Influence of broadleaf forest vegetation on atmospheric deposition of airborne radionuclides.
The activities of airborne radionuclides 7Be and unsupported 210Pb (210Pbus) were measured in moss samples taken from 17 different locations. The objective was to estimate the influence of the broadleaf forest vegetation on atmospheric deposition of airborne radionuclides attached to aerosols. Two moss samples were collected at each location: within the forest stand (inside the area of the tree canopy projection) and within forest openings (outside the area of the tree canopy projection). Samples were taken in the spring season, before the leaves of trees came forth and in the autumn season, right before fall defoliation. A measurement indicates an absence of variation in 210Pbus concentration, however spring/autumn ratios of 7Be concentrations in mosses showed the expected seasonal difference in 7Be deposition. It was also noted that atmospheric deposition of 7Be at the forest openings was about two times higher than deposition in the forest. Using very simplified models, these measurements can be used to get estimation at how long 7Be and aerosols can reside on the leaves before precipitation eventually wash it to the ground mosses. It was estimated that the mean residence time of aerosols in the leaves was up to 50 days.