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Holocene environmental change at Lake Njulla (999 m asl), northern Sweden: a comparison with four small nearby lakes along an altitudinal gradient
Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Ekologi och geovetenskap.
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2003 (Engelska)Ingår i: Journal of Paleolimnology, ISSN 0921-2728, E-ISSN 1573-0417, Vol. 29, nr 1, s. 13-29Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

We assess Holocene environmental change at alpine Lake Njulla (68degrees22'N, 18degrees42'E, 999 m a.s.l.) in northernmost Sweden using sedimentary remains of chironomid head capsules and diatoms. We apply regional calibration sets to quantitatively reconstruct mean July air temperature (using chironomids and diatoms) and lake-water pH (using diatoms). Both chironomids and diatoms infer highest temperatures (1.7-2.3degreesC above present-day estimates, including, a correction for glacio-isostatic land up-lift by 0.6degreesC) during the early Holocene (c. 9,500-8,500 cal. yrs BP). Diatoms suggest a decreasing lake-water pH trend (c. 0.6 pH units) since the early Holocene. Using detrended canonical correspondence analysis (DCCA), we compare the Holocene development of diatom communities in Lake Njulla with four other nearby lakes (Lake 850, Lake Tibetanus, Vuoskkujavri, Vuolep Njakajaure) located along an altitudinal gradient. All five lakes show similar initial DCCA scores after deglaciation, suggesting that similar environmental processes such as high erosion rates and low light availability associated with high summer temperature appear to have regulated the diatom community, favouring high abundances of Fragilaria species. Subsequently, the diatom assemblages develop in a directional manner, but timing and scale of development differ substantially between lakes. This is attributed primarily to differences in the local geology, which is controlling the lake-water pH. Imposed on the basic geological setting, site-specific processes such as vegetation development, climate, hydrological setting and in-lake processes appear to control lake development in northern Sweden.

Ort, förlag, år, upplaga, sidor
2003. Vol. 29, nr 1, s. 13-29
Nyckelord [en]
Abisko, chironomids, diatoms, lake development, lake-water pH, mean July air temperature, plant macrofossils, quantitative reconstruction, subarctic lakes, vegetation change
Nationell ämneskategori
Geovetenskap och miljövetenskap
Identifikatorer
URN: urn:nbn:se:umu:diva-2798DOI: 10.1023/A:1022850925937ISI: 000183141800002OAI: oai:DiVA.org:umu-2798DiVA, id: diva2:141072
Tillgänglig från: 2001-11-01 Skapad: 2001-11-01 Senast uppdaterad: 2018-06-09Bibliografiskt granskad
Ingår i avhandling
1. Diatoms as indicators of Holocene climate and environmental change in northern Sweden
Öppna denna publikation i ny flik eller fönster >>Diatoms as indicators of Holocene climate and environmental change in northern Sweden
2001 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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.

Ort, förlag, år, upplaga, sidor
Umeå: Ekologi och geovetenskap, 2001. s. 19
Nyckelord
Physical geography and sedimentology, diatoms, Holocene, paleolimnology, climate change, lake sediments, transfer functions, quantitative environmental reconstructions, northern Sweden, Abisko, Naturgeografi och sedimentologi
Nationell ämneskategori
Naturgeografi
Forskningsämne
naturgeografi
Identifikatorer
urn:nbn:se:umu:diva-144 (URN)91-7305-134-9 (ISBN)
Disputation
2001-12-06, Umeå, 10:00
Opponent
Handledare
Tillgänglig från: 2001-11-01 Skapad: 2001-11-01 Senast uppdaterad: 2018-01-13Bibliografiskt granskad

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