Sandimirov S.S. Catalogue of lakes in the Russian, Finnish and Norwegian Border Area. Finland, Jyvaskyla: Kopijyva Oy, 2008.

ades. Acidification is determined by a number of factors: the amount of acid-forming oxides, deposition levels in the catchment area and the duration of acidifying deposi­ tion, the geochemical features of the region, hydrochemistry and morphology of the water bodies etc. Acidifying deposition is the main reason for the drop in pH in water bodies in the northern hemisphere. For precipitation to be called “acidic”, it should have a pH of less than 5.6. The main acidifying compound in the Arctic is sulphur di­ oxide. It is formed during the combustion of fossil fuels (coal, brown coal, oil products) and during the roasting and smelting of sulphide ores. Lakes and rivers with a small buffering capacity (small reserves of compounds that neutralize acidic compounds) and low ionic strength are the most sensitive to the influence of acidifying compo­ nents. Acidification ofwater bodies is usually accompanied by the dissolution of heavy metals from the bottom sediments, and increased migration of ions such as Cd2+, Pb2+, Hg2*. A sharp reduction in the biodiversity and productivity of water fauna and flora is typical of acidified lakes and rivers. In many cases valuable aquatic species are killed off. Specific features of the Finnish, Norwegian and Russian border area The border area of Finland, Norway and Russia is located in the eastern and north-east­ ern parts of the large water­ shed Maanselka, which curves up from south-eastern Lap­ land far into the north. The watercourses in this region flow via different routes into the Barents Sea. The River Paz, which links Lake Inari with the Barents Sea, is a regulated watercourse with storage pools, blocked by dams. There is a large number of water bodies in the Vatsari region, extending to the north-east of Lake Inari, the water bodies covering an area of 50 000 ha out of a total area of 155 000 ha. There is a large number of isolated lakes without any apparent in­ flowing or outflowing watercourses. One characteristic feature of the Vatsari area is the mosaic structure of lakes, streams, mineral soil and exposed bedrock. The Jarfjord region is characterized by a high proportion of small lakes, and the basin of the Russian part of the River Paz consists of a multitude of lakes, swamps and rivers with rapids and small waterfalls. The mountain lakes ofJarfjord are located about 30 km to the north of Nickel. The average area of the lakes is 6 ha. The geology of the Jarfjord and Vatsari areas is dominated by extremely sparingly soluble bedrock, which makes the lakes highly sensitive to a rise in acidity. There are acidification problem in Sor-Varanger: the lakes in this area, lying between Kirkenes and the Russian border, is suffering from a rise in acidity. The watercourses in the border area have, in general, a high degree ofwater transparency, and low levels of mineralization and organic matter. However, there is also a large number of lakes with a relatively high water colour index, Fig. 1-2 The area covered by the project. Catalogue o f Lakes in the Russian, Finnish and Norwegian BorderArea 7