FEATURES OF MIGRATION OF HEAVY METALS IN THE SYSTEM ''BOTTOM WATER - PORE WATER - SURFACE LAYER OF BOTTOM SEDIMENTS'' OF THE COASTAL ZONE IN THE EASTERN PART OF THE GULF OF FINLAND

The relevance of the research is caused by the need to study the secondary pollution of the aquatic environment with metals in spring-summer, when various biogeochemical processes are activated that affect the change in the physicochemical state of the surface layer of bottom sediments. The aim of the research is to study the patterns of formation and migration of soluble forms of metals in the system ''bottom sediments - pore water - bottom water'' depending on the spring-summer season and conditions of the coastal zone in the eastern part of the Gulf of Finland. Objects: samples of the surface layer of bottom sediments, pore and bottom water from five stations in the coastal zone in the eastern part of the Gulf of Finland. Methods: potentiometric method for determining pH and Eh in sediments and bottom water. The bulk concentrations of Fe, Zn, Cd, Pb, Cu in bottom sediments were determined by inductively coupled plasma mass spectrometry (ICP-MS). Concentrations of dissolved forms of metals (Fe, Cu, Cd, Zn, Pb) in the pore, bottom waters were determined by inductively coupled plasma mass spectrometry on an Agilent 7700x instrument (Agilent Technologies). Results. The authors have established the regularities of the formation and migration of soluble forms of metals at the ''bottom sediment - water'' boundary in the coastal zone of the eastern part of the Gulf of Finland, depending on temperature changes, oxygen regime in bottom waters and redox processes formed in the surface layer of bottom sediments. It is shown, that at the end of the spring season, reducing conditions are established in the bottom sediments of the eastern part of the Gulf of Finland, contributing to the reduction of iron hydroxides accumulated on the bottom. As a result, there is a flow of dissolved forms of Fe, Cu, Zn, Cd, Pb into the pore and bottom layers of water. In July, the pollution of pore and bottom waters with all studied metals decreases.