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Identification of dissolved organic matter size components in freshwater and marine environments

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  • Eero Asmala, University of Helsinki
  • ,
  • Philippe Massicotte, Takuvik Joint International Laboratory / UMI 3376, Université Laval
  • ,
  • Jacob Carstensen

Dissolved organic matter (DOM) in the transition zone from freshwater to marine systems was analyzed with a new approach for parameterizing the size distribution of organic compounds. We used size-exclusion chromatography for molecular size analysis and quantified colored DOM (CDOM) on samples from two coastal environments in the Baltic Sea (Roskilde Fjord, Denmark and Gulf of Gdansk, Poland). We applied a Gaussian decomposition method to identify peaks from the chromatograms, providing information beyond bulk size properties. This approach complements methods where DOM is separated into size classes with pre-defined filtering cutoffs, or methods where chromatograms are used only to infer average molecular weight. With this decomposition method, we extracted between three and five peaks from each chromatogram and clustered these into three size groups. To test the applicability of our method, we linked our decomposed peaks with salinity, a major environmental driver in the freshwater-marine continuum. Our results show that when moving from freshwater to low-salinity coastal waters, the observed steep decrease of apparent molecular weight is mostly due to loss of the high-molecular-weight fraction (HMW; >2 kDa) of CDOM. Furthermore, most of the CDOM absorbance in freshwater originates from HMW DOM, whereas the absorbing moieties are more equally distributed along the smaller size range (< 2 kDa) in marine samples.

TidsskriftLimnology and Oceanography
Sider (fra-til)1381-1393
Antal sider13
StatusUdgivet - apr. 2021

Bibliografisk note

Funding Information:
We are grateful for Lumi Haraguchi from Finnish Environment Institute, and Berit Langkilde Møller and Janus Larsen from Aarhus University for their assistance in the lab and in the field. We would like to thank Colin Stedmon from DTU Aqua for the DOC analysis, and the captain and crew of the R/V Alkor. EA and JC were supported by the BONUS COCOA project (grant agreement 2112932‐1), funded jointly by the EU and Danish Research Council. EA was also supported by the Academy of Finland (Grant No. 309748).

Publisher Copyright:
© 2021 The Authors. Limnology and Oceanography published by Wiley Periodicals LLC. on behalf of Association for the Sciences of Limnology and Oceanography.

Copyright 2021 Elsevier B.V., All rights reserved.

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