Changes in chemical parameters in the Bulgarian Black Sea coastal area as an indication of the ecological state of the environment

Abstract

In the present paper the main trends in the principal chemical parameters and the phytoplankton communities in the close coastal area are discussed, aimed at evaluating the present ecological state of the environment and water quality in comparison with historical data. The results reveal a decrease in the content of PO₄ and Si, while there is no apparent trend in the N-NO₃ variability. In seasonal terms a change in the minima and maxima of some parameters is evident, and a seasonal dynamic closer to the natural annual cycle in the Black Sea. A decrease in the average annual phytoplankton biomass is established, especially pronounced during the summer period. The results suggest a positive sign of evolution of the environmental characteristics of the coastal zone, which should be treated rather tentatively due to the still high level of nutrients and the capacity of the ecosystem to produce and maintain high phytoplankton biomass.