PARENT SESSION
Organized Oral Session 5: Mercury cycles: Sources, mass balances, bioaccumulation, and options to manage affected systems
Organizer(s): EPH Best, JG Wiener, and D Planas
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 511 C, Level 5, Palais des congrès de Montréal
Bioaccumulation of methylmercury in lacustrine food webs: Controlling factors in a mercury-sensitive landscape.
Wiener, James*,1, Knights, Brent2, Sandheinrich, Mark1, Jeremiason, Jeffrey3, Kallemeyn, Larry4, Rolfhus, Kristofer1, 1 University of Wisconsin-La Crosse, La Crosse, Wisconsin, USA2 US Geological Survey, La Crosse, Wisconsin, USA3 Gustavus Adolphus College, St. Peter, Minnesota, USA4 US Geological Survey, International Falls, Minnesota, USA
ABSTRACT- We illustrate selected aspects of the methylmercury problem with information from small lakes in the Voyageurs National Park on the US Canadian border. Analyses of soils, rock, and sediment cores have shown that atmospheric deposition is the dominant source of mercury in this ecosystem and that most of the deposited mercury is from anthropogenic sources. Concentrations of mercury in northern pike (Esox lucius) varied substantially among small interior lakes of the Park, exceeding federal (0.3 mg/kg wet weight) and state criteria (0.2 mg/kg) for the protection of human health in most or all lakes. To identify factors influencing mercury bioaccumulation in these waters, we examined the relation between selected ecosystem variables and mercury concentrations in yellow perch (Perca flavescens) and northern pike. The concentrations of total mercury in whole 1-year-old yellow perch and in axial muscle of northern pike varied substantially among lakes. Predicted concentrations of mercury in 55-cm northern pike from 15 lakes, which ranged from 0.24 to 1.75 mg/kg wet weight, were strongly correlated with concentrations in coexisting yellow perch. Statistical models showed that concentrations of mercury in these fishes reflected the influence of ecosystem factors known to affect the microbial production and abundance of methylmercury. Key predictor variables in these models were lake water pH, dissolved sulfate, and total organic carbon (an indicator of wetland influence). These findings are consistent with published mass balance and methylation studies showing that the methylation of mercury in lakes and in adjoining wetlands substantially influences the supply of methylmercury to lacustrine food webs. Atmospheric deposition has caused substantial contamination of predatory fish in the Park, which we consider to be a mercury-sensitive landscape. Potential options for reducing methylmercury contamination and exposure in this ecosystem include (1) reducing sources contributing to mercury and sulfate in atmospheric deposition, (2) preventing disturbances and environmental changes that could increase methylmercury production, and (3) continued risk assessment and communication of advice to persons who consume fish from lakes in the Park.
Key words: mercury, bioaccumulation, fish, landscape