Watershed Influences on Transport, Fate, and Bioavailability of Mercury in Lake Superior

EPA Grant Number: R827629
Title: Watershed Influences on Transport, Fate, and Bioavailability of Mercury in Lake Superior
Investigators: Hurley, James P. , Armstrong, D. E. , Back, Richard C. , Shafer, Martin M.
Current Investigators: Hurley, James P. , Armstrong, D. E. , Back, Richard C. , Manolopoulos, Helen , Shafer, Martin M.
Institution: University of Wisconsin - Madison , Lake Superior State University , Wisconsin Department of Natural Resources
EPA Project Officer: Hiscock, Michael
Project Period: October 1, 1999 through September 30, 2002 (Extended to September 30, 2003)
Project Amount: $829,384
RFA: Mercury: Transport and Fate through a Watershed (1999) RFA Text |  Recipients Lists
Research Category: Water and Watersheds , Mercury , Water , Safer Chemicals


Watersheds exert a strong influence on the biogeochemical cycling of mercury (Hg). Several studies have shown that land use and land cover, soil type and glacial deposits are strong predictors of fate and transport (St. Louis et al. 1994; Hurley et al. l99S; Babiarz et al. 1998). Our preliminary efforts on several rivers in the Lake Superior Basin (Hurley et al. 1999) support this theory; we have recently demonstrated that wetland- and forest dominated watersheds attenuate total Hg (HgT) transport. More importantly, these watershed types enhance the production of the bioaccumulative and toxic form of Hg, mono-methyl Hg (MeHg). Preliminary estimates suggest that while direct atmospheric deposition dominates HgT input to the Basin (820 kg - atmos.; 320 kg watershed), watershed inputs dominate for MeHg (8.9 kg watershed; 1.3 kg atmos.). Furthermore, while atmospheric MeHg inputs are distributed across the vast surface area of Lake Superior, watershed influences are concentrated in specific nearshore zones. While watershed environmental characteristics have been shown to influence Hg speciation, transport, and transformation, the specific chemical factors regulating bioavailability need to be identified and quantified. For instance, MeHg may be produced within a watershed, but may be unavailable for bioconcentration, due to its association with high molecular weight organic colloids and/or specific soil types.

The Lake Superior ecosystem offers a unique opportunity to assess the fate and transport of Hg derived from its watersheds (and to relate these inputs and processes to in-lake cycling), due to contrasts in geology and biology represented in the Superior Basin. As fish consumption advisories have been issued for Lake Superior (indicating that Hg bioaccumulation is occurring), our study will investigate potential sites for enhanced bioaccumulation including sub-watershed regions, estuarine mixing zones, and pelagic areas. We will supplement our field-based work with detailed laboratory studies assessing fate, transport, and bioavailability of Hg and MeHg.

Objectives: The goal of this study is to assess the importance of watersheds in controlling sources, transport, fate, and bioavailability of Hg in a northern temperate lake system. Specific objectives of the study are to. l) Determine the speciation and bioavailability of Hg transported to Lake Superior by representative tributaries/watersheds; 2) Determine the importance of watershed-specific characteristics (soil type, land use surficial deposits) that control physical/chemical forms of Hg transported downstream; 3) Identify key mechanisms controlling Hg bioavailability and speciation in near-shore zones relative to open lake regions; and, 4) Provide process-level information to compliment concurrent development of Hg fate and transport models of the Lake Superior ecosystem.


Our approach combines field and laboratory studies with modeling to assess the importance of watershed processes in controlling Hg fate and transport in Lake Superior. Each phase (field studies, laboratory studies, modeling efforts) is strongly linked to provide feedback for the remaining phases. Frequent interaction among project participants (group meetings, conference calls) will allow for adjustments to better assess important processes for success of objectives. Our approach builds on research conducted by our group on Lake Superior tributaries from 1995-1998 and develops new research objectives 1n fate and transport of Hg, including factors regulating bioavailability. Techniques developed and adapted by our group during previous projects (i.e., "clean" ultrafiltration, resin techniques, biota processing) will be supplemented by new techniques (i.e., stable isotope Hg analysis by ICP-MS; phytoplankton and zooplankton uptake experiments, "bio-reporter" work by Canadian colleagues). Modeling efforts combine efforts of ongoing GIS-based watershed yield modeling with the Dynamic Mercury Cycling Model (D-MCM) model development at Tetra Tech, Inc.

Expected Results:

Our results will provide necessary information on the links between atmospheric Hg deposition and accumulation of Hg in biota within the Lake Superior Basin and will be of benefit to water quality managers and risk assessors (such information will eliminate gaps in knowledge of watershed processing of Hg, as indicated by USEPA in the Mercury Study Report to Congress). Our predictive capabilities are enhanced by our association with Tetra Tech, Inc., who will incorporate our results into the D-MCM for Lake Superior. The model (which is mechanistic and time-dependent) predicts the cycling and fate of the major forms of mercury in lakes, including methylmercury, Hg(ll), and elemental mercury, and will be applied to our three field focal areas. Also, we will incorporate rate constants and partitioning data from our laboratory results. The D-MCM model will be a great asset for water resource managers and for establishing water quality criteria for the Lake Superior Basin.

Publications and Presentations:

Publications have been submitted on this project: View all 36 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 9 journal articles for this project

Supplemental Keywords:

Great Lakes, EPA Region 5, Wisconsin, Michigan, Minnesota, heavy metals, biology, hydrology, biology, environmental chemistry, Scientific Discipline, Geographic Area, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Bioavailability, Hydrology, Environmental Chemistry, State, Fate & Transport, Air Deposition, Ecology and Ecosystems, EPA Region, Great Lakes, Mercury, aquatic, fate and transport, Minnesota, MN, colloidal particles, fish consumption, soils, mercury cycling, geochemistry, watershed influences, Lake Superior, water quality, Wisconsin (WI), wetland, Region 5, atmospheric deposition, lake ecosystems, metals

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 Progress Report
  • Final Report