2001 Progress Report: 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 , University of Maryland
Current 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 Period Covered by this Report: October 1, 2000 through September 30, 2001
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

Objective:

In this research project, a basic and unanswered question in the understanding of the mercury cycle is to be resolved: "How much does methylmercury in ecosystems change in response to a change in mercury loading?" This will be accomplished by studying methylmercury (MeHg) production as part of a whole-ecosystem mercury (Hg) loading experiment. This study is a key part of a multidisciplinary, whole-ecosystem experiment to study the relationship between atmospheric Hg loading and fish Hg concentrations (METAALICUS). The research is being carried out at the Experimental Lakes Area (ELA) in northwestern Ontario. The study site is the entire catchment and a first order drainage lake (L658), including uplands, wetlands, and the lake itself. The study includes initial pilot studies in 1999 and 2000, and full-scale experiment Hg additions in 2001 and 2002. METAALICUS is being accomplished by a team of researchers from the United States and Canada. This EPA grant supports the methylation component of the study.

To provide comparison in a very different ecosystem type, and a different region of North America, Hg loading studies are being conducted in a subtropical wetland, the Florida Everglades. In the Everglades, Hg addition experiments will be conducted within enclosures. Work in the Everglades is an extension of a study of biogeochemical cycling Hg across that ecosystem, the ACME study, conducted in collaboration with the U.S. Geological Survey (USGS), the South Florida Water Management District (SFWMD), and the Florida Department of Environmental Protection (FL DEP). In both study ecosystems, the amount of Hg loading to the study ecosystems will be increased using stable Hg isotopes. This unique approach will allow tracking of the the fate of newly deposited Hg separately from the larger existing pools, and tracking of the bioavailability of new Hg over time and across the components of the lake and watershed.

The primary objective of this project is to determine the response of MeHg production and accumulation to a change in ecosystem Hg loading. Other specific objectives are to: (1) determine the bioavailability of Hg delivered to different parts of the watershed for methylation; (2) determine the contribution of newly deposited Hg to MeHg production relative to existing Hg pools in sediments and soils, and how the bioavailability of new Hg changes over time; (3) develop stable isotope techniques for tracing Hg cycling in watersheds, making simultaneous Hg methylation and demethylation rate measurements, and examining the bioavailable pool of Hg(II); and (4) examine regional and habitat type differences in the response of MeHg to Hg loading by conducting a second Hg loading study in a different ecosystem type, and using process and model-based approaches to transfer results to other ecosystems.

Progress Summary:

During 1999, preliminary studies were conducted at ELA, including assessment of candidate watersheds and development of stable isotope methylation/demethylation techniques. In 2000, work included pilot-scale Hg isotope additions to lake enclosures, wetland plots, and upland plots. Lake 658 was selected as the study site, and background data were collected for 1 year. Full-scale stable isotope Hg additions to L658 and its watershed began in June 2001. The biogeochemistry of net Hg methylation was followed intensively through time and space in lake sediments, in the wetland, and in the upland. Experimental studies in lake enclosures, wetland plots, and upland plots outside of L658 continued. During 2001, preliminary experiments were conducted to examine how the speciation and behavior of Hg in rain compares to the ecosystem spikes.

In spring 2000, stable isotope Hg-dosing studies were begun in enclosures at four sites in the Everglades. Enclosures were sampled in spring and summer and dosed again in the fall. Also during 2000, Hg and MeHg levels were examined in phosphate-amended mesocosms.

Hg newly delivered to sediments is methylated quickly. Maximal methylation occurs in hours to days in the Everglades and days to weeks in an Ontario lake. The fraction of new Hg converted to MeHg in days/weeks following deposition is much higher than the fraction of "old" background Hg found as MeHg. The bioavailability of new Hg varies significantly among sites in the Everglades. MeHg production from new deposition is a good predictor of total MeHg concentrations in surface sediments, supporting the idea that mainly freshly deposited Hg is available for methylation. These findings also suggest that Hg bioavailability for methylation decreases rapidly over time after deposition from the atmosphere, and Hg emission controls may have a rapid impact on MeHg production and bioaccumulation.

The complexation of Hg in deposition, or in a ecosystem spike, effects its behavior in terms of particle reactivity, reduction and evasion, and probably methylation. Therefore, understanding the complexation of mercury in rain, and the behavior of that Hg after deposition, is critical to interpreting METAALICUS results, modeling MeHg production from new deposition compared to Hg pools stored in sediments and soils, and best management of Hg emissions.

Future Activities:

During 2002, another year of full-scale stable isotope additions to L658 is planned. To supplement the whole-watershed Hg response study, a series of dose-response studies at multiple doses are planned, using lake enclosures. These studies will mimic dose-response studies in mesocosms in the Everglades. Enclosures will be sampled into 2002. In addition, we are piggy-backing on a phosphate mesocosm study that is being done by Newman, et al., at the SFWMD. A second ACME enclosure experiment will begin in November 2001, in which the effects of Hg, sulfate, and dissolved organic carbon (DOC) on MeHg production will be assessed separately and together. Sulfate, Hg, and DOC additions are being made to ACME mesocosms, with a focus on responses to sulfate additions at low-sulfate sites. DOC was isolated from Everglades surface waters. Sampling will continue through February 2002.


Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 44 publications 5 publications in selected types All 5 journal articles
Type Citation Project Document Sources
Journal Article Benoit JM, Mason RP, Gilmour CC, Aiken GR. Constants for mercury binding by dissolved organic matter isolates from the Florida Everglades. Geochimica et Cosmochimica Acta 2001;65(24):4445-4451. R827631 (2000)
R827631 (2001)
R827631 (Final)
R827653 (2000)
R827653 (2001)
R827653 (Final)
  • Full-text: ScienceDirect-Full Text PDF
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  • Other: Smithsonian Library Online - Full Text PDF
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  • Journal Article Benoit JM, Gilmour CC, Mason RP. The influence of sulfide on solid-phase mercury bioavailability for methylation by pure cultures of Desulfobulbus propionicus (1pr3). Environmental Science & Technology 2001;35(1):127-132. R827631 (2000)
    R827631 (2001)
    R827631 (Final)
    R827653 (2000)
    R827653 (2001)
    R827653 (Final)
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  • Journal Article Benoit JM, Gilmour CC, Mason RP. Aspects of bioavailability of mercury for methylation in pure cultures of Desulfobulbus propionicus (1pr3). Applied and Environmental Microbiology 2001;67(1):51-58. R827631 (2001)
    R827653 (2000)
    R827653 (2001)
    R827653 (Final)
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  • Supplemental Keywords:

    atmosphere, water, watersheds, land, soil, sediments, acid deposition, precipitation, chemical transport, risk assessment, human health, bioavailability, dose response, metals, heavy metals, sulfates, bacteria, acid rain, ecosystem, restoration, regionalization, scaling, terrestrial, aquatic, habitat, public policy, decision making, cost benefit., 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, aquatic, fate and transport, mercury loading, contaminated sediment, fish consumption, soils, mercury cycling, biogeochemical cycling, methylmercury, methylation, terrestrial and aquatic fate, wetland

    Relevant Websites:

    http://www.acnatsci.org/research/anserc/biogeochemistry.html Exit
    http://www.acnatsci.org/research/anserc/mercurybiogeochemistry.html Exit
    http://www.acnatsci.org/research/anserc/acme.html Exit
    http://www.acnatsci.org/research/anserc/metaalicus.html Exit
    http://cbl.umces.edu/~mason/welcome.html Exit
    http://www.biology.ualberta.ca/metaalicus/metaalicus.htm Exit
    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:

    Original Abstract
  • 2000 Progress Report
  • 2002
  • Final Report