Hillslope runoff from an ice-cored peat plateau in a discontinuous permafrost basin, Northwest Territories, Canada


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Abstract

Peat plateaus are important landscape features of many high-boreal, wetland-dominated drainage basins. Raised up to 2 m above the surrounding landscape and underlain by permafrost, these forested peatlands provide meltwater drainage to the surrounding wetlands, and to basin runoff. Understanding the factors that control the volume and timing of runoff from peat plateaus is the essential first step towards developing methods of accurately predicting basin runoff from wetland-dominated basins in the region of discontinuous permafrost, as well as understanding the basin response to hydrological changes brought on by the thermal degradation and thaw of permafrost peatlands. In this study, a water balance approach and the Dupuit-Forchheimer equation were used to quantify sub-surface runoff from a forested peat plateau at Scotty Creek, a small (152 km2), wetlanddominated discontinuous permafrost basin in Northwest Territories, Canada. These two computations yielded similar results in both years of study (2004–2005), and showed that runoff accounted for approximately half of the moisture loss from the peat plateau, most of which occurred in response to snowmelt inputs. The melt of ground ice was also a significant source of water during the study periods, which was largely detained in soil storage. Soil moisture conditions prior to soil freezing were a major factor controlling the volume of runoff from the hillslope. Sub-surface drainage rates declined dramatically after the snowmelt runoff period, when the majority of water inputs went to soil storage and évapotranspiration. The minimal lag between rain events and hydrograph response in both years suggests that much of the runoff produced from rain events is rapidly transported to the adjacent wetlands. These results give insight into how current climate warming predictions for northern latitudes could affect the hydrological response of forested peat plateaus, and the basins which they occupy.

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