Materials and Methods of Study

Proceeding from the problems raised when choosing the region of work we were guided by the following basic criteria: climatic zonality, river run-off value, type of rivers (plain, mountain) and estuaries (see Chapter 3). The important role of climatic zonality and formation of river organic matter composition was pointed out by V.I. Vernadsky: “Already it is possible to determine two separate types of fresh river waters, tightly bound up with the certain climatic zones...These are near-pole rivers with light brown water and black rivers of tropical and subtropical regions. The chemical studying of the waters of these rivers is urgently required” (Vernadsky, 1960). To compare the trends of organic matter transformation processes in the line suspension-bottom sediments in estuaries of northern and tropical rivers the following studies were performed in the southern part of Dvinsky Bay on the section North Dvina—sea and the Amazon estuary.