SUMMARY
Climate change is mobilizing vast stores of carbon previously held in permafrost and altering the flow of water from land to aquatic systems; these changes should fundamentally affect stream chemistry and ecology. Pockets of unfrozen permafrost called taliks, provide connections between unfrozen areas of the soil during winter and may facilitate the export of carbon and other materials to streams. Despite widespread development of taliks in the Canadian subarctic, the specific influence of taliks during different seasons on subarctic rivers is poorly understood. If taliks are facilitating the release of highly biodegradable carbon and nutrients during winter, this carbon may be easily lost as carbon dioxide as it is processed downstream. This project aims to 1) characterize the nature of the winter carbon and nutrient pools in subarctic streams, 2) directly assess biological processing of carbon in these streams, and 3) determine if taliks are responsible for observed differences in water chemistry.by examining flow paths. To do this, winter flow was studied by sampling icings, which are an archive of winter subsurface flow and can be used to study winter water chemistry; seven icings near Yellowknife, NT were sampled in 2021. In addition to ice cores, streams that appear in the same locations as icings and their upstream lakes were sampled from spring-summer. Samples were analyzed for organic carbon parameters, nutrients, cations and trace metals. An incubation experiment was performed to assess biological processing of carbon.
It was found that ice samples were distinct from open water samples in organic carbon parameters and nutrient concentrations. Ice samples displayed organic carbon characteristics reflecting a more biodegradable carbon pool, and higher concentrations of reactive nitrogen and phosphorus. Cations and trace metals, which are indicators of changing flow paths and possible talik flow, were higher in some ice samples compared to open water flow, suggesting that deeper flow paths/taliks are being accessed at different times during the winter. Lastly, the incubation experiment revealed some evidence of rapid biological processing of organic matter into carbon dioxide, however these results were not statistically significant and unexpected results in some sample groups point towards the occurrence of non-biologically mediated processes acting on organic matter.
It was found that ice samples were distinct from open water samples in organic carbon parameters and nutrient concentrations. Ice samples displayed organic carbon characteristics reflecting a more biodegradable carbon pool, and higher concentrations of reactive nitrogen and phosphorus. Cations and trace metals, which are indicators of changing flow paths and possible talik flow, were higher in some ice samples compared to open water flow, suggesting that deeper flow paths/taliks are being accessed at different times during the winter. Lastly, the incubation experiment revealed some evidence of rapid biological processing of organic matter into carbon dioxide, however these results were not statistically significant and unexpected results in some sample groups point towards the occurrence of non-biologically mediated processes acting on organic matter.