HR: 0800h
AN: B41B-0182    [Abstracts]
TI: Soluble Organic Carbon In Size Fractionated Arctic Tundra Soils, Alaska
AU: * Xu, C
EM: ftcx@uaf.edu
AF: Chunhao Xu, School of Natural Resources and Agriculture Sciences, University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AU: Dou, F
EM: fdou@iarc.uaf.edu
AF: Fugen Dou, Laodong Guo, International Arctic Research center, University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AU: Guo, L
EM: guoiarc.uaf.edu
AF: Fugen Dou, Laodong Guo, International Arctic Research center, University of Alaska Fairbanks, Fairbanks, AK 99775 United States
AU: Ping, C
EM: pfclp@uaa.alaska.edu
AF: Chien-Lu Ping, Palmer Research Center, University of Alaska Fairbanks, Palmer, AK 99645 United States
AB: Mounting evidence suggests an amplified warming in the Arctic region, resulting in the thawing of permafrost and releasing of soil organic carbon into the aquatic system. However, the transport mechanisms and the biogeochemical fate of tundra soil organic carbon in aquatic environments remain poorly understood. Recent studies indicate a second layer of organic matter often accumulated in the lower active layer and upper permafrost in Arctic tundra soils due to cryoturbation. Soil samples from the upper permafrost of two major types of tundra soils, acidic and non-acidic, were collected from Arctic Alaska and characterized for particle size distribution, organic C and total N contents, and stable isotope (13C, 15N) compositions. DOC production potential of these soils, including bulk and size fractionated samples, were evaluated under different leaching time, temperature, soil to water ratio, and microbial degradation conditions. Within the bulk soluble organic pool, high molecular weight (> 3 kDa) and low molecular weight (<3 kDa) DOC species were further quantified using ultrafiltration methods. DOC production from the acidic tundra soils (2.6% of TOC) was significantly (p<0.05) higher than that from nonacidic tundra soils (1.8%), indicating that vegetation cover type controls DOC export. The different vegetation cover types also result in the difference of 13C abundance, with 0.8‰ higher in acidic soils. Carbon stores associated with the particle size fractions follow the order of 53-250 mu m > 250-2000 mu m > less than 53 mu m. DOC released from bulk acidic soils contain 65.6% of high molecular weight DOC and 34.4% of low molecular weight DOC, while 45.7% and 54.3% respectively in nonacidic soil DOC. In acidic soils, the largest (250-2000 mu m) and the finest (<53 mu m) fractions contribute the highest percentage of TOC to DOC pools, while in nonacidic tundra soil each particle size fraction contributed equally around 2% of TOC to the DOC pools. Although the 53-250 mu m size fraction contains 30-74% of organic carbon in both acidic and nonacidic tundra soils, it produced the least amount of water soluble organic matter. Acidic tundra soils have higher potential for DOC to be released to aquatic systems than nonacidic tundra soils under a warming climate.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 4806 Carbon cycling (0428)
DE: 4870 Stable isotopes (0454, 1041)
SC: Biogeosciences [B]
MN: Fall Meeting 2005