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A. Lukin et al. / The Science o f the Total Environment 306 (2003) 73-83 75 ervation in Lugol’s solution and neutralization in formaldehyde, phytoplankton were identified and counted following common methods according to the nomenclature described by Tikkanen (1986) in a Zeiss inverted microscope. The volume of phytoplankton species was calculated using ordi­ nary geometric figures (Tikkanen, 1986). Zooplankton samples were taken from Lake Kuetsjarvi in August 1993 and 1994 and July 1996. Quantitative zooplankton samples were tak­ en with a 6 l, 1 m-long tube sampler from depths of 0 -5 m, 5-10 m, 10-13 m. The water was sieved through a net with a mesh size of 40 mm. Additional qualitative samples from each station were obtained using a plankton net with a mesh size of 40 mm from bottom to the surface. All samples were fixed in Lugol’s fixative. The num­ ber o f species and biomass (wet weight) were calculated. Invertebrate samples were taken between 1990 and 1992, 2 -3 times in summer. Samples were collected from different habitats (lake littoral and profundal zones, inlets and outlets of lakes, streams and rivers). Qualitative samples from the lake shore were collected using a hand net (mesh size 0.5 mm) for 1-3 min. Quantitative samples were taken using an Ekman grab (covering an area of 213 cm2) along five profiles from the lake shore to the deepest profundal area. A total of 3-5 samples were collected from each site. The sam­ ples were washed through a sieve with 0.25-mm mesh size. All animals were picked out and pre­ served in 70% ethanol. Polycentropodidae caddisfly larvae and Chiron- omus chironomids were collected from the littoral habitat and at 15-m depth, respectively, to assess metal bioaccumulation in 1991. Each sample con­ sisted of approximately 50-100 elder instar cad­ disfly larvae or 80-100 chironomids, respectively They were placed in plastic containers with dis­ tilled water to remove the intestine contents for approximately 12 h. After that, samples were rinsed with distilled water, dried with high purity chemical filter paper and stored at the laboratory frozen in refrigerator. Fish were caught in June 1992 and September 1990-1996 with a standard gillnet series, consist­ ing of 9 fleets (10, 12.5, 16, 21, 25, 30, 35, 38, 45 mm bar mesh size) (Rosseland et al., 1979). Gillnets were placed in the littoral and profundal zones at a depth from 1.5 to 12 m. All fish samples were analyzed for body length and weight, sex, gonad maturity, fat content o f intestine and stom­ ach fullness. Scales, otoliths, cleitrums and oper- cula were collected for age determination according to standard methods (Jonsson, 1976; L’Abee-Lund, 1985). Pathomorphological analysis to examine devia­ tions in the function o f vital organs was used to assess fish condition. The analysis was based on the method of visual expert assessment of patho­ logical changes in fish organs and tissues support­ ed by histological description. The damage to each organ was estimated on a four-point scale (0, 1, 2, 3), where 0 was the absence ofvisible pathologies, 1—initial stage of visible modifications, 2—aver­ age degree of damage, 3—distinct pathological modifications proving the process irreversible. Dif­ ferent morphs of whitefish were identified accord­ ing to common standard taxonomic methods (Reshetnikov, 1980). Heavy metal concentrations in tissues and organs were determined for the following species: brown trout, whitefish, perch and pike. Subsamples were collected from the gills, liver, kidney, muscles and skeleton. Whitefish was chosen as the indica­ tor for assessment of heavy metal accumulation in fish depending on their content in water and sediments. Data on the concentrations o f heavy metals in whitefish from Lake Umbozero (central part o f the Kola Peninsula) were used as the control. Concentrations of heavy metals in the sediments, invertebrates and fish were determined by atomic absorption spectrophotometer (Perkin Elmer 460 and 560) using the standard addition technique. The concentrations o f metals in the surface layer (0-1 cm) of sediments and Cf values were used as the indicator of the pollution level (Hakanson, 1980). Simple linear regression was used to assess variation o f heavy metal levels in fish with Cf in sediment. 3. Results The proximity of smelters largely influenced the hydrochemical parameters measured in Lake