Atmospheric fluxes and marsh‐soil inventories of 7Be and 210Pb

Abstract

The atmospheric flux of 7Be over a 2‐year period at a coastal site (Norfolk, Virginia) and at an inland site (Oak Ridge, Tennessee) typically supports inventories ranging from 1.0 to 2.0 pCi/cm2 (1 pCi = 0.037 Bq), with the highest inventories generally occurring in the spring and the lowest occurring in the fall. The calculated average daily fluxes required to support these inventories range from 0.013 to 0.026 pCi cm−2 d−1. Despite the different production‐source terms for 7Be and 210Pb, there is a high degree of correlation between their measured total monthly deposition reflecting the importance of washout in removing both radionuclides from the atmosphere. Beryllium 7 inventories in soil and vegetated marsh cores compare favorably with inventories calculated from the atmospheric deposition data. Lead 210 inventories in soil and vegetated marsh cores may be enriched (by 20–30%) in relation to inventories calculated from its depositional flux to bucket samplers. Possible explanations for this enrichment are that above‐ground vegetation is more efficient at collecting dry aerosols (containing short‐lived radon daughters) than buckets or that foliage is an effective trap for particles containing sorbed 210Pb which may be eroded from unvegetated surfaces by wind or water. The vertical distribution and inventory of both 7Be and 210Pb in marsh cores are affected by the presence of vegetation and the location of the groundwater table.