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Extensive processing of sediment pore water dissolved organic matter during anoxic incubation as observed by high-field mass spectrometry (FTICR-MS)
Helmholtz Zentrum Munich, Germany.
Univ Maryland, MD 20688 USA.
Helmholtz Zentrum Munich, Germany; Tech Univ Munich, Germany.
Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences. Univ Fed Rio de Janeiro, Brazil.
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2018 (English)In: Water Research, ISSN 0043-1354, E-ISSN 1879-2448, Vol. 129, p. 252-263Article in journal (Refereed) Published
Abstract [en]

Dissolved organic matter (DOM) contained in lake sediments is a carbon source for many microbial degradation processes, including aerobic and anaerobic mineralization. During anaerobic degradation, DOM is partially consumed and transformed into new molecules while the greenhouse gases methane (CH4) and carbon dioxide (CO2) are produced. In this study, we used ultrahigh resolution mass spectrometry to trace differences in the composition of solid-phase extractable (PPL resin) pore water DOM (SPE-DOM) isolated from surface sediments of three boreal lakes before and after 40 days of anoxic incubation, with concomitant determination of CH4 and CO2 evolution. CH4 and CO2 production detected by gas chromatography varied considerably among replicates and accounted for fractions of similar to 2-4 x 10(-4) of sedimentary organic carbon for CO2 and similar to 0.8-2.4 x 10(-5) for CH4. In contrast, the relative changes of key bulk parameters during incubation, such as relative proportions of molecular series, elemental ratios, average mass and unsaturation, were regularly in the percent range (1-3% for compounds decreasing and 4-10% for compounds increasing), i.e. several orders of magnitude higher than mineralization alone. Computation of the average carbon oxidation state in CHO molecules of lake pore water DOM revealed rather non-selective large scale transformations of organic matter during incubation, with depletion of highly oxidized and highly reduced CHO molecules, and formation of rather non-labile fulvic acid type molecules. In general, proportions of CHO compounds slightly decreased. Nearly saturated CHO and CHOS lipid-like substances declined during incubation: these rather commonplace molecules were less specific indicators of lake sediment alteration than the particular compounds, such as certain oxygenated aromatics and carboxyl-rich alicyclic acids (CRAM) found more abundant after incubation. There was a remarkable general increase in many CHNO compounds during incubation across all lakes. Differences in DOM transformation between lakes corresponded with lake size and water residence time. While in the small lake Svarttjarn, CRAM increased during incubation, lignin-and tannin-like compounds were enriched in the large lake Bisen, suggesting selective preservation of these rather non-labile aromatic compounds rather than recent synthesis. SPE-DOM after incubation may represent freshly synthesized compounds, leftover bulk DOM which is primarily composed of intrinsically refractory molecules and/or microbial metabolites which were not consumed in our experiments. In spite of a low fraction of the total DOM being mineralized to CO2 and CH4, the more pronounced change in molecular DOM composition during the incubation indicates that diagenetic modification of organic matter can be substantial compared to complete mineralization. (C) 2017 Elsevier Ltd. All rights reserved.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD , 2018. Vol. 129, p. 252-263
Keywords [en]
Solid phase extraction; DOM; FTICR-MS; Sediment; Methane; Anaerobic respiration
National Category
Geochemistry
Identifiers
URN: urn:nbn:se:liu:diva-145467DOI: 10.1016/j.watres.2017.11.015ISI: 000424716800025PubMedID: 29153878OAI: oai:DiVA.org:liu-145467DiVA, id: diva2:1188376
Note

Funding Agencies|Swedish Research Council VR [2012-00048]; Swedish Research Council STINT [2012-2085]; ERC [725546]; Brazilian National Counsel of Technological and Scientific Development (CNPq) [290004/2014-4]; Alexander von Humboldt Foundation; CAPES (Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior); STINT (The Swedish Foundation for International Cooperation in Research and Higher Education)

Available from: 2018-03-07 Created: 2018-03-07 Last updated: 2018-03-07

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