Comparison of spatial patterns of ¹³⁷Cs and ⁴⁰K in natural grassland soil and soil-to-plant relationship

¹ Universidad Nacional de San Luis, Ejército de los Andes 950, 5700 San Luis, Argentina
² IMASL, Instituto de Matematica Aplicada San Luis, CONICET, Consejo Nacional de Investigaciones Científicas y Tecnologicas, 5700 San Luis, Argentina
³ ANPA, Agenzia Nazionale per la Protezione dell'Ambiente, Roma, Italy

Abstract

^l37Cs and ⁴⁰K activity in natural grassland was studied at two sampling locations in the North-East of Italy, during 1997 and 1999. The present spatial patterns of ¹³⁷Cs and ⁴⁰K, their mobility and availability for uptake and transfer to grass. To know the spatial and temporal variation of these factors is essential for prediction the radioelement transfer; GIS tools (ILWIS) were applied. The spatial pattern of distribution evidence element redistribution in soil as consequence of the following parts : 1.- ⁴⁰K migration allows ¹³⁷Cs adsorption by clay soil components, although clays have low retention capacity. 2.- Lateral migration is predominant over vertical migration for both radioelements as consequence of: clay content of low retention capacity, higher porosity and strong acidic pH in site 1 ; low O.M. content, clay content of low retention capacity and moderate acidic pH in site 2. Multitemporal analysis evidences high increment of ¹³⁷Cs soil inventory which varies between one and six times. The spatial and temporal variation in ¹³⁷Cs soil inventory might be attributed to radioelement redistribution in soil, as shown by the spatial and temporal pattern. Radiocaesium redistribution determines changes in spatial patterns of soil contamination in time. Multitemporal analysis evidences loss of ⁴⁰K soil inventory.