Selected areas of Saronikos Gulf

Bacteria taxonomy-related biomass expressed as carbon per unit volume of the water column; Bacteria taxonomic abundance in water bodies

The results of a yearlong survey of bacterial indicators of faecal pollution in the Saronic Gulf, before and after the Psyttalia treatment plant began operating, are presented. The treatment plant is located on Psyttalia Island, unlike the previous Central Sewage Outlet which was on the Piraeus coast. At the Psyttalia treatment plant primary treatment is applied, whereas prior to this there had been no treatment of Attica area sewage. Two pipes release the treated sewage at a depth of approximately 50m according to the thermocline. A significant decrease in the water's dissolved oxygen has already been observed, mainly in the west basin of the Gulf. Samples were collected monthly from 12 pelagic and 9 coastal sampling points. At the various pelagic sampling points, the maximum counts for TC, FC and TS were 8x10*2-9x10*5 cfus/100ml, 2x10*2-4x10*5 cfus/100ml and 2x10*2-3.8x10*5 cfus/100ml respectively. The minimum values were 0-4x10*3 cfus/100ml, 0-10*4 cfus/100ml and 0-2x10*2 cfus/100ml respectively. Those sampling points that were constantly negative for bacterial-indicators were located at a distance of 3-4 km from the outlets. The microbiological loading at the sampling stations did not present any significant fluctuation with regard to depth. In winter, according to the circulation study, the water column is homogenized: the surface samples appear to have higher microbiological loading than samples collected from greater depths. Most surface samples collected during the summer months were negative and the microbiological loading was concentrated principally at the sewage outlet depth or deeper. The highest counts for the bacterial indicators were recorded in August 1998 and in February-March 1999. All these sampling points were practically negative for bacteria- indicators before the operation of the Psyttalia treatment plant. At the coastal samples water temperature was 13-27 degrees C. The maximum values for TC, FC, FS were 25-2.4x10*6 cfus/100ml, 19-2.4x10*6 cfus/100 ml and 4-10*4 cfus/100ml respectively. Most samples at several sampling stations were negative. The microbiological loading differs according to the sampling station. High counts of bacteria were recovered in September 1998, perhaps due to the unusually high temperatures, and July 1999. In order to estimate the potential decrease in the microbiological quality of the waters in this area, an attempt was made to compare the results of the present survey with similar work carried out before the Psyttalia treatment plant began operating. There has been a substantial increase in the microbiological quality of the water at most sampling points that were formerly affected by the Athens Central Sewage Outlet, at a distance of up to 2 km from the outlet. The decrease of the median values of the various bacteria-indicators was 2-5 log. Nevertheless, an increase in the microbiological counts was recorded at the sampling points located on Salamis Island, which can be attributed to the Psyttalia plant since according to circulation studies the sewage dispersion flow is westerly. Considerable microbiological loading was recorded in the Piraiki Akti sampling station on the mainland, which has not been recorded in the past and requires further investigation.

Athens School of Hygiene, Microbiology Department
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115 21
Greece