- 5 - 
effect by strong northerly winds. Variations in the discharge rates were due to the changes in 
wind direction. 
At the beginning winds transported the river water along the Usedom coast, then along the 
Polish coast. In August main transport occurred through the western part of the Pomeranian 
Bay into the Arkona Sea. 
Odra flood waters reached the Swina Strait outlet on 30 July, indicated by very low salinity in 
the entire water column and by considerably increased concentrations of all nutrients. 
The calculated amounts of nutrients (in tonnes) transported into the Pomeranian Bay over the 
period of 1 June - 31 August 1997 are given in Table 1. For comparison also 1995 values are 
given. 
Table 1. Amounts of nutrients (in tonnes) transported into the Pomeranian Bay 
during June-August 1997 and 1995. 
1997 / tonnes 
1995 / tonnes 
NOj 
2600 
550 
O 
a, 
890 
347 
total-N 
16 500 
7500 
Si0 4 
26 000 
3300 
The maximal nitrogen and phosphate concentrations in the Pomeranian Bay were similar to 
maximal concentrations normally observed during spring run-off, whereas concentrations of 
silicate were exceptionally high. Nitrate concentrations decreased very rapidly beyond the 
outlet area due to biological uptake, whereas phosphate and silicate were simply diluted. 
Nutrient load caused a higher primary production, leading to oxygen oversaturation in the 
surface water. In the near bottom water degradation processes were intensified by enhanced 
loads of organic matter leading partly to anoxia in the coastal strip of the Bay. 
The effects of the flood remained restricted to the Pomeranian Bay and did not influence the 
open Baltic Sea. On the turn of October/November 1997 the situation regarding nutrients in 
the Pomeranian Bay had returned to normal conditions. 
In the Gulf of Gdansk and the Pomeranian Bay, considerable growth of phytoplankton 
occurred. The flooding water created a bloom which can be recognized as a sort of spring 
bloom. Instead of the typical summer situation with a lot of blue-green algae the flood water 
created a bloom with lots of diatoms, typical for the spring, and also a massive freshwater 
flora. 
It is important to underline that the enormous blue-green bloom appearing in most parts of 
the Baltic Sea at the same time had nothing to do with the flood event.