heightened concentrations of the SOM components are observed in the spring–
summer period. Their seasonal variations are noticeably smaller than those in the
areas affected by the riverine discharges. In all the seasons the transformed detritus
constitutes the SOM predominant component.
The distribution pattern of the bio-optical parameters in NWBS is a good
agreement with the obtained experimentally seasonal distribution of the chlorophyll
a concentrations. Comparison of the seasonal chlorophyll a concentration values
determined by experimental and satellite data has shown some differences. The
concentration close values differing within the range 10–30% were obtained in the
summer-autumn period in the western and the northern areas and during the year –
in the central area. The greatest differences were observed in winter and spring in
the areas affected by the riverine discharges.
In course of the whole year the seasonal distributions of the bio-optical parameters in the coastal waters of the sea western part are characterized by a decrease of
the parameters’ absolute values in the southern direction. The maximum values are
obtained in the Danube region, the minimum ones – in the Bosporus region. In the
Danube region the increased values of the parameters were usually observed in the
spring-summer period. To the south from this region in coastal areas, the maximum
values of the chlorophyll a concentration and the absorption coefficient were
monitored in autumn when phytoplankton bloomed actively in these areas. 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 distributions of the chlorophyll a concentration and the absorption coefficient in different seasons are considered on the section along the sea western coast
located at the 7–15 km distance from the coast.
The inter-annual variations of the SOM components’ content in the winterspring period in areas affected by the riverine discharges are mainly conditioned
by the volume of the nutrient-enriched riverine discharge and by the air temperature
(severe winters); in the central area – by the air temperature only. In summer and
autumn, the interannual variations of the SOM component’ content is mostly
dependent on the temperature regime (during the period of observations and in
the previous periods). In the central area, variability of the SOM components’
content is also significantly influenced by the transformed river waters which, in
their turn, depend on the water circulation pattern in the NWBS. The increase of the
SOM components’ concentration has been observed in the summer-autumn period
in late 1980s and early 1990s, with the highest values in 1992.
The inter-annual variations of the chlorophyll a concentration (the MODIS
scanner data) in the NWBS the Danube area in the winter-spring periods,
1998–2015, are less dependent on the changes in the Danube discharge volume
as compared to the previous time interval (1978–1995). These variations (especially in spring) were conditioned to a greater extent by the water temperature
changes. A good agreement between of the variation patterns of the Danube
discharge volume and С Chl was observed in summer. In autumn such an agreement
was absent. In the NWBS central area the С Chl inter-annual variations in winter did
not practically depend on the air temperature and the Danube discharge volume. In
10 Seasonal Changes of Hydrobiological and Bio-Optical Parameters in the. . .
177
summer period. Their seasonal variations are noticeably smaller than those in the
areas affected by the riverine discharges. In all the seasons the transformed detritus
constitutes the SOM predominant component.
The distribution pattern of the bio-optical parameters in NWBS is a good
agreement with the obtained experimentally seasonal distribution of the chlorophyll
a concentrations. Comparison of the seasonal chlorophyll a concentration values
determined by experimental and satellite data has shown some differences. The
concentration close values differing within the range 10–30% were obtained in the
summer-autumn period in the western and the northern areas and during the year –
in the central area. The greatest differences were observed in winter and spring in
the areas affected by the riverine discharges.
In course of the whole year the seasonal distributions of the bio-optical parameters in the coastal waters of the sea western part are characterized by a decrease of
the parameters’ absolute values in the southern direction. The maximum values are
obtained in the Danube region, the minimum ones – in the Bosporus region. In the
Danube region the increased values of the parameters were usually observed in the
spring-summer period. To the south from this region in coastal areas, the maximum
values of the chlorophyll a concentration and the absorption coefficient were
monitored in autumn when phytoplankton bloomed actively in these areas. 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 distributions of the chlorophyll a concentration and the absorption coefficient in different seasons are considered on the section along the sea western coast
located at the 7–15 km distance from the coast.
The inter-annual variations of the SOM components’ content in the winterspring period in areas affected by the riverine discharges are mainly conditioned
by the volume of the nutrient-enriched riverine discharge and by the air temperature
(severe winters); in the central area – by the air temperature only. In summer and
autumn, the interannual variations of the SOM component’ content is mostly
dependent on the temperature regime (during the period of observations and in
the previous periods). In the central area, variability of the SOM components’
content is also significantly influenced by the transformed river waters which, in
their turn, depend on the water circulation pattern in the NWBS. The increase of the
SOM components’ concentration has been observed in the summer-autumn period
in late 1980s and early 1990s, with the highest values in 1992.
The inter-annual variations of the chlorophyll a concentration (the MODIS
scanner data) in the NWBS the Danube area in the winter-spring periods,
1998–2015, are less dependent on the changes in the Danube discharge volume
as compared to the previous time interval (1978–1995). These variations (especially in spring) were conditioned to a greater extent by the water temperature
changes. A good agreement between of the variation patterns of the Danube
discharge volume and С Chl was observed in summer. In autumn such an agreement
was absent. In the NWBS central area the С Chl inter-annual variations in winter did
not practically depend on the air temperature and the Danube discharge volume. In
10 Seasonal Changes of Hydrobiological and Bio-Optical Parameters in the. . .
177