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10.3.4 Observations on Dissolved Oxygen
and Nutrients of the Water Column
Dissolved oxygen (DO) and inorganic nutrient data of 12
months samplings during November 2009–October 2010,
as well as from the 170 cruises obtained during 1987–2010,
used to describe the oxygen and nutrient dynamics of the
inner Saronikos Gulf in phase with stratification of the water
masses and the sewage discharge from the Psittalia Island
sewage treatment plant.
Depth profiles of nutrients at the Psittalia outfall showed
that during the warm/stratified period, SRP and ammonium
concentrations increased markedly into and/or below the
pycnocline, directly related to the sewage plume discharging
from the Psittalia Island sewage treatment plant through the
pipe at 63-m depth. This was prominent only after September 1996. Before that period an increase of nutrients in the
surface layer (0–20 m) was sometimes observed (Figs. 10.6
and 10.7). After 2004, where the secondary stage of treatment operated on Psittalia Island, a significant decrease in
Fig. 10.6 Vertical distribution
of phosphate and ammonium at
the sewage outfall (station S7)
in cold (February or March/nonstratified) and warm (August or
September/stratified) periods
during 1987–2010