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Annually resolved impact of climate and catchment properties on the sediment diatom assemblage in a varved, boreal lake since AD 1930
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för ekologi, miljö och geovetenskap. (Paleolimnology)
(engelsk)Manuskript (preprint) (Annet vitenskapelig)
Abstract [en]

Assessing ecosystem dynamics beyond experimental time-scales is a prerequisite to understand effects of ongoing environmental change and essential to improve predictions of future conditions. In this study, we analyze a time series of an annually resolved sediment record from a boreal lake (Nylandssjön) in northern Sweden, consisting of diatom data since AD 1931 and geochemistry data since AD 1953. The aim of this paper is to quantify to which extent the main primary producers (i.e., diatom assemblage) in a typical boreal lake are related to processes in the lake catchment, sediment properties, and climate variables (temperature, precipitation, circulation patterns). The diatom assemblage consists mainly of Cyclotella taxa (C. glomerata, C. radiosa, and C. rossii), Asterionella formosa, Fragilaria delicatissima and other small Fragilaria taxa. Although the dominant taxa remain the same over the entire sediment record, their relative abundances exhibit some distinct shifts. We use ordination techniques and variance partitioning to quantify the explanatory power of environmental variables to explain shifts in the diatom assemblage composition. A series of redundancy analyses (RDA) using one sole constraining variable showed that both geochemical proxies and climate variables explained a statistically significant amount of the variance in the diatom data. The most powerful sediment proxy variables were Pb (ppm, 17.9%), C (%, 16.8%), N (%, 15.7%) and sedimentation rate (g cm-2 yr-1, 13.2%). For climate variables, temperature during winter/spring (April 6.4%, May 5.0%, February 4.6%) and the Northern Atlantic Oscillation index (NAO 6.4%) showed the highest predictive power, whereas precipitation data did not turn out to be a powerful predictor. Variance partitioning showed that sediment proxies (sedimentation rate, C, N; 20.8%), variables associated with pollution (Pb, Cu, P; 23.1%) and climate (winter/spring temperature, NOA; 10.4%) explained significant amounts of the variance in the diatom data. This quantification indicates to which extent sediment properties and climate conditions are jointly responsible for shaping the ecosystem properties in boreal lakes, highlighting in particular the importance of winter climate.

Emneord [en]
Diatoms, geochemistry, boreal lake, varves, climate, variance partitioning
HSV kategori
Identifikatorer
URN: urn:nbn:se:umu:diva-135330OAI: oai:DiVA.org:umu-135330DiVA, id: diva2:1098104
Tilgjengelig fra: 2017-05-23 Laget: 2017-05-23 Sist oppdatert: 2018-06-09
Inngår i avhandling
1. Combining limnology and paleolimnology: a refined understanding of environmental sediment signal formation in a varved lake
Åpne denne publikasjonen i ny fane eller vindu >>Combining limnology and paleolimnology: a refined understanding of environmental sediment signal formation in a varved lake
2017 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Umeå: Umeå University, 2017. s. 29
Emneord
varved lake sediments, diatom sediment signal formation, sequential sediment trap, seasonal process timing, ice thinning, varve compaction, climate impact, catchment properties
HSV kategori
Forskningsprogram
geovetenskap med inriktning mot miljöanalys
Identifikatorer
urn:nbn:se:umu:diva-135231 (URN)978-91-7601-603-9 (ISBN)
Disputas
2017-06-15, KB3A9, KBC, Umeå, 10:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2017-05-24 Laget: 2017-05-22 Sist oppdatert: 2024-07-02bibliografisk kontrollert

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