EVALUATION OF TROPHIC STATUS OF AGRAKHAN BAY (THE NORTH CASPIAN SEA) AS A PART OF ECOLOGICAL MONITORING OF SPECIALLY PROTECTED AREAS

Abstract. Aim. Hydrochemical composition of waters of Agrakhan Bay (the North Caspian Sea), degree of pollution, structure and quantitative characteristics of phytoplankton, zooplankton and zoobenthos is given in the paper. Evaluation of a trophic status of the bay and seasonal trophodynamics are given as a result of study.
Material and methods. The study is based on original materials from expeditions of 2012 (Autumn) and 2013 (Spring and Summer) in Agrakhan Bay. The complex materials are collected on stations with distance 3.5 km. Totally was made 16 marine stations, where samples of water, phytoplankton, zooplankton and benthos were taken.
Results. Agrakhan Bay is eutrophic by level of dissolved oxygen and its BOD. However, the oxygen deficiency is not observed. concentration of oxygen is high almost in all seasons, that has a beneficial effect on hydrobionts. Seasonal dynamics indicates that Agrakhansky bay is oligotrophic within a year, but its trophic status increases to mesotrophic and even to hypertrophic in some periods. The northern part ща the bay is eutrophic. Difference in trophic levels of different parts of the bay is the result of significant differences in depth and area of water surface.
Conclusions. Anthropogenic impact on Agrakhan Bay increases its trophic status. Seasonal trophic level of Agrakhan Gulf except natural processes depends on the "purity" of the Terek River sediments, which are the main source of biogenic elements. Typically, the absolute concentration of biogenic elements in Agrakhan Bay increases with the increase of eutrophication.

the Northen Caspian Sea, Agrakhan Bay, biogenic elements, oxygen concentration, trophic status, phytoplankton, zooplankton, benthos

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