Impact of permafrost thaw on the turbidity regime of a subarctic river: the Sheldrake River, Nunavik, Quebec

Abstract

In order to assess the impact of seasonal active layer thaw and thermokarst on river flow and turbidity, a gauging station was installed near the mouth of the Sheldrake River in the discontinuous permafrost zone of northern Quebec. The station provided 5 years of water level data and 3 years of turbidity data. The hydrological data for the river showed the usual high water stage occurring at spring snowmelt, with smaller peaks related to rain events in summer. Larger and longer turbidity peaks also occurred in summer in response to warm air temperature spells, suggesting that a large part of the annual suspension load was carried during midsummer turbidity peaks. Supported by geomorphological observations across the catchment area, the most plausible interpretation is that the rapid thawing of the active layer during warm conditions in July led to the activation of frostboils and triggered landslides throughout the river catchment, thus increasing soil erosion and raising sediment delivery into the hydrological network. These results indicate that maximum sediment discharge in a thermokarst-affected region may be predominantly driven by the rate of summer thawing and associated activation of erosion features in the catchment.

Keywords

• permafrost
• northern quebec
• thermokarst
• turbidity
• subarctic river