Icing dynamics in the lake-dominated, discontinuous permafrost Taiga Shield, and effects on fluvial biogeochemistry, carbon cycling and microbial communities

• Author / Creator

  Alsafi, Nora

• Climate warming is affecting freshwater systems across the western Canadian subarctic, due to widespread shifts in precipitation regimes, permafrost degradation, and multi-decadal increases in winter baseflow. These changes are significant on the Taiga Shield, which comprises ~20% of North America’s permafrost-covered area, encompassing an area of over 1.3 million km^2. This region is characterized by “fill and spill” hydrology, where runoff is generated by the exceedance of lake basin storage thresholds across the landscape. In response to increasing winter baseflow, hydrologic connectivity between the lakes which dominate this region is also increasing. In addition, taliks, zones of unfrozen ground within or above the permafrost layer, are expanding in spatial extent and occurrence across the Taiga Shield. These changes are expected to alter the export of novel chemical constituents, including dissolved organic matter (DOM), to fluvial networks, with potential implications for carbon cycling and the structure of microbial communities, which comprise the base of aquatic food webs. Despite this, the impact of warming on wintertime fluvial biogeochemistry on the Taiga Shield is poorly understood.

  In this thesis, I use icings, which are sheet-like masses of layered ice which form when subsurface flow is pushed to the ground surface, as a tool to understand wintertime chemistry. Working in the Yellowknife, NT, region, I developed and tested a conceptual model to consider how hydrological processes and source water characteristics affect icing chemistry. I additionally coupled icing samples to surface water samples from winter, spring, and summer to explore seasonal and icing-driven variation in water chemistry, microbial community structure, and carbon processing rates. I found that icing chemistry was driven by physico-chemical processes, notably anoxia, solute exclusion and sediment-water interaction occurring within icing source waters and along flow paths to sites of icing formation. Icing formation and morphology were driven by temperature and antecedent precipitation levels, which worked together to control wintertime fill and spill hydrology. Icing formation also modified wintertime flow via solute exclusion; icing chemistry was unique, and dominated by DOM that was characteristically aliphatic, protein-like, and was preferentially mineralized to CO2 during an incubation. Seasonal differences in DOM composition also supported unique microbial communities. Overall, these results suggest that winter flow is dynamic, and icings have the potential to modify the composition of water actively flowing through fluvial networks in the winter, and as they thaw in the spring and summer; thus, changes in icing dynamics due to warming may have significant effects on wintertime chemistry and carbon cycling in this region.
   

• Subjects / Keywords

  • climate change
  • icing
  • aufeis
  • subarctic
  • winter
  • aquatic chemistry
  • water chemistry

• Graduation date

  Fall 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-bz61-db39

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.