Second-Phase Eutrophication of the Black Sea Shelf

O. A. Yunev

A. O. Kovalevsky Institute of Biology of the Southern Seas of RAS, Sevastopol, Russia

e-mail: o.yunev@ibss-ras.ru

Abstract

The objective of this paper is to study possible mechanisms of the Black Sea shelf eutrophication. The research was based on the analysis of long-term changes in eutrophication indicators (phosphates, nitrates, and oxygen) and was performed for various sea layers with averaging for different periods: the nutrient concentration in the surface layer (January – March) and oxygen concentration in the surface layer and layer under thermocline (May – September). The data on oxygen content variability in the two layers were used as an indirect indicator of the summer primary production change in the photosynthetic zone. The nutrients concentration at the north-western shelf in winter was marked by a gradual increase in the 1970s through the first half of the 1980s, decrease in the second half of the 1980s, and stabilization in the 1990s. At the same time, simultaneous changes in oxygen content in the surface layer and layer under thermocline indicated an increase of summer primary production up to the early 1990s. Analysis of these results showed that two stages can be identified in the Black Sea shelf eutrophication. From the early 1970s to the first half of the 1980s, the major source of shelf eutrophication was unusually intense nutrient input to the sea with river runoff. In the second half of the 1980s and early 1990s, when nutrient input to the sea with river runoff stabilized, regenerated nutrients, which entered the water layer from bottom sediments, became a eutrophication source.

Keywords

eutrophication indicators, long-term changes, Black Sea shelf, eutrophication phases.

Acknowledgments

The research is performed under state order No. AAAA-A18-18021490093-4 on topic “Functional, metabolic and toxicological aspects of existence of hydrobionts and their popultaions in biotops with different physical and chemical regime”. The author is grateful to Elena E. Sovga, Leading Research Associate of MHI RAS, Dr.Sci. (Geogr.), for valuable comments on the paper.

For citation

Yunev, O.A., 2020. Second-Phase Eutrophication of the Black Sea Shelf. Ecological Safety of Coastal and Shelf Zones of Sea, (2), pp. 80–91. doi:10.22449/2413-5577-2020-1-80-91 (in Russian).

DOI

10.22449/2413-5577-2020-2-80-91

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