Prior to the operation of the new major wastewater treatment and sea disposal system (Athens Sea Outfall) an assessment of the existing ecological state of the Saronikos Gulf constitutes a prerequisite, since it will provide the background against which any changes that may occur following the treatment of the wastewater and the new disposal system will be evaluated. Main objective is the evaluation of the extent of eutrophication and associated adverse water quality. The results showed that eutrophication is intensified in the vicinity of the present untreated sewage discharge, where occasionally low oxygen values occur, whereas nutrients, chlorophyll-α and Zooplankton have high values and exhibit disturbed annual variability patterns. Also, the benthic communities have been modified and dense concentrations of subsurface deposit-feeding polychaetes predominate. Beyond this region the impact of the discharge is indirect; the nutrient values remain low and the diatom-based phytoplankton ecosystem displays well defined annual cycles with maxima in spring and autumn; however, the copepod-based Zooplankton ecosystem shows some signs of instability. The conclusions reached indicated that the existing discharge has detrimental effects on the ecology of the Saronikos Gulf, especially pronounced in its innermost part, and advocate the urgent replacement of the present scheme by the Athens Sea Outfall.

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