A CASE-STUDY OF SEASONAL-VARIATION IN THE CHEMICAL-COMPOSITION OF ACCUMULATING SUSPENDED SEDIMENTS IN THE CENTRAL GULF-OF-FINLAND

A study was made of suspended sediments from a basin in the eastern pa rt of the Baltic Sea, in the central Gulf of Finland. In this investig ation, moored sediment traps were used to collect suspended particulat e material during the half-year period from April to October 1996. An equivalent to the primary net sedimentation was estimated through stud ies of the variations in the content of dry matter, carbon, nitrogen, phosphorus, arsenic, cadmium, cobalt, chromium, copper, nickel, lead, titanium, vanadium, iron, manganese, aluminium and zinc in accumulated particulate matter through the period. Two algal blooms, the spring b loom and the summer bloom, were included in the period. The accumulati on rate of total particulate matter (TPM) increased during the blooms by a factor of 2.5 - 3.0. In autumn there was clearly an additional pe riod of increase in the TPM accumulation, not connected with an actual algal bloom. Metal accumulation was lowest during the spring bloom bu t started rising immediately after that, being highest in the autumn. Calculations show that the metal concentrations accumulated in the tra p moored 20 m above the sea bottom correspond to 20-37 % of the concen trations that are deposited in the bottom sediments. According to the TPM accumulation, resuspension seems to correspond to at least 10 - 35 % of the matter in the trap moored 11 m above the sea floor. (C) 1997 Elsevier Science Ltd.