Soil properties and distribution of radionuclides of selected soil profiles from Southern Costa Rica

In soil profiles from southern Costa Rica, physical and chemical soil properties as well as mineralogical characteristics were analyzed. The investigated sites differ in their geomorphologic situation and floristic composition. Radiometric characterizations of the soils were undertaken, to allow a closer view on soil genesis as well as transport and migration mechanisms. Both natural and artificial radionuclides were used. The soils were classified as Cambisols and Acrisols. The parent materials of the soils are tuffites and basalts. 40K distribution shows a high spatial variability, 238U inventories are generally very low and 226Ra is rather homogenously distributed. The high excess lead values are caused by intensive precipitation in the region and the resulting high rates of 210Pb deposition. Amphibole minerals in the upper soil horizons probably originate from recent volcanic ashes. The circumstances of these depositions are unknown and need further investigation.