A watershed approach to quantify the impacts of permafrost disturbances on the hydrogeochemistry of streams in the Richardson Mountains and Peel Plateau region, northwestern Canada.

Abstract:

Retrogressive thaw slumps are one of the most dramatic thermokarst features in ice-rich permafrost landscapes and their growth may pose significant terrestrial and aquatic impacts. In the Richardson Mountains and Lower Peel River watersheds (northwestern Canada), thaw slumps are abundant along hillslopes. Runoff from active slumps is characterized by conductivity and solute concentration nearly 1 order of magnitude higher than in pristine streams. As such, the objective of this study is to evaluate the potential cumulative impacts of thaw slumps to aquatic ecosystems and determine the watershed scale at which the impacts of slumps can be detected. This is accomplished by: i) compiling the distribution of active and stable thaw slumps in the Richardson Mountains and Peel Plateau; ii) determining the hydrogeochemistry (major ions, total dissolved solids) of pristine and slump impacted streams in this region; and iii) representing this information on watershed platforms (4^th to 6^th order scale). The results indicate a positive relation between slump density, cumulative surface area of slumps and average ionic concentrations within the various sub-watershed scales. Solute concentrations along streams reveal that ionic content increases immediately downstream of a slump and that for slumps with surface area greater than 5ha, the solute concentrations remain significantly higher in impacted streams, even at the 4^th-order watershed scale. The broad scale impacts of thaw slumps are indicated by a significant increase in solute concentrations in the Peel River (70,000 km² watershed scale). These observations illustrate the nature and magnitude of hydrogeochemical changes that can be expected as ice-rich landscapes adjust to a rapidly changing climate.