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Abstract-The uptake, distribution, and subsequent emission of mercury to the atmosphere were investigated in five plant species ( [Labill]) with different ecological and physiological attributes. Transfer coefficients for mercury in the soilplant system were calculated. Plant-to-atmosphere emissions of mercury were determined using a controlled environment gasexchange system and ranged from 10 to 93 ng/m 2 /h in the light; emissions in the dark were an order of magnitude less. Transfer coefficients for mercury within the soil-plant system increased acropetally (root-to-leaf axis) by orders of magnitude. Estimated mercury emissions from plants in the Carson River Drainage Basin of Nevada over the growing season (0.5 mg/m 2 ) add to the previously reported soil mercury emissions (8.5 mg/m 2 ), resulting in total landscape emissions of 9 mg/m 2 . For L. latifolium, 70% of the mercury taken up by the roots during the growing season was emitted to the atmosphere. For every one molecule of mercury retained in foliage of L. latifolium, 12 molecules of mercury were emitted. Within this arid ecosystem, mercury emissions are a dominant pathway of the mercury cycle. Plants function as conduits for the interfacial transport of mercury from the geosphere to the atmosphere, and this role is undervalued in models of the behavior of mercury in terrestrial ecosystems and in the atmosphere on a global scale.

This paper documents the atmospheric mercury concentrations above anthropogenically contaminated and naturally enriched sites in central western Nevada. Atmospheric mercury concentrations were measured at five representative regional sites (1.2−7.5 ng/m3) and two anthropogenically contaminated areas (13−866 ng/m3) in the Carson River Superfund Site. The highest regional concentrations were measured at the Steamboat Geothermal area, where mercury mineralization occurs naturally. Concurrent with atmospheric sampling, environmental conditions were monitored to assess their covariance with mercury concentrations. Atmospheric mercury concentrations were influenced by multiple factors with dominance exerted by substrate mercury concentration, site surface characteristics, and local and synoptic scale air masses. A mercury flux of 5−125 (±50%) μg of mercury m-2 h-1 was estimated via modified K-theory for a contaminated location. This flux was scaled up to estimate the contribution of atmospheric mercury from mine wastes within the Carson River Superfund Site. The estimated annual flux (150−400 kg/yr) is comparable to that from a 1000 MW coal-fired power plant (300 kg/yr). The projected longevity of this diffuse source exceeds 104 years, so the cumulative contribution over time from this region far exceeds the corresponding contribution of a coal-fired power plant whose life time is measured in decades.

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Approximately 5.5 x 109 g (4.0 x 105) of mercury was discharged into the Carson River Drainage Basin of west-central Nevada during processing of the gold- and silver-rich Comstock ore in the late 1800s. For the past 13 decades, mercury has been redistributed throughout 500 km2 of the basin, and concentrations are some of the highest reported values in North America. This article documents the concentrations of mercury in the air, water, and substrate at both contaminated and noncontaminated sites within the basin and discusses the implications for risk assessment. At contaminated areas, the range of mercury concentrations are as follows: mill tailings, 3-1610 micrograms/g; unfiltered reservoir water, 53-591 ng/l; atmospheric vapor, 2-294 ng/m3. These values are three to five orders of magnitude greater than natural background. In all media at contaminated sites, concentrations are spatially variable, and air and water mercury concentrations vary temporally. The study are in situated in a natural mercuriferous belt, and regional background mercury concentrations in all environmental media are higher than values typically cited for natural background. As a mercury-contaminated site in North America, the Carson River Drainage Basin is unusual for a number of reasons, including its location in a natural mercuriferous belt, high and sustained levels of anthropogenic mercury inputs, long exposure time, aridity of the climate, and the riparian setting in an arid landscape, where biological activity is concentrated in the same areas that contain high levels of mercury in multiple media. Images Figure 1. Figure 2. Figure 3. Figure 4. Figure 4. Figure 4.