The role of biochemical processes in formation of waters and bottom sediments after reduction of anthropogenic pollution

The article is devoted to anthropogenic and biogeochemical processes that affect the water and bottom sediment (BS) formation of the subarctic Lake Imandra. The data of long-term observations were presented, showing changes in the water chemical composition during the period of maximum pollution and after decrease in anthropogenic load within the last 30 years. It was found that the content of toxic metals in water decreased, but due to climate warming, the input of organic matter and nutrients increased, which stimulated an increase in the intensity of production processes. Enrichment of water during the period of intensive heavy metal pollution led to their accumulation in bottom sediments (BS); the highest metal concentrations detected in the surface layers, which belong to the modern period of sedimentation. The development of oxygen-free conditions in bottom horizons due to sedimentation and oxidation of organic matter, which leads to metal cycling that prevents their burial was shown. Physicochemical and biogeochemical processes are considered as explaining the diffusion of metals to the surface of bottom sediments and the formation anomalously high concentrations of metals in the surface layers of BS. The hypothesis of the appearance of the diagenesis initial stage in bottom sediments was proposed.