Short-term seasonal variability in ~7Be wet deposition in a semiarid ecosystem of central Argentina

摘要

The ~7Be wet deposition has been intensively investigated in a semiarid region at San Luis Province, Argentina. From November 2006 to May 2008, the ~7Be content in rainwater was determined in 58 individual rain events, randomly comprising more than 50% of all individual precipitations at the sampling period. ~7Be activity concentration in rainwater ranged from 0.7 ± 0.3 Bq l~(-1) to 3.2 ±0.7 Bq 1~(-1), with a mean value of 1.7 Bq l ~1 (sd = 0.53 Bq l~(-1)). No relationship was found between ~7Be content in rainwater and (a) rainfall amount, (b) precipitation intensity and (c) elapsed time between events. ~7Be ground deposition was found to be well correlated with rainfall amount (R = 0.92). For the precipitation events considered, the ~7Be depositional fluxes ranged from 1.1 to 120 Bqm~(-2), with a mean value of 32.7 Bqm~(-2) (sd = 29.9Bq m~(-2)). The annual depositional flux was estimated at 1140 ± 120 Bq m~(-2) y~(-1). Assuming the same monthly deposition pattern and that the ~7Be content in soil decreases only through radioactive decay, the seasonal variation of ~7Be areal activity density in soil was estimated. Results of this investigation may contribute to a valuable characterization of ~7Be input in the explored semiarid ecosystem and its potential use as tracer of environmental processes.