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2 Studia Quaternaria

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Recent sedimentation and eutrophication of kruklin lake after artificial drop in water-level in the middle of 19th century

100%

Gąsiorowski M. , Hercman H.

tom Vol. 22

17-25

Sediments of two short cores collected from two basins of Kruklin Lake were studied by means of 210Pb and Cladocera analyses. The 210Pb allowed to date sediments and was helpful to obtain changes of sedimentation rate during the last two centuries. The CRS model was applied to calculate sediments age. Sedimentation rate differed strongly (from 0.55 cm/yr to 6.25 cm/yr) not only in time, but also between each basin. An accurate chronology of sediments was the basis for tracking of palaeolimnological changes with Cladocera analysis. Cladoceran planktonic:littoral ratio reflects event of artificial drop of lake water-level in the middle of nineteenth century. However, this event was recorded only in sediments of the southern, shallower basin and we suggest, that cladoceran planktonic:littoral ratio is better representative in shallow lakes. Changes of Cladocera assemblage composition suggest also strong eutrophication of lake water during the last century.

Late holocene water-level changes in lake iso lehmalampi, southern finland, reflected in subfossil cladocerans and chironomids

86%

Nevalainen L. , Luoto T. P. , Sarmaja-Korjonen K.

tom Vol. 25

33-42

Analyses of subfossil cladocerans (Crustacea: Cladocera) and chironomids (Diptera: Chironomidae) were applied to examine water-level changes in a small and oligotrophic lake in southern Finland over the past 2000 years. Major changes in the invertebrate communities occurred ca. 400 AD onwards when the littoral cladoceran Alonella nana started to replace the planktonic Eubosmina as the dominant species and chironomids Psectrocladius sordidellus group and Zalutschia zalutschicola increased. These changes were most likely due to a decreasing water level and an enlarging proportion of the littoral area, providing suitable vegetative habitats, e.g. aquatic bryophytes (mosses), for these taxa. The lowering water level reached its minimum just before the Medieval Warm Period, ca. 800-1000 AD, after which the lake level rose again and remained high until modern times. A prominent change in the chironomid assemblages occurred during the 20th century when Ablabesmyia monilis and Chironomus anthracinus type increased, presumably due to changes in water chemistry, caused by anthropogenic load of pollutants.