PARENT SESSION
MA7 - Mercury: Fate, Transport, & Bioaccumulation
Chair: Kidd, Karen1, 1 Freshwater Institute, Winnipeg, MB
8:00 AM to 12:00 PM - Monday, 18 November 2002
Room Ballroom A
(228) Reconstruction of Mercury Fallout in Southeastern Idaho using Lake Sediment Cores.
Abbott, Michael*,1, Van Metre, Peter2, Budahn, James3, 1 Idaho National Engineering and Environmental Laboratory, Idaho Falls, ID, USA2 U.S. Geological Survey - National Water Quality Assessment Program, Austin, TX, USA3 U.S. Geological Survey, Denver, CO, USA
ABSTRACT- Sediment cores from two lakes (Sandhole and Mud Lakes) in southeastern Idaho were obtained in July 2001 to investigate historical fallout trends of mercury in the region. The lakes are located in a low mercury background area in the western U.S. but 60-km downwind of a relatively large anthropogenic mercury source that operated from 1964 - 2000. Nine cores (5-8 cm dia by 25-cm long) were obtained using a hand-coring device and sliced into 1-cm thick samples. Samples were analyzed for mercury at the U.S. Geological Survey's (USGS) Mercury Research Laboratory in Madison, WI. Gamma-emitting radionuclides were analyzed at the Idaho National Engineering and Environmental Laboratory and by the USGS in Denver, CO. Two different radiodating techiques were used to age-date the layers: 1) scaling relative to the 1964 137Cs fallout peak marker and sample interval mass accumulation (assumes a constant sedimentation rate) and 2) the 210Pb constant rate of supply (CRS) model, which can account for variable sedimentation rates. Although the two lakes are in close proximity to each other and would have received the same annual atmospheric fallout, both 137Cs concentrations and mercury accumulation rates varied substantially between the two, indicating significant diagenetic processes and/or differing rates of sediment input from the watershed. Using the different age-dating methods, mercury accumulation rates (from both fallout and watershed input) are estimated to have generally increased from 4-15 ug/m2/yr in the mid-1800s to a present day rate of 26-43 ug/m2/yr. These rates indicate a 2 to 9-fold increase in mercury accumulation since pre-industrial times compared to the 3 to 5-fold global background increases observed in other published sediment studies.
Key words: mercury, sediment, fallout, reconstruction