MAP Technical Reports Series No. 106 UNEP

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values near the Bosphorus. The cause is believed to be the sewage outfall from the city of
Istanbul (population 2,000,000). To the West, the orthophosphate values gradually decreased.
The sites with the most abundant phytoplankton biomass were the areas immediately to the
West of the Bosphorus and near the Dardanelles. The phytoplankton populations consisted
mainly of dinoflagellates (dominant species of Gymnodinium with maximum concentration
540,000 cells/l) and Coccolithophorideae (mainly Coccolithus pelagicus and Emiliania huxleyi
with densities between 10,000 and 1,900,000 cells/l), while diatoms were not plentiful.
In contrast, (Uysal et al., 1988) report that diatoms generally dominated during a long
period (September 1985 - January 1987) in the eastern part of the Sea of Marmara (close to the
Bosphorus) and their abundance was closely correlated with the nutrient inputs. Conditions of
anoxia in the bottom waters accompanied by widespread bottom fauna kills have been reported
in the eastern most part of the Sea of Marmara (Basturk et al., 1990). Referring to a case in
August 1989, the authors attribute the event to a combination of strong haloclines and marked
stability in the basin during the summer, large inputs of nutrients and organic particulates from
the city of Istanbul that caused high primary production.
The Bay of Gemlik (south-eastern part of the Sea of Marmara) shows clear signs of
eutrophy as a result of nutrient-rich emissions of agricultural origin from the area near Lake of
Iznik (Aral, 1992).
Western coasts. Yaramaz and Tuncer (1986) studied the nutrient levels at ten coastal
stations between the towns of Canakkale (North-eastern Aegean) and Bodrum (South-eastern
Aegean) on the western coast of Turkey. High values were found at a station near the coast of
the Bay of Izmir (sampling by coastal line), with means of 16.6, 1.0 and 2.5 mg-at/m 3 for
ammoniacal nitrogen, nitric nitrogen and orthophosphate, respectively. Nutrient concentrations
in the innermost parts of the Bay of Izmir, referred to by many authors as seriously degraded,
show particularly high values, especially compared to those obtained in unpolluted neighbouring
bays (Balci et al., 1994). Koray and Buyukisik (1988) report a bloom of the dinoflagellate
Alexandrium minutum (a microalga producing group PSP toxins) that occurred in May 1983 in
a zone particularly affected by large amounts of nutrients. The phenomenon was followed by
anoxia in the bottom waters and bottom fauna kills.
The recurrent algal blooms in this area are due to algae which produce PSP-group
toxins (Koray, 1990; Koray et al., 1992); amongst these Alexandrium minutum with peaks of
10,000,000 cells/l (dominant in March, April, May and June), Gonyaulax poliedra with 50,000
cells/l (in April, May and June) and Gonyaulax spinifera with 20,000 cells/l (particularly in May
and June). Such algal blooms cause cases of anoxia in the bottom waters.
Using a multiple regression model Koray (1988) demonstrates that increases in
diatoms in the Bay of Izmir are correlated in 70 % of cases with high nutrient values; the 30%
failure rate is attributed to the grazing action of the zooplanktons or inhibitor effects deriving from
pollutants. Koray and Buyukisik (1992) reach the same conclusions that increases in autotrophic
biomass are generally directly correlated with increases in phosphorus, nitrogen, light and
temperature.
Comparing the polluted Bay of Izmir with the unpolluted Bay of Gulbahce, Buyukisik
(1988) states that while in the innermost part of the Bay of Izmir the main trophic indicators are
high (5.3 mg/m 3 of chlorophyll-a, 10.1 mg-at/m 3 of total inorganic nitrogen, 1.4 of orthophosphate
and 6.7 of silicates; 1984-85), the mean values in the Bay of Gulbahce are much lower (0.85 mgat/m
3 , 2.3 mg-at/m 3 , 0.1 mg-at/m 3 and 5.7 mg-at/m 3 , respectively), representing conditions of
oligotrophy, normal for the area.