Phytoplankton biomass investigation in the Saronikos Gulf, winter 1973

Abstract

        The influence of the sewage from Athens and Piraeus introduced at the apex of the Saronikos Gulf was measured in January 1973 using the chloro­phyll a, phytoplankton carbon, phytoplankton cell numbers and C¹⁴ uptake determined for March 1970.

        To recognize the amount and the extent of the eutrophication, baseline values for chlorophyll a, phytoplankton carbon, cell numbers in January 1973 and for C¹⁴ uptake in March 1970 were found.

       From measured chlorophyll a and phytoplankton carbon data, the exten­tion of the polluted area can be defined. The eutrophic zone extended to the western region more than 30 km into the Gulf of Megara, in the south about 21 km to the north coast of Aigina and in the eastern part 12 km. The mean values of the three parameters in the polluted area (the outfall excluded) represented increases over baseline values of a two fold for chloro­phyll a, a 2.7 fold for phytoplankton carbon, and a 6.6 fold for C¹⁴ uptake. The corresponding maximum values near the outfall represented respectively 4.2 and 4.9 and 11 fold increases over the baseline values.

        The difference in the extent of the eutrophic area, using the distribution of chlorophyll a and P_c, between the east and west is obvious. It may be explained by a circulation flowing counter clockwise in the upper Saronikos such that Aegean water is brought in along the Attikis coast, mixed with sewage outfall water, and then moved south and southwest towards Aigina.