Kathy L. Young

Influence of Local Topography, Soils, and Vegetation on Microclimate and Hydrology at a High Arctic Site, Ellesmere Island, Canada

Influence of topography, soils, and vegetation on the microclimate and hydrology of four slopes and a plateau site located within a 1-km2 area in the continuous permafrost zone of Arctic Canada was...

HYDROGEOMORPHOLOGY OF PATCHY WETLANDS IN THE HIGH ARCTIC, POLAR DESERT ENVIRONMENT

Patchy wetlands are commonly found in the polar desert at localities where ample water supply is available during the thawed season. These wetlands can occur on a wide range of topography, and they support more luxuriant vegetation than their surrounding areas. Snowbank wetlands are characterized by a zonation of vegetation, with increasingly rich plant coverage away from the snowbed edge. Ground-water wetlands usually occupy topographic concavities or depressions, with exfiltration of subsurface water to sustain a high water table and to provide an enrichment of nutrients. Riverine wetlands experience prolonged flooding during the peak snowmelt season, and their vascular plant cover is low owing to inundation by the cold, turbulent stream water. Lakes and ponds are associated with topographic depressions, receiving surfaceand ground-water inputs from catchment areas larger than the surface extent of the water bodies. Their evaporation rates are high, but the open water season is curtailed by ice cover. Lake outflow wetlands are supported by spillage and seepage from lakes, and they maintain a relatively lush vegetation cover. Coastal wetlands form narrow strips enclosed by raised beaches, with high salinity that limits plant diversity. Strong interactions exist among the water and heat fluxes to the wetland, the vegetation, and the hydrogeomorphology. Locally enhanced water supply and shallow permafrost enable frequent saturation, augmenting nutrient enrichment and encouraging vegetation development. Slow vegetation decay in a cold environment facilitates the formation of peat. The saturated soil conditions give rise to large ground-ice content in the winter, requiring much latent heat for ground thaw in subsequent summers. This, together with the insulating properties of the organic layer, creates shallow frost tables during the summer and produces a positive feedback that maintains high water tables in the wetlands to favor plant growth.

SURFACE ENERGY BALANCE OF A PERENNIAL SNOWBANK, MELVILLE ISLAND, NORTHWEST TERRITORIES, CANADA

The energy balance of a large perennial snowbank located in the continuous permafrost zone was examined during the summer of 1986. Three meteorological towers allowed energy fluxes to be determined for separate zones of the snowbank. Over the melt season, net radiation accounted for 85% of the energy absorbed by the snow surface, while sensible heat contributed 15% and latent heat was a net loss of 2%. Albedo varied across the snowbank due to an irregular distribution of surface aeolian deposits. Direct measurements of snowmelt from a snow survey compare favorably with calculated values obtained from the energy balance. The net shortwave radiation flux was a significant influence on ablation, explaining on average 77% of the variance in the measured melt. The predominance of the radiant fluxes is attributed to the large size of the snowbank and its sustained melt through the cool arctic summer.

Representativeness of arctic weather station data for the computation of snowmelt in a small area

This study determines how representative the snowmelt values computed using arctic weather station data are of the melt in its surrounding area. Simultaneous measurements of meteorological variables were made at several sites to permit comparisons of their calculated snowmelt with the weather station at Resolute. Northwest Territories, Canada. Like most other stations, the Resolute site is located near the coast, at an airport and close to human settlement, making it warmer and its snow albedo lower than its adjacent sites. Snowmelt rates at Resolute are higher than that of a flat site away from the airport, This latter site has snowmelt conditions more typical of the rolling terrain nearby, but its melt rates are higher than those for an inland site where the snow remains longer than at the coastal zone, Through these simultaneous observations and systematic comparisons, this study indicates that the point data from coastal, arctic stations are unlikely to be representative of their surrounding areas. Thus, caution should be exercised when applying such information directly to the computation of snowmelt for entire grid cells of macro-hydrologic models.

Hydrology of a perennial snowbank in the continuous permafrost zone, Melville Island, Canada

The hydrologic processes of a perennial snowbank located in an area of continuous permafrost were examined. The major source of water for the snowbank was surface ablation, while the major sinks were outflow and basal ice growth. Subsurface flow from the active layer upslope and summer precipitation were unimportant as an inputs. Each diurnal outflow hydrograph exhibited a distinct plateau following the rising limb. This characteristic has not been observed in other studies of arctic snowmelt and is attributed to the great thickness of snow and the spatial heterogeneity of snow depths at the field site. Lag times between surface energy inputs and outflow did not follow a regular trend over the summer but recession limbs showed a slight steepening, reflecting gradual thinning of the snowbank.

High Arctic Patchy Wetlands: Hydrologic Variability and Their Sustainability

Wetlands in the polar desert environment of the High Arctic provide a special ecological niche for the tundra plants, insects, birds, and animals. Non-tidal patchy wetlands exhibit a hydrologic regime that includes a high water table and extensive flooding in the snowmelt period, followed by a gradual summer drying that is interrupted by rainfall events that raise water levels. These wetlands are also prone to inter-annual variations in wetness. Given sufficient local water supply, they are self-sustaining entities in which soil saturation favors ground ice formation, but the ice-rich permafrost prevents deep percolation while vegetation growth and peat development further insulate the ground. Several processes can alter this balance: a change in drainage can reduce inflow; excessive melting of ground ice leading to thermokarst can modify wetland morphology and flow pattern. On a regional scale, projected climatic warming of the Arctic may extend the thawed season, enhance evaporation, and eliminate the late-lying snowbanks that feed some patchy wetlands. Under such a scenario, patchy wetlands in the High Arctic are considered to be highly vulnerable.

Preferential groundwater flow through a sorted net landscape, Arctic Canada

Preferential suprapermafrost groundwater flow was observed in deepened channels lying between raised frost mounds. Here, saturated hydraulic conductivity, k, ranged from 90 to 1000 m/day but was only 0·1–1·0 m/day in the mound centres. A high proportion of fines occurs in the frost mound centre due to particle sorting, while channels contain gravels. Three approaches of areal weighting of k and groundwater flow, Qs, across a wetland–upland boundary were explored. When percentage area covered by channels, mounds or gravel was considered, estimates of water flow on a daily and seasonal basis fell by 30 to 50 per cent. This study is of relevance to northern scientists who require reliable estimates of groundwater flow across patterned ground landscapes. Copyright

Simple approaches to modelling solar radiation in the Arctic

Abstract Solar radiation was modelled for an Arctic location using hourly and twice daily meteorological data. Results indicate that a total cloud model (TC o ) employing cloud opacity data and cloud layer models (CL o ) utilizing cloud opacity and cloud amount data (CL a ) perform equally well; and they are better than a total cloud model (TC a ) employing cloud amount data. The performance of TC o , CL o , and CL a models improve greatly when averaged over 4 days, indicating the feasibility of utilizing rudimentary meteorological observations to broaden the radiation database for the vast Arctic region of North America.

Snow cover and snowmelt of an extensive High Arctic wetland: spatial and temporal seasonal patterns

Abstract This study examined the end-of-winter snow storage, its distribution and the spatial and temporal melt patterns of a large, low gradient wetland at Polar Bear Pass, Bathurst Island, Nunavut, Canada. The project utilized a combination of field observations and a physically-based snowmelt model. Topography and wind were the major controls on snow distribution in the region, and snow was routinely scoured from the hilltop regions and deposited into hillslopes and valleys. Timing and duration of snowmelt at Polar Bear Pass were similar in 2008 and 2009. The snowmelt was initiated by an increase in air temperature and net radiation receipt. Inter-annual variability in spatial snowmelt patterns was evident at Polar Bear Pass and was attributed to a non-uniform snow cover distribution and local microclimate conditions. In situ field studies and modelling remain important in High Arctic regions for assessing wetland water budgets and runoff, in addition to model parameterization and validation of satellite imagery. Editor Z.W. Kundzewicz Citation Assini, J. and Young, K.L., 2012. Snow cover and snowmelt of an extensive High Arctic wetland: spatial and temporal seasonal patterns. Hydrological Sciences Journal, 57 (4), 738–755.

Hydrologic Thresholds of Ponds in a Polar Desert Wetland Environment, Somerset Island, Nunavut, Canada

Evaluation of the water storage in several ponds near Creswell Bay, Somerset Island, Canada, an area experiencing a polar desert climate (cool, moist), served to reveal factors that are important in the sustainability of these freshwater ecosystems within a larger wetland complex. Our study focused on the hydrology of 12 ponds of different sizes in various geomorphologic settings: moraine, bedrock, and coastal areas. A positive water balance plays an important role in the survival of the ponds experiencing variable climatic conditions and survival over the season depends largely on the local enrichment of water through various hydrologic linkages. Pond inputs and losses are governed by the pond catchment topography, substrate, hydrology, and seasonal climatic conditions. Low hydrologic energy and long hydroperiod (e.g., ponds in surface-flow dominated systems with multiple hydrologic linkages) are associated with a high degree of pond sustainability. Ponds with high hydrologic energy and short hydroperiods (e.g., ponds in precipitation and groundwater-dominated systems) show limited hydrologic sustainability. We suggest that these latter ponds in this polar desert environment will be the most vulnerable to future climate warming in the Canadian High Arctic.