Influence of wildfire and permafrost thaw on dissolved organic carbon (DOC) in northern peatlands; implications for lability and downstream transport

  • Author / Creator
    Burd, Katheryn
  • Peatlands in Canada’s western boreal forest are a major source of dissolved organic carbon (DOC) to downstream ecosystems, where DOC regulates carbon cycling, and can affect ecosystem productivity and habitat quality. Subarctic ecosystems are becoming increasingly vulnerable to the effects of climate change, particularly to disturbances such as wildfire and permafrost thaw. These disturbances have the ability to alter aboveground vegetation structure, soil thermal regimes, and hydrologic flow paths, and ultimately affect the quantity and composition of exported DOC. In high-latitude regions, the spring freshet is traditionally understudied, yet represents an important component of the annual DOC budget. To better constrain and quantify the impact of wildfire and permafrost thaw on aquatic carbon cycling in boreal peatlands I conducted a first study that comprised three in-situ incubation experiments (spring, summer, fall) with porewater collected from a partially burned peatland, investigating how wildfire and permafrost thaw affects DOC susceptibility to microbial and photochemical transformations. In spring, recently thawed sites exhibited greater microbial DOC lability (26% DOC loss) compared to unburned sites with intact permafrost (11%), while sites with mature permafrost thaw or sites that had recently burned both exhibited decreased lability (<5%). All sites exhibited higher microbial lability in the spring than in the summer or fall (2% and 4%, respectively). Also in the spring, microbial lability was strongly correlated to DOC chemical composition, including both its bulk aromaticity and carbon to nitrogen ratio. In contrast, no influence of DOC composition was found on photochemical lability. In a second study, I investigated whether the effects of wildfire on porewater DOC composition were reflected at the catchment outlet. For this, I continuously monitored water chemistry, ii discharge, and DOC composition at a paired burned and unburned catchment from early spring to fall. Both catchments exhibited similarities in terms of the timing and magnitude of runoff and DOC export; more than 50% of annual DOC export occurred during the spring period. Despite only lasting 8 days, the early spring period exported more than 25% of annual DOC, and this DOC was of particularly high molecular weight and aromaticity. Aside from increased DOC export during the summer at the burned catchment, there was no clear impact of wildfire at the catchment outlet. This suggests that shifting hydrology due to a changing climate may be more important for controlling catchment DOC export than wildfire. Together, our results highlight the potentially opposing effect of wildfire and permafrost thaw on porewater DOC composition, while stressing the importance of the spring period.

  • Subjects / Keywords
  • Graduation date
    Fall 2017
  • Type of Item
  • Degree
    Master of Science
  • 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.