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

详细信息    查看全文

• 作者：Joshua D. Landis ; Carl E. Renshaw ; James M. Kaste
• 刊名：Environmental Science & Technology
• 出版年：2014
• 出版时间：October 21, 2014
• 年：2014
• 卷：48
• 期：20
• 页码：12022-12030
• 全文大小：360K
• ISSN：1520-5851

文摘

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 ⁷Be and ²¹⁰Pb, as well as their activities in leaves of colocated trees, for three years in New Hampshire, U.S. The accumulation of both ⁷Be and ²¹⁰Pb 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 鈥渨ash off鈥?processes that remove ⁷Be and ²¹⁰Pb 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 ⁷Be and ²¹⁰Pb on leaves is thus quantitative and permanent, coupling the fate of ⁷Be, ²¹⁰Pb and similar atmospheric species to that of the leaf matter itself. These findings demonstrate that the long-standing paradigm of a short 鈥渆nvironmental half-life鈥?for atmospheric contaminants deposited on natural surfaces must be re-evaluated.