Effects of chronic radiation exposure on phytoplankton communities in special industrial reservoirs of Mayak PA

A comparative study of phytoplankton communities inhabiting six reservoirs in the Southern Urals with different levels of radioactive contamination is presented. Along with increasing the level of radioactive contamination, the diversity of the phytoplankton species is decreases, however the abundance of surviving species and their biomass did not depend on the level of radiation contamination in the studied reservoirs. There were found no signs of ecological regression of phytoplankton communities caused by radioactive contamination up to 6.5 kBq l-1 in the reservoirs of the Techa river Reservoir Cascade R-11, R-10, R-4 and R-3. Ecological regression of the phytoplankton community was observed in reservoirs R-17 and R-9, with a total activity of β-emitting radionuclides 470 kBq l-1 and higher, a total activity of α-emitting radionuclides 220 kBq l-1 and higher. Ecological regression of communities was registered as a decrease in species diversity, fluctuations in the number of algae in the high ranges, and the predominant development of one species. Reduction of species diversity in adverse conditions and violations of interspecies relationships in the community often leads to sharp fluctuations in the biomass and abundance. Moreover, the highest biomass of the algal communities can result from either excessive species gain or species loss. In the most contaminated R-9 (Karachai Lake) species diversity is dramatically decreased to monoculture of a single cyanobacteria species, dominant species could vary in different years of the study.