Assessment of contamination of the estuarine area of the Northern Dvina River by calculating background concentrations (Fe, Mn, Zn, Cu, Cd, Pb, and Ni)

This publication is a continuation of research on the quantitation of the heavy metal contamination level (Fe, Mn, Zn, Cu, Cd, Pb, and Ni) in the ecosystem components of the estuarine area of the Northern Dvina River. To assess the contamination level with these metals in the ecosystem of the Northern Dvina estuarine area in the spot of the highest anthropogenic load (the area of Novodvinsk – Arkhangelsk – Severodvinsk urban agglomeration), we use the method of comparative analysis of the study object with the background plot – the river section above urban development. Using spatial mapping of the enrichment factor values for the aquatic ecosystem components, areas with abnormal excess of metal content in mollusc tissues, bottom sediments, and bottom water layer were determined. As established, the area adjacent to the city center and to an industrial zone on the left bank is subject to the highest anthropogenic load in the water area of the river delta top. The most likely sources of contamination with the considered heavy metals are the inflow of surface wastewater (meltwater and rain storm runoff), untreated municipal wastewater, and direct short-range atmospheric transport. The analysis of mollusc tissues proved to be a more informative and indicative approach to the assessment of the heavy metal contamination in water areas with complex hydrological and hydrochemical environmental gradients than the analysis of bottom water layer and bottom sediments.