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Temporal variation in the accumulation of organic carbon and nitrogen in the suspended matter and silty surface sediment of the western Gulf of Gdansk (southern Baltic Sea) - comparison with the Atlantic Bay of Marennes Oleron

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Maksymowska D., Feuillet-Girard M., Jankowska H., Heral M.

Oceanological Studies

1997

vol. 26

issue 2-3

91-116

The temporal changes of organic C and N concentration and in atomic C:N ratio in both suspended particulate matter (SPM) and surface sediments (0-5cm) are discussed. The investigations were conducted in May, August, November 1994 and January 1995, at a sampling station located in the western Gulf of Gdansk (depth 37 m).The respective concentrations of organic carbon and nitrogen in SPM range from 0.285 to 0.655 mg dm-3, and from 0.033 to 0.075 mg dm-3. The temporal changes in the concentrations of these elements are due to the seasonal variation in primary production, and are also influenced by the inflow of terrestrial discharges. The atomic C:N ratio reflects seasonal changes in SPM composition, and generally indicates that particular organic matter (POM) in this part of the Gulf of Gdansk consists to a large extent of detritus or terrigenous material. However, in the summer, there is a substantial proportion of fresh planktonic material in the particulate organic matter (the C:N atomic ratio falls to 8.5 - 10.5).Significant temporal changes in organic carbon and nitrogen concentrations were also recorded in the surface sediment (0-1 cm); these range from 28.5 to 49.6 mg g-1 of dry sediment and from 3.12 to 4.6 mg g-1 of dry sediment for carbon and nitrogen respectively. Values were highest in May and November, and indicate a possible inflow of organic matter to the sediments following the spring and autumn phytoplankton blooms. The considerably lower values of both parameters noted in August suggest that large quantities of organic carbon and nitrogen are lost in summer, a process governed by the rise in temperature of the near-bottom water. The C:N atomic ratio in the first surface sediment layer indicates that the inflow of fresh organic matter is predominant in spring, when C:N is lowest (8.75). The summer and winter values (10.5 - 11.1) reflect the presence of degraded matter. Values were highest in early November (14.4), which is indicative of the inflow of highly degraded or terrigenous organic material. These results are compared to those of different ecosystems, particularly with an Atlantic coastal area, the estuarine Marennes - Ol?ron Bay in France, where the authors took the same approach. SPM concentrations are considerably higher (50 to 360 mg dm-3) than in the Gulf of Gdansk. The respective concentrations of organic carbon and nitrogen in SPM range from 0.95 to 14.9 mg dm-3 and from 0.2 to 1.5 mg dm-3. However, these high values are not reflected in the accumulation of organic matter in the surface sediment layer, where the carbon and nitrogen contents were low at 7.5 mg g-1 and 1.3 mg g-1 of dry sediments respectively. In this bay such differences are explained by the sediment resuspension caused by strong currents inducing considerable turbidity.

Carbon and nitrogen content and degradation ratio of suspended matter and surface sediments of the Gulf of Gdansk in spring 1995

86%

Maksymowska D.

Oceanological Studies

1996

vol. 25

issue 3

79-95

Changes in organic carbon and nitrogen concentrations as well as the atomic C/N ratio in suspended matter and vertical profile of surface sediments (0-5cm) from different sedi-mentation areas of the Gulf of Gdansk (Southern Baltic) were studied in late spring 1995. Concentrations of organic carbon and nitrogen in suspended particulate matter (SPM) varied between 0.14 and 1.20 mg dm-3, respectively. The deeper parts of the Gulf of Gdansk (station U20) and station remaining under the direct influence of the riverine discharges (W2 and JR), are characterised by nigh values of organic carbon and nitrogen concentrations. C/N ratio in SPM in euphotic layer of the water column reveals significant spatial variability connected with organic matter origin; the highest values (10.11-10.46) were observed at sta-tions: W2 and JR which remained under riverine runoff. At the other sampling stations located in the eastern part of Puck Bay and open part of the Gulf of Gda?sk C/N ratio reached values: 8.93 - 9.87, what indicates a bigger proportion of the autochthonous organic matter. Variability in concentrations of organic carbon and nitrogen in surface sediments is controlled by sediment dispersion and its sorption properties, location of the station in respect of the main sources of the terrestrial and riverine discharges. The lowest concentrations of organic carbon and nitrogen were observed in sandy sediments, while the highest ones in clay sediments of the deep open part of the Gda?sk Basin. The highest values of C/N ratio (11.56-13.49) in the surface sediments were observed at sta-tions being under direct influence of rivers (W2, JR), while the lowest ones (8.89-9.61) oc-curred in sediments of the open part of the Gulf of Gdansk, which is to the lesser extent influ-enced by the riverine inflow. At station JR (sandy sediments), located in the inner Puck Bay, high C/N ratio as well as rela-tively large content of both organic carbon and nitrogen in surface sediments could also be influenced by migration of highly degraded refractory organic matter from deeper sediment layers (peat and calcareous gyttja).

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2 Oceanological Studies

1 1997

1 1996

2 Maksymowska D.

1 Feuillet-Girard M.

1 Heral M.

1 Jankowska H.

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Temporal variation in the accumulation of organic carbon and nitrogen in the suspended matter and silty surface sediment of the western Gulf of Gdansk (southern Baltic Sea) - comparison with the Atlantic Bay of Marennes Oleron

Carbon and nitrogen content and degradation ratio of suspended matter and surface sediments of the Gulf of Gdansk in spring 1995