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Using a decadal diatom sediment-trap record to unravel seasonal processes important for the formation of the sedimentary diatom signal
Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences. (Paleolimnology)
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Sediment trap studies are of great importance to develop a deeper understanding of how environmental processes are influencing sediment deposition. We analyzed diatom assemblages from 2002 to 2015 in a sediment-trap record from a boreal lake (Nylandssjön, Sweden) together with environmental parameters, and compared the diatom record in the trap with the corresponding annually laminated sediments. In general, our data set indicates a large year-to-year variability of diatom succession and abundance patterns, which is well reflected in the varved sediments. The relative abundance of major taxa seems primarily controlled by seasonal characteristics, such as above-average winter air temperature and autumn runoff. Specifically, Cyclotella glomerata dominated the annual sediment trap record (and also the corresponding sediment varves) in years with warmer air temperatures in March-April, and Asterionella formosa dominated the annual sediment assemblages in years characterized by higher runoff before autumn lake over-turn. This study highlights that short-term environmental conditions and extreme events are of major importance for interpreting annual sediment signals.

Keyword [en]
Diatoms, sediment trap, varved lake sediment, seasonal air temperature, discharge
National Category
Climate Research
Identifiers
URN: urn:nbn:se:umu:diva-135329OAI: oai:DiVA.org:umu-135329DiVA: diva2:1098101
Available from: 2017-05-23 Created: 2017-05-23 Last updated: 2017-05-23
In thesis
1. Combining limnology and paleolimnology: a refined understanding of environmental sediment signal formation in a varved lake
Open this publication in new window or tab >>Combining limnology and paleolimnology: a refined understanding of environmental sediment signal formation in a varved lake
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Paleoclimatic archives, such as lake sediments, extend our understanding of terrestrial and aquatic ecosystem dynamics in relation to climate variability beyond the period covered by instrumental data. In this context, annually laminated (i.e. varved) lake sediments are particularly valuable, as they offer high temporal resolution and undisturbed sediment. However, in order to extract reliable climate information from lake sediments, a careful calibration with the processes controlling the sediment formation is essential. This thesis combines limnological and paleolimnological data from a varved, boreal lake in northern Sweden (Nylandssjön, Nordingrå) collected over different time scales. The main aim of the thesis is to gain a more refined insight into which processes are reflected in the sedimentary diatom assemblage. More specifically, sequential sediment trap records were coupled with physical, chemical and biological lake monitoring and environmental data for comparison and validation with the varved sediment record. The main result of the thesis is that timing, succession and inter-annual variability of key limnological and environmental processes (e.g. ice-cover duration, lake over-turn or catchment run-off) are of major importance for the sedimentary diatom assemblage formation. Continuous monitoring of physico-chemical parameters over three consecutive years identified varying winter air temperature as a major factor influencing in-lake processes and hence the diatom record. Timing of lake over-turn and catchment run-off seemed to be the driver for monospecific diatom blooms, which are reflected in the annual sediment signal. The integrated annual diatom signal in the sediment was dominated by spring or autumn blooms, resulting either from a Cyclotella glomerata dominated spring bloom after relatively warm winter conditions, or a Asterionella formosa dominated autumn bloom after relatively cold winter conditions. The analysis of the diatom stratigraphy in the varved sediment over several decades corroborated the importance of climatic variables (late winter air temperature and NAO), even though the variables with the most predictive power for variance in the diatom data were associated with sediment composition (C, N and sedimentation rate) and pollution (Pb and Cu). Overall, the analysis of the drivers of inter-annual and decadal diatom assemblage fluctuations emphasizes the importance of winter air temperature, indicating that weather extremes may be disproportionately represented in annual sediment records in contrast to nutrient concentrations or sedimentation rate.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2017. 29 p.
Keyword
varved lake sediments, diatom sediment signal formation, sequential sediment trap, seasonal process timing, ice thinning, varve compaction, climate impact, catchment properties
National Category
Earth and Related Environmental Sciences
Research subject
Earth Sciences with Specialization Environmental Analysis
Identifiers
urn:nbn:se:umu:diva-135231 (URN)978-91-7601-603-9 (ISBN)
Public defence
2017-06-15, KB3A9, KBC, Umeå, 10:00 (English)
Opponent
Supervisors
Available from: 2017-05-24 Created: 2017-05-22 Last updated: 2017-05-24Bibliographically approved

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Maier, Dominique Béatrice
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  • apa
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