HR: 08:15h
AN: B41F-02    [Abstracts]
TI: Warming in the Yukon River Basin is Likely to Release Substantial Amounts of Soil Organic Carbon
AU: Juday, G P
EM: g.juday@uaf.edu
AF: University of Alaska, P.O Box 757200, Fairbanks, AK 99775 United States
AU: * Huntington, T G
EM: thunting@usgs.gov
AF: U. S. Geological Survey, 196 Whitten Rd., Augusta, ME 04330 United States
AB: In recent decades the Yukon River Basin (YRB) in northwestern Canada and central Alaska has experienced a substantial warming trend resulting in a variety of geophysical and biological responses. Climatologic measurements consistent with rapid warming in the YRB during the last several decades of the 20th century include surface air temperature (especially daily minima), number of frost-free days, and the number of very warm days. During the 20th century daily maxima in the warm season in the YRB have increased only weakly, and modest autumn cooling occurred. Indirect indicators of warming include shrinkage in lake area, decreases in glacier mass, increased fire frequency and annual area burned, and changes in permafrost thickness and permafrost temperature. Changes in tree growth rates and susceptibility to pests have been related to warming and drying in interior Alaska. Oral histories of Alaska Natives have also revealed many other warming related changes in the YRB. If ongoing warming trends continue there is a concern that large stores of soil organic carbon (SOC) will be at risk for release to the atmosphere through heterotrophic decomposition. Warming tends to accelerate microbial decomposition at a faster rate than net primary productivity. One of the most important effects of warming in the YRB is likely to be its influence on the hydrologic and cryospheric regimes. Warming may be accompanied by soil drying and lowering of the water table in wetlands and lakes exposing more SOC to aerobic decomposition. A substantial portion of the YRB is underlain by permafrost that thaws to a variable depth (active layer) each summer. Increasing the thickness of the active layer exposes more SOC to microbial decomposition. Increasing the burned area results in direct SOC losses by oxidation during the fire and decreases albedo that warms surface soils and increases the thickness of the active layer. Warming and increasing length of the growing season increases seasonal evapotranspiration and results in enhanced soil drying and lowering of the water table. Warming decreases tree growth rates on many sites, triggers insect defoliation, and causes widespread fires which all decrease aboveground organic inputs to soils. Warmer and drier conditions are likely to result in a reduction in the area of black spruce that would likrly act to reduce future fire frequency. Changes in forest species composition towards assemblages adapted to a warmer and drier climate and the possible introduction of earthworms could result in losses of SOC.
DE: 3322 Land/atmosphere interactions (1218, 1631, 1843)
DE: 4808 Chemical tracers
SC: Biogeosciences [B]
MN: Fall Meeting 2005