land cover change. There is currently no agreement on the best way to quantify basin storage. This study compares results of a combined hydrometric and isotopic approach for characterizing inter-basin differences in storage across the Oak Ridges Moraine (ORM) in southern Ontario. The ratio of the standard deviation of the stable isotope signature of streamflow relative to that of precipitation has been shown to be inversely proportional to mean water transit times, with smaller ratios indicating longer water transit times and implying greater storage. Stable isotope standard deviation ratios were inversely related to baseflow index values. Basins demonstrating longer transit times were associated with hydrological characteristics that promote infiltration and recharge of storage.

Author Keywords: baseflow, basin storage, climate change, mean transit time, Oak Ridges Moraine, stable isotopes