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Ecosystem-scale methane (CH 4 ) exchange was observed in a poorly-drained black spruce forest over permafrost in interior Alaska during the snow-free seasons of 2011–2013, using the eddy covariance technique. The magnitude of average CH 4 exchange differed depending on wind direction, reflecting spatial variation in soil moisture condition around the observation tower, due to elevation change within the small catchment. In the drier upper position, the seasonal variation in CH 4 emission was explained by the variation in soil water content only. In the wetter bottom, however, in addition to soil temperature and soil water content, seasonal thaw depth of frozen soil was also an important variable explaining the seasonal...
Intensification of permafrost thaw has increased the frequency and magnitude of large permafrost slope disturbances (mega slumps) in glaciogenic terrain of northwestern Canada. Individual thermokarst disturbances up to 40 ha in area have made large volumes of previously frozen, highly weatherable fine-grained sediments available for leaching and transport to adjacent streams, significantly increasing sediment and solute loads in these systems. To test the effects of this climate-sensitive disturbance regime on the ecology of Arctic streams, we explored the relationship between physical and chemical variables and benthic macroinvertebrate communities in disturbed and undisturbed stream reaches in the Peel Plateau...
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Changes in permafrost distribution in the southern discontinuous zone were evaluated by repeating a 1964 survey through part of the Alaska Highway corridor (56 degrees N-61 degrees N) in northwest Canada. A total of 55 sites from the original survey in northern British Columbia and southern Yukon were located using archival maps and photographs. Probing for frozen ground, manual excavations, air and ground temperature monitoring, borehole drilling and geophysical techniques were used to gather information on present-day permafrost and climatic conditions. Mean annual air temperatures have increased by 1.5-2.0 degrees C since the mid-1970s and significant degradation of permafrost has occurred. Almost half of the...
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Thermokarst is developing in the boreal forests of Alaska where ice-rich discontinuous permafrost is thawing. Thawing destroys the physical foundation (ice-rich soil) on which boreal forest ecosystems rest causing dramatic changes in the ecosystem. Impacts on the forest depend primarily on the type and amount of ice present in the permafrost and on drainage conditions. At sites generally underlain by ice-rich permafrost, forest ecosystems can be completely destroyed. In the Mentasta Pass area, wet sedge meadows, bogs, thermokarst ponds, and lakes are replacing forests. An upland thermokarst site on the University of Alaska Campus consists of polygonal patterns of troughs and pits caused by thawing ice-wedge polygons....
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We examined the effects of fire disturbance on permafrost degradation and thaw settlement across a series of wildfires (from ~1930 to 2010) in the forested areas of collapse-scar bog complexes in the Tanana Flats lowland of interior Alaska. Field measurements were combined with numerical modeling of soil thermal dynamics to assess the roles of fire severity and climate history in postfire permafrost dynamics. Field-based calculations of potential thaw settlement following the loss of remaining ice-rich permafrost averaged 0.6 m. This subsidence would cause the surface elevations of forests to drop on average 0.1 m below the surface water level of adjacent collapse-scar features. Up to 0.5 m of thaw settlement was...
Most spatial modelling of climate change impacts on permafrost has been conducted at half-degree latitude/longitude or coarser spatial resolution. At such coarse resolution, topographic effects on insolation cannot be considered accurately and the results are not suitable for land-use planning and ecological assessment. Here we mapped climate change impacts on permafrost from 1968 to 2100 at 10m resolution using a process-based model for Ivvavik National Park, an Arctic region with complex terrain in northern Yukon, Canada. Soil and drainage conditions were defined based on ecosystem types, which were mapped using SPOT imagery. Leaf area indices were mapped using Landsat imagery and the ecosystem map. Climate distribution...
Thermokarst processes characterize a variety of ice-rich permafrost terrains and often lead to lake formation. The long-term evolution of thermokarst landscapes and the stability and longevity of lakes depend upon climate, vegetation and ground conditions, including the volume of excess ground ice and its distribution. The current lake status of thermokarst-lake landscapes and their future trajectories under climate warming are better understood in the light of their long-term development. We studied lake-rich southern marginal upland of the Yukon Flats (northern interior Alaska) using dated lake-sediment cores, observations of river-cut exposures, and remotely-sensed data. The region features thick (up to 40 m)...
Caribou Poker Creeks Research Watershed is a boreal forest watershed in Interior Alaska that is susceptible to regional warming and permafrost thaw. We measured seasonal foliar N concentrations of the black spruce understory shrubs, Vaccinium uliginosum L., Vaccinium vitis-idaea L., and Ledum palustre L. on north- and south-facing sides of the watershed. We predicted that the shrubs would respond to small-scale changes in active layer and soil climate, and we expected similar responses according to growth strategy (evergreen or deciduous). Overall, foliar N in shrubs was higher on warmer, drier soils with deep active layers: +7.9% N in V. uliginosum, +11.1% N in V. vitis-idaea, and +9.4% N in L. palustre. Each shrub...
ABSTRACT: Wetlands exist in a transition zone between aquatic and terrestrial environments which can be altered by subtle changes in hydrology. Twentieth century climate records show that the United States is generally experiencing a trend towards a wetter, warmer climate; some climate models suggest that this trend will continue and possibly intensify over the next 100 years. Wetlands that are most likely to be affected by these and other potential changes (e.g., sea-level rise) associated with atmospheric carbon enrichment include permafrost wetlands, coastal and estuanne wetlands, peat lands, alpine wetlands, and prairie pothole wetlands. Potential impacts range from changes in community structure to changes...
In this study carbon dioxide and methane fluxes were measured in three dominant vegetational communities in a taiga peatland located within the zone of discontinuous permafrost in the Alaskan interior. Trace gas (CO2 and CH4 ) flux measurements were made across spatial scales from excised roots to in situ peatland ecosystems. Temperatures increases and local water tables decreases from 1991 to 1993 affected methane emission two sites. Mid season methane emissions in the tussock meadow was fairly constant, ranging from 56.3 ± 29.8 mg CH4 /m2 /day in 1991 to 62.3 ± 37.2 mg CH 4 /m2 /day in 1993. Emissions dropped in the drier dwarf spruce scrub from 12.2 ± 8.1 mg CH4 /m2 /day in 1991 to zero in 1993. In the floating...
Machine-learning regression tree models were used to extrapolate airborne electromagnetic resistivity data collected along flight lines in the Yukon Flats Ecoregion, central Alaska, for regional mapping of permafrost. This method of extrapolation (r?=?0.86) used subsurface resistivity, Landsat Thematic Mapper (TM) at-sensor reflectance, thermal, TM-derived spectral indices, digital elevation models and other relevant spatial data to estimate near-surface (0?2.6-m depth) resistivity at 30-m resolution. A piecewise regression model (r?=?0.82) and a presence/absence decision tree classification (accuracy of 87%) were used to estimate active-layer thickness (ALT) (< 101?cm) and the probability of near-surface (up to...
Boreal soils in permafrost regions contain vast quantities of frozen organic material that is released to terrestrial and aquatic environments via subsurface flow paths as permafrost thaws. Longer flow paths may allow chemical reduction of solutes, nutrients, and contaminants, with implications for greenhouse gas emissions and aqueous export. Predicting boreal catchment runoff is complicated by soil heterogeneities related to variability in active layer thickness, soil type, fire history, and preferential flow potential. By coupling measurements of permeability, infiltration potential, and water chemistry with a stream chemistry end-member mixing model, we tested the hypothesis that organic soils and burned slopes...
Issue Title: Hydrogeology of Cold Regions In cold regions, hydrologic systems possess seasonal and perennial ice-free zones (taliks) within areas of permafrost that control and are enhanced by groundwater flow. Simulation of talik development that follows lake formation in watersheds modeled after those in the Yukon Flats of interior Alaska (USA) provides insight on the coupled interaction between groundwater flow and ice distribution. The SUTRA groundwater simulator with freeze-thaw physics is used to examine the effect of climate, lake size, and lake-groundwater relations on talik formation. Considering a range of these factors, simulated times for a through-going sub-lake talik to form through 90 m of permafrost...
While much of the dissolved organic carbon (DOC) within rivers is destined for mineralization to CO2, a substantial fraction of riverine bicarbonate (HCO3) flux represents a CO2 sink, as a result of weathering processes that sequester CO2 as HCO3. We explored landscape-level controls on DOC and HCO3 flux in subcatchments of the boreal, with a specific focus on the effect of permafrost on riverine dissolved C flux. To do this, we undertook a multivariate analysis that partitioned the variance attributable to known, key regulators of dissolved C flux (runoff, lithology, and vegetation) prior to examining the effect of permafrost, using riverine biogeochemistry data from a suite of subcatchments drawn from the Mackenzie,...
Accurate representations of subsurface flow in hydrologic models of permafrost terrain during spring thaw require an understanding of soil thaw and soil thaw rates. Field data, including daily photographs for snowcover estimation and meteorological measurements, and measurements of soil thaw depth, soil temperature and soil moisture content, were acquired on an organic-covered hillslope in Granger Basin, Yukon Territory, to quantify relationships between net radiation and soil thaw energy. The infiltration and freezing of meltwater into the soil likely contributes to pre-thaw warming. When this energy (1.82 MJ m super(-2)d super(-1)) is taken into consideration, the daily mean contribution to soil thaw from net...
map background search result map search result map Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests SPATIAL AND THERMAL CHARACTERISTICS OF MOUNTAIN PERMAFROST, NORTHWEST CANADA Multi-decadal degradation and persistence of permafrost in the Alaska Highway corridor, northwest Canada Observations of Thermokarst and Its Impact on Boreal Forests in Alaska, U.S.A Methane exchange in a poorly-drained black spruce forest over permafrost observed using the eddy covariance technique Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests Methane exchange in a poorly-drained black spruce forest over permafrost observed using the eddy covariance technique SPATIAL AND THERMAL CHARACTERISTICS OF MOUNTAIN PERMAFROST, NORTHWEST CANADA Multi-decadal degradation and persistence of permafrost in the Alaska Highway corridor, northwest Canada Observations of Thermokarst and Its Impact on Boreal Forests in Alaska, U.S.A