Seasonal and inter-annual variation of Beryllium-7 deposition in birch-tree leaves and grass in the northeast upland area of the Czech Republic

The activity concentrations of Beryllium-7 (⁷Be), a naturally occurring radioisotope produced in the atmosphere, were measured in leaves of birch-trees, above-ground parts of grass, soil and rainwater in the mountain massive Kralicky Sneznik (the northeast of the Czech Republic, altitude about 750 m) in the years of 2005, 2006 and 2007. Dried and ground samples of the plants and soils, and water samples from wet deposition were used to determine the ⁷Be content using a semiconductor gamma spectrometer. The ⁷Be values ranged from 147.0 to 279.6 Bq kg⁻¹, from 48.7 to 740.8 Bq kg⁻¹, from 2.1 to 8.7 Bq kg⁻¹, and from 0.6 to 1.9 Bq kg⁻¹ in birch-tree leaves, grass samples, soils, and rainwater, respectively. Insignificant inter-annual variations but significant increase in the ⁷Be activity concentrations during the spring and summer months were observed in birch-tree leaves and grass samples. The seasonal variation of the ⁷Be concentrations in grass samples correlated (R² = 0.4663 and 0.6489) with precipitation. No similar correlation was found for ⁷Be in birch-tree leaves. Beryllium-7 content in birch-tree leaves and in aerial parts of grass was mainly caused by direct transport of ⁷Be from wet deposition into aerial parts of the observed plants.