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Long-term development and trajectories of inferred lake-water organic carbon and pH in naturally acidic boreal lakes
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. (Arcum)
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap.ORCID-id: 0000-0001-9659-2722
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. Paleoecological Environmental Assessment and Research Laboratory (PEARL), Department of Biology, Queen's University, ON, Kingston, Canada. (Arcum)ORCID-id: 0000-0002-8208-496x
Department of Geography and Environment, School of Geosciences, University of Aberdeen, Aberdeen, United Kingdom.
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2021 (Engelska)Ingår i: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 66, nr 6, s. 2408-2422Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Monitoring of surface waters in the boreal region over the last decades shows that waters are becoming browner. This timeframe may not, however, be sufficient to capture underlying trajectories and driving mechanisms of lake-water quality, important for prediction of future trajectories. Here we synthesize data from seven lakes in the Swedish boreal landscape, with contemporary lake-water total organic carbon (TOC) concentrations of 1.4–14.4 mg L−1, to conceptualize how natural and particularly human-driven processes at the landscape scale have regulated lake-water TOC levels over the Holocene. Sediment-inferred trends in TOC are supported by several proxies, including diatom-inferred pH. Before ~ 700 ce, all lakes were naturally acidic (pH 4.7–5.4) and the concentrations of inferred lake-water TOC were high (10–23 mg L−1). The introduction of traditional human land use from ~ 700 ce led to a decrease in lake-water TOC in all lakes (to 5–14 mg L−1), and in four poorly buffered lakes, also to an increase in pH by > 1 unit. During the 20th century, industrial acid deposition was superimposed on centuries of land use, which resulted in unprecedentedly low lake-water TOC in all lakes (3–11 mg L−1) and severely reduced pH in the four poorly buffered lakes. The other lakes resisted pH changes, likely due to close connections to peatlands. Our results indicate that an important part of the recent browning of boreal lakes is a recovery from human impacts. Furthermore, on a conceptual level we stress that contemporary environmental changes occur within the context of past, long-term disturbances.

Ort, förlag, år, upplaga, sidor
John Wiley & Sons, 2021. Vol. 66, nr 6, s. 2408-2422
Nationell ämneskategori
Miljövetenskap Ekologi
Identifikatorer
URN: urn:nbn:se:umu:diva-183358DOI: 10.1002/lno.11761ISI: 000646653900001Scopus ID: 2-s2.0-85104986862OAI: oai:DiVA.org:umu-183358DiVA, id: diva2:1557204
Forskningsfinansiär
Vetenskapsrådet, 2008-03741Vetenskapsrådet, 2011-03638Vetenskapsrådet, 2014-05219Tillgänglig från: 2021-05-25 Skapad: 2021-05-25 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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Myrstener, ErikNinnes, SofiaMeyer-Jacob, CarstenBindler, Richard

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