Hydrological and Hydrochemical Responses From Thawing Permafrost in the Canadian Arctic

Abstract

The objectives of this research are to better understand: (1) how Arctic watersheds respond in terms of hydrological processes to deepening active layers, (2) what the short and long-term changes are to surface water chemistry in watersheds impacted by thermal and physical permafrost disturbances, (3) which key factors control permafrost chemistry and runoff solute loads, and (4) where in the Canadian Arctic are changes to surface water chemistry expected to be the most pronounced with continued climate warming.

During exceptionally warm and wet summers, deep ground thaw enhances the infiltration and storage of rainfall and has the potential to solubilize inorganic ions previously stored at depth in the transient layer. Subsequent mid to late- summer rainfalls act as a hydrological flushing mechanism, mobilizing solutes from the subsurface thus substantially increasing ion concentrations in surface runoff. Exposure and mobilization of soluble ions in near surface soil because of physical permafrost disturbance is shown to be a key control over dissolved ion concentrations. Runoff in a disturbed catchment showed increased total dissolved solute (TDS) concentrations and seasonal TDS fluxes, and changes to the relative composition of individual ions in an undisturbed catchment. Impacts in the disturbed watershed persisted for the seven years after disturbance, consistent thaw of the solute-rich transient layer and upper permafrost. Thermal perturbation increased TDS concentrations and seasonal fluxes in runoff for up to two years as ions released from ground thaw were available for flushing in subsequent summers. Bulk ion concentrations in near-surface ground ice differ across the Canadian Arctic by several orders of magnitude. Regional differences in bulk ionic concentrations in transient layer and near-surface permafrost ground ice are controlled by geomorphic factors such as elevation, surficial geology and landscape history. Highly localized factors that control drainage (e.g., ground ice content and soil texture) appear to influence the solute storage patterns in ground ice. Low elevation coastal areas may be more at risk to water quality impacts from permafrost degradation compared to higher elevation, inland areas. Contributions from this research are critical for anticipating changes to water quality, aquatic systems, community water supplies and land-ocean transfers in the Canadian Arctic.