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Molecular determinants of dissolved organic matter reactivity in lake water
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.ORCID iD: 0000-0002-5884-1684
Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - BMC, Analytical Chemistry.
Carl von Ossietzky Univ Oldenburg, Inst Chem & Biol Marine Environm, Res Grp Marine Geochem MPI Bridging Grp, Oldenburg, Germany. (Research group for Marine Geochemistry)
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.ORCID iD: 0000-0003-3509-8266
2017 (English)In: Frontiers in Earth Science, ISSN 1096-231X, E-ISSN 1664-8021, Vol. 5, article id 106Article in journal (Refereed) Published
Abstract [en]

Lakes in the boreal region have been recognized as the biogeochemical hotspots, yet many questions regarding the regulators of organic matter processing in these systems remain open. Molecular composition can be an important determinant of dissolved organic matter (DOM) fate in freshwater systems, but many aspects of this relationship remain unclear due to the complexity of DOM and its interactions in the natural environment. Here, we combine ultrahigh resolution mass spectrometry (FT-ICR-MS) with kinetic modeling of decay of \textgreater1,300 individual DOM molecular formulae identified by mass spectrometry, to evaluate the role of specific molecular characteristics in decomposition of lake water DOM. Our data is derived from a 4 months microbial decomposition experiment, carried out on water from three Swedish lakes, with the set-up including natural lake water, as well as the lake water pretreated with UV light. The relative decay rate of every molecular formula was estimated by fitting a single exponential model to the change in FT-ICR-MS signal intensities over decomposition time.We found a continuous range of exponential decay coefficients (kexp)within different groups of compounds and show that for highly unsaturated and phenolic compounds the distribution of kexp was shifted toward the lowest values. Contrary to this general trend, plant-derived polyphenols and polycondensed aromatics were on average more reactive than compounds with an intermediate aromaticity. The decay rate of aromatic compounds increased with increasing nominal oxidation state of carbon, and molecular mass in some cases showed an inverse relationship with kexp in the UV-manipulated treatment. Further, we observe an increase in formulae-specific kexp as a result of the UV pretreatment. General trends in reactivity identified among major compound groups emphasize the importance of the intrinsic controllers of lake water DOMdecay. However, we additionally indicate that each compound group contained a wide spectrum of reactivities, suggesting that high resolution is needed to further ascertain the complex reasons behind DOM reactivity in lake water.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2017. Vol. 5, article id 106
Keywords [en]
Dissolved organic matter, FT-ICR-MS, molecular composition, DOM degradation
National Category
Geology
Identifiers
URN: urn:nbn:se:uu:diva-316890DOI: 10.3389/feart.2017.00106ISI: 000419451700001OAI: oai:DiVA.org:uu-316890DiVA, id: diva2:1079254
Funder
Swedish Research Council, 2011-3475-88773-67Knut and Alice Wallenberg Foundation, KAW 2013.0091Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2018-02-20Bibliographically approved
In thesis
1. Dissolved organic matter in lakes: Chemical diversity and continuum of reactivity
Open this publication in new window or tab >>Dissolved organic matter in lakes: Chemical diversity and continuum of reactivity
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Dissolved organic matter (DOM) is the largest pool of organic carbon in aquatic systems and an important component of the global carbon cycle. Large amounts of DOM are decomposed within lakes, resulting in fluxes of CO2 and CH4 to the atmosphere. Therefore, there is a considerable interest in understanding the controls of DOM decomposition in freshwaters. There is evidence that in lakes intrinsic controls related to DOM composition are of primary importance, yet our knowledge about molecular drivers of DOM degradation is limited. This thesis addresses the link between chemical composition and reactivity of lake DOM by applying an experimental approach, molecular-level DOM characterization, and kinetic modeling of DOM decay.

The first study shows that photoinduced transformations and partial removal of colored aromatic components of DOM have profound effects on DOM degradation kinetics, mediated by the shifts in the relative share of rapidly and slowly degrading DOM fractions. Two following studies estimate exponential decay coefficients for each individual molecular formula identified within bulk DOM. A continuous distribution of exponential decay coefficients is found within bulk DOM, which directly corroborates the central and previously empirically untested assumption behind the reactivity continuum model of DOM decay. Further, individual decay rates are evaluated in connection to specific molecular properties. On average, highly unsaturated and phenolic compounds appear to be more persistent than compounds with higher aromatic content (plant polyphenols and polycondensed aromatics), and aliphatic compounds demonstrate the highest decay rates. The reactivity of aromatics additionally increases with increasing nominal oxidation state of carbon. Molecular analysis further indicates that increasing reactivity of DOM after UV exposure is caused by disintegration of supramolecular complexes. Study IV shows that changes in relative proportion of terrestrial versus algal DOM control degradability of DOM through seasons. Under ice, when algal-derived DOM is maximally depleted, DOM degradation potential converges to similarly low levels, regardless of lake type (productive or humic), and bacterial respiration primarily relies on terrestrial carbon. This suggests a general pattern of baseline metabolism across boreal lakes. I conclude that DOM is a dynamic reactivity continuum and a tight link exists between DOM behavior and compositional properties.

Place, publisher, year, edition, pages
uppsala: Acta Universitatis Upsaliensis, 2017. p. 44
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1486
Keywords
dissolved organic matter, DOM, dissolved organic carbon, DOC, PARAFAC, reactivity continuum model, ultrahigh resolution mass spectrometry, FT-ICR-MS, organic matter characterization, decomposition kinetics, baseline metabolism
National Category
Natural Sciences
Research subject
Biology with specialization in Limnology
Identifiers
urn:nbn:se:uu:diva-316893 (URN)978-91-554-9840-5 (ISBN)
Public defence
2017-04-28, Friessalen, EBC, Norbyvägen 14, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-04-07 Created: 2017-03-08 Last updated: 2017-04-21

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