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  • diatoms  (2)
  • 1
    ISSN: 1573-0417
    Keywords: paleohydrology ; lake level ; lake depth ; diatoms ; subarctic ; arctic ; hydrology ; lakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract Several recent studies have successfully applied diatom-based paleolimnological techniques to infer past hydrological changes in arctic and subarctic regions. For example, we summarize arctic studies that attempt to determine changes in peat water content, flood frequency, river discharge, effective moisture and ice cover in northern regions. Some of the investigations are still in preliminary stages, but represent innovative approaches to study arctic and subarctic paleohydrology. New data demonstrate that lake depth, which may be related to changing hydrological conditions, is a significant variable influencing the distributions of diatom taxa in lake surface sediment calibration sets from Wood Buffalo National Park (WBNP), on the border of Alberta and the Northwest Territories, Canada, and from Fennoscandia (mainly northwest Finland). Weighted averaging regression and calibration methods were used to develop quantitative inference models for lake depth using diatom assemblages preserved in surface sediments. The predictive abilities of the transfer functions were relatively high (for WBNP r2 = 0.70 and RMSE = 2.6 m, and for Fennoscandia r2 = 0.88 and RMSE = 1.8 m). However, evaluating the transfer functions using jack-knifing procedures indicated lower predictive abilities, possibly reflecting the relatively small sample size and/or short gradients used in these calibration sets. Such transfer functions can be used to track overall trends in lake levels, and provide an objective assessment as to directions of changing lake levels. Any interpretations of inferred lake levels, especially those related to climate change, must be made cautiously and must include some understanding of the local, present-day hydrological system.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of paleolimnology 7 (1992), S. 1-22 
    ISSN: 1573-0417
    Keywords: hydrosere ; natural acidification ; zooplankton ; diatoms ; water level fluctuations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract The hydroseral development of a former small lake in Southern Finland was studied by means of subfossil cladoceran remains, diatoms, pollen, plant macrofossils and other sediment data. The diatom analysis shows the lake to have become markedly acid during the Early Holocene. This is reflected in the cladoceran communities in the form of a fall in the proportions of Bosmina longirostris etc. and a reciprocal rise in Bosmina (Eubosmina) longispina, an increase in the proportions of the chydorid species indicative of acidity, and the appearance of certain new morphotypes. The concentrations of both planktonic and littoral species and the numbers of such species increase with acidification. Advancement in the hydroseral succession is reflected in the disappearance of benthic species from the chydorid communities and a pronounced increase in exclusively phytophile species. Sedimentation and the drop in water levels are seen to have led to a spread of helophytes and floating-leaved plants over the water body around 6500–7000 B.P., and a vegetation-filled swamp was created at the site. The zooplankton was practically exterminated, but the concentrations of littoral cladocerans reached their peak at this point. The basin became overgrown completely at the beginning of the Subboreal chronozone (approx. 4600–4800 B.P.), simultaneously with the low-water phase observed in many lakes. It became covered with a Sphagnum stand, and this in turn led to complete destruction of the cladoceran communities. The planktonic/littoral ratio among the Cladocera closely reflected the relation between open water and the macrophyte zone as a function of time. Climatically induced rises and falls in water level are shown to have played a significant role in promoting the advancement of the hydroseral succession.
    Type of Medium: Electronic Resource
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