Title

Photochemical and Microbial Alteration of Dissolved Organic Matter in Temperate Headwater Streams Associated with Different Land Use

Authors

Yuehan Lu, Department of Geological Sciences, University of AlabamaFollow
James E. Bauer, Aquatic Biogeochemistry Laboratory, Department of Evolution, Ecology and Organismal Biology, Ohio State University
Elizabeth A. Canuel, Department of Physical Sciences, Virginia Institute of Marine Sciences
Youhei Yamashita, Faculty of Environmental Earth Science, Hokkaido UniversityFollow
R. M. Chambers, Department of Biology, College of William and Mary, WilliamsburgFollow
Rudolf Jaffe´, Southeast Environmental Research Center and Department of Chemistry and Biochemistry, Florida International University,Follow

Abstract

[1] Photochemical and microbial transformations of DOM were evaluated in headwater streams draining forested and human-modified lands (pasture, cropland, and urban development) by laboratory incubations. Changes in DOC concentrations, DOC isotopic signatures, and DOM fluorescence properties were measured to assess the amounts, sources, ages, and properties of reactive and refractory DOM under the influence of photochemistry and/or bacteria. DOC in streams draining forest-dominated watersheds was more photoreactive than in streams draining mostly human-modified watersheds, possibly due to greater contributions of terrestrial plant-derived DOC and lower amounts of prior light exposure in forested streams. Overall, the percentage of photoreactive DOC in stream waters was best predicted by the relative content of terrestrial fluorophores. The bioreactivity of DOC was similar in forested and human-modified streams, but variations were correlated with temperature and may be further controlled by the diagenetic status of organic matter. Alterations to DOC isotopes and DOM fluorescence properties during photochemical and microbial incubations were similar between forested and human-modified streams and included (1) negligible effects of microbial alteration on DOC isotopes and DOM fluorescence properties, (2) selective removal of ¹³C-depleted and ¹⁴C-enriched DOC under the combined influence of photochemical and microbial processes, and (3) photochemical alteration of DOM resulting in a preferential loss of terrestrial humic fluorescence components relative to microbial fluorescence components. This study provides a unique comparison of DOC reactivity in a regional group of streams draining forested and human-modified watersheds and indicates the importance of land use on the photoreactivity of DOC exported from upstream watersheds.

Comments

©2013. American Geophysical Union. All Rights Reserved

The definitive publisher-authenticated version is available online at http://dx.doi.org/10.1002/jgrg.20048

This material is based upon work supported by the National Science Foundation through the Florida Coastal Everglades Long-Term Ecological Research program under Cooperative Agreements #DBI-0620409 and #DEB-9910514. Any opinions, findings, conclusions, or recommendations expressed in the material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Recommended Citation

Lu, Y., J.E. Bauer, E.A. Canuel, R.M. Chambers, R. Jaffe. 2013. Photochemical and microbial alteration of dissolved organic matter in temperate headwater streams associated with different land use. Journal of Geophysical Research 118(2): 566-580. DOI: 10.1002/jgrg.20048