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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2016-263
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
https://doi.org/10.5194/bg-2016-263
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Submitted as: research article 30 Jun 2016

Submitted as: research article | 30 Jun 2016

Review status
This discussion paper is a preprint. It has been under review for the journal Biogeosciences (BG). The revised manuscript was not accepted.

Seasonal variability of dissolved organic matter in the Columbia River: In situ sensors elucidate biogeochemical and molecular analyses

Urban Johannes Wünsch1,2, Boris Peter Koch2,1, Matthias Witt3, and Joseph Andrew Needoba4 Urban Johannes Wünsch et al.
  • 1University of Applied Sciences Bremerhaven, An der Karlstadt 8, D-27568 Bremerhaven, Germany
  • 2Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, Am Handelshafen 12, D-27570 Bremerhaven, Germany
  • 3Bruker Daltonik GmbH, Fahrenheitstraße 4, D-28359 Bremen, Germany
  • 4Oregon Health and Science University Institute of Environmental Health, 3181 Southwest Sam Jackson Park Road, Portland, Oregon 97239-3098, United States of America

Abstract. The in situ detection of fluorescent dissolved organic matter (FDOM) at high temporal resolution is a powerful proxy to follow dissolved organic matter (DOM) dynamics and DOM flux to coastal oceans when FDOM measurements and dissolved organic carbon (DOC) are highly correlated. Here, we investigated the relationship between FDOM sensors and DOC concentration in the lower Columbia River, USA in spring and summer 2013. Furthermore, we studied the seasonal variability of FDOM and chromophoric DOM (CDOM) optical indices, as well as the seasonal and spatial variability for the molecular characteristics of DOM using ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The fieldwork was conducted concurrently with the operation of in situ sensor platforms that recorded physical and biogeochemical data at hourly intervals. In situ FDOM and DOC concentration was highly correlated and the relationship was used to quantify the river's DOC flux between March and August 2013. The average flux was 0.93 Gg d−1, which included over three-fold temporal variability (0.45 to 1.62 Gg d−1) associated with seasonal biogeochemical variability. Spectrofluorometry measurements demonstrated that FDOM parameters correlated with major seasonal biogeochemical shifts in the river associated with phytoplankton blooms and river discharge and thus revealed predictable seasonal patterns in DOM quality. FT-ICR-MS analyses elucidated these shifts on the molecular level: the relative abundance of 561 formulas, most of which contained N and S, correlated significantly with chlorophyll a, while 417 formulas (mostly CHO) correlated with CDOM absorbance at 254 nm.

Urban Johannes Wünsch et al.
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Interactive discussion
Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Urban Johannes Wünsch et al.
Urban Johannes Wünsch et al.
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Short summary
We used a combination of continuously measuring water chemistry sensors and periodic sampling efforts to assess the seasonal variability of dissolved organic matter (DOM) in the Columbia River in spring and summer 2013. We found that our sensors can provide detailed data on carbon export that far exceed usual monitoring efforts. The detailed data help to understand the impact of short-lived events, such as rainstorms, on the overall terrestrial carbon flux in the Columbia River.
We used a combination of continuously measuring water chemistry sensors and periodic sampling...
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