Multiple Methods for Assessing the Sustainability of Shallow Subarctic Ponds in Churchill Region: Hudson Bay Lowland, Canada
Parrott, Jennifer Alisha
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This thesis examines the occurrence of hydrologic variability in subarctic ponds within the Churchill region of the Hudson Bay Lowland (HBL) and investigates the utility of using remote sensing studies to characterize changes in pond surface area. The thesis also characterizes hydro-climatic change over the past ~60 years, and compares this to pond sustainability within the region of Churchill. A multiple-methods approach incorporating field research, simple water balance modeling and remote sensing is used to address these objectives. Research findings demonstrate the occurrence of natural fluctuations in pond surface area and water levels in the Canadian subarctic. These fluctuations in pond water levels (and thus surface area) are caused by differences in antecedent hydrologic conditions, which are easily detected using remotely sensed imagery and may produce unrepresentative estimates of pond surface area change. Resulting from a 4.5 - 11.8 cm variation in water depth, pond surface areas were significantly altered by antecedent precipitation (average: 3,711 m²), intra-seasonal variability (average: 2,049 m²) and inter-annual climatic variations (average: 1,977 m²). These noteworthy pond boundary and water level differences reinforce the importance of accounting for hydrologic variability when delineating representative pond coverage and sustainability. Contemporary pond sustainability findings reveal significant regional climatic change, changing pond hydrologic conditions and overall pond physical stability between 1947 and 2008. Specifically, the Churchill region has become warmer and wetter. Occurring at a rate of 1.37 mm/yr over the study period, changing atmospheric conditions caused a decrease in open water pond hydrologic deficits. During the hydrologic recharge period, modeled pond water levels exhibited an increasing trend (August +0.72 mm/yr, September 0.51 mm/yr), which suggests ponds are filling closer to their maximum storage capacity prior to freeze-up. A remote sensing analysis of pond boundary modifications in mid-summer revealed no change in contemporary physical pond sustainability. Detected surface area changes from imagery were mainly attributed to naturally induced hydrologic variability. Overall, this thesis suggests a new methodological approach for conducting remote sensing pond sustainability research within the arctic/subarctic environment. As well, this study determined pond sustainability within the Churchill region over the last ~60 years.