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78 A. Lukin et al. / The Science of the Total Environment 306 (2003) 73-83 hudsoni, Keratella cochlearis, Bosmina longispina, Daphnia cristata ; in August 1994 - Kellicottia lon­ gispina, Bosmina longispina, Daphnia cristata and in July \996-Notholca caudata, Keratella quad- rata, Polyarthra vulgaris. Other common species were Asplanchna priodonta, Conochilus unicornis, Bosmina longirostris, Eudiaptomus grasilis. Biomass calculations [g m -3 wet weight (ww)] showed differences between years (Fig. 4 ). Bio­ mass level in 1993 was not high (0.35-g m -3 ww). High biomass volume was recorded in the southern part (Ku-1) in 1994. It was due to high abundance of Cladocera (Bosmina longispina, Daphnia cristata) and Copepoda (Eudiaptomus gracilis). Low biomass (0.27 g m -3 ww) was recorded in the northern part (Ku-2) in 1996. It was probably associated with a much lower abun­ dance of cladocerans and copepods. 3.4. Zoobenthos Fifty-six taxa were identified in benthic samples from kick and grab samples. The highest species richness was recorded in shallow lake areas with luxuriant macrophyte vegetation. Large numbers of Cricotopus, Stictochironomus, Orthocladius and Tanytarsini chironomids , water beetles were col­ lected in the littoral zone. Other invertebrates of importance in the lake littoral zone were Limne- philidae and Polycentropodidae caddisflies, and Pisidium mussels. In deeper areas chironomids made up more than 70% of the species number and 80% of invertebrate specimens, respectively Chironomus was the dominant genus among chi- ronomids in grab samples. Maximum densities and biomass of invertebrates at a depth of 15-20 m were 4633 individuals m -2 and 21.1 g m -2, respectively The mean abundance and biomass of zoobenthos recorded in grab samples from Lake Kuetsjarvi were 2267 individuals m -2 and 12.1 g m -2, respectively. Chironomids dominated the invertebrate fauna in grab samples from profiles 1-4 , while Tubifi- cidae oligochaeta worms were abundant in sam­ ples from the fifth profile (the most contaminated area near the Kolosjoki stream mouth), where the highest abundance of invertebrates was found (Fig. 5). The lowest species richness of invertebrates was also found in samples from profile 5, where only Tubificidae worms, Chironomus, Sergentia coracina and Monodiamesa bathyphila were recorded. Considerably higher species richness was recorded in parts of the lake distant from the Kolosjoki stream mouth. Chironomus larvae had higher concentrations of all metals studied than caddisfly larvae, except for Ni and Cd. Invertebrates of the lake are character­ ized by high concentrations of Ni. Distribution of metal concentrations was N i> C u > Z n > P b > Co > Cd for chironomids, and Ni > Zn > Cu > Pb > Cd>Co for caddisflies. Fig. 5. Mean abundance of zoobenthos in grab samples from different depths of five profiles of Lake Kuetsjarvi.