Cladoceran and diatom evidence of lake-level fluctuations from a Finnish lake and the effect of acquatic-moss layers on microfossil assemblages |
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| Authors: | Kaarina Sarmaja-Korjonen Pentti Alhonen |
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| Institution: | (1) Department of Geology, Division of Geology and Palaeontology, University of Helsinki, P.O. Box 11, Finland |
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| Abstract: | We studied Holocene lake-level fluctuations from a small lake, Iso Lehmälampi, southern Finland, utilizing cladoceran and diatom analyses. We report data from a sediment core (A) taken from the deepest part of the lake (8.1 m) where two layers of moss, mixed with gyttja, were found. These layers were formed in situ during the early Holocene (1. ca. 8100-7900, 2. ca. 7300 BP). Lake-level fluctuations were inferred also from another core C, which did not have moss layers. According to the ratio of planktonic/littoral Cladocera, the water level was high around 9000 BP and started to fall before 8000 BP. The lowering continued until 7000 BP and the moss layers were formed during this lowering. Water level was high again ca. 6000 BP and lowered towards ca. 4000 BP. The late Holocene is characterized by several rapid fluctuations of lake-level. The ratio of planktonic/littoral Cladocera and the diatom species composition in core A showed drastic changes between the moss layers and the non-moss gyttja sections of the core. We suggest that they reflect changes in sedimentary facies between the local moss environment and the pelagic bottom. Thus, cores which contain moss layers may lead to erroneous interpretations of lake-level fluctuations. |
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| Keywords: | Lake-level changes acquatic-moss layers Cladocera diatoms pollen cladoceran planktonic/littoral ratio |
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