Effects of retrogressive thaw slumping on particulate organic carbon dynamics in the Northwest Territories, Canada

  • Author / Creator
    Shakil, Sarah
  • Climate change is increasing the frequency and intensity of thermokarst and accelerating the delivery of terrestrial organic material from previously sequestered sources to aquatic systems, where it is subject to further biochemical alteration. Rapid climate change in the glacially conditioned ice-rich and ice-marginal terrain of the Peel Plateau, western Canada, is accelerating thaw-driven mass wasting in the form of retrogressive thaw slumps, which are rapidly increasing in area, volume and thickness of permafrost thawed. Permafrost thaw can mobilize substantial amounts of organic carbon to streams where it can be decomposed to greenhouse gases during transport or re-sequestered in sediments. While studies have shown that organic carbon in dissolved form can be readily decomposed in aquatic systems, a substantial portion of organic carbon released to aquatic systems because of permafrost thaw can also occur in particulate form. Few studies have examined how permafrost thaw can alter the composition of particulate organic material in aquatic systems, and none have properly assessed the degree to which the organic carbon portion of this particulate organic matter (POC) can be decomposed. The purpose of this thesis is to examine the mobilization (Chapter 2), in-stream processing (Chapter 3), and downstream transport (Chapter 4) of POC from thaw slumps. We found that organic carbon mobilized to streams from thaw slumps can increase by orders of magnitude, though the magnitude of increase varies substantially in relation to slump morphology, stream power, and landscape position. Furthermore, increases in organic carbon are almost entirely due to mobilization of POC which is relatively more recalcitrant than organic carbon in unaffected streams (Chapter 1). Experiments provide further evidence that slump-mobilized POC is resistant to biodegradation in stream water and mineral-associated processes (e.g., sorption, chemoautolithotrophy) could act to protect and sequester carbon (Chapter 2). Finally, while material eroded by slumps can exceed the transport capacity of streams creating centuries to millennial scale sedimentary deposits in valley bottoms (Chapter 1), the order of magnitude increases in TOC can be sustained for kilometers downstream and have likely resulted in a regime shift in the Peel River organic carbon loads (Chapter 3). This research highlights particle flux as a key variable in the release of permafrost carbon from abrupt thaw. Targeted quantification of the multitude of biotic and abiotic processes acting on the carbon, organic matter, and minerals associated with these particles will be of critical importance in accurately predicting the affect of continued regional permafrost erosion on the carbon cycle and aquatic systems affected.

  • Subjects / Keywords
  • Graduation date
    Spring 2022
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.