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

At the present time the watershed of Lake Porojarvi is subjected to rela­ tively low anthropogenic impacts from the “Pechenganikel” smelter. However, the water system of the lake is exposed to pollutant emissions from the smelter. The main pollutants are sulphur com­ pounds and heavy metals (Ni, Cu etc.). In recent years there has a been a reduction in the deposition load, but higher concen­ trations of Ni (up to 11 |ig/l) still occur during flood periods. Cu, цд/і 2A 2.0-3.1 6.2 Ni, цд/І 2.1-11.0 18 Al, цд/І 16-21 0.27 Pb, мд/І 0.09-0.45 1.12.2. Lake bottom sediments Table 12. The organic matter contents (LOI, %) and heavy metal concentra­ tions (fjg/g, dry weight) in the surface (0-1 cm) and pre-industrial (22-23 cm) sediment layers. Cf and Cdare contamina­ tion factor and degree of contamination values, respectively. The sediments of Lake Porojarvi have relatively low organic matter contents: the LOI value in the uppermost 1 cm layer is slightly more than 20% (Table 12).The lake is lo­ cated at a distance of 20 km from the “Pechenganikel”smelter, and subjected to pollu­ tion by heavy metals (Ni, Cu, Co) and chalcophile elements (Pb, As, Cd and Hg).The uppermost 1-2 cm of the lake sediments are the most strongly polluted by Ni, Cu and Co. Pollution by chalcophile elements began earlier because they have accumulated especially in the top 5-6 cm layer (Fig. 9). The contamination factor values of these toxic elements range from 1.9 to 8.9 (Table 12), i.e. the values correspond to moderate to high contamination. Pb has the highest Cfvalue.The degree of contamination value (30.1) for this lake corresponds to considerable contamination. Lake Layer, cm LOI Cu Ni Zn Co Cd Pb As Hg cd Porojarvi 0-1 22-23 22.95 15.16 131 68 173 42 110 161 27.8 11.8 0.50 0.09 26.0 2.9 38.2 13.7 0.215 0.058 cf 1.9 4.1 0.7 2.4 5.6 8.9 2.8 3.7 30.1 Fig. 9. Vertical distribution of the concentrations of Ni, Cu, Pb, Cd and Hg (pg/g, dry weight) in the sediment core ofLake Porojarvi. 40 Catalogue o f Lakes in the Russian, Finnish and Norwegian BorderArea