Ežerų nuosėdos - gamtinių ir antropogeninių pokyčių metraštis

• Main Authors: Šeirienė, Vaida, Mažeika, Jonas, Petrošius, Rimantas, Kabailienė, Meilutė, Kasperovičienė, Jūratė, Paškauskas, Ričardas
• Format: Article in Journal/Newspaper
• Language: Lithuanian; English
• Published: 2008
• Subjects: Lake sediments; Anthropogenic changes; Complex studies; Late glacial; Holocene; Tundra
• Online Access: http://vu.lvb.lt/VU:ELABAPDB4027311&prefLang=en_US

Our multidisciplinary study was undertaken to better understand the long-term environmental changes and supplemem the existing post- glacial environmental change models with new important data. The identified pollen composition indicates that during the Older Dryas the upland vegetation probably consisted of sparse shrub and herb/grass communities on barren and unstable soils. Diatoms infer that sedimentation took place in cold oligotrophic palaeobasins rich in oxygen and nutrients and high water level, tow pigment concentrations point on low lakes productivy. A change in pollen composition from an assemblage with a high amount of herbs to one dominated by Pinus shows forestation of the area during the Atlerod. Nevertheles the lakes remained rather cold water and oligotrophic. The decrease in number of trees, especially Pinus, suggests the decline of pine-birch forest and the formation of open herb-grass-shrub vegetation with tundra elements during the Younger Dryas period. A decline of epiphytic diatom species and predominance of representatives of plankton indicate the rising water level in the lakes. The slight rise in number and variety of diatoms implies a beginning of an increase in organic productivity. Overall, the changes in upland vegetation indicate the slight improvement in climate conditions during the Preboreal. Tundra and forest-tundra vegetation declined and tree vegetation experienced significant proliferation. Betula forest, however not dense, with admixture of pine (Pinus) and spruce (Piced) trees dominated. No significant changes of ecological conditions in the palaeobasins appeared. From the Boreal time Pine forests spread in the investigated area.Significant environmental changes appeared during the Holocene climatic optimum (Atlantic). Differentiation of forests was growingly manifested. Alms, Corylus, Ouercus, Ulmus appeared in the territory. A significant increase in diatom diversity, diatom and pigment concentrations and decrease in C/N ration clearly indicate the growing productivity in the lakes and most favorable climatic conditions during the period studied. At the end of the period eutrophication processes intensified in all the lakes. The complex isotope studies allowed ascertaining the sedimentation parameters. Recent sedimentation modulus varies from 0.05 to 0.16 g/cm/years. The mean values correspond to linear accumulation rate from 0.9 to 2.3 cm/years. The mean sedimentation rate during were lesser than recent and fluctuated from 0.8 mm/year to 1.6 mm/year.