in the majority of the seaweed samples of the North Sea coast I 131 
was very severely enriched, in comparison to that in the seaweed 
samples of the Baltic Sea coast the enrichment of Ru 103 dominated. 
It was not possible to estimate a radiation burden for people wande- 
ring along the beach, because the areal coverage of the seaweed on 
the beach was not known. On the basis of the uneven distribution of 
the seaweed, it was not to be assumed that from this source a signi- 
ficant radiation burden was emitted. 
In a follow-up investigation on 03.08., in one seaweed sample from 
the Lübeck Bight, only comparably slight concentrations of Ruthenium 
isotopes could still be detected (see Table 2). 
Distribution of the radioactivity in the North Sea and 
the Baltic Sea 
5 
Temporal course of the contamination of the seawater in 
the Federal German coastal region 
As can already be seen from the total Gamma-measurements, the radio- 
activity concentration in the surface water already attained the 
highest values on 3rd May after the passage of the thunder storm 
front. They decreased very quickly after that. In order to be able 
to follow the temporal course of the concentrations of the Chernobyl 
input, water samples were taken at regular intervals at three sta- 
tions of the German Bight and the western Baltic Sea, and analyzed 
for the long-lived, highly soluble isotope Caesium 137 (Fig. 14). 
The strong decrease of the activity concentrations after the initial 
peak values, which can be seen in that diagram, are exclusively an 
effect of the dilution and distribution - and are not determined by 
the radioactive decay of the short-lived isotopes, as was the case 
with the total Gamma-measurements. 
In the long run, the activity decreased in the German Bight more 
quickly than in the western Baltic Sea. On the basis of the known 
water mass transport in the North Sea, the water in the south- 
eastern North Sea will be forced out within a few months by uncon- 
taminated water from the Channel. As can be seen from Fig. 17, this 
water is onlvy slightlvy contaminated bvy the accident at Chernobvl. 
The uneven course of the fall in concentration near the Light Ves- 
sels "Borkumriff” and "Elbe 1” in the German Bight (Fig. 14) indi- 
cates different water exchange. The investigation in August (Fig. 
20) indicated that, to this point in time in the western part of the 
German Bight the contaminated water was forced out by the water from 
the Channel; whereas, in the eastern part - owing to slower water 
exchange time - as well as by the inflow of the higher contaminated