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Diatoms as indicators of climatic and limnological change in Swedish Lapland: A 100-lake calibration set and its validation for paleoecological reconstructions
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
Umeå University, Faculty of Science and Technology, Ecology and Environmental Science.
2002 (English)In: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 27, no 1, 97-115 p.Article in journal (Refereed) Published
Abstract [en]

This study investigated the distribution of subfossil diatom assemblages in surficial sediments of 100 lakes along steep ecological and climatic gradients in northernmost Sweden (Abisko region, 67.07degrees N to 68.48degrees N latitude, 17.67degrees E to 23.52degrees E longitude) to develop and cross-validate transfer functions for paleoenvironmental reconstruction. Of 19 environmental variables determined for each site, 15 were included in the statistical analysis. Lake-water pH (8.0%), sedimentary loss-on-ignition (LOI, 5.9%) and estimated mean July air temperature (July T, 4.8%) explained the greatest amounts of variation in the distribution of diatom taxa among the 100 lakes. Temperature and pH optima and tolerances were calculated for abundant taxa. Transfer functions, based on WA-PLS (weighted averaging partial least squares), were developed for pH (r(2) = 0.77, root-mean-square-error of prediction (RMSEP) = 0.19 pH units, maximum bias = 0.31, as assessed by leave-one-out cross-validation) based on 99 lakes and for July T (r(2) = 0.75, RMSEP = 0.96 degreesC, max. bias = 1.37 degreesC) based on the full 100 lake set. We subsequently assessed the ability of the diatom transfer functions to estimate lake-water pH and July T using a form of independent cross-validation. To do this, the 100-lake set was divided in two subsets. An 85-lake training-set (based on single limnological measurements) was used to develop transfer functions with similar performance as those based on the full 100 lakes, and a 15-lake test-set (with 2 years of monthly limnological measurements throughout the ice-free seasons) was used to test the transfer functions developed from the 85-lake training-set. Results from the intra-set cross-validation exercise demonstrated that lake-specific prediction errors (RMSEP) for the 15-lake test-set corresponded closely with the median measured values (pH) and the estimations based on spatial interpolations of data from weather stations (July T). The prediction errors associated with diatom inferences were usually within the range of seasonal and interannual variability. Overall, our results confirm that diatoms can provide reliable and robust estimates of lake-water pH and July T, that WA-PLS is a robust calibration method and that long-term environmental data are needed for further improvement of paleolimnological transfer functions.

Place, publisher, year, edition, pages
2002. Vol. 27, no 1, 97-115 p.
Keyword [en]
Northern Fennoscandia, Abisko, diatoms, lake sediments, pH, temperature, training-set, transfer functions, weighted averaging partial least squares regression (WA-PLS), intra-set cross-validation
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:umu:diva-2795DOI: 10.1023/A:1013562325326ISI: 000173086500008OAI: oai:DiVA.org:umu-2795DiVA: diva2:141069
Available from: 2001-11-01 Created: 2001-11-01 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Diatoms as indicators of Holocene climate and environmental change in northern Sweden
Open this publication in new window or tab >>Diatoms as indicators of Holocene climate and environmental change in northern Sweden
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The objective of the thesis was to explore the potential of diatoms (Bacillariophyceae) as indicators of Holocene climate and environmental change in northern Sweden (Abisko region, 68°21'N, 18°49'E). A modern surface-sediment calibration set including 100 lakes was developed and lake-water pH, sedimentary organic content (assessed by loss-on-ignition) and temperature were identified as most powerful environmental variables explaining the variance within the diatom assemblages. Transfer functions based on unimodal species response models (WA-PLS) were developed for lake-water pH and mean July air temperature (July T), yielding coefficients of determination of 0.77 and 0.70, and prediction errors based on leave-one-out cross-validation of 0.19 pH units and 0.96 °C for lake-water pH and July T, respectively. The transfer functions were validated with monitoring data covering two open-water seasons (lake-water pH) and meteorological records covering the 20th century (July T). The good agreement between diatom-based inferences and measured monitoring data confirmed the prediction ability of the developed transfer functions.

Analysing a Holocene sediment core from a lake nearby Abisko (Vuoskkujávri), diatoms infer a linearly decreasing July T trend (1.5 °C) since 6,000 cal. BP, which compares well with inferences based on chironomids and pollen from the same sediment core. The lake-water pH inference shows a pattern of moderate natural acidification (c. 0.5 pH units) since the early Holocene, reaching present-day pH values at c. 5,000 cal. BP. By fitting fossil diatom samples to the modern calibration set by means of residual distance assessment within canonical correspondence analysis (CCA), the early Holocene (between 10,600 and 6,000 cal. BP) was identified as a problematic time-period for diatom-based inferences and, consequently, reconstructions during this period are tentative. Pollen-based inferences also show 'poor' fit between 10,600 and 7,500 cal. BP and chironomids probably provide the most reliable July T reconstruction at Vuoskkujávri, with 'poor' fit only during the initial part of the Holocene (between 10,600 and 10,250 cal. BP).

Possible factors confounding diatom-based July T inferences were investigated. Using detrended CCA (DCCA), Holocene sediment sequences from five lakes indicate that during the early Holocene, mainly physical factors such as high minerogenic erosion rates, high temperature and low light availability may have regulated diatom assemblages, favouring Fragilaria species. In all five lakes, diatom assemblages developed in a directional manner, but timing and scale of development differed substantially between lakes. The differences are attributed primarily to the geological properties of the lake catchments (with strong effects on lake-water pH), but other factors such as climatic change, vegetation, hydrologic setting and in-lake processes appear to regulate diatom communities in each lake differently. The influence of long-term natural acidification on diatom assemblages progressively declined during the Holocene with corresponding increase of the influence of climatic factors.

Place, publisher, year, edition, pages
Umeå: Ekologi och geovetenskap, 2001. 19 p.
Keyword
Physical geography and sedimentology, diatoms, Holocene, paleolimnology, climate change, lake sediments, transfer functions, quantitative environmental reconstructions, northern Sweden, Abisko, Naturgeografi och sedimentologi
National Category
Physical Geography
Research subject
Physical Geography
Identifiers
urn:nbn:se:umu:diva-144 (URN)91-7305-134-9 (ISBN)
Public defence
2001-12-06, Umeå, 10:00
Opponent
Supervisors
Available from: 2001-11-01 Created: 2001-11-01Bibliographically approved

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