Jaanus Terasmaa

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.

Recent patterns of sediment accumulation in a small closed eutrophic lake revealed by the sediment records

A short-core palaeolimnological investigation was undertaken with the aim ofacquiring knowledge of sediment deposition. Analyses of the lithological composition of sediments from the whole-lake basin were performed on the small eutrophic L. Linajärv (northern Estonia) and the concentrations of mineral and organic matter were measured on 647 sub-samples from 14 sediment cores. The accumulation rate of the sediment sequences was established and C/N ratios of organic matter in some cores were recorded. Results indicate that the water depth, basin slopes and distance to the shore have the most important impact on the physical sediment properties. It was shown that variations in the mineral matter concentrations were influenced by the changes in deposition conditions in the areas with steep slopes. The study indicated that more objective information about the sedimentation mechanisms is obtained using analysis of the concentration ratio of mineral and organic matter since it reduces the implied role of diagenetic compaction.

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.

Designing Learning Experiences Outside of Classrooms with a Location-Based Game Avastusrada

Mobile technology with numerous affordances provides opportunities to take learning outside of classrooms, into authentic contexts. This paper presents a location-based tool – Avastusrada - which allows teachers to easily create learning tracks by developing different types of tasks connected to specific locations. The paper reports preliminary results of teachers’ experiences with the tool and their perceived affordances of the tool for various educational purposes. In addition, emerged shortcomings of the tool and further suggestions for improvements will be outlined. The first pilot study with K-12 school teachers and students demonstrated that the tool has a great potential to be used in outdoor formal learning contexts because of its ease of use and its potential to enhance numerous competencies outlined in the national curriculum.