Response of Methylmercury Production and Accumulation to Changes in Hg Loading: A Whole-ecosystem Mercury Loading Study

EPA Grant Number: R827631
Title: Response of Methylmercury Production and Accumulation to Changes in Hg Loading: A Whole-ecosystem Mercury Loading Study
Investigators: Gilmour, Cynthia C. , Heyes, Andrew , Mason, Robert P. , Rudd, John M.
Institution: Academy of Natural Sciences , Chesapeake Biological Laboratory , Freshwater Institute , University of Maryland Research Centers
EPA Project Officer: Hiscock, Michael
Project Period: October 1, 1999 through September 30, 2002 (Extended to September 30, 2003)
Project Amount: $848,029
RFA: Mercury: Transport and Fate through a Watershed (1999) RFA Text |  Recipients Lists
Research Category: Water and Watersheds , Mercury , Water , Safer Chemicals

Description:

In this study we propose to resolve a basic and unanswered question in our understanding of the mercury cycle - "How much does methylmercury in ecosystems change in response to a change in mercury loading?" - by studying methylmercury (MeHg) production as part of a whole-ecosystem mercury (Hg) loading experiment. This proposal is a key part of a multi-disciplinary, whole-ecosystem experiment to study the relationship between atmospheric Hg loading and fish Hg concentrations. The research will be carried out at the Experimental Lakes Area (ELA) in northwestern Ontario by a team of researchers from the US and Canada. The study site will be an entire catchment including uplands, wetlands and a first order drainage lake. In this proposal, we request funds to support the methylation component of the ELA Hg Loading Study.

We will measure, in upland and wetland soils and lake sediments, net accumulation of MeHg, instantaneous MeHg production and degradation rates, and the key biogeochemical parameters in each of these locations that affect Hg bioavailability and methylation. The ELA is representative of northcentral and northeastern US ecosystems that are impacted by Hg. To provide a comparison in a very different ecosystem type, and another region of North America, we also propose to do Hg loading studies in a subtropical wetland, the Florida Everglades. In the Everglades, Hg addition experiments will be conducted within wetland enclosures.

Approach:

We propose to use two novel and powerful techniques to accomplish our objective; one, the use of stable Hg isotopes, and two, the manipulation of a whole watershed with Hg. An understanding of the relationship between Hg loading and MeHg production and bioaccumulation requires a whole-ecosystem approach because there are many steps between the entry of inorganic Hg to the ecosystem, its conversion to the methylated form, and bioaccumulation in fish. The use of Hg stable isotopes will allow us to track the fate of "new" Hg in deposition vs. "old" Hg stored in sediments and soils, and to track the bioavailability of new Hg over time and across the components of the watershed. Aquatic ecosystems for which Hg cycling is well understood, in which MeHg production is high, and in which the PIs have significant experience were chosen for study.

Expected Results:

This study will give us the ability to predict changes in MeHg from changes in Hg loading over the range of Hg loadings that would result from regulatory action. By examining the MeHg response in two ecosystems, we will also provide data on regional and landscape variations that affect MeHg production and subsequent accumulation in fish. In its review of EPA's recent report on Hg to Congress, the EPA Science Advisory Board stated, "Although there are many areas of uncertainty in the modeling of Hg fate and transport, the lack of information about methylation and bioaccumulation of Hg in various ecosystems is the area which contributes the greatest uncertainty to the overall modeling effort". With this major new study, we hope to resolve much of that uncertainty.

Publications and Presentations:

Publications have been submitted on this project: View all 44 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 5 journal articles for this project

Supplemental Keywords:

Scientific Discipline, Geographic Area, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Contaminated Sediments, Environmental Chemistry, Chemistry, Fate & Transport, Ecological Risk Assessment, Ecology and Ecosystems, Biology, International, Environmental Engineering, Mercury, fate and transport, aquatic, contaminated sediment, mercury loading, fish consumption, mercury cycling, soils, biogeochemical cycling, methylation, methylmercury, terrestrial and aquatic fate, wetland

Relevant Websites:

Synthesis Report of Research from EPA’s Science to Achieve Results (STAR) Grant Program: Mercury Transport and Fate Through a Watershed (PDF) (42 pp, 760 K)

Progress and Final Reports:

  • 2000 Progress Report
  • 2001 Progress Report
  • 2002
  • Final Report