SEDIMENTATION AND PELAGIC RETENTION OF PARTICULATE C, N AND P IN THE COASTAL NORTHERN BALTIC SEA

Sedimentation and pelagic retention capacity of particulate carbon, ni trogen and phosphorus as well as the impact of resuspension and preser vation on sedimentation rates were studied during spring and summer in the SW coast of Finland, Baltic Sea. Formaldehyde preservation result ed in significantly higher carbon, nitrogen and chlorophyll a sediment ation rates when compared to traps without preservative. This was main ly attributable to contamination by vertically migrating micro-organis ms in traps with formaldehyde and mineralization inside the non-preser ved trap cylinders. During the spring bloom, stoichiometric ratios of settled and suspended particulate material indicated that phosphorus w as retained in the pelagic system almost twice as effectively as carbo n and nitrogen, while carbon and nitrogen were settling at equal rates . During summer, when sedimentation rates were low, nutrient ratios of settled and suspended matter indicated that both N and P were recircu lated in the pelagic system more effectively than carbon while P was r etained 1.4 times more effectively than nitrogen. High current velocit ies and increase of deep-water salinity correlated with increased sedi mentation of particulate material, with low N:P, C:P and high C:N rati os indicating input of resuspended phosphorus during upwelling events. Wind velocity and direction did not have any clear relationship to th e quality of settled material, denoting that wind-induced wave action and transport of littoral material had minor impact on sedimentation r ates. Primary sedimentation of carbon corresponded to 57% of the total primary production during the study period from April to August, whil e that of nitrogen was 42% of estimated nitrogen assimilation, indicat ing that the overall export of carbon was more effective than that of nitrogen from the pelagic system. (C) 1998 Academic Press Limited.