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Following the community and ecosystem consequences of labile DOM transformations in aquatic ecosystems

Adam Wymore1, Jane Marks2, Stuart Grandy1, Bill McDowell1
1 University of New Hampshire
2 Northern Arizona University

O 7.8 in Controls of dissolved organic matter fluxes in ecosystems

14.07.2014, 16:15-16:35, H19

The optical properties of stream water are often used to assess the composition, origins and ecosystem functionality of dissolved organic matter (DOM). However, what is assessed in bulk water samples is typically a largely recalcitrant and biologically unavailable DOM pool that likely represents the end product of a series of microbial transformations. Conclusions derived from structure-function relationships of this surface water DOM are valuable in interpreting the role of this residual DOC, but may not provide insights that are applicable to the DOM that originally enters streams. Here we present results from a series of laboratory-based studies that follow the processing of a labile yet complex DOM source (i.e. leaf litter) as it enters stream water and becomes part of the larger ambient DOM pool. We show that the standard set of rules governing DOM structure-function relationships is not applicable to all DOM types and does not predict well how microbial communities respond. To follow these transformations we take advantage of high-throughput pyrosequencing to describe initial changes in the microbial community, gas chromatography to measure rates of respiration and denitrification, and fluorescence and absorbance spectroscopy in concert with pyrolysis GC-MS to describe changes in the optical properties and chemistry of DOM as it is processed. Results indicate that the optical properties and bioavailability of unprocessed DOM differ from both ambient stream water and soil samples, and that the microbial response to labile DOM likely plays a fundamental role in determining the composition of ambient stream water DOM.



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last modified 2014-04-08