CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Biology. Ecology

Volume 54 No. 3 September 2005

Bottom topography and sediment lithology in two small lakes in Estonia; 171–189

Jaanus Terasmaa

Abstract. In small lakes (< 10 ha) the process of sedimentation is not influenced very strongly by wind and wave activity and spatio-temporal variations in the composition of sediments are related with the topography of the current basin. Investigations on surface sediments (LOI, grain-size composition) in two small Estonian lakes – Lake Viitna Linajärv and Lake Väike Juusa – showed that up to 50% of the lithological composition of sediment is determined by the slope inclination, distance to the shore, and water depth. A composite dimensionless parameter (CP) developed enables to use the same approach to the description of the location of the site in lakes of different size, bottom topography, and hypsographic curve. Using the CP value it is possible to estimate the location of the sampling site in either an accumulation area (A area) or erosion–transportation area (E + T area) with A < CP = 2.5 ± 0.5 < E + T.

Key words: small lakes, lake sediment, textural analysis, grain size, slope inclination, composite parameter.

Vertical structure of horizontal currents and vertical velocities observed off the Estonian coast using a recording Doppler current profiler; 190–209

Ülo Suursaar, Tiit Kullas, and Mikk Otsmann

Abstract. The 3D current structure was studied in Muuga and Küdema bays using RDCP 600 current profiler data from autumn 2003 and early summer 2004. Altogether 245 hours of flow measurements from up to nine depth layers were obtained. Despite calm weather conditions (average wind speed 3.4 m/s during the three measuring periods), the maximum horizontal current velocity reached 37 cm/s. As all the mooring sites were relatively close to the coast, downwind horizontal transport with relatively small differences over the vertical profile prevailed. The average modula of vertical velocities were between 0.47 and 0.60 cm/s, being 10–20 times smaller than the simultaneous horizontal velocities. This may suggest that at least above sloping bottoms and within the upper 10–20 m layer, rapid vertical spread of both hydrochemical and hydrobiological properties is hydrodynamically favoured. However, higher than expected measured vertical velocities indicate a disagreement with certain theoretical considerations. The possibility that the particles backscattering the RDCP signals were not neutrally buoyant should be investigated in detail in the future.

Key words: currents, vertical velocities, upwellings, RDCP, ADCP, flow measurements, Baltic Sea.

The effect of hydrodynamics on the phytoplankton primary production and species composition at the entrance to the Gulf of Finland (Baltic Sea) in July 1996; 210–229

Inga Lips, Urmas Lips, Kaisa Kononen, and Andres Jaanus

Abstract. A 10-day multidisciplinary experiment with the aim to study the development of late summer phytoplankton bloom and the controlling hydrodynamic mechanisms was carried out at the entrance to the Gulf of Finland in July 1996. Clearly defined physical phenomena – a downwelling, near-slope jets, and a mesoscale anticyclonic eddy – were observed in the area during the study period. Due to the relatively strong currents connected to the jets and eddy periphery (current velocity up to 35 cm s^–1), the advection of different water masses through the sampling area gave rise to a noteworthy variability of biological parameters. However, the formation of the eddy was reflected in horizontal patterns of the patchiness of phytoplankton productivity and species composition in the upper layer. The largest value of primary production was observed in the water mass trapped inside the anticyclonic eddy. The flagellates abundance was the highest inside the eddy, while the proportion of cyanobacteria in the plankton community was the largest outside. Our conclusion is that the vertical motions associated with the mesoscale eddy and occasional mixing events on the background of low concentrations of dissolved inorganic N and P created horizontally different conditions, which favoured simultaneous development of different groups of phytoplankton in a small spatial scale.

Key words: primary production, phytoplankton species composition, hydrodynamic control, Gulf of Finland.

Smelt (Osmerus eperlanus L.) in the Baltic Sea; 230–241

Heli Shpilev, Evald Ojaveer, and Ain Lankov

Abstract. Smelt, a cold-water anadromous fish, has well adapted to the conditions in the brackish Baltic Sea and has formed local populations. The species is common in coastal waters but the most important marine smelt stocks are confined to the areas where the water of low temperature and relatively high oxygen content persists year round, in the neighbourhood of large estuaries and lagoons. The abundance of smelt is higher in the northern and eastern Baltic: in the Gulf of Bothnia, eastern Gulf of Finland, Gulf of Riga, and Curonian Lagoon. Smelt populations of these areas differ in growth rate, maturation, reproduction conditions, abundance and catch dynamics, etc. Smelt reproduction depends on temperature, it starts and finishes earlier in the southern areas than in the north. The growth rate of the fish is higher in the south and decreases towards north. In the Gulf of Riga the size of younger smelt has increased since the end of the 1960s. However, beginning with the early 1990s the weight of older fish has declined.

Key words: smelt stocks, abundance dynamics, growth, reproduction.

A retrospective view of occupational exposure to asbestos-containing dust in a cement factory; 242–248

Maie Kangur

Abstract. A retrospective view of occupational exposure to asbestos-containing dust during the processing of asbestos-cement sheets is presented. Total dust concentrations were determined by the gravimetric method and airborne fibre levels by the phase contrast optical microscope method. All the samples were collected at stationary measuring points (area samples). Airborne fibre and total dust concentrations varied in a large range during processing. The average airborne fibre concentrations at the workplaces were from 0.02 to 4.40 fibres/cm³ and the average total dust concentrations were from 1.20 to 8.60 mg/m³. At the present time asbestos is not used industrially in Estonia.

Key words: chrysotile asbestos, total dust, occupational exposure.