WHAT IS METAALICUS?
Mercury Experiment to Assess Atmospheric Loading in Canada and the United States (METAALICUS) project is a whole-watershed mercury loading experiment being carried out at the Experimental Lakes Area (ELA) in northwestern Ontario . The study provides a unique opportunity to study the relationship between atmospheric mercury deposition and bioaccumulation of mercury in food webs, at a watershed scale.Mercury is an environmental contaminant that negatively impacts fish and wildlife populations and has resulted in human health advisories worldwide. Mercury emissions reductions have taken place or are being considered in many countries including the U.S. However, the timing and magnitude of a response in fish mercury levels to emissions reductions are unknown. This study seeks to understand those relationships through an experimental addition of mercury to a small lake and its watershed (Lake 658).
Our overall objective is: -How much, and how fast, does mercury in fish change in response to a change in mercury loading?-
Or, put a different way: -Will controls on atmospheric Hg emissions be effective in reducing mercury in freshwater fish, and if so, how rapidly will this happen?-
WHERE IS METAALICUS BEING DONE?
The study is being conducted at the Experimental Lakes Area, near Dryden, Ontario. The ELA is freshwater research station with a long history of limnological research, including studies based on the manipulation of lakes. The ELA is part of the Canada Department of Fisheries and Oceans. The study site is the entire catchment of a small first order drainage lake (Lake 658).
For more information on the Experimental Lakes Area, see:
Canada Dept. of Fisheries and Oceans
METAALICUS is being accomplished by a multidisciplinary team of about 50 researchers from the US and Canada. METAALICUS incorporates two powerful techniques that are novel to the Hg research community to accomplish that objective; one, the use of stable Hg isotopes, and two, the manipulation of a whole watershed. The Hg load to the study ecosystem is being increased by a factor of about 5 over current local atmospheric ambient deposition, using highly-enriched stable Hg isotopes. Three separate isotopes are being used to dose the upland, wetland and lake. This unique approach is allowing us to track the fate of newly deposited Hg separately from the larger existing pools, through time, and across various habitats. Importantly, the use of stable isotopes gives us the ability to follow the fate and transport of newly deposited Hg relative to existing Hg pools in sediments and soils.
We have hypothesized that newly deposited mercury in more readily converted to MeHg than Hg that is stored in sediments and soils. Our results support that hypothesis. This is important, because more than 150 years of elevated Hg emissions in the US have resulted in mercury accumulation in sediments at soils. If all of this mercury is available for methylation and bioaccumulation, it will take a very long time (decades) to reduce Hg levels in fish. However, if MeHg is formed mainly from newly deposited mercury, emissions reductions should be more rapidly effective in reducing Hg levels in fish.
HOW MUCH MERCURY IS BEING ADDED TO LAKE 658 AND ITS WATERSHED?
The Experimental Lakes Area is remote from human activities and therefore receives relatively low rates of atmospheric mercury deposition, about 4 ug per square meter per year. The METAALICUS project adds another 22 ug/m2 y. The study is designed to simulate deposition rates in contaminated areas. We began adding mercury June 2001, and continued additions through 2006. Future additions will depend on 2006 results.
The experimental mercury load to Lake 658 is roughly double the mercury deposition in suburban Maryland in 2005. Mercury wet deposition rates are currently measured at three locations in Maryland, including the SERC Mercury Deposition Network site.
WHAT DOES SERC DO IN METAALICUS?
Researchers at SERC study microbial mercury methylation within the L658 ecosystem. A key process in the biogeochemical cycling of Hg is the microbial production of methylmercury (MeHg), which is the form of Hg that accumulates in food webs. Methylmercury is produced by natural bacteria found in sediments and wet soils. We study how the MeHg production process responds to changes in Hg deposition. In particular, the study examines how changes in the chemical form of mercury, after deposition and as mercury moves through watersheds, affect the ability of bacteria to take up and methylate mercury.
Some of the important questions being addressed by this study are: 1) Does recently-deposited mercury behave in the same way as mercury deposited in the past? 2) Does mercury deposited to different parts of watersheds behave differently? and 3) Can changes in fish mercury concentrations in response to changes in deposition be adequately modeled?
Answers to these questions are helping us to predict how fast ecosystems will respond to controls on atmospheric Hg emissions. The results of this study have significant impact on environmental policy formulation regarding control of atmospheric Hg emissions, particularly the potential effectiveness of controls and the time frame in which they will begin to have an effect.
Fish methylmercury concentrations responded rapidly to changes in mercury deposition over the first 3 years of study. Essentially all of the increase in fish methylmercury concentrations came from mercury deposited directly to the lake surface. In contrast, <1% of the mercury isotope deposited to the watershed was exported to the lake. Steady state was not reached within 3 years. Lake mercury isotope concentrations were still rising in lake biota, and watershed mercury isotope exports to the lake were increasing slowly. Therefore, we predict that mercury emissions reductions will yield rapid (years) reductions in fish methylmercury concentrations and will yield concomitant reductions in risk. However, a full response will be delayed by the gradual export of mercury stored in watersheds. The rate of response will vary among lakes depending on the relative surface areas of water and watershed.
Orihel, D.M., M. J. Paterson, P. J. Blanchfield, R.A (Drew) Bodaly, C. C. Gilmour, and H. Hintelmann. Temporal changes in the distribution, methylation, and bioaccumulation of newly deposited mercury in an aquatic ecosystem. Environmental Pollution, online Feb 2008.
Harris, R.C., J.W.M. Rudd, M. Amyot, C.L. Babiarz, K.G. Beaty, P.J. Blanchfield, R.A. Bodaly, B.A. Branfireun, C.C. Gilmour, J. Graydon, A. Heyes, H. Hintelmann, J.P. Hurley, C.A. Kelly, D.P. Krabbenhoft, S.E. Lindberg, R.P. Mason, M.J. Paterson, C.L. Podemski, A. Robinson, K. Sandilands, G.R. Southworth, V.L. St. Louis, and M. Tate. 2007. Rapid response of fish mercury concentrations to whole-catchment additions of isotopically-enriched mercury. PNAS. 104: 16586-16591. (pdf)
Miller, C.M., C.C. Gilmour, A. Heyes and R.P. Mason. 2007. Influence of dissolved organic matter on the complexation of Hg under sulfidic conditions. Environ. Tox. Chem. 26: 624-633.(pdf)
Munthe, J., R.A. (Drew) Bodaly, Brian Branfireun, Charles T. Driscoll, Cynthia Gilmour, Reed Harris, Milena Horvat, Marc Lucotte, Olaf Malm. 2007. Recovery of mercury-contaminated fisheries. Ambio. 36: 33-44. (pdf)
Orihel, D.M., Michael J. Paterson, Cynthia C. Gilmour, R.A (Drew) Bodaly, Paul J. Blanchfield, , Holger Hintelmann, Reed C. Harris, John W. Rudd. 2006. Effect of loading rate on the fate of mercury in littoral mesocosms. Environ. Sci. Tech. 40(19); 5992-6000.(pdf)
Paterson, Michael J., Paul Blanchfield, Cheryl Podemski, Holger H. Hintelmann, Cynthia C. Gilmour, Reed Harris, N. Ogrinc, John W.M. Rudd, and Ken A. Sandilands. 2006.Bioaccumulation of newly-deposited mercury by fish and invertebrates: an enclosure study using stable mercury isotopes. Can. J. Fish. Aquat Sci. 66:2213-2224.(pdf)
Sandilands, K.A., J.W.M. Rudd, C.A. Kelly, H. Hintelmann, C.C. Gilmour, and M.T. Tate. 2005. Application of enriched stable mercury isotopes to the Lake 658 watershed for the METAALICUS project, at the Experimental Lakes Area, northwestern Ontario, Canada. Can. Tech. Rep. Fish. Aquat. Sci. 2597: viii + 48 p.
Babiarz, C.L., J.P. Hurley, D.P. Krabbenhoft, C.C. Gilmour, and B.Branfireun. 2003. Application of ultrafiltration and stable isotopic amendments to field studies of mercury partitioning to filterable carbon in lake water and overland runoff. Sci. Total Environ. 304: 295-303.(pdf)