COS 67-3 - Decomposition of dissolved organic carbon across a hillslope chronosequence in the Kuparuk River region, Alaska

Wednesday, August 5, 2009: 2:10 PM
Pecos, Albuquerque Convention Center
Kyle A. Whittinghill , School of Natural Resources & Environment, University of Michigan, Ann Arbor, MI
Jacques C. Finlay , Ecology Evolution and Behavior, University of Minnesota, St. Paul, MN
Sarah E. Hobbie , Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, MN
Background/Question/Methods

A thorough understanding of how landscape heterogeneity affects organic matter processing in arctic soils is necessary to predict how future climate changes will affect arctic carbon cycling. Previous research has shown significant differences in soil organic matter decomposition and dissolved organic carbon production among landscapes of different ages (i.e., time since glaciation) in the Kuparuk River region, Alaska. Significant differences in soil water dissolved organic carbon concentrations have also been observed along hillslope toposequences in the Kuparuk River region. Differences in dissolved organic matter bioavailability across the chronosequence or within hillslopes may drive observed differences in soil respiration rates, dissolved organic carbon production, and soil water dissolved organic carbon concentrations. To test this hypothesis we conducted a long-term incubation of dissolved organic carbon extracted from soils within hillslopes across the chronosequence. We selected three hillslopes within four distinct landscape ages in the region. Within each hillslope we extracted three soil samples (with water) from the organic layer in each of three transects: a) within upslope tussock tundra vegetation, b) along the vegetation boundary between upslope and streamside vegetation, and c) adjacent to the stream.

Results/Conclusions

There were no significant differences in specific UV absorbance of dissolved organic carbon in extracts among either landscape ages or hillslope transects. However, dissolved organic matter fluorescence (fluorescence index) was significantly higher in streamside transects, indicating potential differences in dissolved organic matter composition. Dissolved organic carbon concentrations in soil extracts did not differ among landscape ages, but were significantly lower in streamside transects than upslope transects. Decomposition of dissolved organic carbon after four months was not significantly different among either landscape ages or among transects, suggesting that the bioavailability of dissolved organic carbon may not an important factor leading to differences in organic matter processing between landscape ages or within hillslopes.

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