The case study was based on the analysis of phytoplankton samples collected in the Pomeranian Bay during five cruises in the years 1993, 1996 and 1997.
In each season a number of phytoplankton assemblages were formed under the impact of the hydrological and hydrochemical conditions gradually changing along an axis from the outlets of the Szczecin Lagoon towards the open sea. The most distinct assemblages could be described as 'river-mouth', 'open-Bay' and 'open-sea' assemblages.
The highest phytoplankton biomass was noted near the mouth of the Swina Strait in the 'river-mouth' assemblages, where the concentration of chlorophyll a was 4 to 5 five times higher in comparison with the 'open-sea' values. The phytoplankton biomass in the 'open-Bay' assemblages was roughly twice as high as that in the 'open-sea' assemblages.
Because of the high N:P ratio in the Odra waters, phosphorus was very probably the factor limiting phytoplankton primary production in the Pomeranian Bay during periods of intensified inflow of riverine waters. The species dominating the phytoplankton of the Pomeranian Bay during the present study were found to be the same as those recorded in this region 40 years earlier.