Sandimirov S. Pollution of the Sediments of the Paz River basin / In State of the environment in the Norwegian, Finnish and Russian border area. The Finnish Environment. Finland, Jyvaskyla: Kopijyva Oy. 2007, №6, 98p.

5. Pollution of the Sediments of the Finnish Lakes of the Inari Lake - Paz River basin During expeditions of 2005 (April, September and October) seven Finnish Lakes o f the Inari Lake - Paz River basin (Aitojarvi 2, Mellalompolo, Nammijarvi, Inari Vasikanselka, Kanto- jarvi, Suovaselkajarvi, Kivijarvi) have been investigated to study chemical composition o f sediment cores and assess the pollution o f water ecosystems. Data o f lake sediments collected earlier and kindly presented by Dr. Jaakko Mannio (Lampi 222, Nitsijarvi, Sieramjarvi and Pah- tajarvi) have been also used in the investigations. 5.1. Background Concentrations The minimum background concentrations o f investigated heavy metals in sediments o f Finnish lakes o f the Lake Inari - River Paz system were found in Suovaselkajarvi for almost all ele­ ments, and only Cu was noticed in the lowest concentration in the Sieramjarvi (Table 10). The maximum background concentrations o f heavy metals recorded in the Nammijarvi (Cu, Ni), Nitsijarvi (Zn, Cd), Inari Vasikkaselka (Pb, As), Kivijavri (As) o f the Lake Inari - Paz River ba­ sin result from the geochemical and morphometric features o f the lake and its drainage basin (Table 10). The background concentrations o f heavy metals and As in the abovementioned lakes were established to be higher than those in other lakes by a factor o f 10 in average. The average background concentrations o f some heavy metals (Ni, Zn, Cd) in the investigated Finnish lakes o f the Lake Inari - River Paz system are approximately equal to those in the small lakes o f background concentrations o f heavy metals in sediments o f 42 small lakes in Kuusamo, North­ Eastern Finland (Myllymma, Murtoniemi, 1986). The average background concentrations o f Cu in the investigated Lakes in more than 2 times higher than those in the small lakes in Kuusamo, Co and Pb - in 2 times lower. 5.2. Vertical Distribution of Heavy Metals in Bottom Sediments The vertical distribution o f Cu, Zn and Co in the sediment cores o f the investigated Finnish lakes o f the Inari Lake - Paz River system shows usually decreasing concentrations towards sediment surface (Fig. 10). This pattern is characterized for lakes Lampi 222, Aitojarvi 2, Nitsi­ jarvi, Nammijarvi, Suovaselkajarvi, Kivijarvi (see Figures 10 - 20). In some o f the investigated Finnish lakes the subsurface maximum o f the Cu concentrations was fixed - lakes Aitojarvi 2 (on the depth 5 cm), Nitsijarvi (11 cm), Inari Vasikanselka (3 cm), Kantojarvi (3 cm), Suovasel­ kajarvi (5 cm), Kivijarvi (3 cm). This fact may be explained by two reasons - 1) decreasing at­ mospheric emissions o f the main Cu pollution sources o f this Region - smelters o f the Pechen- ganickel Company, and 2) influences o f acidification processes on the behaviour o f such mobile heavy metal as Cu, Zn, Co. Almost all investigated lakes have water pH values lower than neu­ tral, closer to subacid up to 6.0. Profiles o f heavy metals versus depth in sediment cores o f acidified lakes typically exhibit subsurface maxima. This phenomenon could be explained by: 1) remobilization o f metals from the sediments, 2) lower metal sedimentation rates due to de­ creased metal sorption to suspended particles in the water column and decreased availability o f adsorbing surface (Nelson, Campbell, 1991). Concentrations o f Cu, Ni, Cd, Zn, Al in the top sediments of the 15 lakes o f the Finnish Lapland decreased with reduction o f water pH (Dauval- ter, 1997). Increasing Cu concentrations in the top layers o f the investigated Finnish lakes were found in lakes, situated quite close to the smelters o f the Pechenganickel Company (Mellalom- polo - 54 km, Sieramjarvi - 135 km). Overwhelming majority o f the investigated Finnish lakes show increasing concentrations o f Ni towards sediment surface and maximum contents have in the top (0 - 1 cm) or subsurface layers, 33