LAUSR

Abstract This study presents 1) the results of a stable isotope and subfossil Cladocera analyses of lacustrine sediments from Maliszewskie Lake (E Poland) and next 2) different reaction of the lake environments depending on the lake's localization. Maliszewskie Lake is located in North Podlasie Lowland ca. 30 km to the south of the Vistulian ice sheet limit. The approximately 4.80-m-thick sediments (Maliszewo I profile) are mainly comprised of calcareous gyttja covered by peat and organic detritus gyttja. Pollen analysis documents that the sediments accumulated from the Late Glacial (Allerod period) to recent times. Based on the results of stable isotope and subfossil Cladocera analyses of sediments, the lake environmental changes were reconstructed. A positive trend in δ18O and δ13C values documents a gradual climatic warming. The fluctuations of the oxygen isotopic values suggest the multiple oscillation of water level due to a change in the evaporation/precipitation ratio. The subfossil cladoceran fauna in the Maliszewo I profile is represented by 21 species belonging to five families. Three zones of Cladocera development were distinguished. The Cladocera species indicate the initial oligotrophic status of the lake and its subsequent increase of trophic status. Currently, Maliszewskie Lake is a very shallow, declining reservoir. The initial period of its existence probably saw its maximal depth. In presented studies we compared our results with data from three other sites documenting the reaction of the lake environment during the Late Glacial and Holocene transformation. At that time we observed different reactions to the climate amelioration. In the northern, postglacial lakes, the Holocene warming at first provoked an input cold melting water characterized by more negative oxygen isotope values and then a rise in water temperature. In the lakes further away from the glaciation border (periglacial lakes), the increase in water temperature, documented by e.g. more positive oxygen isotopic immediately occurred. The climate warming is commonly manifested by a significant increase of number of species and individuals of Cladocera.