Thermal Perturbation and Rainfall Runoff have Greater Impact on Seasonal Solute Loads than Physical Disturbance of the Active Layer

Climate warming in the Arctic will alter hydrological processes and biogeochemical exports from the landscape. Studies have reported that thermokarst disturbances and active‐layer deepening increase solute concentrations in surface waters, but neither the spatial extent nor duration of the impacts of these changes is well understood. We measured total dissolved solute (TDS) concentrations and normalised seasonal TDS fluxes (kg mm‐1) in a series of small headwater catchments in the Canadian High Arctic over three consecutive summers (2007–09) to examine the impact of thermal perturbation (increased soil temperatures) and physical disturbance (active‐layer detachment slides) on solute dynamics in permafrost catchments. We find that usually high July soil temperatures (thermal perturbation) in 2007 resulted in a near‐doubling of solute fluxes during the two subsequent summers, including in a catchment where there was no physical disturbance despite significantly cooler conditions. Solute concentrations increased with the spatial extent of physical disturbances, especially towards the end of the melt season. However, total seasonal solute fluxes did not always increase with the spatial extent of physical disturbances. The results show that the impact of the disturbance area on seasonal solute flux is limited by discharge and hydrological connectivity of the disturbed areas, and that summer rainfall allows for enhanced export of solutes from catchments subject to physical disturbance. Hence, seasonal solute export in these permafrost catchments was more sensitive to thermal perturbations and rainfall runoff than to physical disturbance of the active layer. Copyright © 2013 John Wiley & Sons, Ltd.