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    Widespread capacity for denitrification in soils, streams, and thermokarst lakes of boreal Alaska

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    Author
    Burnett, Melanie S.
    Chair
    Harms, Tamara K.
    Committee
    Ruess, Roger W.
    Walter Anthony, Katey M.
    Keyword
    Dentrification
    Interior Alaska
    Soils
    Soil nitrogen content
    Lakes
    Lake nitrogen content
    Forest soils
    Taiga ecology
    Permafrost forest ecology
    Permafrost ecosystems
    Permafrost forests
    Nitrogen
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    URI
    http://hdl.handle.net/11122/12543
    Abstract
    Rapid warming in Alaska is causing permafrost to thaw, especially in the region of discontinuous permafrost, where soil temperatures may only be a few degrees below 0 °C. An intensifying fire regime may also be exacerbating permafrost thaw with more frequent and severe fires removing insulating organic layers above permafrost. Permafrost thaw releases carbon and nitrogen (N) into the actively cycling pools, and whereas carbon emissions following permafrost thaw are well documented, the fates of N remain unclear. Denitrification and release of nitrous oxide (N₂O) or nitrogen gas (N₂) could result in N loss from ecosystems, but the contributions of these processes to the high-latitude N cycle remain uncertain. I quantified microbial capacity for denitrification and nitrous oxide production in boreal soils, lakes, and streams, and assessed correlates of denitrifying enzyme activity in interior Alaska to determine if denitrification could contribute significantly to N loss from the boreal forest. Across all landscape positions, median potential denitrification rate under anoxic conditions with nitrate and organic carbon amendment was 4.15 [mu]g N₂O-N /kg dry soil*h (range -6.39 to 479.94). Denitrification potential was highest within and along streams in both sediments and adjacent riparian soils, upland soils were intermediate, and lakes supported lower rates, whereas deep permafrost soils supported little denitrification. Time since last burn had no effect on denitrification potential in upland soils. Across all landscape positions, denitrification potential was negatively correlated with ammonium pools. In lakes, potential rate of denitrification declined with sediment depth, and was positively driven by organic matter content. In this era of anthropogenic climate change, pervasive N loss to denitrification in the boreal forest could constrain the capacity for N-limited primary producers to preserve carbon stocks in soils following permafrost thaw.
    Description
    Thesis (M.S.) University of Alaska Fairbanks, 2021
    Table of Contents
    General introduction -- Chapter 1: Widespread capacity for denitrification in soils, streams, and thermokarst lakes of boreal Alaska -- General conclusions.
    Date
    2021-05
    Type
    Thesis
    Collections
    New theses and dissertations

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