HR: 16:45h
AN: C24A-04    [Abstracts]
TI: Permafrost Thawing and Vegetation Change Alter the Seasonal C Dynamics of an Arctic Tundra Ecosystem
AU: * Vogel, J
EM: jvogel@ufl.edu
AF: University of Florida Botany Dept, 220 Bartram Hall, Gainesville, FL 32611 United States
AU: Schuur, E
EM: tschuur@ufl.edu
AF: University of Florida Botany Dept, 220 Bartram Hall, Gainesville, FL 32611 United States
AU: Dutta, K
EM: kdutta@ufl.edu
AF: University of Florida Botany Dept, 220 Bartram Hall, Gainesville, FL 32611 United States
AU: Lee, H
EM: hannalee@ufl.edu
AF: University of Florida Botany Dept, 220 Bartram Hall, Gainesville, FL 32611 United States
AU: Crummer, G
EM: gracec@ufl.edu
AF: University of Florida Botany Dept, 220 Bartram Hall, Gainesville, FL 32611 United States
AB: Permafrost thawing and thermokarst are likely to increase as the result of arctic warming. As ice-rich permafrost thaws, the ground subsides, creating micro-scale topography and drainage patterns. These changes then create variability in soil moisture, temperature, nutrient availability and vegetation dominance. In moist acidic tundra, we measured gross photosynthesis (GPP), ecosystem respiration (ER), and net ecosystem carbon exchange (NEE, referenced to ecosystem) in 2004 and 2005. Measurements were made with static and automated chambers, both in undisturbed tussock and along a gradient in years-since-thermokarst initiation. Between June 1 and August 30, new and old thermokarst (initiated <20 years and >50 years ago) had significantly greater C uptake (GPP and NEE) (p<0.05) than undisturbed tussock tundra. GPP and NEE were positively correlated to increases in shrub and moss primary production corresponded to greater shrub dominance. This observation supports the hypothesis that arctic C uptake will increase with warming as shrubs replace tussock-forming sedge species. However, new and older thermokarst had a greater ER during the winter than the tussock site and continued releasing C later into the spring season. Both patterns appeared related to the depth of ground subsidence, which resulted in greater winter snow-pack depth and spring soil saturation. The greater snowpack may have insulated the soil during the winter allowing for greater ER, while both a lingering snowpack and saturated conditions inhibited the initiation of spring green-up. Our results corroborate the observation that climate warming and thermokarst generally increase shrub dominance and net C uptake during the growing season. However, our results also suggest that the indirect impacts of thermokarst on winter and spring C respiratory losses can negate the increased C uptake provided by shrubs during the summer growing season.
DE: 0702 Permafrost (0475)
DE: 0708 Thermokarst
DE: 0718 Tundra (9315)
DE: 0793 Biogeochemistry (0412, 0414, 1615, 4805, 4912)
SC: Cryosphere [C]
MN: Fall Meeting 2005