HR: 0800h
AN: B11A-1019    [Abstracts]
TI: Isotopic characterization of carbon dioxide flux and DOC along a moisture gradient at Bonanza Creek LTER, Alaska
AU: * Pruett, L E
EM: lpruett@usgs.gov
AF: USGS, 345 Middlefield Road MS 962, Menlo Park, CA 94025 United States
AU: Harden, J W
EM: jharden@usgs.gov
AF: USGS, 345 Middlefield Road MS 962, Menlo Park, CA 94025 United States
AU: Waldrop, M P
EM: mwaldrop@usgs.gov
AF: USGS, 345 Middlefield Road MS 962, Menlo Park, CA 94025 United States
AU: Doctor, D H
EM: ddoctor@usgs.gov
AF: USGS, 345 Middlefield Road MS 962, Menlo Park, CA 94025 United States
AU: Turetsky, M R
EM: mrt@msu.edu
AF: Department of Plant Biology, Michigan State University, East Lansing, MI 48824 United States
AB: Boreal forests contain 25-30% of global soil carbon. High latitude regions of the world have undergone warming over the past 100 years, a trend that is expected to continue. This temperature increase is often accompanied by a decrease in precipitation over the summer months. Soil organic matter (SOM) decomposition rates are highly dependent on soil temperature and moisture and will therefore increase with increasing temperature and either decrease or increase with decreasing moisture. Accelerated OM decomposition triggered by a warming climate may potentially release large stores of carbon, making carbon cycling studies in the boreal forest crucial to understanding the impact of climate change. Alaskan landscapes are composed of many different vegetative and soil types. In order to better understand the effect that climate change may have on boreal ecosystems, a natural moisture gradient was monitored for soil physical characteristics. Five sampling stations were established along the gradient at areas with distinctive vegetation types, which likely reflect many of the landscapes in Alaska. Their characterization is important for assessing landscape scale carbon cycling dynamics. This gradient, at the Bonanza Creek LTER, has water table depths ranging from 0 to 64 cm below the soil surface. In a month long laboratory incubation, we measured CO₂ and DOC flux from soil samples (0-5 cm) collected in August 2004. At 0 and 26 days, we collected gas samples for isotope analysis. In an effort to better understand differences in the carbon quality and source of these samples, we examined δ¹³C and Δ¹⁴C of respired CO₂, dissolved organic carbon (DOC) leached from these samples, and δ¹³C of the DOC. Δ¹⁴C_CO2 values ranged from 61.7 to 148.8 ‰ two days after sampling and 64 to 185.6 ‰ after 26 days. The initial δ¹³C_CO2 values range from -28.1 to -22.3 ‰. After 26 days, the values ranged from -28.4 to -23.8 ‰. Isotope ratios of respired CO₂ were different among ecosystems, but were not related to soil moisture. In all cases, respired CO₂ became depleted over the course of the incubation. These CO₂ isotopic values likely reflect the unique combination of carbon sources at each of the stations along with decomposition and the root senescence which occurred after sampling. δ¹³C and Specific Ultraviolet Absorbance (SUVA) of the DOC were negatively linearly related, indicating that δ¹³C_DOC may be an indicator of carbon quality. Isotopic trends and correlations will be discussed, along with implications for a landscape manipulation experiment (Alaska Peatland Experiment (APEX)) initiated this year at the site.
DE: 0428 Carbon cycling (4806)
DE: 0429 Climate dynamics (1620)
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0486 Soils/pedology (1865)
SC: Biogeosciences [B]
MN: Fall Meeting 2005