Correlation of fluctuations in cladoceran planktonic:littoral ratio between three cores from a small lake in southern Finland:: Holocene water-level changes

The main aim of the study was to test the cladoceran planktonic:littoral (P/L) method in Holocene lake-level studies with three cores from a small lake (Iso Lehmalampi, 60 degrees 21'N, 24 degrees 36'E), in southern Finland. The cores were analysed for pollen, diatoms and Cladocera, which provided marker horizons, such as appearance level and maxima of species, for correlation with the fluctuations in P/L ratio in the cores. P/L fluctuations appeared to be corresponding and contemporaneous in all three cores and suggested that there were changes of lake level during the Holocene. Water level was high c. 9000-8000 C-14 yr BP and low c. 7000 BP. The time from c. 4000 BP to modern times is characterized by several short-term fluctuations in water level. The P/L record appeared to be most informative in cores taken outside the shallow littoral area where redeposition may 'smooth' the curves. The chydorid species composition was rather uniform in the three cores and showed that analysis from only one core can give a reliable picture of species succession. Although the same P/L fluctuations could be found in all cores, there were large differences in the amplitude of fluctuations in the curves; this suggested that it is not possible to reconstruct the magnitude of lake-level change with this method.