Description:

Mercury (Hg) occurs as volatile phases promoting the cycling of this contaminant between environmental compartments. Mercury is a global pollutant for via the atmospheric pathway. It is transported across regional and international boundaries and contaminates aquatic and terrestrial ecosystems. Recent studies have begun to develop a database on Hg emission and deposition to and from aquatic and terrestrial surfaces; however, our understanding of the mechanisms controlling these processes is only beginning to be developed. Several recent studies have indicated that Hg is exchanged between foliar surfaces and the atmosphere, but the significance of this exchange with respect to the overall biogeochemical cycling of Hg remains unknown. Understanding the mechanisms controlling the exchange of Hg between the atmosphere and abiotic and biotic ecosystem compartments is necessary for development of regulatory controls as well as for assessment of ecological and human health impacts of Hg in the environment.

The goal of this project is to determine the role of plants and soils in controlling the fate and transport of Hg in the environment at the ecosystem level. Much of our mechanistic knowledge for understanding the responses of ecosystems to environmental contaminants is limited to studies of single species or individual samples. Due to natural variability and environmental complexity, the use of field studies to understand mechanisms controlling contaminant flux is extremely difficult.

This project will utilize a large mesocosm (EcoCELL), an experimental setting in which whole system contaminant flux may be monitored under precisely controlled environmental conditions to identify key processes controlling the flux of Hg between ecosystem compartments. Investigation of the fate and transport of Hg at the ecosystem level will allow for development of an understanding of antagonistic and synergistic effects of mechanisms known to control Hg flux on the individual sample scale. Ancillary experiments investigating uptake, storage and emission associated with ecosystem components, using a single pass gas exchange system, Ecopods and a field flux chamber, will provide additional data for understanding mechanisms controlling Hg fate and transport at the ecosystem level.

An understanding of the Hg flux and the mechanisms controlling flux from unvegetated soil surfaces will be developed. A plant community will be established in the EcoCELLs and whole system fluxes as well as individual plant mass balances will be developed as leaf area and rooting volume increases. The working hypothesis is that mercury available as soil gas is readily bioavailable and plants act as a conduit for mercury to be transported from contaminated substrate to the air. One component of this project will assess the potential for phytoremediation of Hg contaminated soils using genetically engineered plants. These plants are known to uptake Hg from soils at very high rates; however, the degree to which they remove mercury from the soil is not known.

Final Report