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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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.
Publication order reference
D.Maksymowska, University of Gdansk, Department of Marine Geology, Al. Pilsudskiego 46, Gdynia, Poland