Grantee Research Project Results
2001 Progress Report: Methylmercury Sources to Lakes in Forested Watersheds: Has Enhanced Methylation Increased Mercury in Fish Relative to Atmospheric Deposition?
EPA Grant Number: R827630Title: Methylmercury Sources to Lakes in Forested Watersheds: Has Enhanced Methylation Increased Mercury in Fish Relative to Atmospheric Deposition?
Investigators: Swain, Edward B. , Engstrom, Daniel , Nater, Edward , Jeremiason, Jeff , Cotner, Jim , Almendinger, James E. , Brezonik, Patrick L.
Current Investigators: Swain, Edward B. , Engstrom, Daniel , Nater, Edward , Jeremiason, Jeff , Cotner, Jim , Almendinger, James E.
Institution: Minnesota Pollution Control Agency , University of Minnesota , St. Croix Watershed Research Station
Current Institution: Minnesota Pollution Control Agency
EPA Project Officer: Chung, Serena
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: $847,690
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:
We hypothesize that mercury (Hg) concentrations in fish in sensitive ecosystems have been exacerbated relative to atmospheric deposition due to enhanced mercury methylation occurring in lake sediments or associated wetlands. Several anthropogenic ecosystem changes became widespread in the post-World War II era and may be responsible for enhanced methylation, including: increased sulfate deposition, increased nutrient loads, increased loading of Hg to wetlands because of soil disturbance, and other unknown processes. The specific objectives of this study are to: (1) conduct microcosm (wetland and lake sediment) and whole wetland experiments to elucidate methylation enhancing processes; (2) establish the relative importance of atmospheric, in-lake, and wetland sources of methyl mercury (MeHg) to lakes in forested watersheds; (3) determine the net retention and source strength of different wetland types; and (4) delineate and classify wetlands in other watersheds and estimate Hg and MeHg watershed loads to receiving lakes.Progress Summary:
This project can be separated into three general levels of research: field, laboratory, and application. The field portion of this project is being conducted at the Marcell Experimental Forest (MEF) in northeastern Minnesota. We have six wetland/upland complexes and one lake (Spring Lake) where work is being conducted. The fieldwork in 2001 consisted of: (1) determination of Hg and MeHg fluxes from six monitored wetlands and two surface and subsurface upland flow collectors; (2) collection of throughfall and litterfall samples under different canopy types; (3) construction of an irrigation system on the S6 wetland; (4) first application of sulfate to the S6 wetland in Fall 2001; (5) analysis of Hg and MeHg in five dated sediment cores from Spring Lake; (6) three porewater equilibrator deployments in Spring Lake and subsequent Hg and MeHg flux estimates; (7) monthly zooplankton, water, and air collections at Spring Lake during the open-water season; and (8) in-lake photo-degradation of Hg2+ and photo-oxidation of Hg0 at Spring Lake. Highlights from 2001: (1) on an annual basis, MeHg fluxes from various wetlands were roughly correlated to water flow; MeHg concentrations in outflow relatively were high (averaging ~1 ng/L); (2) MeHg fluxes from Spring Lake sediment to bottom waters estimated from the porewater equilibrators were low relative to MeHg fluxes from wetlands; (3) MeHg concentrations increased in the S6 wetland porewaters following the first sulfate addition.
The laboratory portion of this project in 2001 consisted of additions of sulfate and organic matter to Spring Lake sediment and the addition of sulfate to wetland microcosms. The purpose of these additions is to test for enhanced methylation of mercury under various loading scenarios. Sediments from Spring Lake were spiked with various combinations of sulfate (ambient to 100 x ambient concentration), and/or organic matter (lactate or acetate), and incubated in flasks, or as intact cores. The flasks were amended with ionic mercury to improve the detection of subtle changes in methylation, while the intact core experiments were conducted at ambient levels to better mimic the natural system. The wetland microcosms were spiked with 5x and 10x ambient sulfate concentrations and monitored over time relative to controls. A few highlights from these experiments include: (1) the addition of sulfate enhanced methylation, but at high sulfate concentrations methylation appears to be inhibited; (2) MeHg concentration did not increase linearly with the level of sulfate addition; (3) addition of labile carbon (acetate or lactate) enhanced sulfate reduction and methylation; (4) sulfate and lactate added together to lake sediment was greatest at enhancing MeHg production; and (5) relative to the 5x addition, only a slight increase in methylation was observed in the 10x sulfate addition in the wetland microcosms.
In the application portion of this project, wetland types and other land cover characteristics have been identified and delineated in 12 other watersheds and have been incorporated into a Geographic Information Systems database. The next step is to relate wetland area/type, land cover, and other landscape features to Hg loading to these lakes and ultimately Hg levels in fish.
Future Activities:
A major effort in 2002 will be the addition of sulfate to the S6 wetland. The first sulfate load was applied in 2001 shortly before snowfall and represented sulfate deposition over the winter and early spring. Sulfate will be added three additional times in 2002, resulting in a 4x increase in the annual load. MeHg in the porewaters and in the outflow from S6 will be monitored intensely throughout 2002. Monitoring at Spring Lake will continue in 2002 and will focus on porewater equilibrator deployments and photodegradation/photooxidation experiments. Additions of sulfate, nitrate, and organic matter to sediment and wetland microcosms will continue in the final year of the project. Stable isotopes of mercury will be used in these experiments to better represent ambient mercury levels.Journal Articles:
No journal articles submitted with this report: View all 16 publications for this projectSupplemental Keywords:
terrestrial, aquatic, hydrology, environmental chemistry, central, EPA Region 5., Scientific Discipline, Geographic Area, Waste, Water, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, Nutrients, Ecology, Contaminated Sediments, Environmental Chemistry, State, Fate & Transport, Air Deposition, Geology, EPA Region, Mercury, aquatic ecosystem, nutrient supply, fate and transport, Minnesota, MN, forested watersheds, food chain, contaminated sediment, benthic food web, atmospheric deposits, mercury cycling, fish consumption, biological integrity, geochemistry, methylmercury, watershed influences, methylation, terrestrial and aquatic fate, ecosystem stress, Region 5, atmospheric deposition, benthic nutrientsRelevant Websites:
http://www.pca.state.mn.us/air/mercury.html Exit
http://www.tc.umn.edu/~cotne002/ Exit
http://www.soils.agri.umn.edu/people/faculty/enater.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)
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.