Die Tropenstation La Gamba

Die „Tropenstation La Gamba“ in Costa Rica – Wissenschaftlicher Bericht
BOSSEW, P. 1996: Radioactive Contamination of Tropical Rainforest Soil in Southern Costa
Rica. Austrian Ecology Institute, Vienna
Soil from four locations in a tropical rainforest near Golfito in Southern Costa Rica was
investigated for radionucleids. For comparison, two nearby locations in open grassland were
measured as well. Each sampling site consisted of 5 soil cores down to a depth of 15 cm. The
mean contamination with 137 Cs was 572 Bq/m² (referenxe date 1 Jan. 1996) and the coefficient of
variation (CV) 50%. The contamination is probably due to global fallout from the atmospheric
atomic bomb tests between 1945 and 1980. The mean contamination is somewhat lower than the
700 Bq/m² expected for the latitude (8°42‘), which may be explainded by that a certain fraction of
the total fallout lies below 15 cm. Out of the total variation of 50%, around 20% can be attributed
to the sampling and measuring process uncertainties, thus leaving a 45% contribution of spatial
variability.
A significant grouping between forest and meadow sites could be detected: the meadow
sites proved to be less contaminated than the forest sites, with 665 and 402 Bq/m², respectively.
This may be explained by the fact that the meadows had been subject to agricultural activities
which results in an increased redistribution of the caesium in the soil and therefore a larger
fraction of the total 137 Cs lying below 15 cm.
The mean 40 K activity concentration was 175Bq/kg d.m. (CV = 69%), for 226 Ra and 228 Ra
concentrations of 9.90 Bq/kg (CV = 23%) and 7.93 Bq/kg (CV = 20%) have been found,
respectively.
Sand samples from a nearby Pacific ocean beach showed a remarably high 137 Cs content,
namely 1.93 Bq/kg d.m.
Anschrift des Autors:
Peter Bossew
Austrian Institute of Applied Ecology
Seidengasse 13, A-1070 Wien
Institute of Physics and Biophysics
University of Salzburg
Hellbrunnerstrasse 34, A-5020 Salzburg
p.bossew@magnet.at
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