Abstract
The chemical composition of bottom sediments is an important indicator of the ecological state of both water systems and watershed areas, since contaminated bottom sediments are a potential source of secondary pollution of aquatic systems. The analysis of recent publications shows that great attention has been paid to the chemical composition of bottom sediments, however, as a rule, these studies are of a local nature, that is, they cover very small areas. This often raises the issue of criteria for assessing the ecological and geochemical status of bottom sediments, since a small number of samples does not allow correctly determining the local geochemical background. In addition, generally accepted norms, for example, the maximum allowable concentrations, do not exist for bottom sediments. In these conditions, data on regional geochemical backgrounds of pollutants are needed. The need for the implementation of the Water Framework Directive in Ukraine, which requires the introduction of water management basin-based, necessitates the determination of the geochemical characteristics of bottom sediments within the river basin territories. To study the distribution of heavy metals and determine their regional backgrounds in the bottom sediments, a database of environmental and geochemical information was used in the GIS, one of the blocks of which is information on the content of chemical elements and compounds in the bottom sediments of watercourses and water bodies of Ukraine, and the electronic map of river basins of Ukraine. Based on the analysis in the GIS of information on the chemical composition of the bottom sediments of the rivers of Ukraine (about 8,1 thousand samples), regional geochemical background of lead, zinc, copper, chromium, nickel and cobalt have been determined. The main regularities of distribution of chemical elements in bottom sediments in the territory of Ukraine are established. For the chemical elements in question, a gradual increase in their content in soils from north to south, that is, from the river basins of the Polissya zone to the basins of the Steppe landscape-climatic zone, is consistent with the geochemical features of the soil cover of the catchment areas. The increased background content of chemical elements in bottom sediments often spatially coincides with the spread of soil differences in the catchment areas, which also have a high content of these elements. The maximum background content of most heavy metals in bottom sediments is naturally clearly recorded within the Carpathian-Crimean metallogenic province. Thus, despite the long and intensive technogenic impact on the surface water bodies of Ukraine, it is necessary to note the priority of natural factors in the formation of the chemical composition of bottom sediments, at least for the heavy metals considered above.