Liisa Puusepp

Diatom assemblages in sediments of Lake Juusa, Southern Estonia with an assessment of their habitat

Diatom analysis of surface sediments and two sediment cores from different sedimentation areas of a small closed lake was undertaken with the aim of acquiring knowledge on the dependence of the distribution of diatom assemblages on lake bathymetry. Lake Juusa was selected for the study because we have for this lake a large data set about the lithological composition of sediments and macrofossil and cladoceran records for the Holocene. A high carbonate content (20–60%) in the sediment sequence indicates high carbonacity and relatively stable pH values during the Holocene. On the basis of comprehensive analysis, abrupt water-level fluctuations and changes in the trophic status were established. Results of this study showed that the fluctuations of the water-level were the leading factor determining the habitats of diatom assemblages in the lake. In the surface sediment samples planktonic species such as Cyclotella spp., Stephanodiscus spp. and Aulacoseira spp. had a depth optimum at 3–4 m and the most abundant periphytic taxa were distributed mostly at depths shallower than 3.5 m. The same regularity was established in sediment cores where a good correlation between planktonic species and lake water depth was found in sediments accumulated at water depths >4 m. Lake Juusa appears to be a proper site for detailed environmental reconstructions over the Holocene, and the results will give us a good opportunity to analyse the history of water-level fluctuations in other small Estonian lakes.

Pollen analysis of honey from the Baltic region, Estonia

Abstract The present study reports the results of pollen analyses of Estonian honey collected from 2000 to 2011. Altogether, the pollen content of 325 honey samples was analysed with an average of 400 pollen grains counted in a sample. The main focus was on the floristic spectrum of plants and on the identification of the most common and important plant sources for honey. More than 120 pollen types were identified in the examined honey samples. The results showed that the pollen types of Rosaceae, Brassicaceae, Salix and Trifolium were the most abundant among the samples. The pollen of Apiaceae, Fabaceae, Asteraceae, Poaceae, Fagopyrum esculentum, Frangula alnus and Calluna were present in more than 25% of samples. Typical Estonian honey is polyfloral, the average number of species is 13 taxa per sample. During the study period, changes observed were that the percentage of the Rosaceae and Calluna pollen types had decreased, while the proportions of the Brassicaceae and Salix pollen grains showed an increase. The concentration of pollen grains per gram of honey varies from 100 to 700 000. The current information provides new insights into the pollen composition of Estonian honey and could be used to develop analytical standards for the pollen content of Estonian honey.

The effects of ecotope, microtopography and environmental variables on diatom assemblages in hemiboreal bogs in Northern Europe

Bogs comprise various niches that are ideal habitats for diatoms. Even though diatoms are widely used bioindicators in many aquatic ecosystems, little is known about their within-site distribution and versatility in bogs. The abundance of bogs in hemiboreal region offers a good opportunity to study the variability of diatom assemblages in different bog habitats and factors influencing it. This study aims to describe the diatom assemblages (1) in the most common bog ecotopes and (2) along the microtopography, and (3) to evaluate the extent to which abiotic environmental parameters (i.e. water table, electric conductivity, pH, moisture and shading) affect the diatom assemblages. According to our results, the most widespread and abundant species are typical bog-inhabiting acidophilic taxa, such as Eunotia paludosa, Kobayasiella parasubtillissima and E. bilunaris. Multivariate analyses showed that some patterns in different microhabitats and ecotopes can be distinguished according to diatom assemblages. In this study, the diatom assemblages were affected by moisture, shading and pH. The study demonstrates the potential usefulness of diatom assemblages as bioindicators to provide additional information about the microsite conditions in bogs.

Sea level changes and Neolithic hunter-fisher-gatherers in the centre of Tallinn, southern coast of the Gulf of Finland, Baltic Sea

Relative sea level (RSL) changes and the palaeogeography of a Neolithic hunter-fisher-gatherer settlement site on the former shore of the Gulf of Finland in the city centre of Tallinn were reconstructed by implementing GIS in landscape modelling based on archaeological, sedimentary and shore displacement data. AMS radiocarbon dating of mammal bones from the cultural layer suggests the existence of the hunter-fisher-gatherer settlement around 5.1–4.8 cal. ka BP on a seaward inclining sandy beach of Tallinn palaeo-bay c. 100 m from the Litorina Sea shoreline and at about 2.4 m above the coeval sea level. The shoreline passed the study site at about 5.8 cal. ka BP and retreated towards northeast with an average speed of 13 m per century, while the RSL lowered by c. 2.5 mm annually. Combining radiocarbon dates of terrestrial and marine mammal bones from the Neolithic cultural layer, a marine reservoir effect of 350 14C years for the brackish-water Baltic Sea was calculated. By using high-resolution archaeological data in combination with RSL and other geological proxies, we demonstrate new possibilities to reconstruct the palaeoenvironment of deeply buried coastal settlement sites and to predict a possible continuation of the cultural layer in heavily built-up areas.