Tiit Vaasma

Historical changes in the concentrations of polycyclic aromatic hydrocarbons (PAHs) in Lake Peipsi sediments

The distribution of 11 individual polycyclic aromatic hydrocarbons (PAHs) was analysed in a 210Pb dated sediment core from the deepest area of Lake Peipsi and in four surface sediment samples taken from littoral areas. According to the concentrations in the core three groups of PAHs may be distinguished: (1) relatively stable concentrations of PAHs within the whole studied time interval; (2) very low concentrations in sediments accumulated before intensive anthropogenic impact (from 19th century up to the 1920s) following a slight increase and (3) an overall increase in PAH concentrations since the 1920s up to the present. Comprehensive analysis of PAHs in the core and monitoring data obtained in the 1980s together with the lithology of sediments show that an increase of anthropogenically induced PAHs correlates well with the history of fuel consumption in Estonia and speaks about atmospheric long-distance transport of PAHs. The continuous increase of PAH concentrations since the 1920s do not support the earlier hypothesis about the dominating impact of the oil shale fired power plants near the lake, because their emissions decreased significantly in the 1990s. The concentration of PAHs in the deep lake core sample correlates well with the content of organic matter, indicating absorption and co-precipitation with plankton in the sediment.

Changes in lake-sediment structure and composition caused by human impact: repeated studies of Lake Martiska, Estonia

This research uses a comparison of the sediment record of Lake Martiska (NE Estonia) with well-documented historical changes in human impact to identify the factors dominantly affecting the sediment lithological composition, and the accumulation of heavy metals and other microelements into the sediments. To this end, comprehensive lithological-geochemical studies of the upper sediment were undertaken in 1986 and repeated in 2003 and 2005. Oil shale mining and processing heavily impacted the area via atmospheric pollution and groundwater extraction. As a result of the fly-ash deposition clear marker horizons of chemical compounds were formed. Historical water-level fluctuations are clearly reflected in the lithological composition and grain-size variations of the studied sediment cores. During regression and transgression phases displacement of the erosion-transport-accumulation limits caused redistribution of previously accumulated sediments and their return into the biogeochemical matter cycling of the lake. The210Pb chronology of the sediment records is in contradiction with the historical records of fly-ash emissions, suggesting that changes in 210Pb flux and focusing of sediments caused by lake-level change have invalidated the dating models.

Past extreme events recorded in the internal architecture of coastal formations in the Baltic Sea Region

ABSTRACT Vilumaa, K.; Tõnisson, H.; Sugita, S.; Buynevich, I.V.; Kont, A.; Muru, M.; Preusser, F.; Bjursäter, S.; Vaasma, T.; Vandel, E.; Molodkov, A., and Järvelill, J.I., 2016. Past extreme events recorded in the internal architecture of coastal formations in the Baltic Sea region. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 775–779. Coconut Creek (Florida), ISSN 0749-0208. The postglacial uplift and transgressive-regressive phases of the Baltic Sea have affected the formation and displacement of sandy accumulation forms in the region. The dune-ridge complexes preserve a geological record of past sea-level fluctuations, coastal evolution, and extreme events, and offer insights into major driving mechanisms. This study aims to improve methodologies for identifying different storm signatures in coastal deposits using examples from Estonia and Latvia. The paleo-beach ridges are typically covered by aeolian sand, and the inter-ridge swales are mostly filled with organic sediments. Ground-penetrating radar surveys corroborate distinct textural patterns in sand layers underneath the ridges and swales. In the ridges, sharp seaward-dipping reflections represent storm scarps. The ridge sequences without dipping reflections suggest either aeolian origin or longshore transport; smaller sandy ridges, which are buried under peat layers, reflect prolonged, calmer phases. Compound dunes with ridges in their cores indicate major coastal events or shifts in atmospheric conditions that would have exposed wide sand areas to wind and facilitated dune development. This study demonstrates that the aeolian processes and changes in storminess have played an important role in the genesis of ridge-swale complexes in the Baltic Sea Region.

Hazardous radioactivity levels and heavy mineral concentrations in beach sediments of Lake Peipsi, northeastern Estonia

Abstract The present study discusses results of heavy mineral analyses and radioactivity of beach sediments of Lake Peipsi. Such analyses are commonly done globally, but had not yet been conducted for the fourth largest lake in Europe. The average heavy mineral content in Lake Peipsi beach sediments along the northern and western coast is higher than usual for Estonian coastal and Quaternary sediments. Concomitantly, elevated radioactivity levels have been measured in several places, with the highest concentrations observed at Alajõe (1885.5 Bq/kg), which is over five times more than the recommended limit. The aim of the present study is to find sites with higher radioactivity levels, because the northern coast of Lake Peipsi is a well-known recreational area.