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Results of analysis of spatial distribution of the nutrient cycle elements in the coastal waters of the Danube region carried out based on the expeditionary research performed by the Marine Hydrophysical Institute in 1997–2013 are represented. Constant inflow of inorganic forms of the nutrient cycle elements (nitrogen, silicon and phosphorus compounds) to the Black Sea northwestern shelf due to the Danube, Dniestr and Dnieper waters provides rich forage reserve for phytoplankton in course of a year. In spring-autumn period in the surface layer of the Danube estuary region the photosynthesis process is accompanied by oxygen generation; and in the bottom layer oxygen is actively spent for oxidation of the precipitated suspended organic matter that periodically results in the bottom hypoxia. Thus in the surface layer phytoplankton consumes the main biogenic cycle elements, whereas in the bottom layer these elements are released due to the organic matter destruction. Influence of different hydrological situations occurring in the estuary region upon spatial distribution of the hydrochemical components is considered. The most important three cases are noted: 1) if the Danube waters propagate rather far (30–50 miles) to the east content of nutrient elements in the oxygen over-saturated surface waters is much lower than in the oxygen undersaturated bottom layers; 2) if the Danube waters are “closed” within the narrow along-coastal belt and the whole estuary region is filled with the open shelf water, practically uniform vertical distribution of nutrient elements is observed beyond the 2–3 mile along-coastal belt; 3) in case of upwelling, the elevated to the surface oxygen under-saturated waters propagating at 20–30 miles off the coast contain much more nutrient elements than the surrounding waters.

Peculiarities of Nutrients Distribution in the Coastal Waters Near the Danube Estuary in 1997 – 2013