Grantee Research Project Results
2000 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 , 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, 1999 through September 30, 2000
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. A variety of anthropogenic ecosystem changes that became widespread in the post-World War II era are possibly responsible for enhanced methylation, including: increased sulfate deposition, increased nutrient loads, increased loading of mercury 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 methylmercury (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 the receiving lakes.Progress Summary:
The field portion of this project is being conducted at the Marcell Experimental Forest (MEF) in northeastern Minnesota. The MEF is a complex landscape of forested uplands (mainly aspen, with some red, white, and jack pine, basswood, and maple species), wetlands (black spruce, alder, tamarack, willow, and sedges), and lakes. There is a significant proportion and variety of wetlands in the watershed, varying from nutrient poor, low pH bogs to nutrient rich, high pH fens. The MEF was of particular interest to this study because it has a large historical database concerning the hydrologic cycling of mercury as well as soils, hydrology, and chemical cycling and transport. Climatic and hydrologic data have been collected continuously at monitoring stations since 1960.
The fieldwork is focused on constructing mass balances of Hg and MeHg in monitored wetlands and in a small lake, Spring Lake. Three MEF wetlands were instrumented for outflow determinations previous to this study, three more weirs and instrumentation were installed during summer 2000. Outflow samples from all the MEF wetland monitoring stations were collected from spring to fall, but no flow or very little flow typified the year due to light snow fall and very dry conditions throughout the summer. Inputs to the wetlands that will be considered include: surface and subsurface runoff, direct precipitation, throughfall, and litterfall. Surface and subsurface runoff collectors are installed in uplands draining to two of the wetlands, but they too had little to no flow throughout the year. Direct precipitation is monitored at a Mercury Deposition Network monitoring site at the MEF. Throughfall and litterfall samplers under several different canopy types were setup during the Summer and samples were collected in the Fall.
In Spring Lake, five sediment cores were collected in April 2000, and have been dated using 210Pb techniques. MeHg and total-Hg accumulation profiles will be determined in each of the cores. A porewater equilibrator was deployed in October 2000 to complement MeHg profiles in the cores. Total-Hg, MeHg and dissolved gaseous mercury samples were collected on a monthly basis. Volatile losses of elemental Hg were estimated on one occasion using a Tekran 2537A mercury analyzer. Zooplankton, one-year yellow perch and northern pike also were collected.
Additions of sulfate, nitrogen, and organic matter will be made to different wetland types and to lake sediments to test for enhanced methylation. Wetland slabs were collected from two wetlands in Winter 2000 and have been transported back to the laboratory. Thirty-five sediment cores were collected on four separate sampling trips in April, June, August, and October. Sulfate reduction rates were determined at depth within eight individual cores and on a transect across the lake. Sulfate reduction rates were generally greatest from 0 to 25 cm and decreased substantially below 25 cm. Sulfate reduction rates, integrated over entire cores, increased with lake depth. Other cores were utilized for flow-through incubation experiments. Sulfate in lake water amended to 2x, 4x, and 10x ambient levels was placed above separate cores for a specified residence time. Influent and effluent water samples will be analyzed for MeHg, pH, alkalinity, dissolved inorganic carbon, dissolved organics carbon, and sulfate.
Wetland types and other land cover characteristics have been identified and delineated in 12 other watersheds and currently are being input to a geographic information system (GIS) database. The purpose of this work is to relate wetland area/type, land cover, and other landscape features to Hg loading to lakes and ultimately Hg levels in fish.
Future Activities:
Additions of sulfate, nitrate, and organic matter to sediment and wetland microcosms will be ongoing throughout the project. The wetland field component of the project will be more intensive next year provided there is significant rainfall. A tele-connection to one of the wetland outflow weirs will allow us to check runoff flow and allow for event sampling in addition to the regular biweekly sampling. Peepers have been installed at two of the wetlands and monthly sampling along transects will occur. A whole wetland (S6 wetland) sulfate addition is planned for spring 2002. A Tekran 2537A also will be available next summer and an attempt will be made to measure elemental Hg fluxes from different wetlands and soils at the MEF. At Spring Lake in 2001, monthly zooplankton and forage fish sampling will be added to complement monthly Hg, MeHg, and dissolved gaseous mercury (DGM) water sampling. DGM production and MeHg photodegradation experiments also are planned for 2001. The Tekran 2537A will be used again to estimate volatile fluxes of elemental Hg from Spring Lake on one or more occasions in 2001.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, Water, Waste, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Nutrients, Ecology, Hydrology, Contaminated Sediments, Environmental Chemistry, State, Fate & Transport, Air Deposition, Geology, Mercury, EPA Region, 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
http://www.tc.umn.edu/~cotne002/
http://www.soils.agri.umn.edu/people/faculty/enater.html
http://www.ce.umn.edu/fns/brezonik/
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.