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

than during the flood period. The highest concentrations of total N (up to 349 pg/l) occur in the spring and beginning of summer. In 1991, however, the maximum total N concentration was 468 pg/l during the ice-coverperiod. Based on the concentrations of mineral nutrients, the lake is classified as oligo- trophic. The lake also has colour values, and organic matter (up to 6.6 mg/l) and Fe concentrations (mean 146 pg/l) typical of small water bodies in the region. The trophic type of the water body is to a considerable degree determined by the location of the River Puldshekjarvi in the hydrographic system: the lake belongs to a lake-river system of a small stream that flows into Lake Puldshekkjarvi. The water exchange index is 0.84, i.e. full water exchange in the lake takes about 8 months. As suspended particles are deposited more intensively in the lake, the bottom of the lake is completely covered with a thick layer of silt consisting of undecomposed zooplankton debris and organic matter. This is of primary importance for the feeding ofwhitefish species.The con­ ditions for the growth of food organisms are obviously highly favourable. Due to the fact that most of the lake is not deep, the circulation ofmineral nutrients in the water is faster in the summer; this also increases the production capacity of the water body. During high water periods and episodes of high precipitation in the autumn, the concentrations of species of mineral nutrients (P 0 43~and N 0 3) that determine the lake productivity are low. The low concentrations of micronu­ trients in the water indicate a low input to the water body from the chemical weathering of mineral material in the watershed. During the period of peak emissions from the smelter in the late 1980s and early 1990s, the Ni and Cu concentrations in the lake water were not excessively high. At the present time, however, airborne pollution results in higher concentrations of Cu (up to 3.4 pg/l) and Ni (up to 3.6 pg/l) during the open-water period. Because of the relatively small area of the watershed area, the Cu and Ni concentrations do not increase during snowmelt and periods of high water. When the water is acidified during flood periods, the concentrations ofA1 (up to 82 pg/l) and Mn (up to 80 pg/l) increase as a result of dissolution and weathering of the soil in the watershed. 1.17.2. Lake bottom sediments The sediments of Lake Virtuovoshjaur have relatively high organic matter contents: the LOI value in the uppermost 1 cm layer is 40% (Table 18) owing to the high productivity of the lake. The lake is located at a distance of 90 km from the Pechen­ ganikel smelter, and is mainly subjected to pollution mainly by chalcophile elements Water colour, deg. 30 17-39 NH4, Mg/I 13 2-51 N03, цд/І 8 1-42 241 Total N, ng/l 165-468 po 4, мд/і 2 1-4 Total P, цд/І 6 1-13 146 Fe, мд/І 16-460 Cu, мд/і 1 2 0.5-3.4 Ni, мд/і 1 2 0.5-3.6 52 AI, Mg/l 12-82 14.3 Mn, мд/і 1.0-80.0 0.4 Pb, мд/і 0 . 1 - 1.2 Catalogue of Lakes in the Russian, Finnish and Norwegian BorderArea