Hydrobionts of a freshwater oil-polluted northern lake: bioaccumulation of heavy metals in fish and the rate of ecosystem recovery

The response of phytoplankton, zooplankton, benthic and fish community structure to one of the biggest oil spill in history of Komi Republic (north-west part of Russia) was investigated using data from a long-term survey off the polluted lake. The characteristics of aquatic freshwater communities observed in the study area 10, 11 and 22 years after the spill (1994) were compared to find out the rate of natural recovery of the ecosystem after oil decontamination of bottom sediments. The concentrations of fifteen trace metals (Al, Cr, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Sb, Pb, U, Bi, Th) were analyzed in the tissues (muscle) of three fish species. The concentrations of Al (3-309 mg/kg), Cr (0,1-3,71 mg/kg), Fe (8,6-317 mg/kg), and Cu (0,09-99 mg/kg) in fishes from polluted lake resulted in most cases higher than reference thresholds. Quantitative and qualitative indicators of aquatic invertebrates from polluted lake reach those one of unpolluted lake but do not fully recover 22 years after the spill, despite that oil concentration in water column and in bottom sediments was lower than reference tresholds. We conclude that natural recovery rate of aquatic freshwater ecosystems in northern regions after oil pollution is extremely low. The purification of water and bottom sediments of oil-polluted northern water bodies is necessary for stimulation of ecosystem restoration