Pathways of Mercury Evasion from Contaminated Wetlands: A Globally Important Source of Atmospheric Mercury?EPA Grant Number: GR832214
Title: Pathways of Mercury Evasion from Contaminated Wetlands: A Globally Important Source of Atmospheric Mercury?
Investigators: Peters, Stephen , Morris, Donald P. , Windham, Lisamarie
Institution: Lehigh University
EPA Project Officer: Carleton, James N
Project Period: January 15, 2005 through January 14, 2008
Project Amount: $298,907
RFA: Greater Research Opportunities: Persistent, Bioaccumulative Chemicals (2004) RFA Text | Recipients Lists
Research Category: Land and Waste Management , Safer Chemicals , Hazardous Waste/Remediation , Health Effects
Mercury (Hg) is a globally occurring pollutant that bioaccumulates and persists in the environment. The global Hg cycle is highly dependant on air/water exchange, as it is one of the primary pathways to deliver Hg to the atmosphere. Although open water systems appear to be net sinks for Hg sequestration (e.g. Chesapeake Bay), nearshore wetland systems may be significant sources of Hg emission due to 1) biogenic release from plant leaves and 2) the increased quantity and quality of dissolved organic carbon. Because estuarine environments are naturally and anthropogenically enriched in Hg, we hypothesize that the evasion of Hg from contaminated wetlands, particularly estuaries, may be a critically important and currently underestimated flux of Hg to the atmosphere.
Two pathways exert primary control over the release of Hg0 from estuarine environments: the abiotic reduction of Hg(II) to Hg0(aq) as moderated by complex interactions of UV radiation, DOC, salinity, and pH in the water column, and by the diffusive release of bacterially reduced Hg0 from plant leaf surfaces during transpiration.
Our objectives are to: 1) determine the relative importance of these two different evasion pathways; 2) investigate the fundamental processes governing chemical interactions within each pathway; and 3) evaluate the net contribution of evasion from Hg contaminated wetlands to the global Hg budget. These objectives will be studied by experimentally and empirically testing hypothesized relationships between measured environmental parameters and Hg behavior in a wetland.
A Hg contaminated estuary in the Meadowlands complex (NJ) will be the site of extensive field measurements. The high productivity, freshwater/marine transitional environment of the estuarine study area enables us to fully examine a matrix of environmental variables including UV transparency, DOC quantity and quality, salinity, pH, and plant communities. Laboratory experiments (e.g laboratory solar simulator) conducted using samples obtained from the field sites will test specific hypothetical relationships. We plan to investigate the use of stable Hg isotopes to label and trace different pathways and also the natural mass-dependant fractionation of Hg isotopes along evasion pathways to ascertain its utility for future studies.
We expect to improve our understanding of the ultimate fate and transport of Hg in estuarine environments, including possible predictions of responses to increasing UV-B radiation and environmental change. Especially useful to environmental managers will be what we learn about the relative pathways of Hg transport in contaminated wetland ecosystems, and what steps would be most/least appropriate for long-term management.