Soil 137Cs activity in a tropical deciduous ecosystem under pasture conversion in Mexico

Soil profiles of 137Cs were measured in a tropical deciduous ecosystem under pasture conversion on the Pacific Coast of Mexico. Soil samples were taken from unperturbed forest, and from pasture plots following forest conversion. The average total 137Cs areal activity of non-eroded forest sites indicated a base level of 5 315 ± 427 Bq m−2. On average, total areal activity on hill-tops was significantly higher (range 10 to 47%) in the forest than in the pastures. A significant correlation was found between the total 137Cs areal activity and soil organic matter content (r2 = 0.16). This correlation can be explained by a soil physical-protection hypothesis. The redistribution of 137Cs in the landscape is explained by soil erosion processes.