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Dissolved organic matter in lakes: Chemical diversity and continuum of reactivity
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Limnology.ORCID iD: 0000-0002-5884-1684
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. , 44 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1486
Keyword [en]
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: urn:nbn:se:uu:diva-316893ISBN: 978-91-554-9840-5 (print)OAI: oai:DiVA.org:uu-316893DiVA: diva2:1079256
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
List of papers
1. Effects of compositional changes on reactivity continuum and decomposition kinetics of lake dissolved organic matter
Open this publication in new window or tab >>Effects of compositional changes on reactivity continuum and decomposition kinetics of lake dissolved organic matter
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2016 (English)In: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 121, no 7, 1733-1746 p.Article in journal (Refereed) Published
Abstract [en]

To address the link between the composition and decomposition of freshwater dissolved organic matter (DOM), we manipulated the DOM from three boreal lakes using preincubations with UV light to cleave large aromatic molecules and polyvinylpyrrolidone (PVP) to remove colored phenolic compounds. Subsequently, we monitored the dissolved organic carbon (DOC) loss over 4months of microbial degradation in the dark to assess how compositional changes in DOM affected different aspects of the reactivity continuum, including the distribution of the apparent decay coefficients. We observed profound effects on decomposition kinetics, with pronounced shifts in the relative share of rapidly and more slowly decomposing fractions of the DOM. In the UV-exposed treatment initial apparent decay coefficient k(0) was almost threefold higher than in the control. Significantly higher relative DOC loss in the UV-exposed treatment was sustained for 2months of incubation, after which decay coefficients converged with those in the control. The PVP removed compounds with absorbance and fluorescence characteristics representative of aromatic compounds, which led to slower decomposition, compared to that in the control. Our results demonstrate the reactivity continuum underlying the decomposition of DOM in freshwaters and highlight the importance of intrinsic properties of DOM in determining its decomposition kinetics.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-304303 (URN)10.1002/2016JG003359 (DOI)000382581900002 ()
Funder
Swedish Research Council, 2011-3475-88773-67Knut and Alice Wallenberg Foundation
Available from: 2016-10-04 Created: 2016-10-04 Last updated: 2017-03-08Bibliographically approved
2. The emergence of the reactivity continuum of organic matter from kinetics of a multitude of individual molecular constituents
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(English)Manuscript (preprint) (Other academic)
Keyword
dissolved organic matter, reactivity continuum model, FT-ICR-MS
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-316887 (URN)
Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2017-03-08
3. Molecular determinants of dissolved organic matter reactivity in lake water
Open this publication in new window or tab >>Molecular determinants of dissolved organic matter reactivity in lake water
(English)Manuscript (preprint) (Other academic)
Keyword
Dissolved organic matter, FT-ICR-MS, molecular composition, DOM degradation
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-316890 (URN)
Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2017-03-08
4. Seasonal variability in dissolved organic carbon degradation in boreal lakes: links to composition, sources, and baseline metabolism
Open this publication in new window or tab >>Seasonal variability in dissolved organic carbon degradation in boreal lakes: links to composition, sources, and baseline metabolism
(English)Manuscript (preprint) (Other academic)
Keyword
DOC, bacterioplankton, boreal lakes, seasonality, carbon source, baseline metabolism
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-316892 (URN)
Available from: 2017-03-08 Created: 2017-03-08 Last updated: 2017-03-08

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