Assessment of Self-Cleaning from Heavy Metal Contamination of the European Territory of Russia Northern River Ecosystem

Self-purification from heavy metals (Cu, Ni, Pb, Zn, Cd and Cr) was assessed in the estuary area of the one of the largest river ecosystems in the European territory of Russia – the Northern Dvina River estuary. The conditional degree of self-purification of river waters and bottom sediments for winter and summer is calculated. It is noted that the highest values of self-purification of river waters are observed in winter for Cu (54%), Pb (25%), Cd (67%), Cr (82%), and in summer – Zn (44%) and Ni (50%). It was found that the processes of migration of Ni, Zn and Pb from bottom sediments to water predominate in winter, while in summer this process is typical for Pb, Cd and Cu. The index of river water pollution in the seasonal dynamics of heavy metal content was established.