UVM Theses and Dissertations
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Print
Author:
Juillerat, Juliette I.
Dept./Program:
Plant and Soil Science
Year:
2011
Degree:
MS
Abstract:
Mercury (Hg) is a pollutant affecting the health ofpeople and ecosystems worldwide. Mercury can have deleterious health effects when it accumulates in food, especially in fish, in the form of methyl-mercury (MeHg). Aquatic ecosystems have long been known to be affected by Hg pollution due to biomagnifications of Hg in the food chain. Terrestrial non-piscivorous species have generally not been considered at risk ofHg toxicity. However, recent research indicates that at least some upland systems are also directly affected. Atmospheric deposition of Hg occurs in precipitation; it also occurs by being deposited to surfaces and subsequently leached (throughfall), and by entering leaves via the stomata before being deposited to the ground in the leaf litter (litterfall). Litterfall is thought to be responsible for the majority of the Hg flux to a forested watershed. Mercury accumulates in soils and eventually leaches out to aquatic systems, either as dissolved Hg, or along with soil particles. The importance of forest characteristics on the flux of Hg in litterfall and on Hg accumulation in the upper layers ofthe soil is not yet fully understood.
This research evaluated the importance ofspecies composition, forest structure, and site characteristics on Hg deposition and accumulation in forest soils. We measured total Hg at eighteen research sites distributed throughout Vermont, USA, in three forest types (northern hardwood, lowland red spruce-balsam fir, and mixed forest). There were significant differences in Hg concentration between tree species; Acer pennsylvanicum (striped maple) had significantly greater Hg concentration than any other species. Factors that may relate to species-specific differences were investigated. Leaves differed in Hg concentration depending on their origin (height) on trees, with leaves closer to the ground accumulating more Hg. Mercury concentration in leaves was positively related to the surface-to-weight ratio of leaves. There were no significant differences in litterfall Hg flux between forest types, but southern Vermont had greater litterfall Hg deposition fluxes than northern Vermont.
Soil Hg concentrations were similar to those reported for the region. Mercury pools in the Oi horizon (litter layer) was not related to litterfall flux or modeled total Hg deposition. There were significant differences in Hg concentration and Hg/C ratio among soil horizons but not between forest types. Despite having smaller Hg concentration, the upper mineral soil (A horizon) had greater Hg pools than organic soil horizons (forest floor) due to greater bulk density of the mineral soil. Consequently, factors that affected the depth ofthe forest floor also affected Hg pools in the upper layers ofthe soil (0-9 cm). Soil drainage, slope and pH of deep soil horizons were all related to organic soil horizon depth and therefore to THg pools in the upper soil layers. Soils with thin forest floor had greater Hg pools to a fixed depth.
This research evaluated the importance ofspecies composition, forest structure, and site characteristics on Hg deposition and accumulation in forest soils. We measured total Hg at eighteen research sites distributed throughout Vermont, USA, in three forest types (northern hardwood, lowland red spruce-balsam fir, and mixed forest). There were significant differences in Hg concentration between tree species; Acer pennsylvanicum (striped maple) had significantly greater Hg concentration than any other species. Factors that may relate to species-specific differences were investigated. Leaves differed in Hg concentration depending on their origin (height) on trees, with leaves closer to the ground accumulating more Hg. Mercury concentration in leaves was positively related to the surface-to-weight ratio of leaves. There were no significant differences in litterfall Hg flux between forest types, but southern Vermont had greater litterfall Hg deposition fluxes than northern Vermont.
Soil Hg concentrations were similar to those reported for the region. Mercury pools in the Oi horizon (litter layer) was not related to litterfall flux or modeled total Hg deposition. There were significant differences in Hg concentration and Hg/C ratio among soil horizons but not between forest types. Despite having smaller Hg concentration, the upper mineral soil (A horizon) had greater Hg pools than organic soil horizons (forest floor) due to greater bulk density of the mineral soil. Consequently, factors that affected the depth ofthe forest floor also affected Hg pools in the upper layers ofthe soil (0-9 cm). Soil drainage, slope and pH of deep soil horizons were all related to organic soil horizon depth and therefore to THg pools in the upper soil layers. Soils with thin forest floor had greater Hg pools to a fixed depth.