Role of Biochemical Processes in the Formation of Waters and Bottom Sediments after Reduction in the Anthropogenic Pollution

The paper is devoted to anthropogenic and biogeochemical processes that effect the formation of the water and bottom sediment (BS) of subarctic Imandra Lake. The data of long-term observations are presented that show changes in the chemical composition of the water during the period of maximum pollution and after the reduction in the anthropogenic load over the past 30 years. The concentrations of toxic metals in the water has decreased, but climate warming has increased the inflow of organic matter and nutrients, and this intensified the production processes. The enrichment of the water in heavy metals during the period of intense pollution resulted in the accumulation of these metals in the bottom sediments, with the highest concentrations of the metals found in the uppermost layers accumulated during the modern sedimentation period. The development of anoxic conditions in the bottom water horizons due to sedimentation and oxidation of organic matter leads to the circulation of metals and hampers their burial. Physicochemical and biogeochemical processes are considered as explaining the diffusion of metals to the surface of the bottom sediments and the accumulation of anomalously high concentrations of metals in the surface layers of BS despite the significant decrease in the concentrations of metals in water. A hypothesis is suggested for the beginning of initial diagenesis stage in bottom sediments.