Meanwhile, compared to the winter period, they were higher by 1.2–1.4 times in the
central area and 1.8–2.2 times in the eastern area. The average C Chl concentration
also decreased in the eastern area but remained the same in the central area
compared to the summer period. The average C/Chl and C/N ratios also decreased
in both areas and constituted 217 and 9.3 in the central area, and 605 and 7.7 in the
eastern area, respectively. We assume that detritus of different stages of transformation was the major component of SOM in both areas during the autumn period,
as was observed during summer.
The C SOM and N SOM concentrations also decreased in the photosynthetic layer
(0–30 m) by 1.2–2.0 times compared to the summer period. The weighted average
C Chl concentration decreased by 1.2 times in the eastern area, but it increased by the
same magnitude in the central area. In comparison to the winter period, the C SOM
and N SOM concentrations in both areas were higher by 1.3–1.5 times, but the C Chl
concentration was less than 1.4 times in the central area and higher by the same
magnitude in the eastern area. The weighted average SOM component concentrations were less than 1.1–1.4 times in the photosynthetic layer compared to the
surface layer. The average C/Chl ratio in the photosynthetic layer decreased
significantly (201) in the central area and remained the same in the eastern area
(404) compared to the summer period. The average C/N ratio increased up to
8.5–9.1 in both areas and did not differ greatly, so we conclude a similar composition of SOM within the photosynthetic layer.
10.2.1.2 Distribution of the Bio-Optical Parameters
Distribution of the seasonal values of the bio-optical parameter is shown in
Fig. 10.5. It is in good agreement with the experimentally obtained seasonal
distribution of the chlorophyll a concentration (Fig. 10.4). The increased seasonal
values of the bio-optical parameters were observed in the areas of constant riverine
discharges (in the western and northern ones), the decreased values – in the central
area (Table 10.2). Note a satisfactory agreement of the seasonal chlorophyll
a concentrations derived by the CZCS (1978–1986) and the SeaWiFS
(1997–2010) color scanners. The minimum values of all the parameters were
observed in NWBS in winter. In spring, due to the additional nutrients brought to
the sea by the river waters, and insolation and water temperature growth, phytoplankton starts to bloom actively. This fact explains increase of the chlorophyll
a concentration in the areas subjected to the river impact (Tables 10.1 and 10.2). In
the western area, the increased values of the absorption and scattering coefficients
were also observed (Table 10.2) that is, apparently, related to a large amount of
yellow substance, and mineral and organic particles of the suspended matter
brought by the Danube waters. In summer the increased values of all the
bio-optical parameters were revealed in NWBS. In autumn the chlorophyll
a content in the western and northern areas decreased, whereas in central one –
increased. During this period the scattering coefficient values in all the areas
decreased up to a minimum value. This fact partially confirms rather high water
164
A.S. Kukushkin
central area and 1.8–2.2 times in the eastern area. The average C Chl concentration
also decreased in the eastern area but remained the same in the central area
compared to the summer period. The average C/Chl and C/N ratios also decreased
in both areas and constituted 217 and 9.3 in the central area, and 605 and 7.7 in the
eastern area, respectively. We assume that detritus of different stages of transformation was the major component of SOM in both areas during the autumn period,
as was observed during summer.
The C SOM and N SOM concentrations also decreased in the photosynthetic layer
(0–30 m) by 1.2–2.0 times compared to the summer period. The weighted average
C Chl concentration decreased by 1.2 times in the eastern area, but it increased by the
same magnitude in the central area. In comparison to the winter period, the C SOM
and N SOM concentrations in both areas were higher by 1.3–1.5 times, but the C Chl
concentration was less than 1.4 times in the central area and higher by the same
magnitude in the eastern area. The weighted average SOM component concentrations were less than 1.1–1.4 times in the photosynthetic layer compared to the
surface layer. The average C/Chl ratio in the photosynthetic layer decreased
significantly (201) in the central area and remained the same in the eastern area
(404) compared to the summer period. The average C/N ratio increased up to
8.5–9.1 in both areas and did not differ greatly, so we conclude a similar composition of SOM within the photosynthetic layer.
10.2.1.2 Distribution of the Bio-Optical Parameters
Distribution of the seasonal values of the bio-optical parameter is shown in
Fig. 10.5. It is in good agreement with the experimentally obtained seasonal
distribution of the chlorophyll a concentration (Fig. 10.4). The increased seasonal
values of the bio-optical parameters were observed in the areas of constant riverine
discharges (in the western and northern ones), the decreased values – in the central
area (Table 10.2). Note a satisfactory agreement of the seasonal chlorophyll
a concentrations derived by the CZCS (1978–1986) and the SeaWiFS
(1997–2010) color scanners. The minimum values of all the parameters were
observed in NWBS in winter. In spring, due to the additional nutrients brought to
the sea by the river waters, and insolation and water temperature growth, phytoplankton starts to bloom actively. This fact explains increase of the chlorophyll
a concentration in the areas subjected to the river impact (Tables 10.1 and 10.2). In
the western area, the increased values of the absorption and scattering coefficients
were also observed (Table 10.2) that is, apparently, related to a large amount of
yellow substance, and mineral and organic particles of the suspended matter
brought by the Danube waters. In summer the increased values of all the
bio-optical parameters were revealed in NWBS. In autumn the chlorophyll
a content in the western and northern areas decreased, whereas in central one –
increased. During this period the scattering coefficient values in all the areas
decreased up to a minimum value. This fact partially confirms rather high water
164
A.S. Kukushkin