Atmospheric Environment 37 (2003) 1613–1622 Accumulation of atmospheric mercury in forest foliage J.A. Ericksen a , M.S. Gustin a, *, D.E. Schorran b , D.W. Johnson a , S.E. Lindberg c , J.S. Coleman b a Department of Environmental Resource and Sciences, University of Nevada-Reno, Mail Stop 370, Reno, NV 89557, USA b Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA c Environmental Sciences Division, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, USA Received 4 July 2002; accepted 22 December 2002 Abstract We used unique mesocosms to examine the role that plants play in accumulating and transforming atmospheric Hg. Several stands of quaking aspen were grown in large gas-exchange chambers in Hg-enriched soil (12.371.3 mgg 1 ), and the Hg content in the vegetation was determined over time. Foliar Hg concentrations increased as a function of leaf age and leveled off after 2–3 months in the oldest tissue with a mean tissue concentration of 150 ngg 1 . Approximately 80% of the total Hg accumulated in the aboveground biomass was found in the leaves, and roughly 1% of that Hg was methylated. Leaves of additional aspen grown within the mesocosms in containers of low Hg soil (0.0370.01 mgg 1 ) exhibited foliar Hg concentrations similar to those of trees grown in the Hg-enriched soil. Leaf rinses and surrogate Teflon surfaces were analyzed to characterize surface deposition processes. Small gas-exchange systems were used to measure stomatal uptake of Hg vapor, and the mean Hg flux was 3.3ngm 2 h 1 . These experiments showed that almost all of the Hg in foliar tissue originated from the atmosphere. Thus, in the fall when deciduous trees enter dormancy and leaves senesce, litterfall would represent a new Hg input to terrestrial ecosystems. r 2003 Elsevier Science Ltd. All rights reserved. Keywords: Plants; Biogeochemistry; Global cycling; Sinks; Uptake 1. Introduction Mercury (Hg) is emitted from anthropogenic and natural sources to the atmosphere, principally in the gaseous form, and can be transported to remote and pristine locations. Elemental Hg (Hg 0 ), the dominant form of Hg in the atmosphere (>95%), has a long atmospheric residence time and is considered a global pollutant (Schroeder and Munthe, 1998). Current research has identified previously undetected sources of atmospheric Hg (Lindberg and Price, 1999; Carpi and Lindberg, 1998; Friedli et al., 2001) and demonstrated that known sources of Hg are greater than realized (Engle et al., 2001; Gustin et al., 2000; Pirroni et al., 2001). With the addition of new and greater sources of atmospheric Hg, researchers have begun to investigate unrecognized sinks (Lindberg et al., 2002). Little has been published in open literature on the fate of mercury in the soil–plant–air continuum (e.g. Hanson et al., 1995; Lindberg, 1996; Leonard et al., 1998; Lindberg et al., 1998), and understanding the relative importance of forested systems within regional or global cycles is critical to developing a global Hg budget (Leonard et al., 1998). For instance, the magnitude of the global Hg pool presently residing in plant biomass has not been estimated. Although litterfall has been demonstrated to be an important source of Hg to the forest floor (Lindberg, 1996; Iverfeldt, 1991; Rea et al., 1996, 2002; St. Louis et al., 2001), where it can leach or erode into aquatic systems, the ultimate source of inorganic or organic Hg in litterfall has not been determined. A central question in the global cycling of *Corresponding author. Tel.: +1-775-784-4203; fax: +1- 775-784-4789. E-mail address: msg@unr.nevada.edu (M.S. Gustin). 1352-2310/03/$-see front matter r 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S1352-2310(03)00008-6