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

In cases where the age of the bottom sediments had been determined, the distribu­ tion of the elements was plotted against the dated bottom sediments. This provided an overall picture of the history of pollution of the lake and its watershed area. Contamination level assessment Hakanson’s method was used to assess the contamination level in the lakes (Hakanson, 1980). The value of the contamination factor (Cfi) was determined for each element: where CQ =the element concentration (i =Ni, Cu, Co, Zn, Cd, Pb, As, Hg) in the up­ permost layer (0-1 cm) ofbottom sediments, taken from the deepest part of the water area (accumulation zone), and Cn‘ =background (pre-industrial) concentration in the bottommost layer of the bottom sediment column. The contamination factor (Cf‘) has been calculated for each pollutant or com­ pound. If CQ‘ >Cn‘, then the element is considered to be a pollutant. If С01! < Cn\ then the element is not regarded as a pollutant. This approach utilizes the following classification of contamination factors (Hakan­ son, 1980): Cf‘ <1 =low (low level of pollution of the bottom sediment by this ele­ ment); 1 <Cf‘ <3 =moderate; 3 <Cf‘ <6 =considerable; C j > 6 =high. The degree of pollution by chalcophile elements (Cd) was determined as the sum of all contamination factors (С£‘) for the given lake or the sampling site: n n Со-1! C,= I C fi= I--------- i = l i = l С 1 n This approach provides a measure of the contamination factor (Cf‘), which depicts the pollution of the water area by both the individual chalcophile elements and their total contribution, which is based on the determination of the degree of contamina­ tion, Cd, which, in turn, expresses the overall pollution of the water body by the ele­ ments in question. Similarly, determination of the contamination degree, which comprises the con­ tamination factors of the individual elements, is based on classification of the Cdval­ ues, as suggested by Hakanson (Hakanson, 1980), as follows: Cd< n =low; n <Cd< 2n =moderate; 2n < Cd< An =considerable; Cd> An =high pollution (n is the number of elements) Classification of the contamination degree for 8 elements is: Cd<8 =low; 8 <Cd<16 =moderate; 16 <Cd<32 =considerable; Cd>32 =high. Catalogue o f Lakes in the Russian, Finnish and Norwegian BorderArea