Brown-water dystrophic lakes have several limnological characteristics that clearly separate them from clear-water oligotrophic and murky eutrophic lakes. In this study, I examined the sedimentary midge (Nematocera) assemblages from 30 shallow boreal lakes of varying humic status to test the influence of dystrophy on community composition. The results indicate differing community assemblages between oligohumic and humic lakes. Several taxa were restricted to clear-water lakes, whereas dystrophic lakes also had their characteristic taxa, which were rare or absent in the clear-water lakes. The most common and abundant nematocerans having statistically significant indicator values for dystrophy were chironomids Zalutschia zalutschicola-type, Tanytarsus mendax-type, and Cladotanytarsus mancus-type, together with the phantom midge Chaoborus flavicans. These results indicate that the level of dystrophy plays a significant role in determining midge distribution in boreal lakes. Therefore, consideration of differences in humic conditions is crucial to contemporary midgebased environmental assessments and long-term paleolimnological investigations, because temporal changes in the humic state may have occurred.
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Vol. 20 • No. 4