HR: 1340h
AN: B13C-0233    [Abstracts]
TI: Accumulation and $\delta$$^{13}$C Composition of Soil Carbon Across a Chronosequence of Dune Complexes at Mono Lake, CA
AU: * Aanderud, Z T
EM: ztaanderud@ucdavis.edu
AF: Universtiy of California, Davis, 1 Shields Avenue, Davis, CA 95616 United States
AU: Shuldman, M I
EM: mishuldman@ucdavis.edu
AF: Universtiy of California, Davis, 1 Shields Avenue, Davis, CA 95616 United States
AU: Richards, J H
EM: jhrichards@ucdavis.edu
AF: Universtiy of California, Davis, 1 Shields Avenue, Davis, CA 95616 United States
AB: The amount of C sequestered and its permanence in some deserts could be higher than normally appreciated. Limited soil water availability and slow decomposition rates in desert soils may induce the long-term accumulation of soil organic C and coarse woody litter. We inventoried C in soils along a chronosequence of {\it Sarcobatus vermiculatus} shrub islands and interspaces at the Mono Basin Ecosystem Research Site, CA. Such shrub-island/interspace dune systems are widespread in basin habitats across the Great Basin Desert. We hypothesized that organic C stores would increase across the chronosequence (48, 84, $\sim$300, and 1800-3000 years since exposure by lake recession) and that $\delta$$^{13}$C values of soil organic C (SOC) would become enriched over time due to isotopic fractionation associated with C mineralization of leaf and root litter. C stores quantified in 0-50 cm soils included: SOC, soil inorganic C (SIC; i.e. carbonates removed by 12 M HCl fumigation), and C in partially decomposed woody and fine litter. The youngest dune system contains at least 13.6 Mg C ha$^{-1}$ and the oldest contains at least 37.9 Mg C ha$^{-1}$. Our data suggest slow turnover rates of SOC (C:N ratios $\sim$10) and substantial accumulation of organic C (coarse litter, fine litter, and SOC) in shrub islands across the chronosequence (islands at the youngest site = 8.0 g kg$^{-1}$ and islands at the oldest site = 24.0 g kg$^{-1}$. Large pools of SOC and C in woody debris are potentially protected in this shrub-dominated desert, especially in shrub islands of "old-growth" dune systems. Most of the C in the soil is SIC (94% in youngest dunes to 83% at the oldest dunes). The decrease in SIC proportion as the dune systems age is correlated with a decrease in pH across the chronosequence (10.6 at the youngest site and 9.7 at the oldest site). As dunes age, total soil C isotopic composition shifts from positive $\delta$$^{13}$C values (2.8 to 3.6 $\permil$), indicative inorganic processes, to slightly negative values (-1.2 to -3.7 $\permil$) as a result of organic C accumulation. Contrary to our hypothesis, however, SOC is not enriched in $\delta$$^{13}$C in older dunes. SOC $\delta$$^{13}$C values (-22.3 to -23.7 $\permil$) are similar to leaf litter inputs (-23.8 to -25.0 $\permil$), suggesting a stronger influence by physical weathering of accumulating litter and less influence by microbial C mineralization processes.
DE: 1040 Isotopic composition/chemistry
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting