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

Boulder beds occur in almost all parts of the littoral zone, and extend to a depth of about 2-2.5 m. The gaps between the boulders are filled with sand and pebbles. Dark green silt deposits are predominant at a depth of ca. 2-3m. 1.18.1. Hydrochemistry The water of the lake is close to neutral and has a low total mineralization (15.7 mg/l) and alkalinity (79 peq/1). During flood periods the pH falls to 6.17 and then rise back to about 6.85, i.e. oxidation processes do not develop due to the buffering capacity of the water. The lake has low concentra­ tions of base cations and anions, with calcium (average 2.11 mg/l) and bicar­ bonate (average 4.8 mg/l) predominat­ ing. The effects of pollution first ap­ peared in the lake during the period of peak emissions from the Pechenganikel smelter in the late 1980s and early 1990s. Maximum concentrations of most ele­ ments, especially sulphate (up to 8.5 mg/l), Cu and Ni, occurred during this period. At the present time, however, the concentrations of these elements, as well as of other elements that determine the state of the water body, are lower. The annual chemical cycle of the lake is characterized by a reduction in total mineralization (up to 13.6 mg/l), an in­ crease in the oxidizability and a drop in pH during flood periods and high pre­ cipitation episodes when the inflow of humic water increases. During low-water peri­ ods (mainly in the autumn and winter) and when the inflow of groundwater is higher, the total mineralization increases slightly to 26. mg/l, the oxidizability drops and the pH increases. The enrichment of water with P and N is one of the most important criteria used in assessing the development of water eutrophication. The concentrations and rela­ tionships between the species of these mineral nutrients vary according to the season, and the dynamics is to a greater degree determined by the level of production and, consequently, the trophicity of the water body. The concentrations of total P (up to 6 pg/l) and total N (up to 190 mg/l) changed slightly during the study period. In 1993 the maximum concentration of total N in the near-bottom layer during the ice-cover period was 549 pg/l, but a peak value of this magnitude has never been found since. Based on the concentrations of mineral nutrients, the lake is characterized as oli- gotrophic. The lake also has colour values, and organic matter (up to 4.5 mg/l) and Fe concentrations (mean 26 pg/l) typical of small water bodies in the region. In 1990 the maximum concentration of Fe during the ice-cover period was 1571 pg/l. The water exchange index, which regulates the concentrations of mineral nutrients in water, is 1.99, i.e. full water exchange in the lake takes about 2 years. Because sus­ pended particles are effectively deposited in the lake, the lake bottom is completely Hydrocnemical properties pH 6.59 6.17-6.85 Electrical conductivity, 26 mS/cm 24-32 Ca, mg/l 2.11 1.40-7.29 Mg, mg/l 0.64 0.53-0.80 Na, mg/l 1.64 1.41-2.00 K, mg/l 0.38 0.31-0.47 HC03 mg/l 4=8 4.3-5.5 S04, mg/l 4J. 3.1-8.5 Cl, mg/l M 1.7-2.4 Total mineralization, mg/l 15.7 13.6-26.0 Alkalinity, |aeq/l Z9 70-90 Catalogue of Lakes in the Russian, Finnish and Norwegian Border Area