William L. Quinton

Subsurface drainage from hummock-covered hillslopes in the Arctic tundra.

In the Arctic tundra, subsurface drainage occurs predominantly through the saturated zone within the layer of peat that mantles the hillslopes. In plan view, the peat cover is fragmented into a network of channels due to the presence of mineral earth hummocks. In cross section, the physical and hydraulic properties of the peat vary with depth and the water transmission characteristics (e.g. hydraulic conductivity) of the upper profile differ distinctly from those of the lower. Water flow through the peat is laminar, therefore the friction factor ( f ) and the Reynolds number (NR) are inversely related. Average values for the coefficientC of the relation f a C=NR; vary from ,300 near the surface to ,14,500 at depth. This large difference in C confirms that the larger-diameter soil pores of the living vegetation and lightly decomposed peat near the surface offer much less resistance to water motion than the finer-grained peat deeper in the profile. Also, the variability suggests that subsurface drainage is strongly affected by the position and thickness of the saturated zone within the peat matrix. A first approximation for a model or simulation of the flow regime may consider a peat profile with depth-varying, resistance properties in respect to subsurface flow. q 2000 Elsevier Science B.V. All rights reserved.

Peatland Hydrology of Discontinuous Permafrost in the Northwest Territories: Overview and Synthesis

Field studies were initiated in 1999 at Scotty Creek in the lower Liard River basin, NWT, Canada, to improve understanding of and ability to predict the major water fluxes and storage processes within a wetland-dominated zone of the discontinuous permafrost region. This paper synthesises a decade of published and unpublished research at Scotty Creek for the purpose of presenting the major factors that should be considered by water scientists and managers as a basis for modelling and management strategies. Five main topics are covered: (1) peatlands of lower Liard River valley; (2) hydrological characteristics of permafrost plateaus, flat bogs, and channel fens; (3) runoff generation on permafrost plateaus; (4) conceptual model of peatland hydrology; and (5) climate warming and implications for basin runoff. This synthesis offers a practical understanding of the hydrology of wetland-dominated basins with discontinuous permafrost. It also offers insight into how landscape changes resulting from climate or human disturbances may influence the basin hydrograph.

Influence of landscape aggregation in modelling snow-cover ablation and snowmelt runoff in a sub-arctic mountainous environment

Abstract Appropriate representation of landscape heterogeneity at small to medium scales is a central issue for hydrological modelling. Two main hydrological modelling approaches, deductive and inductive, are generally applied. Here, snow-cover ablation and basin snowmelt runoff are evaluated using a combined modelling approach that includes the incorporation of detailed process understanding along with information gained from observations of basin-wide streamflow phenomena. The study site is Granger Basin, a small sub-arctic basin in the mountains of the Yukon Territory, Canada. The analysis is based on the comparison between basin-aggregated and distributed landscape representations. Results show that the distributed model based on “hydrological response” landscape units best describes the observed magnitudes of both snow-cover ablation and basin runoff, whereas the aggregated approach fails to represent the differential snowmelt rates and to describe both runoff volumes and dynamics when discontinuous snowmelt events occur.

Linear disturbances on discontinuous permafrost: implications for thaw-induced changes to land cover and drainage patterns

Within the zone of discontinuous permafrost, linear disturbances such as winter roads and seismic lines severely alter the hydrology, ecology, and ground thermal regime. Continued resource exploration in this environment has created a need to better understand the processes causing permafrost thaw and concomitant changes to the terrain and ground cover, in order to efficiently reduce the environmental impact of future exploration through the development of best management practices. In a peatland 50 km south of Fort Simpson, NWT, permafrost thaw and the resulting ground surface subsidence have produced water-logged linear disturbances that appear not to be regenerating permafrost, and in many cases have altered the land cover type to resemble that of a wetland bog or fen. Subsidence alters the hydrology of plateaus, developing a fill and spill drainage pattern that allows some disturbances to be hydrologically connected with adjacent wetlands via surface flow paths during periods of high water availability. The degree of initial disturbance is an important control on the extent of permafrost thaw and thus the overall potential recovery of the linear disturbance. Low impact techniques that minimize ground surface disturbance and maintain original surface topography by eliminating windrows are needed to minimize the impact of these linear disturbances.

Influence of vertical and lateral heat transfer on permafrost thaw, peatland landscape transition, and groundwater flow

Recent climate change has reduced the spatial extent and thickness of permafrost in many discontinuous permafrost regions. Rapid permafrost thaw is producing distinct landscape changes in the Taiga Plains of the Northwest Territories, Canada. As permafrost bodies underlying forested peat plateaus shrink, the landscape slowly transitions into unforested wetlands. The expansion of wetlands has enhanced the hydrologic connectivity of many watersheds via new surface and near-surface flow paths, and increased streamflow has been observed. Furthermore, the decrease in forested peat plateaus results in a net loss of boreal forest and associated ecosystems. This study investigates fundamental processes that contribute to permafrost thaw by comparing observed and simulated thaw development and landscape transition of a peat plateau-wetland complex in the Northwest Territories, Canada from 1970 to 2012. Measured climate data are first used to drive surface energy balance simulations for the wetland and peat plateau. Near-surface soil temperatures simulated in the surface energy balance model are then applied as the upper boundary condition to a three-dimensional model of subsurface water flow and coupled energy transport with freeze-thaw. Simulation results demonstrate that lateral heat transfer, which is not considered in many permafrost models, can influence permafrost thaw rates. Furthermore, the simulations indicate that landscape evolution arising from permafrost thaw acts as a positive feedback mechanism that increases the energy absorbed at the land surface and produces additional permafrost thaw. The modeling results also demonstrate that flow rates in local groundwater flow systems may be enhanced by the degradation of isolated permafrost bodies.

Quantifying errors in discontinuous permafrost plateau change from optical data, Northwest Territories, Canada: 1947-2008.

The discontinuous permafrost zone has been subject to increased air temperatures over recent decades. Permafrost thaw can cause changes to topography, hydrology, vegetation, and trace gas fluxes, and thus it is important to monitor changes in permafrost area through time. Optical imagery can be used to generate time-series databases of near-surface spectra that may be related to permafrost area. This provides a spatial perspective on area permafrost change that is not easily obtained from field data alone. This study examines the cumulative maximum and minimum errors of aerial and satellite imagery used for change detection within the Scotty Creek watershed, Fort Simpson, NWT, Canada. The results illustrate that, unless unchanging linear features are found throughout every image used (e.g., to be used as multitemporal tie points) and radiometric normalization can be applied (problematic for film images), direct image to image comparisons (e.g., subtraction) are not appropriate. Further, measureable cumulative errors are often produced by misclassification of edges, resolution limitations, and increased landscape fragmentation. At Scotty Creek, increased fragmentation of permafrost plateaus occurred from 1947 to 2008. Cumulative maximum and minimum errors result in an approximate 8%–26% error in permafrost area when compared with the total area of the site. Rates of permafrost area reduction within the study area were approximately 0.5% every year, determined from linear correlation (r2 = 0.91, n = 5). Therefore, based on the maximum cumulative error (a worst-case scenario), approximately 21–32 years (for resolutions of 0.18–1.10 m) is required between images to approximate change within this particular site. Increased (decreased) rates of change at other sites will decrease (increase) the timing required to identify change between images beyond error bounds.

A constant-head well permeameter method for measuring field-saturated hydraulic conductivity above an impermeable layer

Hydrologic understanding of mountainous and northern regions of Canada is poor owing to the lack of critical field data such as hydraulic conductivity. A portable field instrument, the Guelph permeameter (GP), is a promising tool for measuring field-saturated hydraulic conductivity in remote watersheds inaccessible by motorized vehicles. In order to extend the applicability of the GP method to relatively thin soils underlain by impermeable bedrock or permafrost, a new set of shape factors was determined by numerical simulation. The new shape factors gave accurate values of field-saturated hydraulic conductivity when tested in the laboratory. The impermeable layer causes flow around the auger hole to be primarily horizontal. Therefore, the GP method measures a predominantly horizontal field-saturated hydraulic conductivity in these thin soils. The measured conductivity represents a weighted average of the soil surrounding the submerged surface of the auger hole. In layered soil, the weight is greater for t...

Snowmelt Processes and Runoff at the Arctic Treeline: Ten Years of MAGS Research

Under the Mackenzie GEWEX Study, extensive snowmelt and runoff research was carried out at the Trail Valley and Havikpak Creek research basins at the tundra-forest transition zone near Inuvik, Northwest Territories. Process based research concentrated on snow accumulation, the spatial variability of energy fluxes controlling melt, local scale advection of sensible heat from snow-free patches to snow patches, percolation of meltwater through the snowpack, storage of meltwater in stream channels, and hillslope runoff. Building on these studies, process based models were improved, as shown by a better ability to model changes in snow-covered area during the melt period. In addition, various landsurface and hydrologic models were tested, demonstrating an enhanced capability to model melt related runoff. Future research is required to accurately model both snow-covered area and runoff at a variety of scales and to incorporate topographic and vegetation effects correctly in the models.

Recent Advances Toward Physically-based Runoff Modeling of the Wetland-dominated Central Mackenzie River Basin

Field studies were initiated in 1999 at Scotty Creek in central Mackenzie River Basin to improve understanding and model-representation of the major water flux and storage processes within a wetland-dominated zone of the discontinuous permafrost region. Four main topics were covered: (1) the major peatland types and their influence on basin runoff, (2) the physical processes governing runoff generation, (3) how runoff processes observed at the hillslope scale relate to basin-scale runoff, and (4) the water balance of Scotty Creek and its adjacent basins. A conceptual model of runoff generation was developed that recognizes distinct hydrologic roles among the major peatland types of flat bog, channel fen and peat plateau. This model contributes to resolving some of the difficult issues in the hydrologic modeling in this region, especially in relation to the storage and routing functions of wetlands-dominated basins underlain by discontinuous permafrost.

CO2 Exchanges within Zones of Rapid Conversion from Permafrost Plateau to Bog and Fen Land Cover Types

Abstract Variability of midday net ecosystem CO2 exchange (NEE) and respiration was measured using a transect of closed system chambers spanning transitions from channel fen, permafrost plateau, and ombrotrophic flat bog land cover types during the spring melt season (26 April—6 June 2008). The primary objective was to compare fluxes from different land cover types and topographic variability within zones adjacent to and including rapid permafrost thaw. During this period, the bog was the greatest net source of CO2 to the atmosphere, followed by plateau, and fen. NEE was slightly positive (indicating CO2 loss to the atmosphere) during the snowmelt period (average = 0.009 ± 0.004 mg CO2 m-2 s-1), and increased to 0.025 ± 0.012 mg CO2 m-2 s—1, on average, possibly due to soil thaw and increased microbial activity within two days of completely snow-free conditions. Near surface soil temperature and depth to the water table were the most significant controls of soil and ground cover CO2 fluxes within chambers at all sites (p < 0.05). Analysis of historical aerial photographs and satellite imagery of the area from 1947 to 2008 indicates that plateaus are converting more rapidly into bogs than fen, where 73% of plateau areas (since 1970) that thawed had become bogs (as opposed to 27% conversion into fen). Future research requires establishment of a full ecosystem or land cover greenhouse gas and soil nutrient exchange/transfer program, including CO2 and water fluxes as well as dissolved organic and inorganic C, and CH4 losses from the soil. These results contribute to a better understanding of northern soil and ground-cover carbon exchanges as greater areas of permafrost plateaus collapse and form bogs.