Eutrophication of the Izmit Bay, Marmara Sea

The elongated Bay of Izmit is one of the most heavily polluted semienclosed basins in Turkey. From systematic data obtained during field studies between 1984 and 1988, it is clear that two distinct water masses are present throughout the year. The brackish water which originated in the Black Sea forms a 10 to 15 m thick surface layer. Its salinity and temperature vary from 22-24 ppt and 20-24 °C in summer, to 26 ppt and 7 °C, in winter. Marine water, which arrived from the Mediterranean, underlies the permanent pycnocline and has much more stable properties: salinity and temperature ranges are 37.5-38.5 ppt and 14-15 °C, respectively. Since the phytoplankton production is limited to the upper layer, including the halocline, nutrients have low surface concentrations in productive seasons and a higher concentration in winter. There is a sharp concentration increase in the halocline to high, almost constant, value in the lower layer. Phytoplankton biomass, in terms of chlorophyll-a concentration, has been found to be as large as 33 pg/L during spring in the more eutrophic inner part of the bay. In March 1988, the production reached the peak value of 3.3 g C/(m2 day) with the mean annual rate of at least 2 to 4 times larger than in the Marmara and Black Seas. Dissolved oxygen concentration decreases in the halocline and varies seasonall