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Syngenetic permafrost forms when alluvial, aeolian and/or colluvial sediment accumulates under cold-climate conditions. Observations from within the CRREL permafrost tunnel near Fairbanks, Alaska, indicate that layered, lenticular-layered and micro-lenticular cryogenic structures are characteristic of this type of permafrost. In contrast, reticulate cryogenic structures indicate local thaw modification. During the growth of syngenetic permafrost, episodes of thermokarst erosion may operate preferentially along ice wedges leading to the development of gullies and tunnels in the near-surface sediments. The local thaw unconformities that result are inferred by the recognition of thermokarst-cave ice (pool ice), and...
To accurately represent subsurface flow in a hydrologic model of permafrost terrain during spring thaw, an understanding of soil thaw and soil thaw rates is required. Research was conducted on an organic-covered hillslope in Granger Basin, Yukon Territory, to quantify relationships between net radiation, snowmelt and soil thaw energy. The infiltration and freezing of meltwater into the soil may contribute to pre-thaw warming. When this energy (1.82 MJ·m -2 ·d-1 ) is taken into account, the daily mean contribution to soil thaw from net radiation is approximately 9%. Measured and estimated soil thaw depths compared well (R2 = 0.75) when energy was distributed across the hillslope. This research contributes to the...
This paper presents the results of field studies, which were initiated to study the variability of snowmelt infiltration to frozen soil. The overall objective of the study is to develop a practical method of transferring point source infiltration to a hillslope scale. Previous work has led to the development of a parametric relationship which provides a means of estimating point source infiltration rates to frozen soil using field obtainable data (Zhao and Gray, 1999). Preliminary work has been carried to field test the developed relationship within variable settings in the boreal forest ecoregion of southern Yukon, Canada. Tested sites include a variety of vegetation types and associated canopy coverages. Hydrometeorological...
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Positive and negative species interactions are important factors in structuring vegetation communities. Studies in many ecosystems have focussed on competition; however, facilitation has often been found to outweigh competition under harsh environmental conditions. The balance between positive and negative species interactions is known to shift along spatial, temporal and environmental gradients and thus is likely to be affected by climate change. Winter temperature and precipitation patterns in Interior Alaska are rapidly changing and could lead to warmer winters with a shallow, early melting snow cover in the near future. We conducted snow manipulation and neighbour removal experiments to test whether the relative...
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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...
Spatial patterns in carbon (C) and nitrogen (N) cycles of high-latitude catchments have been linked to climate and permafrost, and used to infer potential changes in biogeochemical cycles under climate warming. However, inconsistent spatial patterns across regions indicate that factors in addition to permafrost and regional climate may shape responses of C and N cycles to climate change. We hypothesized that physical attributes of catchments modify responses of C and N cycles to climate and permafrost. We measured dissolved organic C (DOC) and nitrate (NO3–) concentrations, and composition of dissolved organic matter (DOM) in 21 streams spanning boreal to arctic Alaska, and assessed permafrost, topography, and attributes...
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Black spruce (Picea mariana) forests represent the dominant vegetation type throughout the North American and Siberian taiga and are generally considered to be pristine, N-limiting environments. The aim of this study was to investigate the fundamental underlying mechanisms which control N availability in these soils with particular reference to the dynamics of dissolved organic nitrogen (DON). Our results showed that in these highly organic and low pH soils, soluble N is dominated by organic forms with correspondingly low concentrations of ammonium and nitrate. Amino acids, which are known to be directly taken up by plants growing in these soils, were calculated to constitute 10–20% of the total DON pool. The microbial...
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The data from nine permafrost thermal monitoring sites at widely separated locations across northern Canada were examined individually, spatially, and temporally. Three sites are in Nunavut (Alert, Iqaluit, and Baker Lake), two in the Northwest Territories (Table Mountain and Wrigley), and four in the Yukon Territory (Wolf Creek, Sixty Mile, Alpine Burwash, and Red Creek). The sites have between one and five boreholes that are instrumented to between 3 and 60 m with records of varying durations. Most of the boreholes are co-located with weather stations recording air temperatures and snow depths. A comprehensive analysis of each site is presented assessing the relations between climate and permafrost temperatures,...
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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...
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Boreal forests contain significant quantities of soil carbon that may be oxidized to CO2 given future increases in climate warming and wildfire behavior. At the ecosystem scale, decomposition and heterotrophic respiration are strongly controlled by temperature and moisture, but we questioned whether changes in microbial biomass, activity, or community structure induced by fire might also affect these processes. We particularly wanted to understand whether postfire reductions in microbial biomass could affect rates of decomposition. Additionally, we compared the short-term effects of wildfire to the long-term effects of climate warming and permafrost decline. We compared soil microbial communities between control...
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To determine the influence of fire and thermokarst in a boreal landscape, we investigated peat cores within and adjacent to a permafrost collapse feature on the Tanana River Floodplain of Interior Alaska. Radioisotope dating, diatom assemblages, plant macrofossils, charcoal fragments, and carbon and nitrogen content of the peat profile indicate ~600 years of vegetation succession with a transition from a terrestrial forest to a sedge-dominated wetland over 100 years ago, and to a Sphagnum-dominated peatland in approximately 1970. The shift from sedge to Sphagnum, and a decrease in the detrended tree-ring width index of black spruce trees adjacent to the collapse coincided with an increase in the growing season temperature...
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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...
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This paper is the first to provide chemical, physical, and morphological properties of the soils in the boreal region of Alaska and to demonstrate the dominant effect of landscape attributes in soil formation. This study was conducted to characterize soils and landscape relationships in the boreal forest of Alaska. Sites representing major landform positions and vegetation communities were selected for study. Well-drained, shallow to moderately deep Inceptisols occur on the drier and warmer south aspect slopes with thin (5-9 cm) organic horizons and loamy textures. Poorly drained Gelisols form on wet and cold north aspect slopes and valley floors with thick (18-52 cm) organic horizons and permafrost within 45 to...
map background search result map search result map Extending Airborne Electromagnetic Surveys for Regional Active Layer and Permafrost Mapping with Remote Sensing and Ancillary Data, Yukon Flats Ecoregion, Central Alaska Advanced snowmelt causes shift towards positive neighbour interactions in a subarctic tundra community Cryostratigraphic record of permafrost degradation and recovery following historic (1898-1992) surface disturbances in the Klondike region, central Yukon Territory. Spatial and temporal variability in permafrost conditions, northern Canada Carbon cycle dynamics in a taiga peatland Impacts of climate, lake size, and supra- and sub-permafrost groundwater flow on lake-talik evolution, Yukon Flats, Alaska (USA) Effects of permafrost melting on CO (sub 2) and CH (sub 4) exchange of a poorly drained black spruce lowland A spatially explicit analysis to extrapolate carbon fluxes in upland tundra where permafrost is thawing Wetland succession in a permafrost collapse: interactions between fire and thermokarst Soil amino acid turnover dominates the nitrogen flux in permafrost-dominated taiga forest soils The role of permafrost in water exchange of a black spruce forest in Interior Alaska Soil Catena Sequences and Fire Ecology in the Boreal Forest of Alaska Interactive effects of wildfire and permafrost on microbial communities and soil processes in an Alaskan black spruce forest Landscape Effects of Wildfire on Permafrost Distribution in Interior Alaska Derived from Remote Sensing Effects of permafrost melting on CO (sub 2) and CH (sub 4) exchange of a poorly drained black spruce lowland Wetland succession in a permafrost collapse: interactions between fire and thermokarst A spatially explicit analysis to extrapolate carbon fluxes in upland tundra where permafrost is thawing Soil Catena Sequences and Fire Ecology in the Boreal Forest of Alaska Interactive effects of wildfire and permafrost on microbial communities and soil processes in an Alaskan black spruce forest The role of permafrost in water exchange of a black spruce forest in Interior Alaska Carbon cycle dynamics in a taiga peatland Soil amino acid turnover dominates the nitrogen flux in permafrost-dominated taiga forest soils Landscape Effects of Wildfire on Permafrost Distribution in Interior Alaska Derived from Remote Sensing Extending Airborne Electromagnetic Surveys for Regional Active Layer and Permafrost Mapping with Remote Sensing and Ancillary Data, Yukon Flats Ecoregion, Central Alaska Impacts of climate, lake size, and supra- and sub-permafrost groundwater flow on lake-talik evolution, Yukon Flats, Alaska (USA) Cryostratigraphic record of permafrost degradation and recovery following historic (1898-1992) surface disturbances in the Klondike region, central Yukon Territory. Spatial and temporal variability in permafrost conditions, northern Canada Advanced snowmelt causes shift towards positive neighbour interactions in a subarctic tundra community