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

(Pb, As, Cd and Hg). The top 5-7 cm layer of the lake sediments is the most polluted by these elements (Fig. 19). The contamination factor values for these toxic elements range from 2.3 to 29.1 (Table 18), i.e. the values correspond to high and considerable contamination. The most toxic of the four chalcophile elements, Hg, has the highest Cfvalue. The contamination factor values of the other heavy metals are moderate. The degree of contamination value (44.6) for this lake corresponds to high contamination. Lake Layer, cm LOI Cu Ni Zn Co Cd Pb As Hg cd Virtuovoshjaur 0-1 39.92 23 25 56 9.0 0.30 26.9 2.33 0.083 16-17 36.43 18 19 83 11.6 0.08 4.9 1.02 0.003 c, 1.3 1.4 0.7 0.8 3.7 5.5 2.3 29.1 44.6 1.17.3. Hydrobiological studies Ichthyofauna. Studies were conducted on the fish community in Lake Virtuov- oshjaur in 1992 and 2005. The Ichthyofauna of the lake consists of seven species belonging to seven fish families: whitefish ( C oregonu s lavare- tus), grayling ( Thumallus Thumallus), pike ( Esox lucius), perch ( Perea flu - viatilis), burbot ( Lota lota), minnow (.Phoxinus phoxinus) and nine-spine stickleback ( Pungitius pungitius). Over­ all, whitefish and perch predominate in Lake Virtuovoshjaur (Fig. 20). Pike, trout, grayling and burbot are occasionally caught, and minnow and nine-spine stickleback in the littoral parts of the lake. Sparsely rakered whitefish is present in the lake (up to 30 gill rakers). Its mean length is 19.6 cm, and weight 94 g (Fig. 21). Whitefish can reach a maximum length of 38 cm and maximum weight 714 g. Fish with a weight to 100 g and length 16-20 cm are the most numerous (Fig. 21). The age limit of the whitefish is 9+: 3-year old specimens predominate and fish older than 7 years are only occasionally caught (Fig. Table 18. The organic matter contents (LOI, %) and heavy metal concnetra- tions (цд/д, dry weight) in the surface (0-1 cm) and pre-industrial (16-17 cm) sediment layers. Cf and Cd are contamina­ tion factor and degree of contamination values, respectively. Fig. 19. Vertical distribution of the concentrations ofPb, As, Cd and Hg (цд/д, dry weight) in the sediment core of Lake Virtuov­ oshjaur. Fig. 20. Distribution offish spe­ cies in Lake Virtuovosh­ jaur. Catalogue o f Lakes in the Russian, Finnish and Norwegian Border Area 57