Zooplankton of subarctic Imandra Lake following water quality improvements, Kola Peninsula, Russia

The composition, species richness and abundance of zooplankton communities were studied in two highly contaminated areas: (1) mainly by heavy metals and other toxic and non-toxic matter, and (2) mainly by fine particles of nepheline and other minerals and organic matter, in the large, subarctic Imandra Lake (northwestern Russia), based on data collected between 1978 and 1990. Reduction in the relative abundance of the typical inhabitants of northern oligotrophic lakes and their substitution by tolerant-to-pollution, widely distributed, circumpolar species were the general trends for the communities. In both lake areas, water quality changes occurred in response to reductions in contamination of metals, mineral particles and organic matter in the mid 1980s. Water chemistry improvements, including decreased concentrations of pollutants, have resulted in partial recovery of zooplankton communities, increase in species richness, density of individuals, and shifts in composition of the dominance group. However, both lake areas are still contaminated and re-establishment of communities typical of a non-polluted lake did not occur between the mid 1980s and mid 1990s.