Biogeochemical impacts of glacial meltwaters across a High Arctic watershed (Lake Hazen, Nunavut, Canada)

  • Author / Creator
    St. Pierre, Kyra
  • Climate change across northern latitudes is fundamentally altering the hydrological cycle there, resulting in increased glacial melt, permafrost thaw and precipitation. Whereas enhanced glacial melt has potentially important implications for water quality and productivity in downstream freshwater ecosystems, little is yet known about how glacial meltwaters impact biogeochemical cycles of both nutrients and contaminants across glacierized watersheds, a critical gap in our ability to predict the future quality of freshwater resources in the North. To address this, we integrated principles from glaciology and limnology in a multi-year (2013-2017) study of freshwater quality and productivity across the glacierized High Arctic Lake Hazen watershed on northern Ellesmere Island in Nunavut Canada, from glacier termini through rivers and lakes to the nearshore marine environment. We first examined nutrient (nitrogen, phosphorus, iron, silica) and carbon retention and mobilization across the glacierized land-to-ocean aquatic continuum (Chapter 2). Largely particle-bound nutrients (total phosphorus, iron, nitrogen) from the glacier-fed rivers were deposited to the depths of the lake by turbidity currents generated by the glacial inflows. Lake Hazen was also a sink for dissolved nitrogen species and dissolved organic carbon, likely due to biological processes, but a source of dissolved inorganic carbon (DIC) to the Ruggles River outflow. To understand this source of DIC, we then focused on DIC and by extension, dissolved carbon dioxide (CO2) concentrations across the watershed (Chapter 3). At the watershed scale, the glacier-fed rivers were a strong, previously overlooked sink of atmospheric CO2 due to the strength of CO2-consuming chemical weathering reactions involving the large loads of comminuted sediments entrained by glacial meltwaters as they traveled across the poorly consolidated proglacial zone. As the reactions consumed CO2, they also generated DIC, resulting in the net export of DIC from Lake Hazen to the Ruggles River. These reactions intensified with increasing discharge and distance from the glaciers and continued into the lake, resulting in CO2 undersaturation even at 267 m depth. Finally, we used a mass balance approach to identify sources and sinks of neurotoxic methylmercury (MeHg) and total mercury (THg) across the watershed (Chapter 4). Glacial meltwaters were annually the most important source of THg to Lake Hazen and MeHg. Because much of this mercury was particle-bound and deposited to the bottom of the lake, Lake Hazen was a large sink for both MeHg and THg, resulting in low MeHg and THg exports to the Ruggles River. However, permafrost slumping and erosion along the banks of the Ruggles River significantly increased exports of MeHg and THg to coastal marine waters. This study highlights the importance of climate change-accelerated glacial melt to the biogeochemistry of downstream aquatic ecosystems.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
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