Investigating molecular changes in organic matter composition in two Holocene lake-sediment records from central Sweden using pyrolysis-GC/MS

Sofia Ninnes (Corresponding Author), Julie Tolu, Carsten Meyer-Jacob, Tim M. Mighall, Richard Bindler

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Abstract

Organic matter (OM) is a key component of lake sediments, affecting carbon, nutrient and trace metal cycling at local and global scales. Yet little is known about long-term (millennial) changes in OM composition due to the inherent chemical complexity arising from multiple OM sources and from secondary transformations. In this study we explore how the molecular composition of OM changes throughout the Holocene in two adjacent boreal lakes in central Sweden, and compare molecular-level information with conventional OM variables, including total carbon (TC), total nitrogen (TN), C:N ratios, δ13C and δ15N. To characterize the molecular OM composition, we employed a new method based on pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), which yields semi-quantitative data on >100 organic compounds of different origin and degradation status. We identify large changes in OM composition after deglaciation (c. 8500 ± 500 B.C.), associated with early landscape development, and during the most recent 40–50 years, driven by degradation processes. With molecular-level information we can also distinguish between natural landscape development and human catchment disturbance during the last 1700 years. Our study demonstrates that characterization of the molecular OM composition by the high-throughput Py-GC/MS method is an efficient complement to conventional OM variables for identification and understanding of past OM dynamics in lake-sediment records. Holocene changes observed for pyrolytic compounds and compound classes known for having different reactivity indicate the need for further paleo-reconstruction of the molecular OM composition to better understand both past and future OM dynamics and associated environmental changes.
Original languageEnglish
Pages (from-to)1423-1438
Number of pages17
JournalJournal of geophysical research-Biogeosciences
Volume122
Issue number6
Early online date15 Jun 2017
DOIs
Publication statusPublished - Jun 2017

Fingerprint

pyrolysis
lacustrine deposit
Holocene
organic matter
gas chromatography
mass spectrometry
degradation
carbon
deglaciation
long-term change
trace metal
organic compound
environmental change
catchment
disturbance
nutrient
nitrogen

Keywords

  • organic matter composition
  • lake sediment
  • Holocene
  • Pyrolysis-GC/MS
  • carbon
  • stable isotopes

Cite this

Investigating molecular changes in organic matter composition in two Holocene lake-sediment records from central Sweden using pyrolysis-GC/MS. / Ninnes, Sofia (Corresponding Author); Tolu, Julie; Meyer-Jacob, Carsten ; Mighall, Tim M.; Bindler, Richard.

In: Journal of geophysical research-Biogeosciences, Vol. 122, No. 6, 06.2017, p. 1423-1438.

Research output: Contribution to journalArticle

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abstract = "Organic matter (OM) is a key component of lake sediments, affecting carbon, nutrient and trace metal cycling at local and global scales. Yet little is known about long-term (millennial) changes in OM composition due to the inherent chemical complexity arising from multiple OM sources and from secondary transformations. In this study we explore how the molecular composition of OM changes throughout the Holocene in two adjacent boreal lakes in central Sweden, and compare molecular-level information with conventional OM variables, including total carbon (TC), total nitrogen (TN), C:N ratios, δ13C and δ15N. To characterize the molecular OM composition, we employed a new method based on pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), which yields semi-quantitative data on >100 organic compounds of different origin and degradation status. We identify large changes in OM composition after deglaciation (c. 8500 ± 500 B.C.), associated with early landscape development, and during the most recent 40–50 years, driven by degradation processes. With molecular-level information we can also distinguish between natural landscape development and human catchment disturbance during the last 1700 years. Our study demonstrates that characterization of the molecular OM composition by the high-throughput Py-GC/MS method is an efficient complement to conventional OM variables for identification and understanding of past OM dynamics in lake-sediment records. Holocene changes observed for pyrolytic compounds and compound classes known for having different reactivity indicate the need for further paleo-reconstruction of the molecular OM composition to better understand both past and future OM dynamics and associated environmental changes.",
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note = "This research was supported by grants from the Swedish Research Council (dnr. 2014-5219) and from the Ume{\aa} University research environment ‘The environment’s chemistry’. We would like to thank Ume{\aa} Plant Science Center for making the Py-GC/MS available to us, and Alexandra Rouillard and one anonymous reviewer for constructive comments on the manuscript. All data presented in the figures in the main manuscript can be found in the supporting information. Raw data will be provided upon request from the corresponding authors.",
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N1 - This research was supported by grants from the Swedish Research Council (dnr. 2014-5219) and from the Umeå University research environment ‘The environment’s chemistry’. We would like to thank Umeå Plant Science Center for making the Py-GC/MS available to us, and Alexandra Rouillard and one anonymous reviewer for constructive comments on the manuscript. All data presented in the figures in the main manuscript can be found in the supporting information. Raw data will be provided upon request from the corresponding authors.

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