Identifying hydrologic vulnerabilities to permafrost change and the effects on carbon transport to aquatic systems

Abstract:

Permafrost in northern latitudes serves as a potential source of carbon (C) upon thaw. The fate of this and other sources of C in arctic and subarctic regions depends on several factors. This study focuses on the influence of hydrologic processes on dissolved C transport to aquatic systems in permafrost environments. The spatial distribution and depth to permafrost are changing in response to climate as a result of direct (solar radiation) and indirect (vegetation, snow cover, soil moisture, wildfire) changes. Furthermore, permafrost thaw may be accelerated by heat transfer via groundwater flow. Such alterations to permafrost configuration, and resulting hydrogeologic framework, have the potential to modify pathways, residence times, and fluxes of water and dissolved constituents. Lengthened flow paths and increased residence times of soil water and groundwater promotes increased mineralization of terrestrial organic matter and subsurface weathering of carbonates. Intensification of groundwater circulation enhances baseflow to rivers and streams as suggested by both observations and modeling studies. These aforementioned changes result in a downward shift in the relationship between dissolved organic C (DOC) concentration and water discharge, an upward shift in the dissolved inorganic C (DIC) concentration – discharge relationship, and a likely decrease in the fraction of biodegradable organic C transported to aquatic systems. However, the expected magnitude and timing of shifts in hydrology and C are dependent on a variety of factors. Drawing from examples in the Yukon River Basin in Alaska (USA), we offer insight on landscape and hydrogeologic characteristics that influence the vulnerability of northern latitude systems to change with respect to hydrology and aquatic C export.