Drivers of Dissolved Organic Matter Quality and Concentration in a Mountainous Subarctic Watershed, Yukon, Canada

Northern permafrost regions contain vast frozen stores of organic carbon that are vulnerable to thaw and mobilization. While considerable attention has been paid to carbon export from large Arctic rivers, gaps remain in characterizing dissolved organic matter (DOM) quality and export in permafrost influenced catchments that contain a mosaic of landscape types. This study examines the spatial and temporal factors influencing DOM quality, concentration and export over a 4-year period across the Wolf Creek Research Basin, Yukon, Canada. Optical indices were used to assess changes in DOM quality across six sites that ranged from permafrost dominated headwaters to forested lowlands and included wetlands and a lake. Results indicate that DOM export was transport-limited with greater exports in years with record high snowpacks and flows. Seasonality was responsible for the greatest variability in DOM quality, yet landscape type was an important factor during the open water season. High SUVA₂₅₄/HIX in headwater streams indicated primarily humic, terrestrially derived DOM, whereas high BIX and comparatively lower SUVA₂₅₄/HIX in a mid-catchment lake indicated autotrophic production of new DOM. DOM quality at the catchment outlet reflected a mixture of upstream sources and increased influence of groundwater. During high snow and streamflow years, DOM was humic and aromatic compared with low flow years, which had a greater portion of the recent microbial and autochthonous production. Results highlight the importance of evaluating DOM quality across all seasons and among years, and the relative influence of different landscape types and responses to rapid environmental change in cold environments.