Formation and Partitioning of Dissolved and Particulate Monomethylmercury in Contrasting Wetland Environments

EPA Grant Number: GF9500482
Title: Formation and Partitioning of Dissolved and Particulate Monomethylmercury in Contrasting Wetland Environments
Investigators: Holloway, Susan Ann
Institution: University of Wisconsin - Madison
EPA Project Officer: Broadway, Virginia
Project Period: September 1, 1995 through January 1, 2000
Project Amount: $26,777
RFA: STAR Graduate Fellowships (1995) Recipients Lists
Research Category: Academic Fellowships , Engineering and Environmental Chemistry , Fellowship - Chemistry


The goal of this research is to characterize the dominant factors and processes controlling temporal and spatial variations of dissolved and particulate monomethylmercury (MeHg) concentrations at two contrasting wetland sites in the continental United States. The research will specifically focus on the role of peatland disturbance, nutrient enrichment, redox cycles associated with periods of wetting and drying, and interactions with suspended particulate matter (SPM) and dissolved organic carbon on the levels and partitioning of MeHg in natural and constructed wetlands. The comparison of contrasting wetland sites will facilitate the identification of key factors influencing MeHg cycling in wetlands. The approach will include a comparison of temporal and spatial trends at two contrasting sites in order to help resolve dominant factors controlling MeHg production and transport. One of the sites selected is the Florida Everglades, a wetland hydrologically dominated by precipitation and groundwater inputs. Although the hydrologic and climatic differences are considerable between the systems, they exhibit similar major ion chemistry because both are in calcareous regions. Both wetlands are hydrologically down gradient from agricultural areas and are affected to varying degrees by inputs of nutrient enriched waters. These similarities should enhance comparisons of temperature and growing season effects on net MeHg production and particle characteristics between the two systems. This project will be coordinated with ongoing USGS research and will be designed to complement, not duplicate, that research. It will address the issue of transferability of results to other natural and constructed wetlands. In Florida samples will be collected within canals that drain agricultural areas adjacent to the Everglades. These canals are thought to transfer nutrient enriched water from the agricultural areas into the wetland when rainfall is heavy. Sampling will also occur along a transect from the outfall of the canal into the Everglades wetland. In addition, samples will be collected from an area that is believed to be relatively undisturbed by human activities, in order to provide a baseline along which to compare results. The research site inWisconsin is a groundwater discharge wetland with strong upward gradients; therefore sampling sites will be vertically aligned at various depths in the peat. Because of previous studies, detailed analysis of MeHg cycling within the peat substrate will be possible. The effect of peat disturbance on rates of methylation and the amount of particulate versus dissolved MeHg are of major interest at this site. The influence of the shorter growing season on methylation rates will likely make the Wisconsin site differ significantly from the Everglades research site in total MeHg production. Particulate MeHg will also be collected on ashed quartz fiber filters to insure reliable particulate collections. SPM of corresponding size fractions would also be collected in order to calculate partition coefficients for mercury species of various size classes. Duplicates of SPM will be taken at each site for error analysis and subsequent digestion to determine the carbon, iron, and sulfur ratios of each size class. These data will be useful in determining the chemical character of the SPM and the ratio of mineral versus organic matter in the particulate phase. Routine limnological parameters such as pH, temperature, and oxygen will be measured at each sampling point as well. This sampling scheme will allow comparisons of MeHg partitioning over the annual growth cycle as well as over spatial gradients of nutrient and hydrologic disturbance. This research project will characterize important factors that facilitate net MeHg production in natural wetlands.

Supplemental Keywords:

RFA, Scientific Discipline, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Limnology, Ecology, exploratory research environmental biology, Environmental Chemistry, Ecosystem/Assessment/Indicators, Ecosystem Protection, Chemistry, State, Ecological Effects - Environmental Exposure & Risk, Southeast, Ecological Risk Assessment, Ecology and Ecosystems, Ecological Indicators, wetlands, Florida Everglades, MeHg production and transport, dissolved MeHg, particulate MeHg, Wisconsin (WI), contrasting wetland environments, Florida, monomethylmercury (MeHg)