Proceedings of the Estonian Academy of Sciences

CONTENTS & ABSTRACTS

In English. Summaries in Estonian

Proceedings of the Estonian Academy of Sciences.

Biology. Ecology

Volume 53 No. 3 September 2004

Spatial variability of diatoms, subfossil macrophytes, and OC/N values in surface sediments of Lake Väike Juusa (southern Estonia); 147–160

Jaan-Mati Punning, Liisa Puusepp, and Tiiu Koff

Abstract. The diatom assemblages, organic carbon to nitrogen (OC/N) ratio, and macrophyte remains in surface sediment samples from small dimictic Lake Väike Juusa in southern Estonia were analysed. The results obtained show that changes in the composition of diatoms, macrophyte remains, and OC/N values are in logical dependence on the water depth in the studied site. So the species richness and number of periphytic diatoms are higher in samples collected in the littoral area, from depths up to 3.5 m. The abundance of macrophyte remains is also higher in the littoral. The OC/N ratio, which reflects the share of planktonic matter in the bulk organic matter, has a tendency to increase from the littoral towards the profundal zone. The data obtained by the three different methods enable to apply this approach to study lake-level change in the past.

Key words: diatoms, macrofossils, OC/N, small lake, surface sediment.

Influence of fast ship waves on the optical properties of sea water in Tallinn Bay, Baltic Sea; 161–178

Ants Erm and Tarmo Soomere

Abstract. Wake waves from fast ferries create significant changes in the optical parameters of sea water in the near-bottom layer with a thickness of about 1 m in coastal areas of Tallinn Bay with depths of about 2–5 m. The suspended matter remains in the water column for about 5 min. Rough quantitative estimates, based on the wave-induced increase of the suspended matter in the water column per unit of bottom of the coastal area (about 1 g m^–2) suggest that the bulk influence of fast ferry traffic in Tallinn Bay may result in an annual loss of the order of 100 L of fine sediments from each metre of the coastal line.

Key words: optical measurements, underwater irradiance, high-speed ships, ship wakes, suspended matter.

Changes in shoreline positions on the Harilaid Peninsula, West Estonia, during the 20th century; 179–193

Reimo Rivis

Abstract. As Estonia has a flat and low-lying coastal zone, climate change and associated coastal processes could strongly affect the structure and development of its coastal ecosystems. Milder winters and increased storminess would result in the destruction of coastal areas. Shoreline changes on the Harilaid Peninsula (northwestern coast of Saaremaa Island) were investigated on three study sites. Maps (topographic and aerial photographs) from different times (1900–1998) and data of direct observations (2000–2002) were used to identify changes in the shoreline contours and position. Analysis of shoreline changes clearly show an increasing activity of shore processes over the last 20 years. Intensification of shore processes is well correlated with increased annual storminess and higher sea levels in recent decades. The diminishing of the ice cover near the coast due to warmer winters significantly enhances shore erosion, transport, and accumulation of sediments.

Key words: shoreline change, storm climatology, shore processes, landscape changes, Harilaid Peninsula, Baltic Sea.

Health concerns in the Baltic States, Nordic countries, and Russia; 194–207

Ott Roots and Vladimir Zitko

Abstract. Principal Component Analysis (PCA) of cancer incidences may indicate interesting differences among the Baltic States, Nordic countries, and Russia. For females the difference between Estonia, Latvia and Russia, and also between Finland and Iceland are likely caused by different incidences of lymphoid leukemia in these countries. In contrast to the incidence of cancer in females, the incidence of many different cancers contributes to the differences between ‘west’ and ‘east’ for cancers in males. It remains to be seen whether the suggestions indicated by the PCA could be substantiated and related to some environmental or sociological factors.

Key words: cancer, Baltic States, Nordic countries, Russia, PCDD, PCDF.

The effect of man-caused disturbances on the development dynamics of forest communities on Abruka Island (West Estonia); 208–225

Toivo Meikar, Kaili Viilma, and Alar Lepp

Abstract. Today’s Abruka Island (West Estonia) hosts a species-rich and lush nemoral forest, which has been regarded as a relict of broadleaf forests once widespread in Estonia that survived thanks to the local mild maritime climate. Written sources until the mid-19th century, however, describe Abruka as a habitat of spruce forests. Spruce-dominated stands were prevalent on the island until at least the 1860s. The 1898 forest survey registered a shift in the dominant tree species to the birch – at that time birch stands constituted up to 84% of the island’s total forest area. In fact, the decisive determinant of forest communities of Abruka Island over the last couple of centuries has been man, who since the early 19th century has clear cut without reforestation or maintenance felling. By the 1930s, when a protection regime was enforced on the island, the percentage of spruce dominated stands had dropped to 0.1% and the overall share of the spruce had shrunk to 8.4%. The enforcement of the protection regime has led to an increse in the forest species diversity and created conditions for restoring the share of the spruce as a tree species well suited to the island’s soil conditions.

Key words: historical forest data, communities development, management plan, broadleaf, man-caused disturbances.

Instructions to authors; 226–229