Annual variation of 7Be soil inventory in a semiarid region of central Argentina

Abstract

Reliable information on environmental radionuclides atmospheric entrance, and their distribution along the soil profile, is a necessary condition for using these soil and sediment tracers to investigate key environmental processes. To address this need, 7Be content in rainwater and the wet deposition in a semiarid region at San Luis Province, Argentina, were studied. Following these researches, in the same region, we have assessed the 7Be content along a soil profile, during 2.5 years from September 2009 to January 2012. As expected, the specific activity values in soil samples in the wet period (NovembereApril) were higher than in the dry period (MayeOctober). During the investigated period (2009 e beginning 2012) and for all sampled points, the maximum value of the 7Be specific activity (Bq/kg was measured at the surface level. A typical decreasing exponential function of 7Be areal activity (Bq/m2) with soil mass depth (kg/m2) was found and the key distribution parameters were determined for each month. The minimum value of areal activity was 51 Bq/m2 in August, and the maximum was 438 Bq/m2 in February. The relaxation mass depth ranges from 2.9 kg/m2 in March to 1.3 kg/m2 in August. 7Be wet deposition can explain in a very significant proportion the 7Be inventory in soil. During the period of winds in the region (September and October), the 7Be content in soil was greater than the expected contribution from wet deposition, situation that is compatible with a higher relative contribution of dry deposition at this period of the year.