Quantitative Retention of Atmospherically Deposited Elements by Native Vegetation Is Traced by the Fallout Radionuclides ⁷Be and ²¹⁰Pb

Abstract

Atmospheric deposition is the primary mechanism by which remote environments are impacted by anthropogenic contaminants. Vegetation plays a critical role in intercepting atmospheric aerosols, thereby regulating the timing and magnitude of both contaminant and nutrient delivery to underlying soils. However, quantitative models describing the fate of atmospherically derived elements on vegetation are limited by a lack of long-term measurements of both atmospheric flux and foliar concentrations. We addressed this gap in understanding by quantifying weekly atmospheric deposition of the naturally occurring radionuclide tracers (7)Be and (210)Pb, as well as their activities in leaves of colocated trees, for three years in New Hampshire, U.S. The accumulation of both (7)Be and (210)Pb in deciduous and coniferous vegetation is predicted by a model that is based solely on measured atmospheric fluxes, duration of leaf exposure, and radioactive decay. Any "wash off" processes that remove (7)Be and (210)Pb from foliage operate with a maximum half-time of greater than 370 days (P > 99%), which is an order of magnitude longer than previously assumed. The retention of both (7)Be and (210)Pb on leaves is thus quantitative and permanent, coupling the fate of (7)Be, (210)Pb and similar atmospheric species to that of the leaf matter itself. These findings demonstrate that the long-standing paradigm of a short "environmental half-life" for atmospheric contaminants deposited on natural surfaces must be re-evaluated.

Direct Channel Precipitation and Storm Characteristics Influence Short‐Term Fallout Radionuclide Assessment of Sediment Source

“…Our model does not explicitly account for leaf matter as a source of FRNs to the channel. Tree canopies have been found to accumulate 7 Be and 210 Pb (Landis et al, ). With approximately one third of the channel area covered by deciduous tree canopy (Table ), litterfall occurs onto our study channel.…”

Joint isotopic mass balance: a novel approach to quantifying channel bed to channel margins sediment transfer during storm events

“…10) while sediment with continuous exposure ages of a year or more have ratios less than c . 2 (Landis et al ., ).…”

Asymmetric hillslope erosion following wildfire in Fourmile Canyon, Colorado

“…Using an average of 12 soil cores from stable, vegetated moderately sloped terrain, we found that the reference inventory for our study area included 137 Cs at 1870 ± 670 Bq m −2 and 210 Pb ex at 6410 ± 2200 Bq m −2 (median ± σ ). The reference locations had a soil 7 Be inventory of 226 ± 180 Bq m −2 , but this is lower than SFB and NFB because of the influence of a dense canopy on capturing a significant fraction (up to half) of the atmospheric 7 Be (Landis et al ., ). It is important to note that these inventories are based on the radionuclide concentration (in Bq kg −1 ) of the < 2 mm soil fraction, multiplied by the bulk density of this size fraction.…”