Long-term ecological changes in Romanian coastal Waters of the Black Sea

Measurements of inorganic nutrients, phytoplankton cell densities and benthos biomass were carried out at different stations off Constanta, on the Romanian shelf and in the Danube River by the Romanian Institute of Marine Research between 1959 and 1992. Measurements in the Sulina branch of the Danube reveal that there was a five- and two-fold increase, respectively, of the total inorganic nitrogen and phosphate loads of the Danube River, whereas the riverine input of silicate decreased to about one-third. In addition, industrial waste waters contribute to this input—especially phosphate. Distinct increases of phytoplankton cell densities, as well as the frequency of algal blooms, were reported. There was a more than double decrease of benthic biomass in the Romanian shelf area due to suboxia in the bottom water after the sedimentation of algal blooms.