University of Oulu

Tomco PL, Zulueta RC, Miller LC, Zito PA, Campbell RW, Welker JM (2019) DOC export is exceeded by C fixation in May Creek: A late-successional watershed of the Copper River Basin, Alaska. PLoS ONE 14(11): e0225271.

DOC export is exceeded by C fixation in May Creek : a late-successional watershed of the Copper River Basin, Alaska

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Author: Tomco, Patrick L.1; Zulueta, Rommel C.2; Miller, Leland C.3;
Organizations: 1Department of Chemistry, University of Alaska Anchorage, Anchorage, Alaska, United States of America
2National Ecological Observatory Network, Inc., Boulder, Colorado, United States of America
3Department of Biological Sciences, University of Alaska Anchorage, Anchorage, Alaska, United States of America
4Department of Chemistry, University of New Orleans, New Orleans, Louisiana, United States of America
5Prince William Sound Science Center, Cordova, Alaska, United States of America
6Ecology and Genetics Research Unit, University of Oulu, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.1 MB)
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Language: English
Published: Public Library of Science, 2019
Publish Date: 2020-03-31


Understanding the entirety of basin-scale C cycling (DOC fluxes and CO₂ exchanges) are central to a holistic perspective of boreal forest biogeochemistry today. Shifts in the timing and magnitude of dissolved organic carbon (DOC) delivery in streams and eventually into oceans can be expected, while simultaneously CO₂ emission may exceed CO₂ fixation, leading to forests becoming stronger CO₂ sources than sinks amplifying rising trace gases in the atmosphere. At May Creek, a representative late-successional boreal forest watershed at the headwaters of the Copper River Basin, Alaska, we quantified the seasonality of DOC flux and landscape-scale CO₂ exchange (eddy covariance) over two seasonal cycles. We deployed in situ fDOM and conductivity sensors, performed campaign sampling for water quality (DOC and water isotopes), and used fluorescence spectroscopy to ascertain DOC character. Simultaneously, we quantified net CO₂ exchange using a 100 ft eddy covariance tower. Results indicate DOC exports were pulse-driven and mediated by precipitation events. Both frequency and magnitude of pulse-driven DOC events diminished as the seasonal thaw depth deepened, with inputs from terrestrial sources becoming major contributors to the DOC pool with decreasing snowmelt contribution to the hydrograph. A three-component parallel factorial analysis (PARAFAC) model indicated DOC liberated in late-season may be bioavailable (tyrosine-like). Combining Net Ecosystem Exchange (NEE) measurements indicate that the May Creek watershed fixes 142–220 g C m-2 yr-1 and only 0.40–0.57 g C m-2 yr-1 is leached out as DOC. Thus, the May Creek watershed and similar mature spruce forest dominated watersheds in the Copper River Basin are currently large ecosystem C sinks and exceeding C conservative. An understanding of DOC fluxes from Gulf of Alaska watersheds is important for characterizing future climate change-induced seasonal shifts.

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Series: PLoS one
ISSN: 1932-6203
ISSN-E: 1932-6203
ISSN-L: 1932-6203
Volume: 14
Issue: 11
Article number: e0225271
DOI: 10.1371/journal.pone.0225271
Type of Publication: A1 Journal article – refereed
Field of Science: 1172 Environmental sciences
Funding: Funding for this project was provided to RC and JW by NASA (grant# NNX10AU07G). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Copyright information: © 2019 Tomco et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.