Grantee Research Project Results
2000 Progress Report: Watershed Influences on Transport, Fate, and Bioavailability of Mercury in Lake Superior
EPA Grant Number: R827629Title: Watershed Influences on Transport, Fate, and Bioavailability of Mercury in Lake Superior
Investigators: Hurley, James P. , Back, Richard C. , Armstrong, D. E. , Shafer, Martin M. , Rolfhus, Kristofer R.
Current Investigators: Hurley, James P. , Back, Richard C. , Armstrong, D. E. , Shafer, Martin M. , Manolopoulos, Helen
Institution: University of Wisconsin - Madison , Wisconsin Department of Natural Resources , Lake Superior State University
Current Institution: University of Wisconsin - Madison , Lake Superior State University , Wisconsin Department of Natural Resources
EPA Project Officer: Packard, Benjamin H
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: $829,384
RFA: Mercury: Transport and Fate through a Watershed (1999) RFA Text | Recipients Lists
Research Category: Watersheds , Heavy Metal Contamination of Soil/Water , Water , Safer Chemicals
Objective:
The goal of this study is to assess the importance of watersheds in controlling sources, transport, fate, and bioavailability of mercury (Hg) in a northern temperate lake system. Specific objectives of the study are to: (1) 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. Techniques developed and adapted by our group during previous projects (i.e., "clean" ultrafiltration, resin techniques, biota processing) are being supplemented by new techniques (i.e., stable isotope Hg analysis by ICP-MS; phytoplankton and zooplankton uptake experiments). Modeling efforts combine efforts of ongoing GIS-based watershed yield modeling with the Dynamic Mercury Cycling Model (D-MCM) development at Tetra Tech, Inc.
Progress Summary:
Our research efforts during the first year of the project were focused on: (1) investigating differences between processes influencing offshore and nearshore bioaccumulation of Hg in Lake Superior, particularly with regards to the spatial/temporal distribution of Hg in near-shore and offshore environments; (2) investigating watershed processes that enhance production and transport of methyl Hg to tributaries; and (3) developing laboratory techniques for "trace-metal clean" plankton culturing/uptake studies.
Two cruises on Lake Superior aboard the EPA research vessel R/V Lake Guardian were conducted during 2000 (April and August). Nineteen open water stations on Lake Superior were visited to determine the spatial/temporal distribution and speciation of Hg. Our results indicate that, as expected, Hg species concentrations are quite low in Lake Superior, similar to Lake Michigan and oceanic waters. Total Hg averaged 0.49 ? 0.22 ng L-1 (mean, sd) for all stations, depths, and cruises, with little difference found between surface and deep samples; 74 percent was 0.7 mm filter passing. Surface water total Hg samples were elevated along the Minnesota north shore in April 2000, indicative of river inputs during this high-flow period. During August 2000, methyl Hg (MeHg) averaged 6.4 ? 3.8 pg L-1 (with no discernable spatial trends), dissolved gaseous Hg was 20 ? 10 pg L-1, and reactive Hg averaged 45 ? 33 pg L-1. For the August 2000 cruise, aqueous samples averaged 1.5 percent MeHg, 3.5 percent Hgo, 10 percent reactive Hg(II), and 85 percent unreactive organic Hg(II) complexes. Initial comparisons of phytoplankton revealed about a two- to three-fold enrichment of MeHg in riverine mixing zones versus offshore regions of the lake. Analyses of the plankton and sediments (solid phase and pore waters) are ongoing.
The role of watershed composition on MeHg transport is being examined in two focused studies: (1) homogeneous watershed subunits have been identified for the south shore of Lake Superior (based upon GIS surficial geology and land use data), whose tributaries have been sampled for Hg speciation in surface waters, and (2) the role of groundwater in producing/transporting MeHg within a forest-wetland dominated watershed. An extensive set of monitoring wells has been placed in the East Creek watershed in the Tahquamenon River; groundwater, stream water, and porewater samples also are being taken to detect areas of enhanced MeHg production and transport. Initial results from 2000 sampling indicate that groundwater and stream porewater are significant sources of MeHg, with wetland-dominated sites exhibiting the highest MeHg concentrations, at times exceeding 12 ng/L.
We also have initiated laboratory studies directed at predicting bioavailability of Hg and MeHg in algal and zooplankton cultures, through a cooperative effort with the Wisconsin State Hygiene Biomonitoring Laboratory, implementing trace-metal clean culturing techniques and constructing laboratory areas for Hg-clean research. We have begun testing various algal growth media (Fraquil, Nutrient Enhanced Fraquil, and Bold's Basal Media) to assess both algal growth and background Hg levels, and are evaluating Hg speciation using MINEQL.
Future Activities:
Our field-related activities during 2001 will target key periods of MeHg input and bioaccumulation in nearshore zones of Lake Superior. Our work has shown that the majority of MeHg enters the lake during spring melt and we will target specific field and laboratory efforts to better evaluate processes affecting MeHg bioaccumulation both at melt and during events in summer and fall. We will compare melt periods with baseflow and event conditions during summer and fall. We expect to conduct detailed transect sampling from nearshore mixing zones to offshore regions. Our watershed work will expand to include a hydrologic component to determine yields of HgT and MeHg from contrasting land use/land cover characteristics.
Our laboratory efforts will be greatly enhanced by the ability to include the use of stable Hg isotopes, through our cooperative work with Dr. David Krabbenhoft of the U.S. Geological Survey's Mercury Research Laboratory in Middleton, WI. We will use stable isotopic techniques in laboratory uptake and partitioning studies and in evaluating sites of methylation and demethylation in Lake Superior.
Journal Articles:
No journal articles submitted with this report: View all 36 publications for this projectSupplemental Keywords:
groundwater, sediments, estuary, heavy metals, terrestrial, environmental chemistry, biology, hydrology, limnology, zoology, Great Lakes, Wisconsin, WI, Michigan, MI, Minnesota, MN., Scientific Discipline, Water, Waste, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, Bioavailability, Environmental Chemistry, State, Fate & Transport, Air Deposition, Ecology and Ecosystems, Mercury, EPA Region, Great Lakes, fate and transport, aquatic, Minnesota, MN, colloidal particles, mercury cycling, soils, fish consumption, geochemistry, watershed influences, water quality, Lake Superior, Wisconsin (WI), wetland, Region 5, atmospheric deposition, lake ecosystems, Michigan (MI)Relevant Websites:
http://www.engr.wisc.edu/groups/mercury/
http://www.wri.wisc.edu/
http://www.engr.wisc.edu/interd/wcp/
http://www.lssu.edu/academics/science/default.html
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 AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.