Date of Award

5-2002

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Terry A. Haines

Second Committee Member

J. Steve Kahl

Third Committee Member

Stephen A. Norton

Abstract

Cross-continental movement of contaminated air masses and prevailing wind direction. Sites covered with softwood vegetation also received higher Hg deposition than other vegetation types because of the higher scavenging efficiency of the canopy structure. MeHg deposition was not affected by these factors. Hg deposition was lower in Cadillac Brook watershed (burned) than in Hadlock Brook watershed (unburned) because regeneration after the fire was dominated by mixed hardwood, whereas softwoods dominate the landscape in Hadlock Brook watershed. The lower deposition could also be a result of the watershed aspect; Cadillac Brook watershed faces southeast to east and Hadlock Brook watershed faces south to southwest. The 1947 fire that burned Cadillac Brook watershed likely removed organic material from the soil through combustion and subsequent erosion. Much of the Hg in the remaining organic material would have been volatilized by the elevated temperature caused by the fire, breaking the chemical bonds between Hg and DOC releasing the Hg, possibly enhancing the soil's ability to sequester Hg more efficiently by. As a result, Cadillac Brook exports less Hg from its watershed than Hadlock Brook, which has unburned soils containing more organic material. Hadlock Brook exports more MeHg, but export cannot be explained by inputs and may be controlled by production in peat and other organic-rich materials in the riparian zone. Hg and MeHg inputs were weighted by season and vegetation type for budget determination because these two factors had the most influence on deposition. Hg volatilization from soils, water, and vegetation surfaces was ignored because of the difficulties associated with analyzing gaseous Hg. The Hg budget for Cadillac Brook watershed was 9.4 μg/m2/year (input) - 0.4 μg/m2/year (export) = 9.0 μg/m2/year, or 95% of the total Hg deposited on Cadillac Brook watershed was retained by the watershed. The Hg budget for Hadlock Brook watershed was 10.2 μg/m2/year (input) - 1.3 μg/m2/year (output) = 8.9 μg/m2/year, or 87% of the total Hg deposited on Hadlock Brook watershed was retained by the watershed. Litter contributed two to five times the Hg to the forest floor as precipitation. Cadillac Brook watershed received 57.1 μg/m2/year of Hg from litter while Hadlock received 29.0 μg/m2/year of Hg, demonstrating that litter fall is a major Hg pathway to the forest floor. The residence time of the Hg from litter and the ultimate fate of the litter itself are unknown. The MeHg budget for Cadillac Brook watershed was 0.05 μg/m2/year (input) - 0.04 μg/m2/year (output) = 0.01μg/m2/year, or 25% of the MeHg deposited was not released by the watershed. The MeHg budget for Hadlock Brook watershed was 0.1 0 μg/m2/year (in) - 0.06 pg/m21year (out) = 0.04μg/m2/year, 39% of MeHg deposited was not released by the watershed. MeHg export appears to be controlled by soil processes in the riparian zone rendering a "MeHg budget" an inaccurate portrayal of MeHg dynamics in these watersheds.

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