transparency in NEBS in autumn (Kukushkin 2013b). Note also the increased
values of the absorption coefficient in all the areas. It testifies to high content of
yellow substance and detritus which condition the value of this coefficient.
Comparison of the seasonal values of the chlorophyll a concentration derived
from the experimental and satellite data showed some differences. The close values
of concentrations differing within the range 10–30% were obtained in summer and
autumn in the western and northern areas and in course of a year – in the central
area. The most significant differences were noted in the winter-spring period in the
areas subjected to the rivers’ impact. In winter the measured concentrations
exceeded the satellite-derived ones by approximately 1.5 times, and in spring –
by 4–5 times.
10.2.1.3 Distribution of the Bio-Optical Parameters in the Western Part
of the Sea
Hydrological and biogeochemical features of the coastal waters in the Romanian
and Bulgarian sea sectors result mainly from the transformed river waters and the
coastal sewage interaction. The transformed nutrient-rich river waters propagate
from NWBS to the south by the alongshore current (Markov and Esin 1979). The
biogeochemical characteristics of the coastal waters are noticeably affected by the
coastal sewage (industrial, domestic, riverine and rainwater, runoff of fertilizers,
etc.). The distribution of the transformed river waters in various seasons is well
traced due to the salinity distribution (Fig. 10.6). In winter these waters with salinity
lower than 17 PSU reach Cape Kaliakra. In spring and summer they migrate up to
the Bosporus, whereas in autumn – up to the Romanian sea sector.
The spatial seasonal distributions of the bio-optical parameters in the western sea
coastal waters are shown in Fig. 10.7. In all the seasons these distributions are
characterized by decrease of the parameters’ absolute values in the southern
direction. The maximum values are obtained in the Danube estuary region, the
minimum ones – in the Bosporus one (Table 10.3). In the Danube region the
increased values of the parameters were usually observed in the spring-summer
period. In the coastal areas located to the south off this region, the maximum values
of the chlorophyll a concentration and absorption coefficient were observed in
autumn when phytoplankton bloomed intensively. At the same time the increased
value of the scattering coefficient was obtained in the spring-summer period when
the transformed river waters flowed into these areas.
The detailed spatial distribution of the chlorophyll a concentration and the
absorption coefficient in different seasons is well seen on the alongshore section
(Fig. 10.8) located at the distance of 7–15 km off the coast. In winter and spring in
the region of the Burgas Bay and Varna, the section crossed a number of coastal
areas (their dimensions did not exceed 20 km) with the increased and decreased
values of these parameters. At that, in winter their absolute values exceeded those
observed in spring. In the summer-autumn period, the chlorophyll a concentration
in this area changed insignificantly. More noticeable changes (especially for the
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A.S. Kukushkin
values of the absorption coefficient in all the areas. It testifies to high content of
yellow substance and detritus which condition the value of this coefficient.
Comparison of the seasonal values of the chlorophyll a concentration derived
from the experimental and satellite data showed some differences. The close values
of concentrations differing within the range 10–30% were obtained in summer and
autumn in the western and northern areas and in course of a year – in the central
area. The most significant differences were noted in the winter-spring period in the
areas subjected to the rivers’ impact. In winter the measured concentrations
exceeded the satellite-derived ones by approximately 1.5 times, and in spring –
by 4–5 times.
10.2.1.3 Distribution of the Bio-Optical Parameters in the Western Part
of the Sea
Hydrological and biogeochemical features of the coastal waters in the Romanian
and Bulgarian sea sectors result mainly from the transformed river waters and the
coastal sewage interaction. The transformed nutrient-rich river waters propagate
from NWBS to the south by the alongshore current (Markov and Esin 1979). The
biogeochemical characteristics of the coastal waters are noticeably affected by the
coastal sewage (industrial, domestic, riverine and rainwater, runoff of fertilizers,
etc.). The distribution of the transformed river waters in various seasons is well
traced due to the salinity distribution (Fig. 10.6). In winter these waters with salinity
lower than 17 PSU reach Cape Kaliakra. In spring and summer they migrate up to
the Bosporus, whereas in autumn – up to the Romanian sea sector.
The spatial seasonal distributions of the bio-optical parameters in the western sea
coastal waters are shown in Fig. 10.7. In all the seasons these distributions are
characterized by decrease of the parameters’ absolute values in the southern
direction. The maximum values are obtained in the Danube estuary region, the
minimum ones – in the Bosporus one (Table 10.3). In the Danube region the
increased values of the parameters were usually observed in the spring-summer
period. In the coastal areas located to the south off this region, the maximum values
of the chlorophyll a concentration and absorption coefficient were observed in
autumn when phytoplankton bloomed intensively. At the same time the increased
value of the scattering coefficient was obtained in the spring-summer period when
the transformed river waters flowed into these areas.
The detailed spatial distribution of the chlorophyll a concentration and the
absorption coefficient in different seasons is well seen on the alongshore section
(Fig. 10.8) located at the distance of 7–15 km off the coast. In winter and spring in
the region of the Burgas Bay and Varna, the section crossed a number of coastal
areas (their dimensions did not exceed 20 km) with the increased and decreased
values of these parameters. At that, in winter their absolute values exceeded those
observed in spring. In the summer-autumn period, the chlorophyll a concentration
in this area changed insignificantly. More noticeable changes (especially for the
166
A.S. Kukushkin