Mercury Experiment to Assess Atmospheric Loading in Canada and the United States (METAALICUS)
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The Mercury Studies Team is addressing fundamental questions on atmospheric loading by adding trace amounts of inorganic mercury (HgII) to ELA Lake 658 (shown at right) and its watershed at the Experimental Lakes Area (ELA), northwestern Ontario over a two or three-year period. The ELA is situated in a region of low atmospheric deposition of mercury, and we plan to temporarily increase the Hg loading to a small ELA watershed by a factor of 4 to simulate the atmospheric loading of mercury to lakes in Eastern Canada (Southern Ontario and the Maritime Provinces). This is a whole-ecosystem experiment, which, in addition to following changes in MeHg concentration of fish, will examine other key biological and chemical processes that determine the rate of MeHg production and its bioaccumulation into fish.
The USGS research on this project is funded by the Toxics Program, and is primarily focused on the biogeochemcial processing and transport of the mercury isotopes that are delivered to the upland forests and the wetland, and then to the lake itself.
There is a broad consensus among mercury experts that the most widespread cause of high fish MeHg concentrations is elevated atmospheric deposition of mercury to lakes and their watersheds. Emissions from the US Midwest and southeastern Canada are transported and deposited in both countries in a pattern similar to the deposition of sulfuric and nitric acids. In addition, there is increased global circulation of Hg in the atmosphere and increased deposition even in remote locations.
One of the major sources of anthropogenicmercury is mercury emitted from coal-fired utilities, and controls on these emissions have recently been proposed. On a North American basis, the estimated cost of these controls would be several billion dollars per year (EPA, 1998). Despite these moves towards controls, mercury experts are in agreement that the relationship between atmospheric mercury deposition and MeHg concentrations in fish is unknown.
Although emission reductions of 50% have been proposed (Conference of New England State Governors and Maritime Province Premiers), there is no understanding of whether this reduction would be inadequate or more than necessary, and this could result in the waste of billions of dollars on control technologies. The uncertainty comes from the fact that the amount of stored Hg in ecosystems is many times greater than annual deposition. If the newly deposited Hg is much more bioavailable than the stored Hg, ecosystems will respond quickly (1-2 yr.) to changes in atmospheric deposition, but if all the Hg is equally bioavailable, response time will be very slow.
We have instrumented the water shed with four flow monitoring and automated sampling stations that take runoff samples in response to rain event, which typically arrive suddenly and do not allow for adequate time get to the field site to sample during storms. In addition, we have water level recorders in the lake and wetland, which will be essential to calculating hydrologic and mercury isotope mass balances.
See fieldwork photos from ELA Lake 658 »