A. Pavlidou et al.
112
increased eutrophication in many near-shore waters. Wastewater discharged into the sea through long underwater outfalls results in sewage decomposition and mineralization.
Local seawater dynamics and data on meteorological conditions are of primary importance in designing a configuration
of the submarine outfall (Goldman 1976; Faganeli 1981).
The Mediterranean Sea has always been considered as
one of the most oligotrophic areas in the world with extremely low nutrient concentrations, especially in the eastern
region (Berman et al. 1984, 1985; Dowidar 1984; Salihoglu
et al. 1990; Krom et al. 1991, 1992, 1993; Yacobi et al. 1995;
Herut et al. 2000; Pavlidou and Souvermezoglou 2006).
The inputs of nutrients to the Mediterranean Sea are significantly lower than the outflow through the Gibraltar Strait.
The nutrient concentration in the Aegean Sea of Greece is 12
times lower than the Atlantic Ocean. Data on nutrient concentration in the eastern Mediterranean Sea during the past
decade showed a depletion of nutrients of the same order of
magnitude as observed by McGill (1965). The nutrient concentration was in the order of Levantine > Ionian > Aegean
(Pavlidou and Souvermezoglou 2006; Stergiou et al. 1997;
Souvermezoglou 1989). Despite the oligotrophic character
of the open Mediterranean Sea, elevated nutrient concentration indicates problem of coastal eutrophication (e.g.,
Eastern Coasts of Spain, Gulf of Lions, Northern Adriatic
Sea, Apulian Coasts, Saronikos Gulf, Thessaloniki Bay, and
Northern Coasts of Greece; Pavlidou and Souvermezoglou
2006).
Coastal areas undergo intense and continuous environmental pressure derived from a number of driving forces
such as urbanization, industrialization, changes in land use,
tourism development, and climate change (Airoldiand and
Beck 2007). In general, the loads of nutrients increased with
increasing human activity in catchments of aquatic ecosystems creating pressure on the aquatic environment. Within
only a few decades, numerous oligotrophic estuarine and
coastal waters have undergone a transformation to more
mesotrophic and eutrophic conditions that result in an increase in phytoplankton and macroalgal biomass, increased
incidences of toxic and noxious algal blooms, consequent
hypoxia and anoxia, and fish and benthos kills. The variation
of nutrient loadings cause a change in nitrogen to phosphorus (N:P) ratios, which control the phytoplankton composition. This plays an important role in the biochemical dynamics and the functioning of marine ecosystems.
In Greece, one-third of the population lives on the coast.
Anthropogenic activities that influence the natural environment of the coastal zone in Greece are urbanization, industry, agriculture, aquaculture, tourism, recreational areas, and
waste disposal. More than 80 % of the industrial activities
in Greece are located on the coast and pollute the coastal
marine ecosystems by direct discharges of industrial and domestic wastes. Besides that, 90 % of tourism activities are
also located on the coast similarly affecting the marine environment with sewage effluent. Athens and Thessaloniki, the
two biggest cities of Greece, are located on the coast and
their sewage influences Saronikos and Thermaikos Gulfs,
respectively (Anagnostou et al. 2005). Overall, the loads of
N and P transferred into the Aegean Sea from the coasts of
Greece were found in the range of 5,000–15,000 t P/y and
3,000–130,000 t N/y (Dassenakis et al. 2000).
Urban sewage usually treated in municipal plants to remove fats, solids, and floating materials (primary treatment);
to degrade the biological content of the sewage(secondary
treatment) and finally to raise the effluent quality before
being discharged into the receiving water bodies (tertiary
treatment) (Azzurro et al. 2010). However, according to a report, only 77 % of Mediterranean coastal cities are provided
with sewage treatment plants, and rest of the 23 % discharge
untreated wastewaters directly into the marine environment
(UNEP/MAP 2004). The sewage discharge is a major problem for management of near-shore ecosystems, especially in
regions like the Mediterranean Sea, which in recent decades
experienced a growing urbanization of coastal areas (Azzurro et al. 2010). The coastal areas of Greece receiving nutrient
loads from sewage have average soluble reactive phosphorus
(SRP) concentrations in the range of 0.50 and 0.70 μΜ, nitrate ~ 1.00 μM and ammonium between 1.10 and 2.00 μΜ
(Pavlidou 2010).
Saronikos Gulfreceives effluents from the Athens metropolitan area having population over 5 million. Until 1994,
the domestic and industrial sewage of Athens discharged
untreated into the surface water layer of Keratsini and Elefis Bays and only after 1994; the sewage primarily treated
in the Psitallia sewage treatment plant and discharged into
the inner Saronikos Gulf (see Fig. 10.1). Additionally, the
secondary stage of the Psittalia sewage plant became operational by the end of 2004 affecting the ecological status of
the Inner Saronikos Gulf (Pavlidou et al. 2008).
In this chapter, we provide an overview of N and P dynamics in the inner Saronikos Gulf which has undergone
changes over the last 25 years because of regular sewage
discharges in it from the sewage treatment plant of Athens in
Psittalia Island. Additionally, the environmental status of the
inner Saronikos Gulf is also examined in the coastal zones
of Greek.
10.2 Description of the Area and Background
Data
The study area covers the Inner Saronikos Gulf surrounded by the islands Aegina and Salamina and the eastern
coast of Attika (Longitude: between 23° 08′ 45.22″ E and
23° 42′ 15.67″ E; Latitude: between 37° 38′ 28.82″ N and
38° 04′ 39.51″ N). The Saronikos Gulf communicates with
112
increased eutrophication in many near-shore waters. Wastewater discharged into the sea through long underwater outfalls results in sewage decomposition and mineralization.
Local seawater dynamics and data on meteorological conditions are of primary importance in designing a configuration
of the submarine outfall (Goldman 1976; Faganeli 1981).
The Mediterranean Sea has always been considered as
one of the most oligotrophic areas in the world with extremely low nutrient concentrations, especially in the eastern
region (Berman et al. 1984, 1985; Dowidar 1984; Salihoglu
et al. 1990; Krom et al. 1991, 1992, 1993; Yacobi et al. 1995;
Herut et al. 2000; Pavlidou and Souvermezoglou 2006).
The inputs of nutrients to the Mediterranean Sea are significantly lower than the outflow through the Gibraltar Strait.
The nutrient concentration in the Aegean Sea of Greece is 12
times lower than the Atlantic Ocean. Data on nutrient concentration in the eastern Mediterranean Sea during the past
decade showed a depletion of nutrients of the same order of
magnitude as observed by McGill (1965). The nutrient concentration was in the order of Levantine > Ionian > Aegean
(Pavlidou and Souvermezoglou 2006; Stergiou et al. 1997;
Souvermezoglou 1989). Despite the oligotrophic character
of the open Mediterranean Sea, elevated nutrient concentration indicates problem of coastal eutrophication (e.g.,
Eastern Coasts of Spain, Gulf of Lions, Northern Adriatic
Sea, Apulian Coasts, Saronikos Gulf, Thessaloniki Bay, and
Northern Coasts of Greece; Pavlidou and Souvermezoglou
2006).
Coastal areas undergo intense and continuous environmental pressure derived from a number of driving forces
such as urbanization, industrialization, changes in land use,
tourism development, and climate change (Airoldiand and
Beck 2007). In general, the loads of nutrients increased with
increasing human activity in catchments of aquatic ecosystems creating pressure on the aquatic environment. Within
only a few decades, numerous oligotrophic estuarine and
coastal waters have undergone a transformation to more
mesotrophic and eutrophic conditions that result in an increase in phytoplankton and macroalgal biomass, increased
incidences of toxic and noxious algal blooms, consequent
hypoxia and anoxia, and fish and benthos kills. The variation
of nutrient loadings cause a change in nitrogen to phosphorus (N:P) ratios, which control the phytoplankton composition. This plays an important role in the biochemical dynamics and the functioning of marine ecosystems.
In Greece, one-third of the population lives on the coast.
Anthropogenic activities that influence the natural environment of the coastal zone in Greece are urbanization, industry, agriculture, aquaculture, tourism, recreational areas, and
waste disposal. More than 80 % of the industrial activities
in Greece are located on the coast and pollute the coastal
marine ecosystems by direct discharges of industrial and domestic wastes. Besides that, 90 % of tourism activities are
also located on the coast similarly affecting the marine environment with sewage effluent. Athens and Thessaloniki, the
two biggest cities of Greece, are located on the coast and
their sewage influences Saronikos and Thermaikos Gulfs,
respectively (Anagnostou et al. 2005). Overall, the loads of
N and P transferred into the Aegean Sea from the coasts of
Greece were found in the range of 5,000–15,000 t P/y and
3,000–130,000 t N/y (Dassenakis et al. 2000).
Urban sewage usually treated in municipal plants to remove fats, solids, and floating materials (primary treatment);
to degrade the biological content of the sewage(secondary
treatment) and finally to raise the effluent quality before
being discharged into the receiving water bodies (tertiary
treatment) (Azzurro et al. 2010). However, according to a report, only 77 % of Mediterranean coastal cities are provided
with sewage treatment plants, and rest of the 23 % discharge
untreated wastewaters directly into the marine environment
(UNEP/MAP 2004). The sewage discharge is a major problem for management of near-shore ecosystems, especially in
regions like the Mediterranean Sea, which in recent decades
experienced a growing urbanization of coastal areas (Azzurro et al. 2010). The coastal areas of Greece receiving nutrient
loads from sewage have average soluble reactive phosphorus
(SRP) concentrations in the range of 0.50 and 0.70 μΜ, nitrate ~ 1.00 μM and ammonium between 1.10 and 2.00 μΜ
(Pavlidou 2010).
Saronikos Gulfreceives effluents from the Athens metropolitan area having population over 5 million. Until 1994,
the domestic and industrial sewage of Athens discharged
untreated into the surface water layer of Keratsini and Elefis Bays and only after 1994; the sewage primarily treated
in the Psitallia sewage treatment plant and discharged into
the inner Saronikos Gulf (see Fig. 10.1). Additionally, the
secondary stage of the Psittalia sewage plant became operational by the end of 2004 affecting the ecological status of
the Inner Saronikos Gulf (Pavlidou et al. 2008).
In this chapter, we provide an overview of N and P dynamics in the inner Saronikos Gulf which has undergone
changes over the last 25 years because of regular sewage
discharges in it from the sewage treatment plant of Athens in
Psittalia Island. Additionally, the environmental status of the
inner Saronikos Gulf is also examined in the coastal zones
of Greek.
10.2 Description of the Area and Background
Data
The study area covers the Inner Saronikos Gulf surrounded by the islands Aegina and Salamina and the eastern
coast of Attika (Longitude: between 23° 08′ 45.22″ E and
23° 42′ 15.67″ E; Latitude: between 37° 38′ 28.82″ N and
38° 04′ 39.51″ N). The Saronikos Gulf communicates with