Impact of Wastewaters from Apatite–Nepheline Production on the Biogeochemical Processes in an Arctic Mountain Lake

The Khibiny alkaline massif and associated apatite–nepheline deposits host the world’s largest reserves of phosphate raw materials, which have been explored for more than 90 years. The perennial hydrochemical and hydrobiological studies of the largest reservoir in the Khibiny alkaline massif, Lake Bolshoy Vudjavr, showed that the influx of waste waters from apatite-nepheline production led to the cardinal changes in natural biogeochemical processes. Mineralization, pH value, the fraction of alkali metals and SO_4^2 - in the ionic composition, the content of nitrogen and phosphorus compounds have significantly increased in the water of the lake. The water column of Lake Bolshoy Vudjavr shows a clear vertical hydrochemical stratification due to the distribution of water flows from two main tributaries in different layers. Phytoplankton communities and their quantitative indicators in Lake Bolshoy Vudjavr significantly differ from the conditionally background values; and the naturally oligotrophic reservoir currently corresponds to the mesotrophic status. The composition of phytoplankton is dominated by diatoms, with less common cyanobacterial species capable of causing blooming and toxic pollution of lake water. The seasonal dynamics of phytoplankton is characterized by a single pronounced July maximum. The development of phytoplankton is affected by pH value and the contents of Si and NH_4^ + , with a definite stimulating role played by Cd. Biogeochemical conditions that determine the ecological state of the reservoir are determined by two main factors: anthropogenic pollution by wastewaters of apatite-nepheline production and the intensity of production processes.