2000 Progress Report: Response of Methylmercury Production and Accumulation to Changes in Hg Loading: A Whole-ecosystem Mercury Loading StudyEPA 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 , Freshwater Institute , 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, 1999 through September 30, 2000
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 conducted 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 U.S. Environmental Protection Agency 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 Aquatic Cycling of Mercury in the Everglades (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 (FLDEP).
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 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, the work included pilot-scale Hg isotope additions to lake enclosures, wetland plots, and upland plots. Lake 658 was selected as the study site.
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, dosed again in the fall, and will be sampled into 2002. 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. Phosphate alone has little effect on net MeHg production in the Everglades. Also, 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. In addition, 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.
Future Activities:An intensive year of background data on L658 will be collected in 2001.
Journal Articles on this Report : 2 Displayed | Download in RIS Format
|Other project views:||All 44 publications||5 publications in selected types||All 5 journal articles|
||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.||
||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.||
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
http://www.acnatsci.org/research/anserc/metaalicus.html 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)