SOIL CS-137 ACTIVITY IN A TROPICAL DECIDUOUS ECOSYSTEM UNDER PASTURE CONVERSION IN MEXICO

Soil profiles of Cs-137 were measured in a tropical deciduous ecosyste m under pasture conversion on the Pacific Coast of Mexico. Soil sample s were taken from unperturbed forest, and from pasture plots following forest conversion. The average total Cs-137 areal activity of non-ero ded forest sites indicated a base level of 5 315+/-427 Bq m(-2). On av erage, total areal activity on hill-tops was significantly higher (ran ge 10 to 47%) in the forest than in the pastures. A significant correl ation was found between the total Cs-137 areal activity and soil organ ic mater content (r(2) = 0.16). This correlation can be explained by a soil physical-protection hypothesis. The redistribution of Cs-137 in the landscape is explained by soil erosion processes.