Integrated Terrestrial and Hydrological Carbon Budgets in High Arctic Watersheds

Abstract

The movement of carbon between terrestrial and aquatic stores and the atmosphere exerts an important control on atmospheric greenhouse gas concentrations, and thus the extent of climate change. Understanding the magnitude of these carbon fluxes, and their controls, is important for informing climate models. High Arctic regions are particularly key areas for carbon cycle research because they are understudied relative to other regions, and because accelerated climate change is altering many processes affecting carbon fluxes, with the net effect of these changes being poorly understood. This research integrates measurements of carbon fluxes directly from terrestrial environments to the atmosphere with the less commonly studied losses of carbon through streams in a High Arctic site on Melville Island, Nunavut. These fluxes are measured and upscaled to the watershed scale based on land cover type in an integrated budget, allowing the total losses of carbon from the watersheds to be calculated, and the relative importance of the different types of carbon fluxes to be compared. The watersheds were net sources of carbon to the atmosphere during the growing season, with terrestrial CO2 emissions overwhelmingly dominating the budgets, accounting for 97.6%-99.6% of total losses. CH4 fluxes were very small compared to CO2, even after converting to CO2 equivalence. Carbon fluxes measured in 2023, a very warm year with more winter snowfall were compared to those from 2024, a cool year with less winter snowfall. The terrestrial CO2 emissions were approximately half as large in 2023 than in 2024, owing both to increased uptake in highly vegetated areas, and smaller emissions in partially vegetated areas. Stream carbon export was nearly twice as large in 2023 than 2024 due to both increased discharge and increased dissolved carbon concentrations. Even with these differences, stream carbon export still only accounted for 1.6% of total carbon losses, confirming that terrestrial CO2 emissions dominate in these watersheds. As climate warming continues, the CO2 sink in this environment is expected to increase due to enhanced CO2 uptake.