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Chlorophyll ä And Phytoplankton Of The Pomeranian Bay 
During And After The Flood Event 
Slawomira Gromisz, Mariusz Zalewski, Stanislaw Ochocki & Janina M. Kownacka 
Sea Fisheries Institute 
ul. Kollataja 1 
81-332 Gdynia 
Abstract 
Studies on the impact of the flood of 1997 on phytoplankton in the Pomeranian Bay were 
based on three cruises, at the beginning and at the end of August, and in October 1997. During 
those studies concentrations of chlorophyll a were measured and also during the second cruise 
phytoplankton composition was investigated. 
On the days 30 July-7 August and 24-25 August 1997 chlorophyll a concentrations were 
highest in vicinity of the Swina mouth and they reached 15-25 mg * nr 3 . They did not, 
however, differ from the maximum values observed in July 1996. On the days 27-28 August 
1997 a strong north-easterly wind caused transport of open Bay waters towards the Swina 
outlet and that resulted in mixing of water masses and transport of plume rich with chlorophyll 
concentrations towards the north-west. 
In the entire southern part of the Pomeranian Bay, within a radius of 30 km from the Swina 
mouth, chlorophyll concentrations were 3-4 times higher than in 1996 and amounted to 5 - 15 
mg * m 3 Further offshore the concentrations were ca. 2 times higher (2 - 5 mg * m 3 ) as 
compared with values of 1996 
Chlorophyll concentrations measured on 19-29 October 1997 remained in the range 2-9 mg * 
m' 3 in the entire Bay and did not differ from those measured on 20 Sep. - 3 Oct. 1993. 
A significant impact of the flood wave on phytoplankton composition in the Pomeranian Bay in 
August 1997 was not observed. Blue-green algae predominated over the entire area, but their 
blooms are typical for summer periods in the Baltic Sea. Four potentially toxic species 
(Anabaena spiroides, Aphanizomenon sp., Microcystis aeruginosa and Nodularia spumigend) 
appeared, but they did not occur in "bloom" quantities. Dinoflagellate Prorocentrum minimum 
also belongs to potentially toxic taxons and its abundance was relatively high in the north 
western part of the region studied, the latter being beyond the direct impact of estuarine 
waters. The listed species regularly occur in summer in the Pomeranian Bay.