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Investigating molecular changes in organic matter composition in two Holocene lake-sediment records from central Sweden using pyrolysis-GC/MS
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.
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2017 (Engelska)Ingår i: Journal of Geophysical Research - Biogeosciences, ISSN 2169-8953, E-ISSN 2169-8961, Vol. 122, nr 6, s. 1423-1438Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

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, total nitrogen, C:N ratios, delta C-13, and delta N-15. To characterize the molecular OM composition, we employed a new method based on pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), which yields semiquantitative data on > 100 organic compounds of different origin and degradation status. We identify large changes in OM composition after deglaciation (circa 8500 +/- 500 B.C.), associated with early landscape development, and during the most recent 4050 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 PyGC/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.

Ort, förlag, år, upplaga, sidor
American Geophysical Union (AGU), 2017. Vol. 122, nr 6, s. 1423-1438
Nationell ämneskategori
Multidisciplinär geovetenskap
Identifikatorer
URN: urn:nbn:se:umu:diva-138425DOI: 10.1002/2016JG003715ISI: 000406520900008Scopus ID: 2-s2.0-85021698702OAI: oai:DiVA.org:umu-138425DiVA, id: diva2:1135334
Tillgänglig från: 2017-08-23 Skapad: 2017-08-23 Senast uppdaterad: 2023-08-28Bibliografiskt granskad
Ingår i avhandling
1. Molecular analysis of lake-sediment organic matter: long-term dynamics and environmental implications in boreal lakes
Öppna denna publikation i ny flik eller fönster >>Molecular analysis of lake-sediment organic matter: long-term dynamics and environmental implications in boreal lakes
2023 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Alternativ titel[sv]
Molekylär analys av organiskt material i sjösediment : långtidsdynamik och miljöpåverkan i boreala sjöar.
Abstract [en]

Lake sediment organic matter is material composed of residues from plants, algae, animals, fungi and bacteria. Its molecular composition is dependent on the sources as well as secondary biotic and abiotic transformations, which combined generates a highly complex matrix. Considering that organic matter plays a key role in carbon and nitrogen cycle, and its composition affects many different biogeochemical reactions, paleolimnologic studies have payed proportionately little attention to the organic matter composition compared with the other sediment fractions, even though organic matter makes up 20–60 % of the dry sediment mass in boreal and subarctic lakes. This thesis therefore primarily aims to explore and evaluate two methods; pyrolysis-gas chromatography/mass spectrometry (Pyrolysis-GC/MS) and diffuse reflectance Fourier-transform infrared spectroscopy (DRIFTS) for characterisation of bulk organic matter at the molecular level, both which have been extensively used for soils and peat and which balances the need for cost and time-effective analysis and for analytical detail.

With pyrolysis-GC/MS the organic matter composition and long-term dynamics in two neighbouring boreal lakes is explored and compared with the conventional bulk carbon and nitrogen contents and their stable isotopes. Both pyrolysis data and conventional data capture the timing of organic matter compositional changes, but only pyrolysis provides detailed information on how the composition changes, which allows for a deeper understanding of the processes behind the changes. The same two lakes are also analysed with DRIFTS and with this approach information on the major organic compound groups aromatics, lignin, aliphatics, proteins and polysaccharides is extracted. In combination with the rapid analysis time and low cost, DRIFTS emerges as a very useful tool for rapid yet informative organic matter analysis. DRIFTS is then evaluated as a stand-alone tool for sediment characterisation in four mountain lakes. The four lakes all have different sediment composition and as a result of the multi-fraction information obtained with DRIFTS compositional differences can be related and explained in terms of their individual lake and landscape settings. The importance of landscape setting is further highlighted in the synthesis of the long-term dynamics of lake-water quality in seven lakes where development trajectories and responses to different types of disturbances are connected to the extent of peatlands within the lake catchments. This thesis demonstrates the advantages of two different approaches for more detailed lake sediment organic matter characterisation and advances our understanding of the molecular organic matter composition in boreal lakes over the Holocene, and how landscape setting affects both the organic matter composition and the sensitivity of lakes to disturbance.

Ort, förlag, år, upplaga, sidor
Umeå: Umeå University, 2023. s. 23
Nyckelord
Lake sediment, Holocene, organic matter, Pyrolysis-GC/MS, mid-infrared spectroscopy, boreal
Nationell ämneskategori
Miljövetenskap
Identifikatorer
urn:nbn:se:umu:diva-213753 (URN)978-91-8070-144-0 (ISBN)978-91-8070-145-7 (ISBN)
Disputation
2023-09-22, NAT.D.450, Naturvetarhuset, Umeå Universitet, Umeå, 09:00 (Engelska)
Opponent
Handledare
Tillgänglig från: 2023-09-01 Skapad: 2023-08-28 Senast uppdaterad: 2023-08-28Bibliografiskt granskad

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Ninnes, SofiaTolu, JulieMeyer-Jacob, Carsten

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