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

Table 27. The organic matter contents (LOI, % ) and heavy metal concentra­ tions (цд/д, dry weight) in the surface (0-1 cm) and pre-industrial (21-22 cm) sedimen t layers. Cfand Cdare con­ tamination factor and degree ofcontamination values, respectively. Fig. 42. Vertical distribution of the concentrations ofPb, As, Cd and Hg (pg/g, dry weight) in the sediment core of Lake Gjokvatn. third of the peak levels of the late 1970s, the deposition of pollutants still affects the water bodies in the area. The average concentrations of Cu, Ni and Al are 2.1 |ig/l, 1.2 |ig/l and 54 |ig/l, respectively. 2.4.2. Lake bottom sediments The sediments of Lake Gjokvatn have organic matter contents (LOI) in the uppermost 1 cm layer of more than 30% (Table 27). Airborne deposition of pollutants from the smelter does not seriously affect water quality of the lake, the pollution mainly consist­ ing of chalcophile elements such as Pb, As, Cd and Hg. The top 4-5 cm sediment layer is the most polluted (Fig. 42). The contamination factor values of these heavy metals range from 1.8 to 5.1 (Table 27), i.e. the values correspond to considerable and moder­ ate (Cd and Hg) contamination. Arsenic has the highest Cfvalue. The contamination factor values of the other heavy metals are moderate to low. The degree of contamina­ tion value (17.2) for this lake corresponds to considerable contamination. Lake Layer, cm LOI Cu Ni Zn Co Cd Pb As Hg cd Gjokvatn 0-1 31.61 73 56 134 36 0.67 34.3 3.03 0.309 21-22 37.33 151 36 236 25 0.33 8.0 0.60 0.168 c, 0.5 1.5 0.6 1.5 2.0 4.3 5.1 1.8 17.2 2.4.3. Hydrobiology investigations No direct hydrobiological investigations have been carried out in this lake. 82 Catalogue o f Lakes in the Russian, Finnish and Norwegian BorderArea