Document Type

Thesis

Abstract

Atmospheric deposition, rather than inputs from local point sources, is the primary mechanism contributing to high levels of mercury in the northeastern United States, particularly in remote high elevation watersheds. However, no studies have yet been published on the effect of elevation on mercury concentrations in soils and vegetation, despite well-known increases in concentrations of other heavy metals at high elevations. In this study I examine the effects of three deposition mechanisms known to cause higher lead levels at higher elevations: 1) orographic precipitation, 2) increasing amounts coniferous vegetation with elevation, and 3) the onset of occult deposition. This study finds that these mechanisms do cause significant increases of mercury at higher elevations. Furthermore, these processes produce an abrupt increase in mercury amounts above the elevation of average cloud base height and the elevation at which vegetation becomes fully coniferous. These effects are clearest in organic horizon soils. From the lowest elevation site of 540 meters to the site located at I 034 meters, mercury amounts increase by nearly six-fold, from 1.36 mg/m2 to 7.65 mg/m2 . The threshold response of mercury to the onset of occult deposition and the change in vegetation leads to 1.49 times more mercury at the 986 meter site ( 4.85 mg/m2 Hg) than at the 934 meter site (3 .25 mg/m2 Hg) and 2.13 times more mercury at the 861 meter site (3 .0 I mg/m2 Hg) than at the 801 meter site ( 1.41 mg/m2 Hg). Thus, this study uncovers high elevation pools of mercury caused by magnification of anthropogenic contamination through three key atmospheric deposition processes. These pools represent potential for long-term contamination of lower elevation soils and watersheds, even in the absence of new mercury inputs.

Date Awarded

2011

Department

Geology

Advisor 1

James M. Kaste

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