Seasonal and spatial nutrient dynamics in saronikos gulf: The impact of sewage effluents from athens sewage treatment plant

Abstract

This chapter provides a long-term case study illustrating responses of a coastal Gulf in the Mediterranean Sea to reduced loading of sewage. Saronikos Gulf receives effluents from the Athens metropolitan area (population over 5 million). Until 1994, sewage discharged untreated into the surface waters of Keratsini and Elefis Bays. Sewage treatment first started in the Psitallia sewage treatment plant where the wastes discharged into inner Saronikos Gulf at 63 m depth. By the end of 2004, the secondary stage of the Psittalia sewage plant was operational. We examined nitrogen (N) and phosphorus (P) dynamics in the inner Saronikos Gulf over the last 25 years in relation to these changes in sewage input. Additionally we described changes in the environmental status of inner Saronikos Gulf. Inorganic nutrient data from 170 cruises obtained during the year 1987–2010 allow us to describe the nutrient dynamics results and data evaluation. The study was focus on changes in nutrient concentrations between three main periods: 1. Before treatment of sewage 2. During primary treatment of sewage 3. During secondary treatment of sewage Significant changes in nutrient dynamics noticed after the operation of primary sewage treatment plant. Nutrient concentration was high in the inner Saronikos Gulf due to the high amount of primarily treated effluents. After the year 2005, when the secondary sewage treatment was operational, there was a general decrease in nutrient concentrations in the inner Saronikos Gulf.